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Soil settlement is an essential criterion in the design and performance assessment of geotechnical structures, often evaluated using results from one-dimensional compression test. However, assessment of the results from this test involves graphical methods, which produces inconsistent interpretations on the parameters to be used in design. The nonlinear compressibility curve is also subjected to bilinear idealization with divergence from the actual behavior at high stresses. In order to overcome these problems, a nonlinear mathematical formulation is developed to represent the soil compressibility with high precision over a wide range of stresses. The adequacy of the formulation is validated against a large and diverse dataset comprised of different geological materials, including undisturbed and reconstituted soils as well as stabilized soils. The proposed formulation is dependent on two fitting coefficients, which are defined in terms of commonly used compressibility parameters compression index, recompression index and preconsolidation pressure. A single expression is also derived to calculate soil settlement without numerical discontinuity. Finally, a method for evaluation of swelling pressure of soils is also developed using the parameters of the same mathematical formulation.

This paper investigates the influence of the structured property of loess on its compressive behaviour and proposes a new method for determining the preconsolidation pressure of structured loess soil. A series of oedometer tests were carried out on undisturbed and remoulded loess samples prepared at various moisture contents. The effects of moisture content on the structured yield stress, the preconsolidation pressure, and the structural strength were also captured. It was found that the influence of the structured property of loess on the compression behaviour is divergent between undisturbed and remoulded loess samples. The discrepancy before and after structural yielding is more remarkable for the undisturbed soil. The Casagrande method realized through the MATLAB program can effectively eliminate human factors and accurately calculate the corresponding preconsolidation pressure for undisturbed soil. The effects of moisture content on the method for determining the preconsolidation pressure considering the structured property of loess were discussed. The determination method can accurately evaluate the loess consolidation state in loess regions. The influencing rules which the moisture content exerts on the structured yield stress, the preconsolidation pressure, and the structural strength all conform to exponential functions. The study is of great significance to correctly differentiating the foundation consolidation states and calculating the ground settlement in loess regions.

Clay is under the coupling influence of both time and temperature in some innovative geomechanical problems. Previous experimental researches have confirmed that time and temperature affect the overconsolidation degree of clay and induce overconsolidated characteristics. However, the experimental findings have not been included in constitutive models so far. This paper presents an innovative thermo-viscoplastic constitutive model based on the unified hardening model for overconsolidated clay. The new model combines the effect of time and temperature on overconsolidation by incorporating a temperature variable and a time variable into the hardening law and simultaneously considers the overconsolidated characteristics of clay by using the unified hardening parameter. The simulated results for laboratory tests show that the proposed model can not only reflect the influence of temperature and strain rate on the preconsolidation pressure, the undrained shear strength and the flow rule, but also describe the failure after undrained heating and creeping.

This study deals with the performance evaluation of the soil improvement using surcharge preloading techniques with prefabricated vertical drains (PVDs) for the Mahshahr oil storage tanks project as a case study. First, the ultimate settlement values were predicted using observational methods, then, to determine the modified preloading design parameters, the involved parameters such as compression index (Cc) and preconsolidation pressure (P'c) were back-analyzed by comparing measured data with the numerical simulations. To this end, the numerical simulation was carried out using Settle3D software. The numerical model results indicated that the settlement value using modified parameters obtained from the back-analysis procedure was lower than the calculated settlement based on the assumed parameters in the initial estimation, which can be attributed to the conservative determination of initial geotechnical parameters. Moreover, optimum spacing and depth of PVDs were evaluated, and soil settlement was compared before and after the preloading operation. It was concluded that after preloading, soil settlement approached acceptable settlement values, which indicates the efficiency of this method for large-scale soil improvement projects.

The increasing demand for building materials in the road industry creates interest for a new source of high-quality aggregates. In order to conserve natural resources, more attention is focused on anthropogenic soils and industrial solid wastes. For the successful application of these types of soil, a series of geotechnical and environmental tests have to be conducted. A potential hazard in the reuse of wastes from thermal degradation in the construction industry, particularly in reinforced concrete (RC) construction, is the migration of heavy metals into the groundwater environment. In this article, a geotechnical assessment of blast furnace slag (BFS) properties is presented. We conducted a series of CBR, and oedometric tests to evaluate the feasibility of BFS application in earth construction. The oedometric test results show acceptable compression characteristics which are in the range of natural aggregates. The CBR shows that this material may be used as a pavement subbase. We also noticed the preconsolidation pressure phenomenon in both Proctor and vibro-compacted soil during the oedometric test. The compression index and recompression index value show that the compression characteristics are close to those of dense sand. Based on the results described in the article, blast furnace slag is a candidate for technological application and can become one of the elements of sustainable development by contributing to a reduction in the negative environmental impact of production and use of building materials.

Increased traffic and environmental loads necessitate re-evaluation of the stability of existing road and railway embankments built on soft sensitive clays. Thus, the current mobilised undrained shear strength needs to be quantified. A methodology to evaluate changes in undrained shear strength under embankment loading is developed and applied for the case of Haarajoki test embankment. The methodology combines boundary value modelling of embankment loading with integration point level stress path probing using the Creep-SCLAY1S model. The changes in the stress state and the relevant state parameters resulting from the boundary value modelling enable the quantification of the mobilised undrained shear strength. The results indicate an increase in the undrained shear strength up to 17% in the most affected clay layer. The high pre-overburden pressure in the top of clay deposit prevents significant changes in the undrained shear strength in the case of Haarajoki. Thus, when assessing changes in the undrained shear strength, one of main parameters to determine is the initial preconsolidation pressure.

In this study, we investigated the preconsolidation pressure (P C) of sedimentary soft rock and its relationship with brittle-ductile transition (BDT) pressure. We proposed a generalized preconsolidation pressure (P G) suitable for both soil and sedimentary soft rock, which is defined in terms of the yield stress of the initial sediment structure under confined lateral compression. We then explored the digenetic effect on P G using 24 sediment types. Next, P G and BDT pressure were verified using confined compression and conventional triaxial tests, respectively, on red-bed soft rock in the Dingxi region of China. Finally, we discussed the BDT mechanism and analyzed the relationship between the two characteristic pressures for a given initial yield surface considered structural strength. We found that the relationship was dependent on the strength parameters, the initial structural strength, and the coefficient of earth pressure at rest. The findings of this study will have a significant impact on the determination of BDT pressure of sedimentary rock in future studies.

