Soil Stress History Research Articles

A thermal state‐dependent bounding surface model for volume change of clay

AbstractThermally induced volumetric strain of clay is crucial for geotechnical applications involving thermal loading. The volumetric response of clay shows a ratcheting pattern during thermal cycles until reaching a thermal stabilized state. It is also affected by the stress history of soil, including over‐consolidation ratio (OCR) and recent stress history (RSH). This paper introduces a new bounding surface model to capture effects of OCR and RSH on thermo‐mechanical behaviour of soil. A thermal state parameter is proposed to characterize the effects of stress history and thermal history. Based on the new thermal state parameter, the commonly recognised thermal softening mechanism is modified and incorporated with a bounding surface. The newly proposed model, with only 10 parameters, can provide an elegant approach to predict the volumetric response under thermal cycles coupled with different stress histories well.

Scoured failure wedge model for analysis of scoured pile-soil interaction in sand

Comprehensive assessment of scour effects is an important consideration in the design of pile foundations in water bodies because they can have a significant impact on the performance and bearing capacity of piles and the integrity of the supported structure. This study presents a scoured failure wedge (SFW) model to simulate the interaction between the laterally loaded pile and sand with local scouring. The developed model is incorporated into an efficient theoretical method to analyze the nonlinear behavior of laterally loaded piles under scour conditions accounting for the scour-hole dimensions and soil stress history. The developed SFW model is validated by comparing its predictions with experimental observations from relevant literature. Subsequently, the validated solutions are utilized to investigate the lateral performance characteristics of the pile under scour conditions. The findings reveal several important insights: (1) the impact of scour on soil properties is primarily confined to the shallow zone, approximately four times the scour depth (4 Hs) below the mudline after scouring; (2) the scour hole dimension has a more pronounced influence on the behavior of laterally loaded piles compared to the soil stress history; and (3) the pile response under lateral loading is positively related to the depth and width of the scour hole and negatively related to the slope angle of the scour hole.

Evaluation of Stress History and Undrained Shear Strength of OC Clayey Soil in Northern Jakarta

It is difficult to determine the accurate undrained shear strength (su) of clay with complicated stress history. In addition to the laboratory tests such as Triaxial UU and Unconfined tests, the in-situ tests such as Vane Shear, SPT, and CPTu tests were conducted for undrained shear strength evaluation. Moreover, the overconsolidation ratio (OCR) by CPTu correlation presented the soil stress history profile along the depth and the Oedometer tests were used to evaluate the results. It was found that the clayey soil is overconsolidated up to -31.0 m below the surface in Northern Jakarta due to groundwater extraction. The Stress History and Normalized Soil Engineering Properties (SHANSEP) formula is widely used to model the relationship between undrained shear strength, OCR, and vertical shear stress. The su results from laboratory and in-situ tests showed good agreement with SHANSEP formula. Moreover, several empirical formulas for OC clayey soil were developed for future deep excavation projects in Jakarta area.

Critical transverse differential settlement between modern tram pile-plank-supported subgrade and surrounding pavement subgrade

Due to the great structural difference between the modern tram pile-plank-supported subgrade and the surrounding pavement subgrade, pavement disease induced by the uncoordinated transverse settlement between these infrastructures continue to appear. A centrifuge model test combined with a finite element method (FEM) was employed to investigate the development law of transverse differential settlement between these infrastructures subjected to long-term operation loads. According to the relationship between horizontal stress and differential settlement rate, the critical transverse differential settlement of tram pile-plank-supported subgrade was proposed. The results showed that the tram track layout, soil stress history and operation time had a great influence on the transverse differential settlement of the tram pile-plank-supported subgrade. During the operation time, the transverse differential settlement rate was linearly related to the horizontal stress of the tram pile-plank-supported subgrade. Finally, according to the requirements of allowable tensile stress of the pavement structure layer, definition of the value of 3.0‰ was suggested as the critical transverse differential settlement rate of the tram pile-plank-supported subgrade.

