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Stomatal conductance (SC) and chlorophyll concentration (CC) are sensitive to soil matric suction (ψ). The relationship between these two plant parameters and ψ in the root zone can help understand the water uptake efficiency and photosynthetic capacity of a plant. This paper aims to quantify the relationships between SC and CC with ψ, for Schefflera arboricola grown in compacted bare silty sand and biochar amended soil (BAS). Plant parameters (SC, CC, leaf area (LA), root length (RL)) and ψ were regularly monitored in an atmospheric controlled room. The maximum recorded SC was greater in BAS than that in bare soil due to the higher water demand of LA. Based on measured data upon evapotranspiration, two equations are proposed to interpret the effects of ψ on plant water uptake and photosynthesis. A fitting equation is established to relate normalized SC with ψ to identify a threshold suction ([Formula: see text]; indicator of drought stress resistance). The magnitude of [Formula: see text] is found to be mainly dependent on LA/RL ratio and root ends. Furthermore, a new relationship between CC and ψ is observed and developed. A decrease in CC at higher ψ is attributed to leaf senescence and stomatal closure, restricting plant to produce more chlorophyll.

Rolling dynamic compaction (RDC) is a soil compaction technique, which is capable of improving thick layers of soil at a relatively fast operating speed. The paper presents the results of laboratory experiments conducted on 1:13 scale models of the four-sided, 8 and 12 t, Broons BH-1300 and BH-1300 HD impact rollers, respectively, to study the performance of the scale model at four different operating speeds. A series of laboratory tests is undertaken using transparent soils and the particle image velocimetry (PIV) technique to investigate the effectiveness of the models. The transparent soil employed in this study consists of fused quartz and a pore fluid that matched the refractive index of the fused quartz. A one-particle thick layer of coloured fused quartz is embedded in the centre plane of the transparent soil to visualize soil internal displacements and a digital camera is used to capture the speckled pattern during the scale model testing process. The results show that the heavier module induces greater soil displacements at each operating speed. The optimal operating speed is approximately 299 mm/s for both module weights. The most significant soil displacements occur within the first 20 passes and no obvious ground improvement is observed after 35 passes. The results of this study demonstrate the unique capability of transparent soil to study soil displacements induced by the ground improvement scale models.

Suction caissons supporting offshore wind turbines are exposed to great horizontal loading above the soil surface, which may lead to overturning failure of the caisson. This paper presents a modified three-dimensional failure mechanism to analyze the anti-overturning bearing capacity of suction caissons. The modified failure mechanism is composed of a meniscus-conical wedge with a meniscus shape at the soil surface and a scooped shape. The analytical solution to the anti-overturning bearing capacity of the suction caisson is deduced in terms of the limit equilibrium method, followed by a parametric study of the wedge depth ratio (c) to optimize the critical failure mechanism that satisfies both the force and moment equilibriums. Thus, the methodologies are relatively easy to implement in traditional spreadsheets, and the analyses tend to perform very quickly. The effects of gap formation at the rear side of the caisson, loading eccentricity, and adhesion factor at the caisson–soil interface on the anti-overturning bearing capacity are also investigated. Compared with the finite element limit analysis results, experimental data, and existing theoretical solutions, it is proved that the presented limit equilibrium analysis can satisfactorily predict the anti-overturning bearing capacity of suction caissons with low aspect ratios for offshore wind turbines in uniform and linearly increasing strength clays.

This paper presents an experimental study on the pullout behaviour of inclined shallow plate anchors subjected to axial pull in sand. The 1g model tests were performed to examine the effects of anchor inclination and sand–anchor interface conditions on the load–displacement response and the associated failure and deformation mechanisms of plate anchors at various embedment ratios and sand densities. The anchor pullout capacity was found to increase continuously with the load inclination angle to the vertical (α), and the increase was more significant for α from 45° to 90°. The effect of sand–anchor interface conditions was negligible for horizontal plate anchors (α = 0°), but it became increasingly significant at larger inclination angles. The effects of these two factors both decreased with an increasing embedment ratio. Their influences on the failure and deformation mechanisms were measured and analysed using a digital image correlation (DIC) technique. Based on the test data and results available in the literature, a simple empirical method for the prediction of pullout resistance of inclined plate anchors in sand is calibrated and recommended.

This paper presents a novel framework of modeling crushable granular materials under mechanical loadings based on the discrete element method (DEM). The framework is featured with the construction of the one-to-one model in which every particle in a physical experiment has its own numerical twin and allows the modeling of irregular shaped fragments during the continuous breakage process. First, image processing techniques and spherical harmonic (SH) analysis were adopted, respectively, to segment and label particles and to construct a one-to-one model mathematically in DEM. Then, a particle crushing criterion based on the maximum interparticle contact force was used to predict the crushing events, showing fitting results that agreed very well with a large number of single particle crushing tests. Next, a statistical approach for the generation of particle fragmentation modes of a given type of sand particles based on the principal component analysis (PCA) was proposed. The aim of the PCA was to analyze the statistical trends of the coefficient matrix, which was composed of the SH coefficients of all the particles involved in the analysis. Finally, a successful modeling of a particle crushing event was achieved by replacing the particle, which was judged by the crushing criterion to undergo crushing, with a few subparticles chosen randomly from a specific fragment template constructed using the microcomputed tomography (micro-CT) data.

This paper presents a case history for the construction of the Pappadai dam in Italy. The dam is constructed from rockfill, with an upstream bituminous membrane, and is built on stiff clay foundations. The instrumentation of the dam and of the foundation soil provides detailed insight into the deformation patterns and pore-water pressure changes during dam construction and for the subsequent 7 years. Two-dimensional plane-strain finite element analyses, using fairly simple constitutive models for soil and rockfill behaviour, were performed to reproduce the soil–structure interaction so that the effects of reservoir impoundment, which has yet to be carried out, could be investigated. The paper shows that a careful choice of parameters and an understanding of the mechanical behaviour of the in situ soils can result in satisfactory predictions of the overall soil–structure interaction.Key words: rockfill, stiff clay, dam, field data, numerical analysis.

A detailed study on the available methods of predicting ground movements due to tunnelling works was carried out during the construction of the Madrid Metro extensions in 1995–1999 and 1999–2003. A total of 100 km were built and commissioned during this period. A numerical model was developed to simulate the earth pressure balance (EPB) excavation procedure and to complement some of the deficiencies found in previous analytical or empirical subsidence estimation procedures. Before the beginning of the works, a total of six different methods were used to estimate ground movements generated by the tunnelling works at some monitored sections placed in all five cities linked by the 1999–2003 extension, and the estimations were published in an earlier paper in this journal. Once all tunnelling works were finished and actual measurements carried out, a number of comparisons between predictions and measurements were made and are included in this paper. Conclusions about the applicability and accuracy of the methods are established with the aim of helping researchers and engineers in their future projects.Key words: ground movements, monitoring, numerical modelling and analysis, settlement, tunnels.

