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A method for the estimation of the non-linear, time-dependent settlement of piled raft foundations (PRFs) embedded in saturated clayey soils subjected to uniformly distributed load under the single-drainage condition was developed. A total of 20 different rectangular PRFs resting on four different types of normally consolidated to moderately overconsolidated clays (overconsolidation ratios of 1, 2 and 5) were analysed to quantify their short- and long-term settlements. Rigorous three-dimensional, elasto-plastic finite-element (FE) analyses were performed with the critical-state-based modified Cam Clay soil constitutive model. Biot's coupled consolidation theory was used to model the time-dependent dissipation of excess pore pressure under the single-drainage condition. The FE analysis results were used to investigate systematically the influence of time and various soil and PRF parameters on the settlement responses of piled rafts. Fitted equations correlating PRF settlements and the degree of consolidation with various influencing parameters were developed. The proposed equations predicted the immediate and primary consolidation settlements and the degree of consolidation with reasonable accuracy and can be used in initial design stages. [ABSTRACT FROM AUTHOR]

The simple but profound standard equation given in BS 1377:1967 is revisited in this paper. According to the equation, plasticity index (PI) is 2.13 times (or simply twice) the linear shrinkage. This standard relationship is widely recognised and employed when determination of the liquid limit or plastic limit is difficult or not possible. The equation is also used as a basic means of checking the accuracy of test results for the Atterberg limits. Data of 180 natural soil samples were used to statistically evaluate the veracity of the equation. It was found that the BS 1377:1967 equation exhibits excellent accuracy and the equation's veracity for practical engineering use was confirmed. However, the method appears to be correct only up to PI values not exceeding 25% and has greater accuracy at lower PI values (<15%). Other studies in the literature also show that the equation may not apply to some soil types or to soils of particular clay mineral types. These possible limitations thus require further investigation. [ABSTRACT FROM AUTHOR]

A detailed experimental programme was conducted to evaluate the liquefaction susceptibility of non-plastic and low-plasticity soils subjected to cyclic loading under undrained triaxial loading conditions. The study mainly focused on examining the influence of the amount of fines and plasticity indices on the liquefaction resistance of sands. After mixing silt and clay fractions into fine sand, 16 soil combinations were prepared. The silty sands contained up to 40% non-plastic fines and the low-plasticity soils contained a clay fraction of 5–40%. Each cylindrical soil specimen was constituted to a medium relative density and saturated specimens were subjected to a confinement pressure of 100 kPa. The consolidated specimens were then subjected to various levels of cyclic stress amplitudes using a sinusoidal wave load form at a frequency of 1 Hz. The results showed that both the non-plastic and low-plasticity clay soils were less resistant to liquefaction than the fine sand. The soils belonging to categories SM and SC (silty sand and clayey sand, respectively, as per Indian standard soil classifications) were susceptible to liquefaction if the fines passing through a 75 μm sieve were ≤ 40%, the liquid limit was ≤ 40%, the plasticity index was < 15 and the saturated water content was about 0.86 times the LL. [ABSTRACT FROM AUTHOR]

Estimated soil clay contents (P0.002) obtained from consistency limits were evaluated by means of comparison with the results of the conventional hydrometer test (P0.002h). In total, 180 soil samples were tested for Atterberg limits, linear shrinkage and clay content to generate the data used for statistical evaluation. It was found that there is a strong correlation between P0.002 and P0.002h, with realistic and valid statistical equality. However, the variability in P0.002 estimations – up to 50% – is quite high for practical purposes. Nevertheless, the findings of the study confirm the credibility of the hydrometer method. [ABSTRACT FROM AUTHOR]

Triaxial tests were performed on artificially cemented gravel–silty clay mixed soils and remoulded samples under consolidated drained conditions. The aim was to investigate the effects of the content of silty clay and confining pressure on the stress–strain, volumetric strain and other mechanical characteristics of the cemented and remoulded samples. The test samples were prepared with different fines contents and effective confining pressures. The results showed that both the confining pressure and the fines content had a great effect on the mechanical properties of the cemented and remoulded samples. During triaxial shearing, the cemented samples underwent dilation and strain-softening, accompanied by the appearance of shear bands at a confining pressure lower than 100 kPa and fines content less than 30%. Otherwise, the cemented samples showed strain-hardening and contraction, accompanied by bulging failure. All the remoulded samples showed strain-hardening and contraction, accompanied by bulging failure during triaxial shearing. The shear strength decreased with increasing fines content and the influence of the fines content increased with an increase in confining pressure. It was also found that, the higher the fines content, the lower the cohesion and friction angle of the cemented and remoulded samples. [ABSTRACT FROM AUTHOR]