Thermomechanical response of kaolin clay–concrete interface in the context of energy geostructures

The analysis and design of energy geostructures are mainly characterised by the mechanical behaviour of the soil–structure interface in non-isothermal conditions. In this study, direct shear tests are conducted to investigate the shear behaviour of soil and soil–structure interface in the practical temperature range of energy geostructures (i.e., 8–45 °C). The interface in this study is formed of kaolin in contact with concrete specimens with different roughness. Tests are performed on normally consolidated and overconsolidated interfaces following the unloading/reloading paths to better understand the impact of thermal strain on the interface behaviour. The volumetric response of the interface is observed to be highly influenced by the thermal strains experienced during heating/cooling. The soil stress level and the most recent soil stress history are identified as the primary determinants of thermally induced changes in interface shear strength. For normally consolidated interfaces, the temperature increase led to higher adhesion and slightly lower friction angle, whereas higher adhesion and identical friction angles were found for tests conducted on cooled specimens. Temperature does not seem to affect the shear strength of overconsolidated interfaces. Finally, a conceptual understanding of the temperature effect on interface shear behaviour is provided by analysing data from the literature.

Geotechnical characterization of the estuarine deltaic deposits in the Guayaquil city through in situ and laboratory tests

According to previously available research and seismic microzonation studies a large area of the Guayaquil (Ecuador, South America) sits on estuarine deltaic deposits which consist of weak and highly compressible clays with diatoms. The nature of these fine-grained deposits may determine difficulties in a proper estimation of the soil properties. In this respect, the paper provides a detailed geotechnical and geophysical characterization of these soft clays, carried out in the estuarine complex of the Ecuadorean city. Borehole logs, standard penetration tests (SPT), piezocone tests (CPTu), a seismic dilatometer test (SDMT), a non-invasive geophysical survey, and laboratory tests were performed and then compared to analyze the static and dynamic geotechnical parameters of these deposits. The interpretation of the results highlighted the higher reliability of CPTu and SDMT rather than SPT and characterization lab testing to estimate soil shear strength, compressibility and stress history due to the soft nature of these clays, underlining also a certain sensitivity to the presence of the diatoms.

Combined Effects of Soil Stress History and Scour Hole Dimensions on Laterally and Axially Loaded Piles in Sand and Clay under Scour Conditions

Removal of soil around a bridge foundation due to scour results in a reduction of the lateral and vertical foundation capacity due to the loss of soil support. The common approach in modeling the scour phenomenon of removal of soil springs without modifying the parameters of the remaining soil fails to consider the change of stress state of the remaining soil and the formation of scour hole geometry around the pile foundation. In practice, both of these factors impact the mechanical properties of the remaining soil and the resulting expected structural response of the pile under loadings. This paper proposed a methodology to comprehensively evaluate the combined effects of stress history and scour hole dimensions on piles under scour conditions in uniform soil. It enabled the examination of the lateral and axial behaviors of a loaded pile subject to scour and is applicable for both cohesive and cohesionless soils. The methodology was validated with results from field tests for no-scour scenarios and verified with existing numerical models for scour scenarios. Quantification of the soil effects was investigated through lateral pile deflection and load-settlement curves for lateral and axial behaviors, respectively. Load-settlement curves demonstrated that including the effect of stress history results in increases of up to 34.1% and 61.1% in estimated pile settlement for sand and clay, respectively, leading to potential unconservative designs if soil effects are not properly included in the analysis.