The paper describes a numerical model that was developed to simulate the response of three instrumented, full-scale, geosynthetic-reinforced soil walls under working stress conditions. The walls were constructed with a fascia column of solid modular concrete units and clean, uniform sand backfill on a rigid foundation. The soil reinforcement comprised different arrangements of a weak biaxial polypropylene geogrid reinforcement material. The properties of backfill material, the method of construction, the wall geometry, and the boundary conditions were otherwise nominally the same for each structure. The performance of the test walls up to the end of construction was simulated with the finite-difference-based Fast Lagrangian Analysis of Continua (FLAC) program. The paper describes FLAC program implementation, material properties, constitutive models for component materials, and predicted results for the model walls. The results predicted with the use of nonlinear elastic-plastic models for the backfill soil and reinforcement layers are shown to be in good agreement with measured toe boundary forces, vertical foundation pressures, facing displacements, connection loads, and reinforcement strains. Numerical results using a linear elastic-plastic model for the soil also gave good agreement with measured wall displacements and boundary toe forces but gave a poorer prediction of the distribution of strain in the reinforcement layers.Key words: numerical modelling, retaining walls, reinforced soil, geosynthetics, FLAC.

The paper describes a series of tests performed in a drum centrifuge on instrumented model displacement piles in normally consolidated sand. These tests examined the influence of the pile installation method, the stress level, and the pile aspect ratio on the increase in lateral effective stress on the pile shaft during static load testing to failure. A parallel series of constant normal load and constant normal stiffness (CNS) laboratory interface shear experiments was performed to assist interpretation of the centrifuge tests. It is shown that although the cycling associated with pile installation results in a progressive reduction in the stationary horizontal effective stress acting on a pile shaft and densification of the sand in a shear band close to the pile shaft, this sand dilates strongly during subsequent shearing to failure in a static load test. The dilation (the amount of which depends on the cyclic history) is constrained by the surrounding soil and therefore leads to large increases in lateral effective stresses and hence to large increases in mobilized shaft friction. The increase in lateral stress is shown to be related to the radial stiffness of the soil mass constraining dilation of the shear band and to be consistent with measurements made in appropriate CNS interface shear tests. The paper's findings assist in the extrapolation of model-scale pile test results to full-scale conditions.Key words: sand, displacement pile, centrifuge tests, shaft friction.

International audience; The main objective of the paper is to present a study on compacted expansive soil strains generated by complex hydric or mechanical loadings and their consequences on tested soil compressibility. In the first part of the paper, the suction controlled testing devices are described (osmotic and salt solutions methods). All the presented tests were performed in the range of suctions comprised between 0 and 40 MPa. The consequences of the strains induced by wetting as a function of the applied mechanical stress were analyzed. The results showed that, under these conditions, strain depends on the followed hydraulic path whereas the slope of the plastic compression line λ(s) was only affected by the suction applied during themechanical loading. The second test series demonstrated that the stress path influenced both deformation and slope λ(s) if suction higher than the initial sample suction was imposed during the test. As a conclusion, it could be stated that the slope λ(s) depends on the suction applied during a mechanical loading and on the maximum suction experienced by an expansive material during its past “history”.; L’objectif de cet article est de présenter une étude sur les déformations d’un sol gonflant provoquées par des sollicitations hydriques et/ou mécaniques complexes ainsi que leurs conséquences sur sa compressibilité notamment. Dans la première partie de l’article, les dispositifs expérimentaux à succion contrôlée employés (méthodes osmotique et solutions salines) pour conduire l’ensemble des essais sont décrits brièvement. Les essais ont été réalisés dans la gamme des succions comprises entre 0 et 40 MPa. Les conséquences d’une sollicitation hydrique monotone (humidification) conduite sous différentes contraintes ont d’abord été caractérisées. Il est apparu que dans ces conditions d’essai, les déformations dépendent du chemin de contrainte contrairement à la pente de compression plastique λ(s) qui ne dépend que de la succion imposée durant le chargement mécanique. Une deuxième série d’essais a permis de montrer l’influence du chemin de contrainte sur les déformations ainsique la pente λ(s) si une succion supérieure à la succion initiale des éprouvettes est imposée au cours de l’essai (dessiccation). En conclusion, la valeur de la pente λ(s) dépend de la succion sous laquelle est effectué le chargement mécanique mais aussi de la plus grande succion connue par le matériau au cours de son « histoire ».

This paper describes the foundation design process adopted for two high-rise buildings in Dubai, the Emirates Twin Towers. The foundation system for each of the towers was a piled raft, founded on deep deposits of calcareous soils and rocks. The paper outlines the geotechnical investigations undertaken, the field and laboratory testing programs, and the design process and describes how potential issues of low skin friction and cyclic degradation of skin friction due to wind loading were addressed. An advanced numerical computer analysis was used for the design process, which was carried out using a limit state approach. This necessitated analysis of a large number of load cases, and the paper describes how the information was processed to produce design information. A comprehensive program of pile load testing was undertaken, and class A predictions of both axial and lateral load–deflection behaviour were in fair agreement with the load test results. Despite this agreement, the overall settlements of the towers observed during construction were significantly less than predicted. The possible reasons for the discrepancy are discussed.Key words: case history, footings and foundations, full-scale tests, piles, rafts, settlement.

The paper presents the results of an experimental investigation of sampling disturbance in cohesive soils through single-element triaxial tests on resedimented Boston blue clay (RBBC). The first part of the paper discusses the effect of the overconsolidation ratio (OCR) (1–8) of the soil on postdisturbance compression and undrained shear behavior. The results demonstrate that sensitivity to disturbance decreases markedly with OCR. It is also found that for the medium-sensitivity soil tested, the estimate of the preconsolidation pressure is not significantly affected by OCR. The second part of the paper discusses laboratory reconsolidation procedures. For OCR1 RBBC, the recompression method is not effective in recovering the stress–strain behavior of the soil and, for greater disturbance, provides an increasingly unsafe estimate of the strength. For OCR4, provided the reconsolidation path reproduces the path that occurred in the field, this procedure succeeds in recovering the intact stress–strain–strength behavior of the soil. SHANSEP reconsolidation was investigated for normally consolidated RBBC only. For modest levels of disturbance, this is an effective means of evaluating both the stress–strain and the strength behavior of the soil. For greater levels of disturbance, the stress–strain behavior is not fully recovered, but the method continues to provide conservative estimates of the undrained strength.Key words: sampling disturbance, clays, overconsolidation ratio, undrained strength, recompression, SHANSEP.

This paper presents the field investigation of a major landslide that occurred in a newly dredged slope for port development in the city of Tianjin, northern China. The dredged slope comprised underconsolidated soft clay of recent marine and river delta deposits. The landslide consisted of a number of individual slides that occurred sequentially and extended retrogressively and laterally into reclaimed land. It lasted for about 1 h, occupying a plan area that is about 200 m long and 150 m wide in the reclaimed land. The failed soil mass was estimated to have a volume of between 700 000 and 800 000 m3. Part of the failed soil mass slipped into a newly dredged open space in the sea. The distance of the debris travel into the berth was about 80 m. The debris surface had a gentle slope of about 3.0°. The angle from the dredged slope crest to the far edge of the debris was about 6.8°. A common rupture surface was found underneath the debris and above the in situ marine mud. It controlled the inland extension of the slope failure. The landslide occupied an inclined area of between 27 000 and 30 000 m2, with an overall slope angle of about 3–4°. A kinematic model is proposed to explain the extension of the landslide into the reclaimed land. Findings of this field investigation are further used in the companion paper for a theoretical investigation of the mechanism of the landslide. The engineering approach and results presented in this study could be useful in the design and construction of dredged slopes in underconsolidated soft soils. Key words: port development, land reclamation, dredge excavation, landslide investigation, soft soils, case studies.