This article presents an experimental study on 81 specimens made from three different mixtures of clay and sand. To ensure uniform initial parameters, all specimens were prepared with an initial water content of 30%. Two series of unconsolidated undrained shear tests under different overconsolidation ratios were conducted on a direct shear apparatus: the first aims to determine the SHANSEP (Stress History and Normalized Soil Engineering Properties) parameters namely S and m, whereas the second is used for evaluating the preconsolidation pressure. This work has provided an opportunity to investigate the influence of sand content on SHANSEP parameters and moreover to study the reliability of the preconsolidation stress estimated by the SHANSEP procedure.

The mechanical behavior of frozen soils plays a central role in the design, construction, and maintenance of buildings and infrastructure in cold regions. We present and discuss the main results of an experimental campaign focused on the mechanical behavior of frozen soils from Alaska. The data set is unique because it involves natural frozen soils and covers a wide range of temperatures (i.e., from −6 °C up to −26 °C) and confinements (i.e., from unconfined conditions up to a cell pressure of 54.6 MPa). An elastoplastic model for frozen soils is presented and validated based on the test results. The elastoplastic model accounts for the effects of temperature and cryogenic suction on key properties associated with frozen soil behavior, namely, increase of preconsolidation pressure, stiffness, and strength with the decrease of temperature. Other aspects such as the volumetric behavior of frozen soils at different temperatures and the smooth transition between elastic and plastic states are also qualitatively well captured by the model. We implemented the constitutive model in a fully coupled thermo-hydro-mechanical simulator and we analyzed the behavior of a foundation in a thawing ground. The proposed approach is able to capture the main feature of frozen soil behavior.

Settlement and slope stability of an embankment are mechanical aspects that play a major role in structural safety. Due to the tendency towards renewable energy, the embankments can be considered as a suitable medium for thermal energy storage. Using horizontal heat exchanger tubes, the thermal energy will be stored in different compacted soil layers in an embankment. Therefore, this structure can be subjected to daily and seasonally temperature variations due to heat extraction. Cyclic temperature variation can modify the mechanical behavior of compacted soils. Thus this study aims to investigate the effect of monotonic and temperature cycles in the range of 5 to 50 oC, on consolidation parameters and shear characteristics of a compacted sandy lean clay. To achieve this, temperature-controlled oedometric and direct shear tests were performed. Results showed that the effect of heating and cooling on mechanical properties is more pronounced under vertical stresses higher than the preconsolidation pressure. By heating, the normal consolidation line shifted to the left and consequently, the apparent preconsolidation decreased. Compression and swelling indexes could be considered independent of temperature variation. Due to the temperature cycles, the volumetric response of the compacted soil in oedometric and shear tests was stress history-dependent. Results of the direct shear tests showed that by temperature variation (heating/cooling and temperature cycles) the cohesion increased and the friction angle remained unchanged.

The results of a series of laboratory tests on unimproved and cement-improved specimens of two clays are presented, and the ability of a bounding surface elastoplastic constitutive model to predict the observed behavior is investigated. The results of the oedometer, triaxial compression, extension, and cyclic shear tests demonstrated that the unimproved soil behavior is similar to that of soft clays. Cement-improved specimens exhibited peak/residual behavior and dilation, as well as higher strength and stiffness over unimproved samples in triaxial compression. Two methods of accounting for the artificial overconsolidation effect created by cement improvement are detailed. The apparent preconsolidation pressure method is considerably easier to use, but the fitted OCR method gave better results over varied levels of confining stresses. While the bounding surface model predicted the monotonic behavior of unimproved soil very well, the predictions made for cyclic behavior and for improved soils were only of limited success.

Summary To accurately predict soil volume changes under thermal cycles is of great importance for analysing the performance of many earth structures such as the energy pile and energy storage system. Most of the existing thermo-mechanical models focus on soil behaviour under monotonic thermal loading only, and they are not able to capture soil volume changes under thermal cycles. In this study, a constitutive model is proposed to simulate volume changes of saturated soil subjected to cyclic heating and cooling. Two surfaces are defined and used: a bounding surface and a memory surface. The bounding surface and memory surface are mainly controlled by the preconsolidation pressure (a function of plastic volumetric strain) and the maximum stress experienced by the soil, respectively. Under thermal cycles, the distance of the two surfaces and plastic modulus increase with an accumulation of plastic strain. By adopting the double surface concept, a new elastoplastic model is derived from an existing single bounding surface thermo-mechanical model. Comparisons between model predictions and experimental results reveal that the proposed model is able to capture soil volume changes under thermal cycles well. The plastic strain accumulates under thermal cycles, but at a decreasing rate, until stabilization. Copyright © 2017 John Wiley & Sons, Ltd.

The investigation deals with the stress distributions of undisturbed soil samples taken by preconsolidation press method from paleoseismological studies in the Gerede (Bolu) segment of the North Anatolian Fault System (NAFS), which is one of the most important intra-continental active transform faults in the world. Taking into consideration of the theoretical principal stress directions causing the faulting in the soil samples, consolidation experiments were carried out in different directions and the preconsolidation pressure values (PPV) of the samples were found by Casagrande method. Relations between the prime stress directions which are effective in the mechanism of fault formation and the values of PPV found by the Casagrande method were revealed. With all these calculations, the principal directions and magnitudes of the principal stresses causing faulting in the near-surface depths on the Gerede segment of the NAFS have been determined by a new method. The Gerede segment of the maximum principal stress (?1) value at N 55.50 W and N 600 W was found 554.08 kPa and 327.54 kPa respectively. The maximum principal stress (?1) direction of the fault was found to be N 55.50 W and the angle value was 44.50. © 2019 MMF2005D3 Part of this study was financially supported by the Çukurova University Research Foundation (Project No: MMF2005D3 ).