Plasticity solutions for ground deformation prediction of shallow tunnels in undrained clay

Elastic-plastic contraction solutions of a cavity within an infinite soil mass are widely used to estimate ground response curves of deep tunnels. The pressure-convergence response of soil around shallow tunnels, however, tends to vary with tunnel embedment ratio. To account for the embedment ratio effect, this paper presents a general solution procedure for undrained contraction analysis of a thick-wall cylinder or spherical shell of isotropically hardening soils, by which a set of analytical and semi-analytical large strain solutions for several Cam-Clay soil models is derived. Results obtained with the new solutions show that the cavity contraction response highly depends on the soil stress history (overconsolidation ratio) and the radial thickness of the surrounding soil. A limit ratio of the outer to the inner radii exists, beyond which the thickness ratio effect becomes negligible. The limit ratio for a spherical shell is smaller than that for a hollow cylinder, and it decreases with the overconsolidation ratio of soil. Based on the analogy between cavity contraction and tunnel convergence, theoretical methods for predicting ground response curves of shallow plane-strain tunnels in clays are proposed and validated by comparing with relevant experimental and numerical simulation results. The solutions can also provide valuable benchmark methods for verifying various numerical programmes.

Analytical method for laterally loaded piles in soft clay considering the influence of soil outside the scour hole on the effective overburden pressure

Scour reduces the effective overburden pressure and the undrained shear strength of soil, thus affecting the lateral load-bearing capacity of pile foundations. Compared with general scour, local scour can decrease the reduction of the effective overburden pressure and the undrained shear strength around the pile due to the existence of soil outside the scour hole. To fully reflect the actual situation at a site, the behavior of laterally loaded piles in soft clay should consider both the scour-hole dimensions and the soil stress history. This paper proposes a closed-form analytical solution for laterally loaded piles in soft clay that can simultaneously account for the changes in effective overburden pressure and undrained shear strength caused by the scour-hole dimensions and the soil stress history based on the p–y curve proposed by Matlock. The average reduced stress is introduced according to Boussinesq’s point load solution. Case studies demonstrate that the analytical method is reliable with reasonable accuracy. According to the parameter study, the load eccentricity is the most sensitive factor compared with the changes in soil properties caused by the scour-hole dimensions and the soil stress history.

Methodology to account for the impact of stress history in layered soils for seismic vulnerability assessment of scoured bridges

Scour has been recognized as one of the leading causes of bridge collapse in the United States. Therefore, it is essential to be able to build models that accurately capture the response of bridges vulnerable to scour, including those located in layered rather than homogeneous soil deposits. Simple removal of soil springs due to scour ignores the effect of stress history for layered soils, which can lead to unconservative designs of foundations. This article proposes a methodology called the equivalent stress history and layered effects (ESHaLE) approach to capture the impact of soil stress history of layered soils on vulnerability assessment of scoured bridges. It utilises conservation of strength and mass to derive corresponding soil and depth parameters. Results show that neglecting to include stress history impacts in layered soils can lead to an underestimation of the single pile axial displacements by up to 35% in static analysis, and underestimation of the probability of exceeding bridge deck deflection thresholds by up to 25% in seismic fragility assessment. The study presents a method to include both soil stress history and layered effects in soil modeling and shows the importance of including these soil effects in the assessment of bridges vulnerable to scour.

Seismic responses of monopile-supported offshore wind turbines in soft clays under scoured conditions

For the monopile-supported offshore wind turbine (OWT), scour can significantly affect the seismic responses of the structure. However, the combined effects of scour and earthquakes are not fully appreciated. This study proposed a new method to evaluate the post-scour seismic responses of monopole-supported OWTs, considering various scour-hole dimensions and soil stress-history changes due to different scour levels. Using the developed computer scripts, a parametric study was conducted, including 198 cases on a monopile-supported OWT in soft clays under different scoured conditions and six crustal earthquakes. The results showed that scour significantly changed the seismic responses of the selected OWT structure. Use of an overpredicted scour depth in the post-scour analysis underestimated the seismic response while simplifying local scour as general scour and ignoring soil stress history overestimated the seismic response of OWT. This research recommends in analysis the use of a cone-shape scour hole with side slope angle of 30°.