This paper presents the analytical study of a major landslide that occurred in a newly dredged slope during port development in the city of Tianjin, northern China. The slope comprised mainly underconsolidated and submerged soft soils. The landslide consisted of a number of individual slides that occurred sequentially and extended retrogressively and laterally into the reclaimed land. The paper proposes a slope stability assessment methodology for the examination of such slope failures, with retrogressive and lateral extension into reclaimed land. Both the total and the effective stress approaches are adopted in the slope stability assessment. Eight different sets of soil shear strength parameters are used in the assessment. They were determined by using different methods in the laboratory and in the field or by back analysis. The assessment results indicate that the total stress approach, together with undrained vane strength values, gives the best result in the stability assessment of the original dredged slope and the subsequent failed slopes. The paper further examines the factors that might have caused or triggered the occurrence of the landslide. Backfilling of a thick general soil layer and a sand cushion for vacuum preloading of the hydraulic fill in the reclaimed land might have rendered the entire slope marginally stable. Lowering of the tidal level might also have had an effect in triggering the landslide. The engineering approach and results presented in this study could be useful in the design and construction of dredged slopes in underconsolidated soft soils.Key words: land reclamation, dredge excavation, slope stability assessment, landslide investigation, marine mud, case studies.

The authors are correct in stating for static loading tests that “there are few full-scale ... pile group load tests reported in the literature.” I agree. However, a few more references are available than those listed by the authors, e.g., O'Neill et al. (1982a, 1982b), Phung (1993), and O'Neill and Reese (1999). Figure D1 shows the load–movement measured by Phung (1993) in comparing the response of a single pile to a group of five piles driven at a centerto-center spacing (c/c) of 5.7 pile diameters in a fine sand. The center pile (pile #1) was installed and tested as a single pile before the other piles were installed and connected by a rigid cap. The load–movement response of the five piles was different, but the difference was limited to the development during the initial loading. Beyond the first about 4 mm of movement, the load– movement curves were essentially parallel. Measurements of load distribution showed that the difference was mostly due to the difference in shaft resistance — the toe resistances were essentially equal for the five piles — and no correlation to location within the group could be discerned. The differences are considered caused by unsystematic compaction of the sand with no apparent effect of the driving sequence or other driving effect. A main observation was that the response in the loading of the center pile as a part of the group in effect was a reloading of the pile. The response at first loading of the pile as a single pile was considerably less stiff. Similar to the authors' work, the references mentioned above involve pile groups that at most consist of nine piles. A group of just a few piles — and nine piles is a very small number, where pile groups are concerned — will show minimal interaction and variation between the piles in supporting a structure. For a small pile group, the difference in load response between the piles in a piled foundation subjected to working load from the supported structure will be more affected by load variations, such as load center, load inclinations, and lateral loads, as opposed to when subjected to a static loading test on the group. Very few well-documented case histories are available in the literature with regard to full-scale studies of the performance of large pile groups under working load. However, a few are; for example, Golder and Osler (1968), Badellas et al. (1988), Goossens and Van Impe (1991), and Savvaidis (2003). The case histories show beyond doubt that the capacity and the load distribution of an individual pile in a large group of piles is of little relevance to the response of the piled foundation. Instead, the response of a piled foundation made up of a good-size pile group constitutes a settlement problem, and the capacity and load distribution of either an individual pile or the group is not the governing issue for a design. Despite that the authors (as do so many others) imply that the static loading test measures pile settlement, what is measured in a loading test is amovement response to a series of applied loads, not settlement. The authors' paper presents the movement response to applied load for a single pile and a few very small pile groups, not the settlement. Of course, settlement assessment relies verymuch on the results of a static loading test; in particular, on the response of the pile toe. However, the actual settlement of a piled foundation due to a working load, whether composed of a single pile, a few piles, or a large group of piles, is a very different issue. The authors present the load–movement response of two single piles and state the capacity criterion that the capacity of the piles is based on the “traditional 10% relative settlement criterion”. Although the criterion is used less often these days, it does keep appearing in the literature. A couple of years ago, I searched an assortment of successively older papers, textbooks, and standards that essentially stated the same criterion — sometimes with a slight modification away from the 10% value. Many did not give reference to the source, but some did, and I found the original source. The criterion has its origin in a mistaken quotation of a now 70 year old statement by Terzaghi (1942). Terzaghiwrote: “the failure load is not reached unless the penetration of the pile is at least equal to 10% of the diameter at the tip (toe) of the pile.” (For full quotation and context, see Likins et al. 2011). Note, Terzaghi did not define the capacity as the load generating a movement equal to 10% of the pile diameter, he emphatically stated that whatever definition of capacity or ultimate resistance used, it must not be applied until the pile toe has moved at least a distance corresponding to 10% of the pile toe diameter. (The pile head will then have moved an additional distance equal to the pile shortening.) Most certainly, Terzaghi did not suggest that a fixed movement value, however determined, could serve as a definition of capacity. Figure D2 shows the load–movement plot of the authors' static loading test on pile DZ1L. The usually very conservative definition called “offset limit”, or Davisson limit, indicates a lower-bound value of 1400 kN. It is here offered for reference. I do not suggest that the offset limit would be the pile capacity, but it does show the load for which the ultimate shaft resistance would have been reached. The Hansen 80-percent method results in an interpreted capacity of 1700 kN, coincidentally the maximum load applied in the test — the pile seems to be plunging. The Chin–Kondner and Decourt extrapolationmethods indicate 1850 kN. Thus, coincidentally, the 1540 kN capacity per the authors' “traditional” definition happens to be a reasonable value to choose from the load– movement curve. For full definitions and description of the methods for determining the capacity from the pile-head load– movement response, see Fellenius (1975, 2012). Figure D3 shows the authors' load distributions as evaluated from the strain-gage measurements in pile DZ1L up to a load of 1440 kN. The authors did not include the distribution for the maximum applied load (1700 kN). I have supplemented the figure with the authors' qc diagram from the sounding pushed nearest the test pile, soil descriptions, and layer boundaries. I have also added a distribution determined bymeans of both total stress and

This paper assesses methods to predict the saturated hydraulic conductivity, k, of clean sand and gravel. Currently, in engineering, the most widely used predictive methods are those of Hazen and the Naval Facilities Engineering Command (NAVFAC). This paper shows how the Hazen equation, which is valid only for loose packing when the porosity, n, is close to its maximum value, can be extended to any value of n the soil can take when its maximum value of n is known. The resulting extended Hazen equation is compared with the single equation that summarizes the NAVFAC chart. The predictive capacity of the two equations is assessed using published laboratory data for homogenized sand and gravel specimens, with an effective diameter d10 between 0.13 and 1.98 mm and a void ratio e between 0.4 and 1.5. A new equation is proposed, based on a best fit equation in a graph of the logarithm of measured k versus the logarithm of d102e3/(1 + e). The distribution curves of the differences “log(measured k) – log(predicted k)” have mean values of –0.07, –0.21, and 0.00 for the extended Hazen, NAVFAC, and new equations, respectively, with standard deviations of 0.23, 0.36, and 0.10, respectively. Using the values of d10 and e, the new equation predicts a k value usually between 0.5 and 2.0 times the measured k value for the considered data. It is shown that the predictive capacity of this new equation may be extended to natural nonplastic silty soils, but not to crushed soils or plastic silty soils. The paper discusses several factors affecting the inaccuracy of predictions and laboratory test results.Key words: permeability, sand, prediction, porosity, gradation curve.