The study area is in a zone under the influence of the Lake Van water changes and the Van fault, which caused a destructive earthquake in 2011. Due to the level changes of Lake Van, sediments with different thicknesses as well as grain sizes were deposited in this region and the characteristics of these sediments were significantly affected by the morphology and lake water fluctuations in the past. A total of six boreholes were drilled along a 3-km line within the study area to determine the preconsolidation pressure (?pc) and the pressuremeter test values of the clayey levels of old lake deposits—which are known to have different physical and mechanical properties—with hopes to gain an insight on how they influence the mechanical tests performed in the field and in laboratory conditions. The relationship between these values was also statistically evaluated. When both datasets were evaluated together, it was determined that the stresses in the area close to the Van Thrust Fault plane caused deformations in the soil, which in turn affected the hanging-wall block of the thrust fault in particular. The inspection of EM and ?pc values for the area within the primary compression zone of the Van Fault revealed that both values of the boreholes on the footwall block were higher compared to other boreholes close to the lake (southwest). This finding indicates that the fault stresses at the footwall block of the fault plane enhance the mechanical characteristics of the soil. The data obtained were also evaluated using regression analysis. Relationships between all available data were investigated and a high coefficient of determination was derived between the Menard deformation modulus (EM) and the preconsolidation (?pc) pressure. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature. 2017-FBA-6347 The Scientific Research Projects Office of Van Yüzüncü Yıl University (YYU-BAP, Project Number 2017-FBA-6347) financially supported this study. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Recently, in Korea, problems related with unstability of slope or sinkhole in urban area due to erosion of compacted granite soil which was used as a backfill or embankment material have been treated as important issues. Small hole might develop inside of backfill area due to erosion of not only weathered granite soil but also clay, silt, fine sand size particles when underground water flows. Once erosion starts in a soil mass, erosion rate increases gradually to cause rapid destruction. In this study, a rotating cylinder test (RCT) was performed to evaluate the hydraulic resistance characteristics of compacted weathered granite soil under various relative densities and preconsolidation pressures. Meanwhile, an image analysis method was introduced to analyze radius of irregularly eroded sample. It was found that image analysis is an effective means of minimizing the error in calculating a critical shear stress and threshold shear stress on the irregularly eroded sample. Furthermore, in general, hydraulic resistance capacity increases with the increase of relative density and preconsolidation pressure.

In this study, research was conducted to examine the performance of the lime pile application, a deep chemical stabilization method to improve the engineering characteristics of marine soil deposits. By using a laboratory-scale model, the marine soil sample was compacted into soil blocks in circular steel test tanks, with the installation of lime piles in them. An experimental program examined the effect of lime piles on physical and engineering properties of the soil in terms of curing periods and lime pile radial distances. Test results showed that clay fines, linear shrinkage, compressibility, and swelling pressure decreased, while permeability, preconsolidation pressure, and stiffness increased significantly with an increase in curing periods and within a close distance to the lime piles. Also, the electrical resistivity of the treated soils was examined to monitor the changes in their electrical properties. Finally, the correlation between the measured electrical resistivity and swell pressur...

The lumpy soil is a by product of the open-pit mining. A composite-lumpy material (in which, the lumps are randomly distributed in the reconstituted soil) is being created due to the degradation of the initial granular structure. In the present study, the compression and failure behaviour of an artificial lumpy material with randomly distributed inclusions are investigated using the finite element method. The computation results show that the stress ratio, defined as the ratio of the volume average stress between the lumps and the reconstituted soil within the inter-lump voids, is significantly affected by both the volume fraction and the preconsolidation pressure of the lumps under an isotropic compression path, while the volume fraction of the lumps plays a minor role under a triaxial compression path. Based on the simulation results, a homogenization law was proposed utilizing the secant stiffnesses.

The study is about the estimation of preconsolidation stress using a correlation method. Disturbance of soil samples can result in the yield point of void ratio-log vertical stress data from oedometer test being unreadable. Therefore, correlations were calculated to estimate preconsolidation stress using effective vertical stress ( σ ′ v 0 ), oedometer modulus ( E oed ) from oedometer tests and unloading-reloading modulus ( E ur ) from triaxial tests. Profile of stress history: Overconsolidation ratio ( OCR ), overconsolidation difference ( OCD ) and overconsolidation gradient ( OCG ) were determined in Kiscelli Clay based on new equations. An additional new parameter, ratio of mechanical preloading component of overconsolidation is defined and analysed.

Compacted clay cores are extensively used in rockfill dams to cut off water flow because of their low permeability and wide availability. Large differential settlement often occurs at certain locations in a dam, causing large shear concentrations in the compacted clay core in the form of shear bands. This raises concern about the permeability evolution in the shear bands in compacted clay during a large shear process. Thus, a ring-shear radial-seepage apparatus was developed for evaluating the permeability of the shear bands in compacted clay. The apparatus tests hollow cylindrical specimens that are held in a shear box, which consists of an upper box, lower box, and inner chamber. The specimen is compressed in the height direction and sheared in the circumferential direction to form a concentrated shear band. The permeability of the shear band is measured by radial-seepage from the inner side to the outer side of the hollow cylinder. To demonstrate the performance of the apparatus, a series of tests was conducted on compacted specimens of a clay used for the core wall of a high rockfill dam. The test results showed that the change in permeability of the shear bands in compacted clay was dependent on the surcharge pressure. If the current surcharge pressure was far less than the preconsolidation pressure caused by the previous compaction process, the permeability of the shear band might increase significantly. This experimental finding can be useful for identifying high-risk leakage zones in a dam with a compacted clay core.

Copper mine tailing (CMT) has the potential to be used as embankment material but thiswaste material contains plasticity. Soils containing plasticity are highly reactive to any form of liquid andconsidered to have greater compressibility when exposed to water. As an embankment material, CMT issusceptible to different environmental condition which can cause significant settlement. One possible causeof volume loss is the compression due to wetting or hydrocompression. This study aims to determine theconsolidation properties and hydrocompression settlement of waste materials with plasticity like copper minetailing when used as embankment material. One-dimensional consolidation tests were performed onreconstituted specimens. The obtained consolidation properties indicate that CMT is very slightlycompressible under over-consolidated condition to moderately compressible under normally consolidatedcondition. The hydrocompression settlement of CMT in relation to initial void ratio, moisture content andvertical pressure was investigated. The hydrocompression settlement increases with increasing pressure untilthe preconsolidation pressure is reached, then decreases with pressure beyond the preconsolidation pressure.Samples with lower density and initial water content less than its optimum exhibit greater hydrocompressionsettlement. The determined hydrocompression strain in every condition is less than 5% which means thatCMT has a degree of collapsibility classified as low to negligible despite of having plasticity. CMT whenused as embankment materials should be prepared with initial moisture content slightly more than itsoptimum, it should be in its very dense condition and preloaded with vertical stress more than itspreconsolidation pressure to make hydrocompression strain negligible.