Loading and unloading of a thick-walled cylinder of critical-state soils: large strain analysis with applications

Thick-walled cylinder (TWC) tests are widely used to obtain soil properties and investigate wellbore instability problems in laboratory-controlled conditions. This paper presents analytical cavity expansion and contraction solutions for modelling undrained TWC tests under three typical loading and unloading programs. Both cylindrical and spherical cavities in critical-state soils with a finite radial extent subjected to monotonic loading or unloading under undrained conditions are considered. The solutions are developed in terms of finite strain formulations, and the procedure is applicable to any isotropically hardening materials. Parametric studies show the boundary effect may significantly affect the cavity expansion/contraction response. A limit outer-to-inner diameter ratio of the soil sample exists, beyond which the boundary effect becomes negligible. The limit ratio varies with the cavity geometry, soil stress history (OCR) and cavity deformation level. For undrained TWC tests, a diameter ratio over 20 should normally be adequate to remove the possible boundary effect. Predicted expansion and contraction curves by the new solutions are compared with published data of TWC tests in the literature, and good agreement is shown in each loading/unloading program. This indicates that the boundary effect, which greatly limits the application of conventional cavity expansion/contraction solutions into TWC problems, is successfully captured by the present solutions. The solutions can also serve as valuable benchmark for verifying various numerical methods involving critical-state plasticity models.

Functional evaluation of the various calculation methods for precompression stress

AbstractPrecompression stress (σp) is commonly used as an indicator for the load carrying capacity of a soil and its stress history. Several calculation methods have been proposed to determine σp, but they have proven to be not interchangeable. The aim of this study was to perform a functional evaluation of seven existing methods to test which method would be most recommended to assess soil strength in cultivated fields. This was achieved by investigating the relation of the obtained σp of undisturbed soil samples to other soil properties and stress history. Additionally, the robustness of the methods was evaluated by checking their sensitivity to perturbation of the measured strains. The two most commonly used methods, the Casagrande method and Gompertz model fit method, were found to be the least suitable to calculate σp. These methods lack robustness and do not yield a significant relation with the relevant soil properties or stress history. Better results were obtained with Intersecting linear regressions or at the inflection point of a fourth‐degree polynomial.

Soil compaction on traffic lane due to soil tillage and sugarcane mechanical harvesting operations

Mechanical sugarcane harvesting increases soil compaction due to the intense traffic of agricultural machinery, reducing longevity of sugarcane crops. In order to mitigate the harmful effects caused by agricultural traffic on the soil structure in sugarcane fields, this study evaluated impacts of mechanical sugarcane harvesting on traffic lane under two soil tillage systems based on load bearing capacity models. The experiment was carried out in the region of Piracicaba, state of Sao Paulo, Brazil, on a Rhodic Nitisol, under conventional tillage (CT) and deep strip-tillage (DST). For CT soil tillage was applied to the entire area with a heavy disk harrow, at operating depths from 0.20 to 0.30 m followed by a leveling harrow at a depth of 0.15 m. For DST, soil tillage was performed in part of the area at a depth of 0.80 m, forming strip beds for sugarcane planting, while the traffic lanes were not disturbed. Undisturbed soil samples from traffic lanes were used in the uniaxial compression test to quantify preconsolidation pressure and to model the soil load bearing capacity. The surface layer (0.00-0.10 m) was most susceptible to compaction, regardless of the tillage system (CT or DST) used. In the DST, the traffic lane maintained the previous soil stress history and presented higher load bearing capacity (LBC) than the traffic lane in the CT. As in CT the soil was tilled, the stress history was discontinued. This larger LBC in DTS minimized the impacts of the sugarcane harvest. Under CT, additional soil compaction due to mechanical sugarcane harvesting in the traffic lane was observed after the second sugarcane harvest. There was a reduction in load bearing capacity from 165 kPa to 68 kPa under CT and from 230 kPa to 108 kPa under DST, from the first to the second harvest at surface layer. Water content at mechanical harvesting was the most relevant factor to maximize impacts on the soil structure in traffic lanes, for both tillage systems.