The paper describes limit equilibrium analyses of two large-scale geosynthetic reinforced soil embankments and one unreinforced soil embankment that were taken to collapse under a strip footing placed close to the crest. One reinforced embankment was constructed with a relatively extensible and weak polypropylene geogrid and the second with a relatively strong and stiff high-density polyethylene geogrid. The geometry of the embankments and the loading arrangement were the same for all three structures. The focus of the paper is on a comparison of the predicted collapse load for the three structures and the actual observed values. A three-dimensional analytical approach is used to account for possible side-wall friction effects due to the test facility in which the large-scale experimental models were built. The paper also reports details on the interpretation of in-isolation constant load tests and strain measurements used to infer tensile loads in the reinforcement at failure. An important conclusion is that a general two-part wedge analysis approach can be used to predict the collapse footing load for both unreinforced and reinforced sand embankments in this investigation provided careful attention is paid to the selection of soil shear strength and reinforcement tensile capacity.Key words: geosynthetics, reinforced embankments, strip footing, large scale, limit equilibrium analyses.

The paper describes an experimental investigation in which two large-scale geosynthetic reinforced soil embankments and one unreinforced soil embankment were taken to collapse under a strip footing placed close to the crest. One reinforced embankment was constructed with a relatively extensible and weak polypropylene geogrid and the second with a relatively strong and stiff high-density polyethylene geogrid. The geometry of the unfaced embankments, sand soil, and loading arrangement were the same for all three structures. The focus of the paper is on the experimental design, construction, testing, and instrumentation techniques used in the investigation and selected test results. The results of the study show that the ultimate footing load capacity increased with an increase in reinforcement strength (and stiffness) and that the reinforced soil embankments had a load capacity up to 1.6–2.0 times that of the nominal identical control embankment without reinforcement.Key words: geosynthetics, reinforced embankments, strip footing, large scale, experimental.

This paper presents the design and construction of a deep excavation for building foundations in saturated soil. This deep excavation was of particular interest because it was located above and beside the Shanghai Metro tunnels. The twin Shanghai Metro tunnels had to be in full operation during the deep excavation. Potential large deformation of the twin tunnels was one of the main concerns during the design and construction for the deep excavation. The paper discusses in detail the criteria and measures for controlling the soil and tunnel deformation. The measures included cast-in-place concrete diaphragm walls with bracing structural members, pumping consolidation, cement–soil mix pile systems, and rational excavation procedures. A simplified theoretical method was proposed to estimate the increment in undrained shear strength in a soft clay layer due to pumping consolidation. Furthermore, conventional finite element methods were used to predict the soil vertical and horizontal displacements induced by the excavation. Using the design and construction methods discussed in the paper, the settlement and horizontal displacement of the tunnels were successfully controlled within 5.0 mm and 9.0 mm, respectively. The curvature of longitudinal deformation curve of the tunnels was less than 1/15 000. The horizontal displacement of the braced diaphragm walls was less than 0.12% of the total excavation depth. Key words: Metro tunnels, saturated soft soil, deep excavation, design, construction, ground improvement, case studies.

The saturated hydraulic conductivity of a soil can be predicted using empirical relationships, capillary models, statistical models, and hydraulic radius theories. A well-known relationship between permeability and the properties of pores was proposed by Kozeny and later modified by Carman. The resulting equation is largely known as the Kozeny–Carman (KC) equation, although the two authors never published together. In the geotechnical literature, there is a large consensus that the KC equation applies to sands but not to clays. This view, however, is supported only by partial demonstration. This paper evaluates the background and the validity of the KC equation using laboratory permeability tests. Test results were taken from publications that provided all of the information needed to make a prediction: void ratio, and, either the measured specific surface for cohesive soils, or the gradation curve for noncohesive soils. The paper shows how to estimate the specific surface of a noncohesive soil from its gradation curve. The results presented here show that, as a general rule, the KC equation predicts fairly well the saturated hydraulic conductivity of most soils. Many of the observed discrepancies can be related to either practical reasons (e.g., inaccurate specific surface value; steady flow not reached; unsaturated specimens, etc.) or theoretical reasons (some water is motionless; hydraulic conductivity of soils is anisotropic). These issues are discussed in relation to the predictive capabilities of the KC equation.Key words: permeability, prediction, gradation curve, specific surface.

This paper describes the development of a flexible wall permeameter apparatus for measuring the water and air coefficients of permeability of residual soils. Water and air coefficients of permeability were obtained for both the drying and wetting cycles for residual soils using the flexible wall permeameter. Volume changes of the soil specimens during unsaturated consolidation and during the water and air permeability measurements were also monitored. Factors that influence the measurements, such as hydraulic and pneumatic gradients and temperature fluctuations are described and discussed in this paper. The developed flexible wall permeameter was found to be capable of measuring water and air coefficients of permeability as low as 10–12m/s.Key words: flexible wall permeameter, permeability, residual soils, unsaturated soils, matric suction, flow rate.

The Terzaghi superposition assumption has been widely used to determine the bearing capacity of shallow footings. Although this assumption always errs on the safe side, a rigorous procedure to calculate the bearing capacity is still of engineering value. This paper presents such a procedure that is free from errors as a result of the superposition assumption. It demonstrates that the ultimate bearing capacity can be precisely expressed by the Terzaghi equation, except that the bearing capacity factor Nγis dependent upon the surcharge ratio. A recently developed numerical method, i.e., the critical slip field method, is used to calculate the modification coefficient for modifying Nγ. It is found that this modification coefficient increases with the surcharge ratio at small values of surcharge ratio and then remains constant for large values of surcharge ratio. However, the errors invoked by the superposition assumption do not exceed 10%. On the basis of numerical calculations, a simple closed-form expression of the modification coefficient is proposed that yields the theoretically rigorous ultimate bearing capacity. In the later part of the paper, errors in bearing capacity calculations owing to the use of conventional procedures are analyzed. It is concluded that the continued use of conventional procedures is justified, but the inherent errors should not be neglected in assessing the performance of shallow foundations.Key words: shallow foundation, strip footing, ultimate bearing capacity, critical slip field.