When saturated, clayey soils are subjected to compressive stress and there is a time lag between the applied stress and the extrusion of pore water; there is thus a lag in the settlement. Soils under structures such as silos, tanks and so on may be subjected to cyclic loading. The theories that can be used for the calculation of consolidated settlement under cyclic loadings, such as triangular cyclic loading, contain errors due to the assumptions used in the derivations of mathematical equations. Thus, using these theories can create significant errors. The characteristics of the cyclic load, the surcharge and the specimen can affect the consolidation settlement as well as the time to achieve a steady state. Thus, in this research, one-dimensional consolidation of clay subjected to triangular cyclic loading was experimentally investigated under several conditions. The results showed that the ultimate consolidation settlement of a clay layer and the time to reach this state decreased with an increase in surcharge and an increase in cyclic time. Furthermore, the experimental results showed significant differences from the results obtained using theoretical methods. [ABSTRACT FROM AUTHOR]

Granular layers are often placed over weaker clay soils to improve the bearing capacity of working platforms and spread foundations. Their design requires the calculation of a two-layer bearing capacity. The commonly used existing calculation models are quite empirical with imprecise input parameters and can err on the non-conservative side in some situations. Other proposed methods tend to involve multiple design charts and are suited only to either strip or circular foundations. In this paper a new and highly practical design method is proposed whose input parameters are derived directly from the shear strengths of the two layers without the need for empirical-based charts. The output can be obtained either from a single chart or a few equations that are straightforward to implement into a spreadsheet. It can be applied quite generally to both surface and shallow embedded foundations, circular and rectangular and with dry or saturated granular layers, and also to working platform design for tracked plant. The method was validated using three independent numerical studies and centrifuge testing. The results showed that, although errors can increase for foundation shapes towards square or circular and with increasing overburden, the errors are smaller than those of the commonly used existing methods and are also conservative. [ABSTRACT FROM AUTHOR]

The aim of the study reported in this paper was to develop practical correlative models capable of predicting the compaction characteristics of clay soils blended with rubber from waste vehicle tyres. Four different clay soils, ranging from intermediate to high plasticity, were adopted for the test programme and each was blended with four different percentages of ground rubber waste. The test programme consisted of cone penetration (consistency limits) and standard Proctor compaction tests. As a result of ground rubber inclusion, the consistency limits and compaction characteristics all exhibited a linear decreasing trend with increase in rubber content. The rate of decrease, however, was greater for the high-plasticity clays. Simple correlative models, linking the compaction characteristics to the consistency limits, were suggested and validated by statistical techniques. The proposed models provide a practical procedure towards predicting the compaction characteristics of ground rubber–clay blends without the hurdles of conducting laboratory compaction tests, and thus can be implemented in practice for preliminary assessments. [ABSTRACT FROM AUTHOR]

Retrogressive or progressive landslides in slopes with highly sensitive quick clays may extend several hundred metres from where the slide was initiated. Reintroducing high salt contents to the pore water of leached low-saline quick clays may inhibit the development of such large landslides. Wells filled with potassium chloride (KCl) were installed in a quick-clay deposit at Dragvoll, Trondheim, Norway, to investigate the impact of changed pore-water chemistry on the geotechnical properties. The clay ceased to be quick due to favourable changed ion composition in the pore water, even at low salt contents, thus inhibiting retrogressive development. The apparent pre-consolidation stress ( p′c) increased with increasing salt contents and the immediate collapse in structure typically seen in quick clays was avoided at loads just beyond p′c by changing the pore-water chemistry. Quick clay treated with KCl may therefore work as a barrier against retrogressive development and reduce the risk of initiation of progressive landslides. [ABSTRACT FROM AUTHOR]

The characteristics of clay soil in the Saga Plain in Japan, as well as the effect of the depositional environment on its engineering properties, have been investigated. While the clay was being deposited there were several large-scale volcanic eruptions in the region. A considerable amount of volcanic ash settled into the clay, which had a marked effect on its engineering properties. The soil is strongly structured and the sedimentation compression curves are well above the sedimentation compression line proposed by Burland, which indicates some degree of cementation. The compression index is high - even for soil samples with in situ vertical effective stresses of 200-300 kPa, the index can be as high as 2·3. The rate of permeability reduction with void ratio is higher than most reported data in the literature. The reason considered is that the compression process involves not only gradual compression of the pores but also breaks down relatively large pores into smaller pores, which can cause rapid reduction of permeability. The stiffness is lower, with results of unconfined compression tests showing that the ratio of undrained shear strength to secant modulus is about 150. [ABSTRACT FROM AUTHOR]