Assessment of Seismic Liquefaction of Soil Site at Mundra Port, India, Using CPT and DMT Field Tests

Cyclic soil liquefaction in the past has resulted in severe damage to structures and lifeline services. Mostly, standard penetration test and cone penetration test (CPT) are used for evaluation of liquefaction; however, the dilatometer test (DMT) is better suitable due to its ability to detect soil stress history and aging. This study aims to compare the DMT-based cyclic resistance ratio (CRR) correlations available in the literature with well-established CPT-based CRR correlation at a site in Mundra, Gujarat, that had moderately liquefied in 2001 during the Bhuj earthquake. The available earthquake history is scaled using attenuation relationship for Peninsular India, and the peak ground acceleration is assessed by ground response analysis using the CPT data. The factor of safety (FSL) against liquefaction is evaluated using field data obtained from CPT and DMT. Also, Liquefaction Potential Index (LPI), settlement (S) and Liquefaction Severity Number (LSN) are evaluated to determine the consequence of liquefaction, and the performance of the foundations supported on liquefied soil. The results verify the liquefaction damage observed in 2001 during the Bhuj earthquake and indicate that the site possesses a moderate risk of liquefaction. It shows that the site is susceptible to minor to moderate consequences of liquefaction, such as sand boils and small damage to existing structures. It also indicates that the CPT-based CRR correlation is conservative compared to DMT-based CRR correlation and warrants the use of independent DMT-based CRR correlations or use of at least two methods to assess liquefaction at critical sites.

Evaluating a new method for simultaneous measurement of soil water retention and shrinkage curves

Water retention and shrinkage curves are two important characteristics of unsaturated soils. Conventionally, two curves are separately measured using multiple carefully prepared “identical” soil specimens. However, it is difficult or impossible to fabricate soil specimens with exactly identical stress history. The measurement of two curves was very time-consuming (each up to several weeks). Recently, a new method has been proposed to simultaneously measure two curves through shrinkage tests. The soil suction, water content, and volume during testing are monitored during testing for the construction of the water retention and shrinkage curves. Preliminary shrinkage test results prove that the new method is efficient in the measurement of two curves. In this study, a series of shrinkage tests on two types of soils were performed to evaluate this new method using a new device in which the soil suction, water content, and volume are, respectively, measured using a high-capacity tensiometer, digital balance, and a non-contact photogrammetric method. Test results indicate that the new method significantly reduces the time required for the measurement of two curves from weeks to 1 day. The new method allows simultaneous determination of the two curves using one single soil specimen, which also eliminates the influence of different stress histories on the test results. The axial strain distribution during drying can also be identified based on the reconstructed three-dimensional model of the soil, which is beneficial for examining the soil deformation non-uniformity and stress history. Finally, some discussions on the measurement of two curves using the new method are presented.

Influence of temperature on soil–pile interface shear strength

Geothermal piles are subjected to daily and seasonal cyclic temperature changes during their life spans. These temperature changes (heat cycles) induce cyclic expansion/contraction along the soil–pile interface that may affect interface properties such as shear strength. A series of direct shear tests was conducted using a temperature controlled direct shear test apparatus to evaluate the effects of heat cycles on soil–pile interface strength. The interface temperature was cycled between 24 ° C and 34 ° C to simulate the real thermal conditions that an energy pile may experience. Non-cyclic and cyclic thermal loading were applied under different stress states and histories. It was found that the shearing behavior of interface under thermal loading is described through thermally induced changes in Mohr–Coulomb’s parameters of the interface. Moreover, the thermally induced changes in interface strength are mainly controlled by the soil stress state and the soil stress history.