A substantial body of laboratory and field observations on compression and consolidation of soft clay and silt deposits as well as organic soils, suggest a soil behavior according to Hypoth...

This paper involves an evaluation of a relationship describing the evolution in yield stress of unsaturated soils during hydraulic hysteresis, and an application of this relationship in an elasto-plastic framework to predict the compression curves of unsaturated soils under drained (free outflow of air and water with constant suction) or undrained (constant water content with no outflow of water and varying suction) conditions. The yield stress was quantified as the apparent mean effective preconsolidation stress obtained from compression tests reported in the literature on specimens that had experienced different hydraulic paths. It was observed that the preconsolidation stress does not follow a hysteretic path when plotted as a function of matric suction, but does when plotted as a function of the degree of saturation. Accordingly, an existing logarithmic relationship between the preconsolidation stress and matric suction normalized by the air entry suction was found to match the experimental preconsolidation stress results. This same relationship was also able to satisfactorily predict the trends in preconsolidation stress with degree of saturation by substituting the hysteretic soil–water retention curve (SWRC) into the place of the matric suction. The relationship between preconsolidation stress and suction was combined with an elasto-plastic framework to predict the compression curves of soils during drained compression, while the wetting-path relationship between preconsolidation stress and degree of saturation was combined with the framework to predict the compression curves of soils during undrained (constant water content) compression. A good match was obtained with experimental data from the literature, indicating the relevance of considering the hysteretic SWRC and preconsolidation relationships when simulating the behavior of unsaturated soils following different hydro-mechanical paths.

The continuous increase of road traffic needs in both developed and developing countries is accompanied by an important growth of highway transportation networks and consequently produce a huge amount of waste tires, and causes numerous environmental issues. On the other hand, due to their lightweight and high damping performance, several researchers are interested in the use of the soil–rubber mixtures for the attenuation of earthquake motions and ground vibrations by their capacity to absorb the external solicitations. However, several questions arise regarding the mechanical behaviour of the soil–rubber mixtures. This paper presents a thorough study on the impact of scrap tire addition on physical properties of Chlef sandy soil. A series of laboratory tests are conducted on sand–rubber mixtures with various percentage of crumb rubber: 0, 0.5, 1.0 and 1.5% by a dry weight. Oedometric tests are carried out in order to explore the influence of rubber particles on the sand compaction and consolidation with focusing on the compressibility parameter. The experimental tests show that the increase of the percentage of crumb rubber leads to an increase of both the compression index Cc and the swelling index Cs of sand–rubber mixtures, contrariwise, a slight decrease in the preconsolidation pressure and the oedometric modulus is observed.

The effect of temperature on the mechanical behavior of the soils around the special geo-structures, such as nuclear waste containers and energy piles can’t be neglected. In this paper, some temperature-controlled laboratory test results are selected and analyzed, based on which and the thermal induced changes of main mechanical features (e.g., shear strength, critical state line, preconsolidation pressure) are identified. A constitutive model is then developed to interpret the temperature dependent behavior of saturated clays under the framework of critical state theory. Only one temperature related parameter is added in the present model comparing with the Modified Cam Clay model, and this parameter can be directly obtained from the yield loci of the soil. The performance of the proposed model is demonstrated with simulating temperature tests under drained condition.

The existence of the threshold hydraulic gradient in clays under a low hydraulic gradient has been recognized by many studies. Meanwhile, most nature clays to some extent exist in an overconsolidated state more or less. However, the consolidation theory of overconsolidated clays with the threshold hydraulic gradient has been rarely reported in the literature. In this paper, a one-dimensional large-strain consolidation model of overconsolidated clays with consideration of the threshold hydraulic gradient is developed, and the finite differential method is adopted to obtain solutions for this model. The influence of the threshold hydraulic gradient and the preconsolidation pressure of overconsolidated clay on consolidation behavior is investigated. The consolidation rate under large-strain supposition is faster than that under small-strain supposition, and the difference in the consolidation rate between different geometric suppositions increases with an increase in the threshold hydraulic gradient and a decrease in the preconsolidation pressure. If Darcy’s law is valid, the final settlement of overconsolidated clays under large-strain supposition is the same as that under small-strain supposition. For the existence of the threshold hydraulic gradient, the final settlement of the clay layer with large-strain supposition is greater than that with small-strain supposition.

It is generally recognized that the low strength and high compressibility are the characteristics of soft soil. In addition to other techniques, reinforcement can also be used in increasing the strength and decreasing the deformation of this kind of soil. The results of an investigation into the effects of a natural fiber on the consolidation and shear strength behavior of Shanghai clayey soil reinforced with wheat straw fibers are presented in this paper. A series of one dimensional consolidation and triaxial tests were conducted on samples of unreinforced and reinforced Shanghai clayey soil with different percentages of randomly distributed wheat straw fibers. The results show that the preconsolidation pressure decreases and the coefficient of swelling and compression generally increase with increasing the fiber content until a optimum content value. Furthermore, the addition of wheat straw fiber leads to a significant increase in shear strength and friction angle of the natural soil and there is an optimum wheat fiber content that makes this increase maximal.

Preconsolidation pressure is a parameter obtained from the soil compression curve and has been used as an indicator of load-bearing capacity of soil, as well as to characterize the impacts suffered by the use of machines. Despite its importance in soil physics, there is a few software or computational routines to support its determination. In this paper we present a computational package in R language, the package soilphysics, which contains implementations of the main methods for determining preconsolidation pressure, such as the method of Casagrande, Pacheco Silva, regression methods and the method of the virgin compression line intercept. There is still a consensus that Casagrande is the standard method, although the method of Pacheco Silva has shown similar values. The method of the virgin compression line intercept can be used when trying to be more conservative on the value (smaller) of preconsolidation pressure. Furthermore, Casagrande could be replaced by a regression method when the compression curve is obtained from saturated soils. The theory behind each method is presented and the algorithms are thoroughly described. We also give some support on how to use the R functions. Examples are used to illustrate the capabilities of the package, and the results are briefly discussed. The latter were validated using a recently published VBA. With soilphysics, the user has all the graphical and statistical power of R to determine preconsolidation pressure using different methods. The package is distribution free (under the GPL-2|3) and is currently available from the Comprehensive R Archive Network (http://CRAN.R-project.org/package=soilphysics). The R platform and all the package dependencies are similarly available from CRAN.