The core of an earth dam is normally made of clayey base soils and protected by a sandy filter. Designing the filter can be very challenging considering the various criteria established today. This study commences with a review of three prominent criteria referred to in designing filters by the indirect method. No-erosion filter tests are then carried out involving 11 fine-grained, base soil samples with different properties; these are a highly dispersive soil, a soil with a medium to high degree of dispersion, a soil with a low-plasticity silt (ML) classification and a soil with a broad gradation curve. These tests represent the direct method. A comparison of results arising from the two methods shows that designing filters the indirect way, by following established criteria alone, is not always safe. Hence, it is proposed that such designs should be experimentally verified using no-erosion filter tests. Furthermore, instead of following the prevalent criteria in the indirect design method, the perfect filtering method for highly dispersive soils and the reduced particle size distribution method for broadly graded soils are proposed to be used, with merits given for each method. Finally, the paper recommends certain filter criteria from the literature for base soils with a moderate degree of dispersion and an ML classification respectively. [ABSTRACT FROM AUTHOR]

Helical screw piles are a popular solution for relatively low-capacity, removable or recyclable foundations supporting road and rail signage or similar light structures. When specifying a helical screw pile, a designer must choose the active length and the helical plate spacing ratio, which are governed by the number, spacing and size of the individual helices. This paper presents an investigation using transparent synthetic soil and particle image velocimetry to observe the failure of helical screw piles with helical plate spacing ratios of 1·5-3 and active lengths up to three times the diameter. For the geometries and properties examined, capacity is shown to be a function of active length and the dominant failure mechanism is characterised by the formation of a cylindrical failure surface. A simple analytical model is developed and used to assess the impact of different design methodologies on immediate displacements under loading. A traditional 'permissible stress' method is shown to be conservative, whereas modern 'partial factor' methods are more economical and lead to greater immediate displacements for a given design load. Designers using modern 'partial factor' approaches, such as Eurocode 7, might benefit from specifying a helical plate spacing ratio of less than 1·5 to maximise the stiffness of the response to axial loading and minimise the immediate displacements experienced upon application of working loads. [ABSTRACT FROM AUTHOR]

The article presents response to a research conducted by Benjamin S. Kyambadde and colleagues regarding influence of gravel on strength and index properties of a clay soil. It informs that shear strengths of the clay–gravel mixtures remain unaffected when the gravel content is less than 45 percent and comments on greater variation in penetration depths in clay-gravel mixture. It also presents response from the authors of the discussed article.

The soils found abundantly along the Konkan belt in peninsular India are lateritic soils and lithomargic clays. The locally available lithomargic clayey soils are problematic in the sense that their strength reduces drastically under saturation conditions, which is typical behaviour of the dispersive type of soil. Most foundations are placed on this soil layer. This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the behaviour of granular columns in these weak (lithomargic clay) grounds. Tests are carried out with two types of loading: with the entire area in the unit cell tank loaded, to estimate the stiffness of the improved ground; and with only the granular column area loaded, to estimate its limiting axial capacity. Investigations were carried out by varying the area ratio (or spacing), diameter of granular columns, end condition and column configuration. The load-settlement behaviour, stiffness and bulging behaviour of granular columns are analysed. It is found that the ground treated with granular columns exhibits a high load-carrying capacity and stiffness, and a significant reduction in settlement, compared with the untreated ground. [ABSTRACT FROM AUTHOR]

The behaviour of solid circular concrete piles in clayey soils under a combination of lateral and vertical loading was investigated by numerical analysis. Piles with different lengths were considered, and ultimate lateral bearing capacity was calculated. The model was verified on the basis of data obtained from a previously published full-scale pile load test. The effect of axial loading on the ultimate lateral bearing capacity has been previously investigated in only a few studies. In this paper, particular attention was devoted to the influence of axial loading on lateral bearing capacity. In addition, a comparison between Flac three-dimensional results and both Allpile and Broms approaches was performed. [ABSTRACT FROM AUTHOR]