The authors mention that the constriction size distribution curve (CSD) was obtained according to Silveira (1965), and this method takes into account only the loose or dense soil relative density. Actually the method of Silveira (1965) takes into consideration only the densest soil state (maximum relative density). In that method, groups of only three particles are considered. The relations presented by the authors belong to the Silveira et al. (1975) method, in which Silveira et al. consider groups of four particles to represent the loosest soil state (minimum relative density). Equation [3] (in the paper under discussion) is basically applicable for the loosest soil state. To check its applicability for determining the CSD of the densest state, analyses were carried out through a computer program written by the discussers originally to determine the CSD for the densest and loosest soil states according to Silveira (1965) and Silveira et al. (1975), respectively. The program results were verified with some published data (e.g., Silveira 1965; Soria et al. 1993; Indraratna et al. 2007) and exact solutions were obtained. Small modifications were made to that program to determine the CSD for the densest state using the procedure described in the paper under discussion, i.e., determination of the angle a, which gives the minimum void area, instead of determination of the maximum void area as suggested by Silveira et al. (1975). The results of the analysis are shown in Fig. D1, in which the CSD curves for the densest state of the method (in the paper under discussion) and the method of Silveira (1965) are compared — it is obvious that there is a considerable difference between the two methods. The results of laboratory tests performed by Soria et al. (1993) show good agreement with the theoretical procedure of Silveira (1965), so the discussers believe that eq. [3] (in the paper under discussion) can not be applied to the determination of the CSD in the densest state. It is worth mentioning that, for the sake of comparison, the CSD curves shown in Fig. D1 are based on the finer percentage by weight, in accordance with the analyses carried out by Silveira (1965). Analyses (not included here) based on the finer percentage by number of particles using eq. [1] (in the paper under discussion) showed the same trend. The authors suggest that the percentages of finer are computed using eq. [1] (in the paper under discussion); actually, that equation represents the percentage of finer based on the number of particles, which over-represents the finer constrictions. Humes (1996) suggested that the percentage of finer based on surface area can represent the filtration analysis more accurately, with the percentage of finer based on surface area, PSA, computed using 1⁄2D1 PSAi 1⁄4 Pmi=Di XN i1⁄41ðPmi=DiÞ

Hansen 1436 Statistically summarizing and prese ting grain-size distribution (GSD) data would appear to be a simple, even mundane task, but actually presents subtle nontrivial challenges. The authors are to be commended for bringing this to the attention of the geotechnical community. The goal of summarizing GSD information in a soil characteristics database will also be a useful outcome. Perhaps because of the hidden difficulties in concisely characterizing such data, the geotechnical community invented their own way of presenting GSDs long ago. To some extent I feel that this paper represents a continued divergence from available approaches. When deciding how to attach a given statistical model (distribution) to a given set of data, statisticians appear to use one of the following two approaches: (1) They compare theoretical probability density functions (PDFs) to histograms describing the observed data (this is the basis for the well-known χ2 test), or (2) They compare cumulative distribution functions (CDFs) to observed percentiles, or to points found using so-called plotting position formulae. In either case, paper with a probability scale is usually used. This scale is most often the probability of nonexceedance of the standard normal deviate. This approach is common in hydrology. However, practicing geotechnical engineers have historically taken neither approach when attempting to present GSDs, and few practitioners would take the time to obtain a statistical model of a given dataset. In addition, rather than using statistical measures that are almost universally understood, such as the standard deviation, the coefficient of variation, and the coefficient of skewness, various uniformity coefficients are used in geotechnical engineering. In my opinion this has tended to make the entire “GSD process” more arcane. Both geotechnical engineers and statisticians do, however, frequently use percentiles, especially the median (“D50” to geotechnical engineers). The median particle diameter almost never has the same value as the mean particle diameter for soils because soil PDFs tend to be skewed. An estimate of the mean particle size from a sieve analysis is (compare eq. [3] in Wagner and Ding 1994)

This paper examines the constitutive behaviour of unsaturated mixtures of compacted sand-bentonite material. Two different techniques have been used to modify soil suction in laboratory specimens to examine the influence of suction on the behaviour of compacted materials. The two methods generated inherent differences in material fabric and therefore in stress-strain behaviour. The difference in microstructure generated by these two preparation techniques created different properties for the two series of specimens. This paper compares the behaviour of the two series of specimens and relates the observed mechanical behaviour to the initial soil fabric created by the two different preparation techniques. Specimens of similar compacted material were taken from two full-scale in-ground experiments conducted at Atomic Energy of Canada Limited's Underground Research Laboratory at Lac du Bonnet, Manitoba and sheared using the same triaxial equipment. The results are compared to the results of shearing laboratory compacted specimens. The research program demonstrates the need to understand the initial volume and suction states of plastic clays in order to predict the change in mechanical behaviour following a change in water content.Key words: constitutive relationships, unsaturation, laboratory tests, expansive soils, clays, shear strength.

The first part of the paper describes the precision and long-term stability that are required in triaxial stress-strain measurements and in stress-path control systems to obtain reliable information on creep in granular media. It is shown that membrane penetration and sample end compliance must be accounted for and that lubricated ends and local strain measurements are essential. The temperature sensitivity of each transducer also needs to be assessed, even when working in a temperature-controlled laboratory. The second part of the paper presents illustrative data that were obtained in tests on sand and Ballotini® glass beads. Considerable creep deformations were observed under both isotropic and anisotropic effective stress conditions, even at relatively low pressures where particle breakage was unlikely to be significant. The experiments show how creep depends on the stress conditions imposed, how the strain increment directions change during creep, and how the creep rates stabilize with time.Key words: sand, creep, triaxial test, yielding, membrane penetration.

This paper presents the results of a field study of hoarfrost formation on insulated test sections located in Québec City. It was established that the surface cooling rate increases sharply when all of the granular material placed above the insulating layer is frozen. The absence of latent heat release makes the pavement surface more sensitive to rapidly changing meteorological conditions. It was also shown that hoarfrost formation occurs when the surface temperature is less than the frost point, and it is not related to the dew point, as generally accepted. The paper also discusses the relationship between the hoarfrost index, HFI, and the total thickness of hoarfrost deposits.Key words: frost penetration, pavement, insulation, surface cooling, differential icing, hoarfrost.