The coefficient of earth pressure at rest K 0 of fine-grained soils is often being estimated empirically from the overconsolidation ratio (OCR). The relationships adopted in this estimation, however, assume that K 0 is caused by pure mechanical unloading and do not consider that a significant proportion of the apparent preconsolidation pressure may be caused by the effects of ageing, in particular by secondary compression. In this work, K 0 of Brno Tegel, which is a clay of stiff to hard consistency (apparent vertical preconsolidation pressure of 1800 kPa, apparent OCR of 7), was estimated based on back-analysis of convergence measurements from unsupported cylindrical cavity. The values were subsequently verified by analysing a supported exploratory adit and a two-lane road tunnel. As the simulation results are primarily influenced by soil anisotropy, it was quantified in an experimental programme. The ratio of shear moduli $$\alpha _G$$ was 1.45, the ratio of horizontal and vertical Young's moduli $$\alpha _E$$ was 1.67, and the value of Poisson ratio $$\nu _{tp}$$ was close to 0. The soil was described using a hypoplastic model considering very small strain stiffness anisotropy. For the given soil, the OCR-based estimation yielded $$K_0=1.3$$ , while Jaky formula estimated $$K_0=0.63$$ for the state of normal consolidation. The back-analysed value of K 0 was 0.75. The predicted tunnel displacements agreed well with the monitoring data, giving additional confidence into the selected modelling approach. It was concluded that OCR-based equations should not be used automatically for K 0 estimation. K 0 of many clays may actually be lower than often assumed.

This study presents the experimental results on the use of cement in modification and stabilization of medium plastic clays. Samples of lean clay were mixed with Portland cement in percentages of 5 and 10 % by dry weight of the soils that had water contents of 40 and 60 %. The curing time of the samples varied between 7 and 28 days. The effects of cement addition on the workability, unconfined compressive strength (UCS) and compressibility of lean clay were examined. The plasticity index showed a steady decrease for all samples leading to higher workability especially in higher cement contents. The results of UCS tests demonstrated that UCS increased up to five times by the addition of 10 % cement to the soil at the end of 28 days. Specimens with lower water content had higher peak strengths. Samples exhibited ductile, semi-brittle, and brittle type of failures depending on their water and cement contents. Brittleness index was used to quantify the mechanical behavior of the soil and the brittleness index increased distinctively as a result of cement treatment. Deformability index was proposed as an alternative to evaluate the deformation behavior of specimens. Moreover, a relationship to determine the UCS development with curing time was proposed. The results of consolidation tests indicated that the compression index decreased and preconsolidation pressure increased by increasing the cement content. The preconsolidation pressure values were found to be related to the UCS values by a ratio of 1.4 for the cement-treated clay.

The stress history as indicated by the profile of overconsolidation ratio (OCR) or preconsolidation pressure of a soil deposit is one of the dominant factors that influence the engineering behavior of soils. A commonly used method to obtain the parameter is a laboratory oedometer test, which is of low accuracy and time consuming because of inevitable sample disturbance. The purpose of this article is to assess the capability of existing interpretation methods and develop new methods to reasonably predict the OCR of clayey soils utilizing the seismic piezocone penetration test (SCPTU) data. Seven sites in Jiangsu province of China were used for this study. At each site, in situ SCPTU tests were performed and soundings of cone tip resistance (q c ), sleeve friction (fs), pore pressures (u 2), and shear wave velocity (Vs) were recorded. High-quality Shelby tube samples were collected close to the SCPTU tests and used to conduct laboratory oedometer consolidation tests to evaluate the reference OCR values. Th...

This work focuses on the uniqueness of rate-dependency, creep and stress relaxation behaviors for soft clays under one-dimensional condition. An elasto-viscoplastic model is briefly introduced based on the rate-dependency of preconsolidation pressure. By comparing the rate-dependency formulation with the creep based formulation, the relationship between rate-dependency and creep behaviors is firstly described. The rate-dependency based formulation is then extended to derive an analytical solution for the stress relaxation behavior with defining a stress relaxation coefficient. Based on this, the relationship between the rate-dependency coefficient and the stress relaxation coefficient is derived. Therefore, the uniqueness between behaviors of rate-dependency, creep and stress relaxation with their key parameters is obtained. The uniqueness is finally validated by comparing the simulated rate-dependency of preconsolidation pressure, the estimated values of secondary compression coefficient and simulations of stress relaxation tests with test results on both reconstituted Illite and Berthierville clay.

The main topic of the study was to characterize the over-consolidation state of stress in the Poznan Clay and estimate the average over-consolidation ratio and pre-consolidation pressure values for different depth of deposits. The Poznan Clay occurs on large area in the region of SW Poland. The shallow occurrence of analysed soils makes them very often the subsoil of engineering structures. The over-consolidated characteristic was done on the basis of the heavy oedometric laboratory tests conducted on the intact samples taken from different depth. The yield stress ratio YSR and yield stress σ’y values were estimated using the Casagrande method. Those values are usually regarded as equal the OCR and σ’y if the pre-consolidation is due to mechanical loading. The study showed that the yield stress ratio YSR is changing with depth. The comparison of the obtained YSR values with the estimated values of OCR (according geological history) showed that they do not correspond to each other. The comparison with other values estimated for soil from other European countries might suggest that the over-consolidation of Poznan Clays could also be related to the age of the deposition.