Estimation of undrained shear strength of fine grained soils from cone penetration resistance

BackgroundMany previous authors have proposed empirical methods for the evaluation of undrained shear strength Su of soft to stiff saturated cohesive soils from CPT cone resistance qc data. Published works are rare on this topic for the cases of unsaturated and overconsolidated clays and therefore further studies are needed to study the Su versus qc relationship for such soils. This paper investigates the qc–Su correlation for Sudanese fine grained soils taking into account the soil type, moisture condition and stress history effects.MethodsDatabase pertaining to many soil samples representing low to high plastic clays and silts collected from thirty different Sudanese states was used in this study for analysis. The Su values were determined from laboratory by the UU triaxial test method on undisturbed soil samples taken from adjacent borings and the CPT was performed by a mechanical adhesion jacket cone type.ResultsThe Su values varied from 30.3 to 460 kPa in the clay soils and from 16 to 252 kPa in the silt soils with average values of 129 and 91 kPa respectively. The consistency of most clay soils could be described as firm to very stiff with few soft and hard samples. The values of empirical cone factor Nk were determined for the soil types considered and found to vary over a wide range of 35.1 to 55.6 with average values of 37.5 for clay soils and 44.1 for silt soils.DiscussionA rigorous analysis of soil database was performed to model the Su–qc relationship taking into account the effects of plasticity index and overconsolidation ratio soil parameters. The cone factor Nk values determined were analyzed and compared to those experienced in previous studies from different countries. The study results revealed that for a given soil the Nk is not a simple constant but depends on several factors such as moisture condition and degree of stiffness prevailing in the field during testing. The Nk values obtained are in close agreement with and confirm the 35 figure reported in previous studies for highly plastic clay and silt soils. The average Nk values obtained are much higher than those reported in several countries for normally consolidated soft to firm saturated cohesive soils but are lower than values found in few studies for hard and overconsolidated soils. Interpretation of the CPT and Su database is different for saturated and unsaturated soils which makes comparison of the Nk values difficult.ConclusionsA reliable correlation cannot be directly developed between Su and qc for soils with different types and characteristics as both variables are influenced by several factors. The effects of soil type, moisture condition and stress history should be considered in studying the qc–Su relationship. Reliable empirical relationships have been developed to estimate Su from CPT qc data for Sudanese clay and silt soils of different OCR values.

Effects of scour-hole dimensions and soil stress history on the behavior of laterally loaded piles in soft clay under scour conditions

Bridge pile foundations in the midst of water current are often subjected to scour, which induces the loss of soil support around the piles and thus results in a significant decrease of foundation capacities or even the failure of bridges. In the current practice, when the scour-affected behavior of the pile foundations is analyzed, either the whole scour-hole geometry or the possible changes in the stress history of the remaining soils is often ignored. In reality, however, scouring creates scour holes with certain dimensions around the pile foundations and the remaining soils that are not scoured away undergo an unloading process at the same time, which will increase the over-consolidation ratios of the remaining soils and accordingly changes of their mechanical properties. This paper examines the behavior of laterally loaded piles in soft clay under scour conditions by using the p-y method. The conventional p-y curves have been modified appropriately to reasonably reflect the effects of three-dimensional scour-hole geometry as well as the stress history of the soils, with the aid of integration of Mindlin’s fundamental solutions. A field test is used to serve as a reference case and to investigate the effects of stress history, scour depth, scour width, and scour-hole slope angle on the responses of laterally loaded piles in soft clay. The results indicate that neglecting the stress history effect can be unconservative for scour-affected pile foundations in soft clay, whereas neglect of the scour-hole dimensions and geometry would lead to over-conservative predictions/design of the laterally loaded piles under scour condition.

General response observed in cyclically loaded cohesive soils

<p>The response of cohesive soils subjected to cyclic loading is affected by different factors; the most important are soil type, stress or consolidation history, and specific test conditions. To better understand the behavior of cohesive soils subjected to cyclic loading, beginning in early 1960’s, a rather substantial body of experimental work has been performed. This has involved different types of soils, tested at different values of overconsolidation ratio, and subjected to different cyclic loading histories. This paper compiles the most important findings of the aforementioned experimental work on cohesive soils. It summarizes the general behavioral trends observed for cyclically loaded cohesive soils. Besides, several key characteristics of cyclically loaded cohesive soils that any rational mathematical simulation must account for have been identified, thus offering the general trends that should be taken into account in the development of new constitutive models used in predicting the response of such soils.</p>