Discussion 770 I have read this paper with interest since its subject matter pertains to our work in embankment dam engineering. As indicated in the paper, there are several procedures devised to locate a shear surface with the lowest factor of safety, and the author has presented one more and compared the results of his procedure with those of others; all based on the limit equilibrium method of slope stability analysis. The new results are about the same as the results previously reported by others. In an attempt to see how the results from a continuummechanics-based procedure will compare with those included in the paper, I made a quick analysis of the six problems using a commercially available computer program, FLAC (Itasca 1995). Also, I made an analysis of the problems using the limit-equilibrium-based slope stability analysis procedure SSTAB2 (Chugh 1992). Results of these analyses form the basis of this discussion. For Example 3, the values of effective internal friction angle, φ′, given in Table 1 of the paper are different from the values in the 1996 Greco paper; in fact they are a repeat of the numbers in the unit weight, γ, column. The values given in the 1996 Greco paper were used for results included in this discussion. For the Case 2 problem, Fig. 15 of the paper was scaled to obtain the data necessary for the analysis. In limit-equilibrium-based numerical procedures, the effectiveness of an automated search procedure depends on the successful performance of a nonlinear equation solver used to adjust trial values of factor of safety, F, and interslice force inclination, θ, to achieve a match between the computed and known values of boundary parameters at the other end of a shear surface. However, there is no assurance that the solution details associated with the critical shear surface thus found will necessarily be reasonable. These solution details are in terms of normal and shear forces at the base of slices, and interslice forces; their inclination and locations. Thus a search procedure which does not involve a criterion for an acceptable solution leaves the task of final selection of critical shear surface up to the user. There is no uniqueness in criteria for an acceptable solution to a slope problem by limit equilibrium procedures. For the location of interslice forces, some engineers prefer the middle third of the interslice boundary on the basis of linear distribution of normal stress, while others accept a solution in which interslice forces remain within the slide mass on the basis of nonlinear distribution of normal stress. Simi larly, when a soil has cohesive strength, some engineers are willing to accept a solution with tensile stresses that are con sistent with the magnitude of the cohesion value, while others consider the tensile strength of the soil to be zero and introduce a crack at the upper end of a shear surface. Inclination of interslice forces affects interslice shear forces. Some computer programs check for interslice shear failures, while others do not. Relying on a computed factor of safety without checking on the acceptability of the associated solution details is a mistake and should be discouraged. It would be helpful to know the criteria the author used in his work. Also, in limit equilibrium slope stability analysis, a search for critical shear surface should be preceded by analysis of shear surfaces of the engineers’ choosing. Such practices sharpen engineers’ skills to judge the path along which a sliding failure is likely, if one were to occur. Some of the shear surfaces included in the paper, especially those with long-drawn reverse curvatures at their exits, must be numerical constructs, as those geometries are unlikely to occur even in an ideal environment where the numerical model conditions could be duplicated, much less in nature. Thus, all of the slip surfaces attempted in the problems included in the paper must not have acceptable solution details. This should affect the final selection of an acceptable critical shear sur face. It would be helpful to know what nonlinear procedure the author used; the slope stability computer program in which he implemented his search procedure; his experiences with their use; and if he checked the computed solutions by examining the details for each shear surface obtained and what he found. Use of eq. [9] does not necessarily preclude occurrence of an unacceptable solution to a slope stability problem in general. Figures D1–D6 show the results of the problems using the continuum mechanics program FLAC. There are three parts to each figure: (a) shows the problem as modeled, (b) the convergence of trial factors of safety, and (c) the material

This paper discusses the geotechnical properties of two families of transparent silica, which can be used to model soil structure interaction and flow problems in transparent soil models. The fundamental premise of this research is that these materials can be used in model tests to study three-dimensional deformation and flow problems, using nonintrusive optical visualization techniques. Triaxial, direct shear, consolidation, and permeability tests conducted in this study indicate that transparent silica gels and amorphous silica have macroscopic geotechnical properties consistent with those of sands and clays, respectively. The materials used in this research have the same refractive index, which permits combining both families in a stratified transparent soil model. The transparent soils described in this paper represent the only system of transparent materials capable of resembling soils that have a wide range of grain sizes including sand and clay using the same pore fluid.Key words : imaging, optical, silica gel, amorphous silica, clay, sand, modeling.

Landslides are a risk to buried gas pipeline infrastructure, but these risks are particularly difficult to assess given the complex nature of landslide movements. This paper presents of portion of research conducted at the University of Manitoba where gas pipelines within active landslide areas were monitored over a 4 year period. Two locations were examined in western Manitoba within the Assiniboine River Valley where a shallow natural gas pipeline runs parallel to the valley slope. A field investigation and monitoring program was undertaken where surficial ground movements and soil and pipe temperatures and pipe strains through strain gauges were measured. Monitoring results identified soil near the pipeline does not freeze, and ground movements are

This paper examines the possible use of a bio-cementation process to reduce excessive bulging that occurs during the loading of granular columns in soft clays. A 12-phase percolation bio-chemical treatment technique was used to bio-cement part of the columns targeting the columns upper section, where bulging usually occurs. Upon application of unit cell surface loads up to 350 kPa, placement of a bio-cemented granular column substantially reduced the vertical strains by 43% to 48% compared with an un-cemented granular column and 56% to 60% compared with unreinforced kaolin clay for just a low replacement ratio of 11%. Bulging was reduced by 62% to 75% following bio-cementation and mostly occurred where bio-cementation was less evident. Scanning electron microscopy and energy dispersive spectroscopy validated the existence of calcium carbonate. This study presents a relatively new alternative to reducing bulging in granular columns using a promising approach.

This paper presents the horizontal bearing characteristics of piles in coral sand and silica sand from comparative experimental studies. Six model piles with different diameters were tested. The horizontal bearing capacity, deformation characteristic, bending moment, p–y curve, change in soil horizontal pressure, as well as particle breakage behaviour of coral sand were investigated. The results show that, in the coral sand foundation, the horizontal bearing capacities of piles and the increments in soil horizontal pressures are obviously greater than those in silica sand. Accordingly, the lateral displacement, rotation of the pile head, bending moment, and corresponding distribution depth in coral sand are significantly smaller than those in silica sand. The p–y curves indicate that the horizontal stiffness of coral sand is greater than that of silica sand. Remarkably, the breakage behaviour of coral sand is mainly distributed in the range of 10 times the pile diameter depth and 5 times the pile diameter width on the side where the sand is squeezed by the pile. Furthermore, in coral sand, the influence of pile size is more pronounced, the squeezing force generated by the pile spreads further, and its influence range is larger compared to those in silica sand.

Although there are several studies indicating that heating increases the long-term shaft resistance of energy piles, the mechanisms by which heating causes this increase have not been adequately evaluated yet. This article presents a comprehensive analysis and discussion to assess the important factors contributing to this increase by integrating the findings from three recently published papers studying the thermo-mechanical behavior of clay and the clay–pile interface. In these three studies, reconstituted kaolin clay was used, and cyclic and monotonic heat ranging between 24 and 34 °C were applied to the clay and interface. The interface was sheared under two stiffness boundary conditions: constant normal stiffness (CNS) and constant normal load (CNL), where normal stresses varied between 100 and 300 kPa. The analysis presented in this article reveals that the increase in strength of the interface under the CNL condition is primarily attributed to clay stiffening at the interface. However, the increase in shaft resistance under the CNS condition is primarily attributed to the heating-induced increase of effective lateral stress, although clay stiffening at the interface also partially contributes to the total increase of shaft resistance.