A saturated soil subjected to a growing total effort will reduce gradually the volume up to excess pore water pressure dissipation, interfering primary consolidation. This process can take a long time and when all excess pressure is dissipated, the soil is considered consolidated. In low permeability soils, from external loading, results in an increase of the normal effort at higher values than the earth preconsolidation pressure, thus having neutral increased pressure followed by a consolidation process where water is expelled from the pores of the soil. The decrease in porosity (soil volume), so produced, is accompanied by a gradual increase of effective pressure and a corresponding decrease in excess pore water pressure. The consolidation process continues until the excess pore water pressure dissipates only complete and upload translates into effective stress. Duration of the process depends on the consolidation characteristics of the soil and drainage ways (with how much drainage paths are longer, the longer is the process of consolidation). The purpose of installing vertical drains is to shorten the drainage ways and time needed to dissipate the neutral pressure. The time to dissipate the excess water pressure in the pores (time consolidation) is so short as the inter-distance between the drains is less. DOI: http://dx.doi.org/10.5755/j01.sace.12.3.12655

Clayey soils could be exposed to thermal cycles in some engineering applications such as geothermal piles and nuclear waste storages. These temperature changes could affect the consolidation behaviour of these soils. In this context, this paper investigates the impact of temperature on the consolidation behaviour of saturated compacted clays. A temperature-controlled oedometric cell has been developed to perform constant rate of strain (CRS) consolidation tests for different strain rates (0.002 – 0.02%/min) within a temperature range of 5 °C – 70 °C. Two different compacted saturated clays were used in these tests. The results indicated that the compression and swelling indices for both materials changed with temperature and strain rate. The preconsolidation pressure of both clays decreased as the temperature increased, while it decreased as the strain rate decreased. The creep index increased as the temperature increased for both clays. These variations were completely dependent on the nature of ...

The undrained shear strength and preconsolidation pressure are key parameters in describing the characteristics of soft clays. The two parameters both reflect the clay’s structure and state of stress, and hence empirical correlations for undrained shear strength normalized with respect to preconsolidation pressure are widely used to assess soil behavior. The empirical correlations given in the literature are typically dependent on liquid limit, or plasticity index, but some studies have questioned the dependency and proposed correlations constant for consistency limits. Data from geotechnical projects often display a considerable scatter and deviate from established empirical correlations. In this thesis, statistical analyses are performed and evaluated qualitatively on direct simple shear, constant rate of strain and fall cone test data from 146 sampling points with a total of 596 soil samples from Stockholm, Gothenburg and Uppsala. The aim is to investigate the correlation between shear strength and the preconsolidation pressure. The thesis evaluates the normalized shear strength’s dependency on liquid limit, how the data corresponds to Hansbo’s (1957) and Swedish Geotechnical Institute’s (2007) linear empirical correlations, and the correction factor applied to shear strength measured by the fall cone test. The results of the study show that the correction factor typically reduces the shear strength from fall cone tests too much with respect to shear strength from direct simple shear tests. The normalized shear strength’s dependency on liquid limit may be rejected for the fall cone test data. The results for direct simple shear test data however, indicates a correlation with liquid limit. The data scatter is considerable, especially for fall cone test data, and the relevance of describing the normalized shear strength from fall cone test with a linear empirical correlation to liquid limit may conclusively be questioned. Skjuvhållfasthet och förkonsolideringstryck är två viktiga jordparametrar för lösa leror. Båda parametrar reflekterar lerans struktur och spänningstillstånd, och empiriska korrelationer för odränerad skjuvhållfasthet, normaliserad mot förkonsolideringstrycket, används därför ofta för att bedöma en leras egenskaper. De empiriska korrelationerna är vanligen kopplade till flytgräns eller plasticitetsindex. Dessa korrelationer har däremot ifrågasatts av studier som i vissa fall istället föreslagit ett konstant förhållande mellan normaliserad odränerad skjuvhållfasthet och plasticitetsgränser. Mätvärden från geotekniska projekt i Sverige visar allmänt stor spridning avseende dessa parametrar och data avviker ofta från etablerade empiriska korrelationer. I examensarbetet har data från direkta skjuvförsök, ödometerförsök och fallkonförsök utvärderats statistiskt och kvalitativt. Totalt omfattar studien 596 jordprover från 146 provtagningspunkter från Stockholm, Göteborg och Uppsala. Syftet med studien är att undersöka korrelationen mellan odränerad skjuvhållfasthet och förkonsolideringstryck. Studien behandlar den normaliserade skjuvhållfashetens flytgränsberoende, Hansbos (1957) och Statens Geotekniska Instituts (2007) empiriska korrelationer, samt den korrektionsfaktor som ska tillämpas på skjuvhållfastheter från fallkonförsök. Resultatet visar att korrektionsfaktorn reducerar skjuvhållfastheten för mycket och att korrigerade skjuvhållfastheter är i sämre samstämmighet med skjuvhållfastheter från direkta skjuvförsök än okorrigerade. Data från fallkonförsök uppvisar inget tydligt flytgränsberoende, medan resultaten från direkta skjuvförsök indikerar ett beroende. Spridningen i data är dock påfallande, särskilt för fallkonförsöket. Relevansen i att tillämpa en linjär empirisk korrelation för odränerad normaliserad från fallkonförsök mot förkonsolideringstryck beroende av flytgräns bör ifrågasättas.

This chapter investigates the topic of compressibility in soils. This represents the first discussion of kinematic quantities such as settlement, deformation, and strain in soils.

Pressure indicated by earth pressure cell (EPC) often deviates from field earth pressure . EPC in normally consolidated soil was analysed with Taylor’s indentation method. It is found that assumes a linear relationship with soil’s compression modulus and . When preconsolidation pressure imposed on overconsolidated soil is unloaded, soil’s rebound strain is greater than EPC’s, and a gap between EPC’s sensing plate and soil appears. Upon reloading, contact between sensing plate and soil resembles spherical contact. This contact was analysed with Hertz’s solution and it is found that is in direct ratio with , and is less than for a relatively low earth pressure and is greater than for a relatively high earth pressure. Earth pressure measurement experiments were conducted with river sand. Experimental results conform to the theoretical analysis herein for a relatively low earth pressure made in this paper.

Multi-phase fluid conditions encountered in geotechnical and geo-environmental problems have led to the development of models that account for the influence of gas solubility and compressibility on the behaviour of soils of various grain sizes. Yet, no consideration has been given to damages related to the nucleation and growth of gas bubbles in fine-grained soils. The purpose of this paper is to present a Cam Clay based constitutive model extended to incorporate such detrimental effects on gassy soils. This is achieved by deriving an analytical expression relating the preconsolidation pressure to a damage parameter dependent on the gas content. That expression is coupled to a deviatoric yield surface accounting for inherent and stress-induced anisotropy. Comparisons of simulations and experimental results attest that introducing a single additional parameter to a conventional Cam Clay type model allows key behavioural features of gas-charged fine sediments to be reproduced.