In this study, the effect of specific surface area on compressibility and permeability characteristics of remoulded and intact clayey soils was investigated. Fifteen remoulded and 15 intact soils with a wide range of physicochemical properties were tested. The results indicate that specific surface area has a significant effect on compressibility and permeability behaviour of clayey soils. In addition to other soil index properties, specific surface area can be used for estimating these engineering properties. Significantly high correlation coefficient ( = 0·97) between compression index ( ) and the specific surface area is observed for remoulded clayey soils with only methylene blue-spot specific surface area. There is no significant correlation between the BET-N specific surface area and . The effect of the remoulded water content on proposed specific surface area and relationship is also investigated. The results show that as specific surface area of soils increases, decreases, indicating the importance of the diffuse double layer on the consolidation process. The results also reveal that permeability is controlled by the specific surface area of soils. In addition, the data obtained in this study indicate that there is a linear correlation between / and , which indicates the significance of initial void ratio on the compressibility characteristics of soils. [ABSTRACT FROM AUTHOR]

Stabilisation of sulphate-bearing soils with lime/cement-based binders has always been problematic, owing to excessive sulphate-induced expansion. This paper reports on investigations conducted on the consistency and compaction properties of Lower Oxford Clay (LOC), a sulphate-bearing soil that has been difficult to stabilise in the traditional manner using lime. In the investigations, LOC was stabilised both in the conventional manner using lime as the control, and also using a wide range of sustainable stabilisers incorporating industrial waste and by-product materials. The sustainable binders included wastepaper sludge ash (WSA) used on its own, as well as binary binders comprising WSA--lime, WSA--Portland cement (PC) and WSA--ground granulated blastfurnace slag. The results obtained showed that the blended stabilisers incorporating WSA were able to modify the soil by reducing the plasticity index, coupled with good compaction, strength and volume stability properties. The findings suggested that there are economic and environmental advantages of utilising WSA and similar industrial by-products in the modification and compaction of soils, including sulphate-bearing clay soils, as equal or at times superior alternatives to the traditional stabilisers of lime and/or PC. [ABSTRACT FROM AUTHOR]

This paper presents the effect of short, discrete, randomly oriented fibres (natural and synthetic) on the mechanical properties of clayey soils. The mechanical properties investigated include peak unconfined compressive strength, stiffness and ductility. Three types of clayey soil were obtained from the eastern part of Irbid city in northern Jordan. Two types of fibre were used in this study: nylon and palmyra fibres, with aspect ratios () equal to 75. The clayey soils were mixed with fibres at five different percentages by volume of solid soil particles: 1%, 2%, 3%, 4% and 5%. The results showed that the peak unconfined compressive strength, stiffness and ductility of the clay-fibre mixture increased with fibre content. The post-peak softening in compression resistance decreased with increasing fibre content. The relative unconfined compressive strength increased with fibre content. Palmyra fibre showed a higher increase in the relative unconfined compressive strength than nylon fibre when mixed with clayey soil, for all fibre contents. Furthermore, the clayey soil with a high activity index showed greater improvement when mixed with fibres than that with a low activity index. [ABSTRACT FROM AUTHOR]

This study investigates the anisotropic behaviour of the shear strength of overconsolidated clayey soils. The results of the study will help engineers and scientists to predict the lateral shear strength of clayey soils from the ordinary vertical shear strength. The main objective of this paper is to investigate experimentally the effect of anisotropy on the shear strength properties of clayey soil. Fifteen types of clayey soil were obtained from various locations in the Irbid area, Jordan, and from different depths. Three undisturbed samples were obtained from each location at three different inclinations (horizontal, vertical, and inclined at 458 to the vertical). Unconfined compression tests were conducted on all soil samples. It was found that the unconfined compressive strength values were greater in the vertical direction than in the inclined and horizontal directions, and increased as the overconsolidated ratio increased. It was also noticed that the failure strain in the horizontal samples was smaller than in the vertical samples. The anisotropic behaviour of clayey soils almost disappeared at greater depth for both unconfined compressive strength and failure stain. [ABSTRACT FROM AUTHOR]

This paper proposes a simple method for estimating the horizontal effective stress in clay soils, from which the mean effective stress can be determined. It is shown that the method is applicable to a wide range of clay soils with varying stress histories, including normally consolidated and heavily overconsolidated clays. Although this paper is expected to be of use to many practitioners in the field of geotechnical engineering, it also has a particular relevance with respect to the effects of moisture abstraction on shrinkable clay soils by vegetation, or simply by seasonal variations. While the effects are well known, the methods for identifying clay desiccation and for calculating heave potential are often relatively expensive, and the results can be inconclusive. Using the proposed method, this paper describes a simple and low-cost alternative method for estimating the in situ mean effective stress in desiccated clay soils. This information can be used to confirm the likely depth of clay desiccation, and provides a means of calculating a further estimate of heave potential. [ABSTRACT FROM AUTHOR]