This paper presents an interpretation technique to quantify the effects of compaction state and matric suction on the undrained shear strength of compacted clay under confined undrained triaxial compression. This novel technique is based on the mathematical frameworks of the “stress history and normalized soil engineering property” (SHANSEP) method for saturated soil and the “Barcelona basic model” (BBM) for unsaturated soil. Test data of compacted Calgary till were analyzed and interpreted using the proposed technique. The interpretation technique is very useful in delineating the relative impacts of the factors on the behavioural trends in measured undrained shear strength. It was found that in addition to the initial compacted void ratio and suction, soil structure and failure mode exert significant influence on the undrained shear strength of compacted clay. This technique is attractive to engineering practitioners because the confined undrained compression tests (with no pore-air and pore-water pressure measurement) are much simpler and less time-consuming compared to rigorous laboratory tests on unsaturated soil.

Various undrained cavity expansion solutions for elastic–plastic soil have been proposed previously. However, no solution has been presented for elastic–viscoplastic (EVP) soil until now. This paper presents a general solution method for solving the classical one-dimensional (1D) boundary value problem (BVP) for undrained cylindrical or spherical cavity expansion in EVP soil with an emphasis on the rate effect of soil. The solution method is summarized as three standard procedures: (i) obtaining the soil displacement and strain under incompressible conditions, (ii) calculating the effective stress of soil through a suitable constitutive law, and (iii) obtaining the pore pressure by numerically solving the stress equilibrium equation through the finite difference method (FDM) or other numerical solution techniques. The numerical algorithms for calculating the effective stress and pore pressure are very simple, without any complex iteration processes, and they require little calculation time but provide high computational accuracy. In addition, some numerical results are given to investigate the influence of the cavity expansion velocity on the cavity expansion response. The proposed solution procedure is general and can be applied not only for the EVP model but also for other plasticity models, and the given EVP solution can be applied to interpret the rate effect of the cone penetration test and pile penetration.

This paper uses the results of a series of laboratory tests with cyclic principal stress rotation to assess the suitability of a number of empirical equations for estimating the development of plastic settlements in railway track foundations. The laboratory tests were carried out on three sand–clay mixes representative of railway track foundation materials, in both free-to-drain and undrained conditions. The results of a non-linear regression analysis demonstrate that the drainage conditions are the key factor affecting the estimation accuracy of the models, with the clay content playing a secondary role. The correlation coefficient was generally higher in free-to-drain than in undrained conditions and reduced slightly with increasing clay content.

The p–y method as a simplified analysis tool has been widely used to analyze the behavior of laterally loaded piles. This paper develops a novel cyclic p–y elastoplastic model within the framework of the single-surface bounding surface theory. The model can capture the soil stiffness degradation during cyclic loading by incorporating the cumulative plastic displacement to an interpolation function of the elastoplastic resistance coefficient. The model is relatively simple with only four parameters that can be determined from standard soil properties and stress–strain responses measured in direct simple shear tests. The performance of developed model is validated by predicting the cyclic lateral response of piles installed in soft clay during field and centrifuge tests published in the literature. The model can reliably simulate monotonic and cyclic responses of piles under different lateral loading patterns, and capture main characteristics of the pile-head load–displacement curve, such as nonlinearity, hysteresis, displacement accumulation, and stiffness degradation. It can also predict the evolution of the lateral deflection and sectional bending moment along the pile during cyclic loading.

Failure of the Merriespruit gold tailings dam in 1994 in South Africa was unusual in that never before had a gold tailings dam in South Africa failed in such a catastrophic fashion. Conventional thinking was that gold tailings would always exhibit dilative characteristics upon loading, primarily because of the method of deposition which allows significant consolidation to occur due to sun-drying. This paper demonstrates that the concept of a steady state line, which separates dilative from contractive behaviour upon undrained loading, is applicable to Merriespruit tailings. Four particle-size distributions of Merriespruit tailings were tested to determine the influence of the percent finer than 75 µm on the position of the steady state line. The tailings with the greater percentage of fines gave a steady state line that plotted above all the others, which translated to the requirement that a greater relative density was necessary to produce noncontractive behaviour than for the low-fines tailings samples. The difficulty of defining a unique steady state line for a particular tailings, due to errors in measurement of initial sizes, is illustrated and it is recommended that error bands be assigned to any steady state line. In a companion paper, evidence from the post-failure investigation is combined with the test results in this paper to explore the likelihood of static liquefaction as the cause of the Merriespruit flow failure.Key words: static liquefaction, tailings, steady state, flow failure.

This paper presents some possible interpretations of the physical meaning of the lumped, toe, and skin Case damping factors, jcL, jct, and jcs, respectively, which are extensively utilized in the dynamic analysis of pile driveability and capacity. A single degree of freedom model is employed to relate the Case damping to the hysteretic damping ratios of soil and pile materials. This relation and the damping ratios of soils and piles show that the Case damping factors for piles in sandy and clayey soils may overlap at all strain magnitudes. Coupling of pile toe and skin resistance is analyzed, and the jcLfactor is found to be a function of the skin and toe resistance ratio of the pile. Consequently, the jcLfactor is an important indicator with which the skin friction and toe resistance of piles can be separated. A database of 133 cases of dynamic pile tests in Florida has been used to substantiate the analyses and interpretations. The effects of the assumptions made in this paper are also discussed.Key words: pile dynamics, wave equation, Case damping, hysteretic damping, bearing capacity, skin friction.

Environmental assessments of proposed infrastructure projects include an appraisal of the vibration that would be generated by potential construction methods. This paper considers one part of that process: prediction of groundborne vibration from percussive piling. Various methods for predicting the magnitude of the groundborne vibration generated by percussive piling have been described in the literature. In general, the accuracy of the predictors is limited. The paper investigates the reasons for this, through the development of theoretical models and analysis of field data from an extensive programme of on-site vibration monitoring. It is found that some widespread assumptions about the relationship between the energy rating of a percussive piling hammer and the vibrational energy developed in the ground are invalid. Ground conditions are shown to have a dominant influence on the magnitude of the groundborne vibration generated by percussive piling, and piling vibration predictors which take no account of soil type yield considerably less accurate estimates than site-specific predictions.Key words: piling, vibration, monitoring, prediction, environmental assessment.

The Canadian geotechnical engineering community has completed a major collaborative 5 year research project entitled the Canadian Liquefaction Experiment (CANLEX). The main objective of the project was to study the phenomenon of soil liquefaction, which can occur in saturated sandy soils and is characterized by a large loss of strength or stiffness resulting in substantial deformations. In many areas of Canada, large structures are constructed on or comprise sandy soils, e.g., some major hydroelectricity earth dams and many tailings impoundments in the mining industry. The behaviour of loose sandy soils can be difficult to predict, but can have a significant financial impact on these types of engineering structures. Consequently, the intent of the CANLEX project was to improve the overall understanding of soil liquefaction. This paper provides an overview of the CANLEX project, outlining the project objectives, major achievements, and conclusions. Four companion papers describe different aspects of the project; thus, together, the five papers provide a summary of the CANLEX project.Key words: geotechnical, liquefaction, CANLEX, collaborative project.