A series of one-dimensional consolidation tests and triaxial creep tests were performed on Nansha clays, which are interactive marine and terrestrial deposits, to investigate their time-dependent behaviour. Based on experimental observations of oedometer tests, normally consolidated soils exhibit larger secondary compression than overconsolidated soils; the secondary consolidation coefficient (Cα) generally gets the maximum value as load approaches the preconsolidation pressure. The postsurcharge secondary consolidation coefficient (Cα') is significantly less than Cα. The observed secondary compression behaviour is consistent with the Cα/Cc concept, regardless of surcharging. The Cα/Cc ratio is a constant that is applicable to the recompression and compression ranges. Compared with the stage-loading test, the single-loading oedometer test can evaluate the entire process of secondary compression; Cα varies significantly with time and is larger than the Cα obtained from the stage-loading test. Based on experimental observations of triaxial creep tests, the creep for the drained state differs from the creep for the undrained state. The behaviour can be predicted by a characteristic relationship among axial strain rate, deviator stress level and time.

An experimental program was conducted to investigate the effect of pore fluid and stress history on the consolidation behavior of two clay soils with low and high plasticity. The soil samples were prepared by slurry method with water and different concentrations (10, 25 and 40%) of two organic fluids (glycerol and ethanol). Consolidation tests were performed on two types of samples (a-slurry samples, b- slurry samples compressed under a pre-defined load to represent the effect of stress history) in an odometer apparatus. The results show that the compression index Cc increases for both soils with increasing the concentration of ethanol but the variations are not considerable for glycerol. On the contrary in the case of samples with stress history there is a decrease in the compression index of soil samples. The preconsolidation pressure increases for the soil with low plasticity but for the soil with high plasticity there is no significant change in preconsolidation pressure. Furthermore the variation of compression index is dependent on the type of soil and chemical composition of pore fluid.

A. OCR = p ′ / vo ′ , where for a natural soil deposit sublayer, p ′ is the preconsolidation pressure and vo ′ is preconstruction effective vertical pressure. B. OCR = p ′ / vc ′ , where vc ′ is a consolidation pressure in the recompression range of a natural soil deposit sublayer with a preconsolidation pressure p ′ . C. OCR = vm ′ / vc ′ , where vm ′ , for a soil sublayer in the field or in the laboratory, is the maximum effective vertical pressure after loading and primary consolidation and vc ′ is a consolidation pressure after unloading and primary rebound.

Cretaceous pyritic roof shale from Onyeama mine in Enugu colliery was studied for the geotechnical and compositional characteristics relevant to its use in civil engineering construction and other industries. Properties investigated included moisture absorption, particle size distribution, plasticity, linear shrinkage, compaction, California bearing ratio (CBR), permeability, consolidation, the pH the sulphate content and chemical composition. The shale had a high fines content of 85%, a liquid limit of 55 %, a good standard Proctor compaction strength of 1690 kg/m3, preconsolidation pressure of 36 kN/m2, pH of 6.1 and sulphate content of 0.37%. The shale-water extract indicated a possibility of sulphate attack on concrete in contact with weathered pyritic shale. Permeability impairment of between 1x10-7cm/s to1x10-8cm/s was observed on the compacted shale exposed to water and atmosphere. This was attributed to the formation of jarosite and ferric oxide which are the oxidation products of shale weathering. The relatively high silica content of 56% and the low combined potash and sodium content of 1.74% pointed to the potential of the oxidized black shale as a foundation for road bed, as a raw material for brick and a wide range of structural ceramics, and as filler for paints and plastics. The objectionable pyrite in the clay shale can be removed prior to use by treatment with sulphur-and iron-oxidizing bacterium-Thiobacillus ferroxidans or by aging the shale stockpile.

In this study consolidation properties of marine clay in south Korea were investigated through standard consolidation tests (SCT) and constant rates of strain (CRS) tests, and Rowe Cell tests. This examination was conducted based on the field data collected in Kwangyang Bay area, which is one of the representative harbor regions in the southern coast of Korea. Consolidation parameters, including preconsolidation pressure (P c ), compression index (C c ), swelling index (C s ), overconsolidation ratio (OCR), vertical and horizontal consolidation coefficient (C v , C h ), vertical and horizontal coefficients of permeability (K v , K h ), were obtained through the statistical analysis. A correlation between these parameters was evaluated by the regression analysis after removing outliers of the collected data. As a result, it was shown that the relationship between swelling index and compression index was C s = 0.0969C c and between modified compression index and compression index was C c ′ = 1.1411C c(lab)...

The preconsolidation pressure is an important index to determine the stress history of soil and also a major calculation parameter for the analysis of soil stratum’s deformation in the different stress history. Casagrade method is worldwide applied to determine the preconsolidation pressure. On the basis of research on consolidation test about the lakeside new district soft clay of Hefei by high pressure consolidation apparatus, and conformed to Casagrande method, the paper adopts quartic polynomial and least square method to fit the compression curve, and the preconsolidation pressure of the lakeside new distract soft clay of Hefei is determined by matlab software. The result provides reference for the calculation of foundation settlement considering stress history.