The pile designer in a seismically active region will generally need to estimate the maximum seismically induced internal moment and shear of the pile in order to provide adequate strength to maintain the structural integrity of the pile. In this paper an effort has been made to provide a simple means of carrying out such an estimation for a single pile embedded in a homogeneous clay layer. The results have been presented in the form of design charts that can be used directly by designers with no or little computational effort. The variables in the design charts include the length and diameter of the pile, the Young's modulus of the pile material, the strength and stiffness of the soil, and the factor of safety against axial failure of the pile. The charts have been obtained from a time domain analysis of pile-soil interaction, and are based on the response of the piles to a range of earthquakes recorded in North America and Australia. [ABSTRACT FROM AUTHOR]

The ‘delayed collapse’ of cuttings in stiff high-plasticity clay is known to be significantly affected by long-term recovery of pore pressures and progressive failure resulting from brittle material behaviour. Limit equilibrium methods are not well equipped to model these effects, but the increasing use of numerical modelling offers new potential to improve understanding of these failure mechanisms. A series of numerical analyses incorporating brittle material behaviour has been undertaken, specifically considering deep-seated first-time failure of cuttings in weathered London Clay. Because of progressive failure, the average mobilised strength is between the peak bulk strength and the residual strength. In current practice, parameter selection is often based on Chandler and Skempton's back-analysis of several deep-seated failures in the ‘brown’ weathered London Clay. This paper considers variation of the critical (minimum) height for delayed deep-seated failure in cuttings in weathered London Clay with slope angle, and variation of mobilised strength with cutting height. [ABSTRACT FROM AUTHOR]

Limited guidance on usage and methodology is currently available to engineers for the most common rapid load pile test, known as Statnamic. In order to improve the analysis of Statnamic testing in clay soils a full-scale instrumented auger bored pile was installed and tested in glacial lodgement till. As a result, improvements have been suggested in the test methodology and analysis. The inclusion of an accelerometer at the pile head would allow direct measurement of acceleration and verification of displacement measurements and velocity calculations. High-precision optical levelling of the pile before and after test cycles would allow multiple loading cycles to be considered cumulatively with greater confidence. The separation of the laser reference source from the test pile should be sufficient to avoid surface wave disturbance. [ABSTRACT FROM AUTHOR]

Dynamic experiments in lateral mode were carried out on model aluminium single piles in a simulated elastic half-space filled with clay soil to determine dynamic constants of the soil-pile system and to study the bending behaviour of piles. Model piles with various lengths were subjected to steady state harmonic vibrations with different magnitudes of force of 7-30 N applied over a wide range of frequencies from 2 Hz to 50 Hz. The load transferred to the pile, pile head displacement and strain gauge readings at different locations on the pile were measured. It is observed consistently that the magnitude of the applied force and the pile length significantly affect the natural frequency of the soil-pile system. It is found that rigid piles behave linearly even at the higher magnitudes of applied force, but that flexible piles behave non-linearly as the magnitude of the applied force increases, which leads to a substantial reduction of the lateral stiffness of the soil-pile system. Damping of the soil-pile system is found to increase with an increase in pile length and magnitude of the applied force, owing to the occurrence of radiation and hysteretic damping. Based on experiments carried out on model piles embedded in clay at low confining pressure, it is found that the maximum dynamic bending moment of long flexible piles is about four times higher than that of short rigid piles. The maximum bending moment under dynamic loads occurs at deeper depth than the corresponding depth for static loads, which indicates an increase of the active length of piles under dynamic load. [ABSTRACT FROM AUTHOR]

This paper presents the results from a field experiment involving the vertical loading to ultimate failure of a shallow pad footing founded on a soft estuarine clayey silt. Data from settlement plates and pneumatic piezometers located beneath the footing are used, in conjunction with estimated stress distributions, to compare the ground's stiffness characteristics with those measured in laboratory tests. The operational undrained shear strength of the clayey silt, inferred from the ultimate vertical load of the foundation, is also compared with in situ and laboratory estimates of undrained shear strength and with operational strengths estimated from a similar footing test. The paper presents the results from a prediction competition held for the footing experiment with a view to assisting assessment of the reliability of standard design prediction procedures. [ABSTRACT FROM AUTHOR]

A letter to the editor in response to the article "Ground heave induced by installing stone columns in clay soils" by B. McCabe and colleagues in a 2013 issue is presented.

An introduction to the journal is presented in which the editors discuss various reports within the issue on topics including the progress towards a Register for UK Ground Engineering Professionals, the interface shear tests and pull-out tests on model piles to study the shear resistance of bitumen coated piles in sand, and field performance data for stone columns in soft clayey soils.