The Canadian geotechnical engineering community has completed a major collaborative 5 year research project entitled the Canadian Liquefaction Experiment (CANLEX). The main objective of the project was to study the phenomenon of soil liquefaction, which can occur in saturated sandy soils and is characterized by a large loss of strength or stiffness resulting in substantial deformations. The intent of this paper is to compare, interpret, and summarize the large amount of field and laboratory data obtained for six sites in Western Canada as part of the CANLEX project. The sites are compared in terms of both flow-liquefaction and cyclic-softening considerations. The paper presents a number of conclusions drawn from the project as a whole, in terms of both fundamental and practical significance.Key words: sand, flow liquefaction, cyclic softening, CANLEX.

This paper presents the results of a full-scale field experiment on the stability of a slurry-filled diaphragm wall trench. The objective of this experiment was to observe the failure pattern of a slurry-supported trench excavated in sandy ground. Ground responses, including settlement and lateral deformation of the surrounding ground adjacent to the experimental trench, were carefully monitored during the experiment. The stability of the trench was examined by lowering the slurry level in stages. The trench was deliberately failed. Field observations indicated that the experimental trench failed in 2 h in a progressive sliding pattern that resulted in a near-hemispherical cave-in of the adjacent ground. In this paper, a failure mechanism of the trench is proposed and an analytical method is adopted to back-analyze the stability of the trench. The stability of the trench and the failure pattern can be accurately analyzed using the method of Tsai and Chang.Key words: full-scale experiment, field test, slurry trench, stability analysis.

The satisfactory disposal of scrap tires is a major environmental problem worldwide. This waste occupies valuable space in landfill sites, and tire stockpiles pose serious health and fire hazards. The use of scrap tires as reinforcement for construction of retaining walls and slopes is a viable method towards reduction of this waste. This paper describes the construction of a 57 m high × 17 m wide instrumented test fill, comprising both retaining wall and reinforced slope sections. Approximately 10 000 whole tires and tires with one sidewall removed, tied together with polypropylene rope, were used in both cohesionless and cohesive backfills. The testing program also included plate loading tests, field pull-out tests on tire mats, water-quality assessment in the field and laboratory, and other complementary laboratory testing. This first paper, in a series of three, demonstrates the practical feasibility of constructing reinforced earth fills using scrap tires. Results of large plate load tests and the field behaviour with particular reference to the design of the retaining wall sections are presented. The paper emphasizes the role of negative wall friction in increasing the active thrust when the retaining wall becomes more compressible than the backfill. Recommendations for the design of retaining walls using scrap tires are presented.Key words: scrap tires, earth reinforcement, retaining walls, reinforced slopes, plate load test, construction, performance.

The disposal of scrap tires has become a major environmental concern. The reuse of scrap tires in the reinforcement of earth structures can provide an attractive solution in reducing the number of used tires disposed in overcrowded landfills. This paper, the second in a series of three papers, discusses the behaviour of slopes reinforced with scrap tires and proposes design recommendations. A mat-reinforced slope can either fail by pull-out of the reinforcement or due to rupture of the attachment tying the tires. A large number of pull-out tests were performed on whole tires and tires with one sidewall removed embedded in sand and cohesive backfill. The pull-out resistance of tire mat reinforcement was primarily governed by the effective shear strength of the soil, and therefore it can provide an efficient means of reinforcement. However, large displacements were required to fully mobilize the ultimate pull-out capacity which must be considered in design.Key words: pull-out tests, scrap tires, reinforced slope, performance, design guidelines.

Discussions 979 The discusser was very happy to read this paper with very interesting experimental data on the static liquefaction of sands just after he had submitted for publication a paper where he has applied the general equations provided by the principle of natural proportionality to describe this type of behaviour (Juarez-Badillo 1999). That paper contains a brief description of the origin of the general equations and the method of determining the values of the parameters from the experimental data. However, the general equations and their graphs applicable to the figures are included in this discus sion.

When sandy soils respond in a strain-softening manner to undrained loading, an estimation of the resulting undrained shear strength (Su) is required to determine the potential for flow liquefaction at a given site. One of the most commonly used methods for estimating the undrained strength of liquefied sand is an empirical standard penetration test (SPT) based chart (originally proposed by H.B. Seed), which was developed using a number of case histories. The original interpretations of these case histories are viewed by many workers and regulatory agencies as the most authoritative measure of the liquefied strength of sand. Consequently, in comparison, other less conservative methods are generally held in an unfavourable light. This paper reexamines the original database of case histories in view of some more recent concepts regarding soil liquefaction. The objectives of this paper are to explore and reassess the issues involved in the original assessment and to offer alternative views of the case records. The conclusions presented here indicate that alternative explanations of the liquefied strength of sand are not inconsistent with the original case histories. Key words: sandy soils, soil liquefaction, undrained strength, standard penetration test (SPT).

To evaluate geotechnical variability on a general basis that will facilitate the use of reliability-based design procedures, it is necessary to assess inherent soil variability, measurement error, and transformation uncertainty separately. The inherent variability and measurement error are addressed in a companion paper, and transformation uncertainty is addressed herein. A second-moment probabilistic approach is applied to combine these uncertainties consistently based on the manner in which the design soil property is derived. The design properties considered in this paper are undrained shear strength, effective stress friction angle, in situ horizontal stress coefficient, and Young's modulus. This paper concludes with specific guidelines on the typical coefficients of variation for these common design soil properties as a function of the test type and the type of correlation used.Key words: transformation uncertainty, undrained shear strength, friction angle, in situ horizontal stress coefficient, Young's modulus, geotechnical variability.

Salt rocks, such as potash and rock salt, show a complex mechanical behavior that is rate and history dependent. Various approaches exist to represent the main features of the response of these rocks through constitutive models. The approach proposed in this paper is to formulate the constitutive equations using internal state variables (ISV) in the context of the unified theory of inelastic flow. To illustrate the application of this approach, the authors use an updated version of a viscoplastic model with reduced expressions for laboratory triaxial tests at relatively high confining pressure. It is shown that, under these conditions, mixed hardening of salt rocks can be described through a combination of scalar and directional ISV. The authors also describe in some detail a procedure to obtain the material parameters for the model equations. The paper shows some characteristics of the model response for various loading paths, illustrating the good agreement with experimental observations and highlighting some of the differences with a classical isotropic hardening model.

This paper first describes the numerical implementation of the coupled formulation for the theory of consolidation of unsaturated soils. The developed computer code is verified using the Mandel-Cryer problem and then is applied to the solution of coupled multidimensional consolidation problems. Using a parametric study, it is demonstrated that, in unsaturated soils, the Mandel-Cryer effect is suppressed and the consolidation process in unsaturated soils is affected significantly by the shape of the soil-water characteristic curve. Finally, the developed model is used to analyze the consolidation of an unsaturated-saturated soil column. Analysis results indicate that the classical "undrained" pore-water pressure response to an externally applied load only occurs in the saturated zone while the pore-water pressure response is subdued in the unsaturated zone. This paper also shows a method of deriving one of the two additional material parameters required for the analysis of unsaturated soils from laboratory test results.Key words: coupled consolidation, unsaturated soils, Mandel-Cryer effect, soil-water characteristic curve.