The paper presents results of experimental works on intact marine clay samples in Malay and Sarawak Basins, which is located in Malaysia. Recent development in economic and search of new energy has brought to the usage of areas with plenty of marine clay inshore and offshore. For offshore area, the seabed foundation support or subsurface installation often create several complexities in geotechnical design due to high compression behavior and low bearing capacity. Knowledge of seabed soils and rocks is very important in designing any structures onshore or nearshore. However, the seabed data properties in Malaysia is less and not many researches have been done to contribute to this database. Series of oedometer tests performed intact clay samples from different depths showed inconsistency patterns of compression behavior. The preconsolidation pressure for all samples ranged from 200 to 500 kPa, which can be compared with the presence literature for the compression behavior towards denser soil. The compression index, Cc ranged from 0.177 to 0.797 and Swelling index, Cs ranged from 0.133 to 0.066.Copyright © 2016 by ASME

The Discussion by Yoichi Watabe of the Port and Harbour/Port and Airport Research Institute (PARI) of “Settlement of Kansai International Airport Islands” is most fitting because PARI conceived, designed, and constructed the airport islands. Although the authors were not directly involved in the project, the first author has been intimately aware of the island construction in Osaka Bay (Mesri 1991). The writers are not aware of the discusser’s experiences using the ILLICON procedure, and in the absence of any references, the discusser’s claims are discarded in light of excellent agreement between the observed and computed surface and subsurface settlements. A relationship between the preconsolidation pressure and the vertical strain rate was first introduced by Mesri and Choi (1979) in terms of Cα=Cc and later refined to include other parameters (Mesri and Choi 1980, 1984; Mesri 1987). These empirical relationships, based on the Cα=Cc law of compressibility, correctly predict the data in Figs. 1–3 of the Discussion (e.g., Fig. 8 in Mesri 1987). These preconsolidation pressure 1⁄2σ 0 p j versus vertical strain rate 1⁄2ev j data, in the slow strain rate range, are a manifestation of secondary compression after the end-of-primary (EOP) consolidation (e.g., Fig. 9 in Mesri and Funk 2015) and in the fast strain rate range the result of a problematic interpretation of very nonuniform vertical strain, ev, and effective vertical stress, σ 0 v, either during primary consolidation in an incremental loading oedometer specimen (Suklje 1957) or in a constant-rate-ofdeformation specimen subjected to vertical strain rates much faster than EOP ev 1⁄4 ep (Mesri and Feng 1992; Mesri et al. 1994). It was previously explained by Mesri (2013) that the Watabe et al. (2012) interpretation of the Cα=Cc law of compressibility in terms of their measurements of preconsolidation pressure as a function of the strain rate is entirely questionable and is definitely not recommended. The Cα=Cc law of compressibility was developed by Mesri and coworkers using the decrease in void ratio as a function of time in oedometer tests, from vertical compression, whose precise measurement is entirely possible for a variety of materials, from granular soils, including rock fill, to amorphous and fibrous peats (Mesri 1987, 2001), whereas determining a strain rate–dependent preconsolidation pressure is sensitive to details of testing procedure and interpretation. On the other hand, Watabe admits that a constant Cα=Cc 1⁄4 0.04 successfully explains part of the 1⁄2σ 0 p j versus 1⁄2ev j data in the Discussion Figs. 1–3. Considering that preconsolidation pressure versus vertical strain rate is not solely a function of Cα=Cc and that Cα=Cc is equal to 0.04 0.01 only for inorganic soft clay and silt deposits, the discusser’s endorsement is not crucial (e.g., Terzaghi et al. 1996, Table 16.1). For example, the preconsolidation pressure–strain rate relationship may also be influenced by thixotropic hardening (Mesri 1993). It is important, however, to recognize that the preconsolidation pressures corresponding to vertical strain rates slower or faster than ep are not the EOP σ 0 p that turns out to be independent of the duration of primary consolidation. There is a fundamental difference, overlooked by the discusser, of the influence of elapsed time during which preconsolidation pressure develops (age, strain rate, secondary compression, thixotropic hardening, possible interparticle cementation) and elapsed time during which a preconsolidation pressure is mobilized during increases in the effective vertical stress (primary recompression). The aging time during which a preconsolidation pressure develops leads to 1⁄2σ 0 p ej , whereas the primary recompression time mobilizes EOP σ 0 p. This very significant implication of Hypothesis A is illustrated by the preconsolidation pressure data in Table 1 and Fig. 1 from over 70 separate field and laboratory measurements on 25 soft clay and silt deposits (Sallfors 1975; Leroueil et al. 1978; Mesri et al. 1995; Mesri 2001). The σ 0 p (field) was determined from pore water pressure measurements in the ground, and EOP σ 0 p is the preconsolidation pressure from the EOP e-log σ 0 v curves of 20 mm thick undisturbed oedometer specimens. This is a most fortunate soil behavior because strain rate–independent EOP σ 0 p values are used every day by geotechnical engineers throughout the world to compute settlement and evaluate undrained shear strength for stability analyses of soft clay and silt deposits and organic soils (Terzaghi et al. 1996). Watabe does not accept the concept of an EOP compression independent of duration of primary consolidation (Mesri 2001), preferring Hypothesis B. Note that geotechnical engineers have been successfully using the EOP e-log σ 0 v relationship from 20 mm thick oedometer specimens for settlement analyses of ground both without (long duration of primary consolidation) and with (short duration of primary consolidation) vertical drains. Notwithstanding the discusser’s incorrect definition of Hypothesis A, it is here asserted that in the entire geotechnical engineering literature there are no reliable observed laboratory or field data that directly support Hypothesis B as it is defined in Fig. 40 of Ladd et al. (1977). It is unfortunate that Watabe and his colleagues at PARI do not present an alternative settlement prediction for Kansai International Airport islands based on their “viscoplastic creep model with overstress viscoplastic theory : : : and large number of long-term consolidation tests for worldwide clays with various characteristics.” For example, a preconsolidation pressure decreasing with decreases in the strain rate can be expected to predict settlements larger than those by the ILLICON procedure based on the uniqueness of the EOP e-log σ 0 v relationship and the Cα=Cc law of compressibility. Watabe’s comments on observed and predicted pore water pressures are somewhat confused. The pore water pressure increase in the seabed under Island I adjacent to Island II construction could have resulted either from the increase in total stress or from pore water pressure redistribution. Either effect could have been included in the ILLICON settlement analyses. However, this factor was considered to be of minor significance, which was confirmed by the observed settlements. The continued presence of excess pore water pressure in some of the clay layers is entirely expected, as shown by the degree of primary consolidation in

This paper presents a critical state constitutive model for cemented sand. The model uses a single capped yield surface as a function of the void ratio, confining pressure, preconsolidation pressure, and stress ratio at the peak of the undrained effective stress path. To model the cemented materials, the formulation of the yield function, elastic moduli, plastic modulus, flow rule, and other components of the model have been modified. Having incorporated the tensile strength and cohesion, the radial-mapping formulation of the bounding surface plasticity is incorporated in the model. The modified model has been calibrated and verified based on experimental results.