Deformation Of Clay Research Articles

A novel model for the cumulative plastic strain of saturated clay under long-term cyclic loading based on the Laboratory test

Long-term cyclic loading applied to clay at stress levels lower than the critical cyclic stress leads to soil deformation without inducing damage. The Monismith model is well-known for its simplicity and ability to describe the trend of cumulative plastic strain under cyclic loading. However, the simulated cumulative plastic strain increases indefinitely with the number of cycles until damage occurs. At lower cyclic stress levels, the cumulative plastic strain tends to be stabilized with an increasing number of cycles, ultimately limits the applicability of the model. To address this issue, a series of axial-torsional bi-directional cyclic loading tests are conducted on saturated clay using a hollow cylinder torsional shear apparatus. An empirical three-parameter mathematical prediction model is proposed by analyzing the development of cumulative generalized shear strain based on test results. The relationships of model parameters a with plasticity index, frequency, generalized shear stress, and mean effective stress; b with plasticity index, and c with frequency and plasticity index are presented as functional expressions. Finally, the predicted results of the empirical model are compared with test results to verify its effectiveness, providing a basis for calculating cumulative deformation in clay under long-term low cyclic stress levels.

Effect of torsional shear stress on the deformation characteristics of clay under traffic load

The soft clay under the road ground will suffer cyclic torsional shear stress encountered traffic load in addition to axial stress, which will cause further deformation of clay. To investigate the effect of torsional shear stress on the cumulative axial strain of clay, a series of undrained tests under cardioid stress path were performed on K0 consolidated undisturbed samples by using a hollow cylinder apparatus (HCA). The effect of vertical cyclic stress ratio (VCSR) and shear stress ratio (η) on the deformation and degradation characteristics of clay was investigated. The results indicate that there is inconsistency between the strain path and stress path. The increase in η further accelerates the accumulation of axial strain, which resulted from the degradation of clay induced by torsional shear stress. Considering the VCSR and η, a calculation method of degradation index was developed. Furthermore, a cumulative axial strain prediction model of clay under the cardioid stress path was established considering the degradation. This model addresses the limitation of traditional prediction models by considering the impact of torsional shear stress on cumulative axial strain.

Study on the effect of deformation and strength characteristics of microencapsulated phase change materials on modified silty clay under dry and wet cycles

To prevent the cracking of silty clay under cyclic wet-dry cycling (W-D), which leads to the increase of deformation and strength attenuation of silty clay, microencapsulated phase change material (mPCM) was used to improve it. The deformation and strength characteristics of silt with different dosages (1 %, 2 % and 4 %) of mPCM and their changing patterns were analyzed and studied by indoor compaction test, crack observation test, consolidation test and straight shear test, and compared with silt without modifier. The results showed that with the increase of mPCM dosage, the optimum water content of silt and the maximum dry density decreased. A 2 % dosage of mPCM inhibited the development of silty clay cracks, reduced crack width and deformation, and increased the compression modulus of the soil samples by nearly 2.3 times. Under dry and wet cycling conditions, the cohesion decay of silty clay is greater than the angle of internal friction. The addition of 2 % mPCM significantly increased the shear strength of silty clay, cohesion by nearly 2.1 times, and internal friction angle by 1.4 times. The mPCM inhibits crack development mainly by regulating the internal temperature field of soil samples, thus improving soil strength. This study provides a reference for inhibiting soil cracking from a new temperature perspective.

Laboratory tests on the traffic-induced cyclic behavior of anisotropically overconsolidated clay under different drainage conditions

In road engineering on clay foundation, the subgrade clay is often anisotropically overconsolidated, and the drainage boundary is commonly partially drained. Considering that few laboratory studies focused on the traffic-induced cyclic behaviors of anisotropically overconsolidated clay, and investigated intensively the differences in deformation between undrained and partially drained conditions, this study performs a series of one-way cyclic tests on the overconsolidated clay with various consolidation stress ratios (K) under different drainage conditions. The emphasis is put on the comparison of undrained and partially drained tests in terms of the permanent axial strain and its accumulated rate, resilient modulus and damping ratio. Test results indicate that the relative magnitude of permanent axial strain and its accumulated rate between the two drainage conditions is highly related to cycle number, K and CSR, with decreasing K and increasing CSR exacerbating the difference. The resilient modulus of partially drained tests is greater than that in undrained tests overall, while the relative relationship of degradation index between the two drainage conditions is reversed. In addition, the increase of consolidation-induced anisotropy degree promotes the strain development and improves the resilient stiffness, which should be noted for the traffic-induced deformation of subgrade clay. Based on the shakedown theory, the allowable cyclic stress ratio is determined as 0.44, and it is affected little by K or drainage condition. Finally, prediction models of permanent axial strain and resilient modulus are established for the anisotropically overconsolidated clay under both drainage conditions, where the deformation prediction is found to be related to the shakedown behavior. It is recommended that the prediction and control of subgrade clay settlement in engineering practice should take into account the in-situ consolidation sate and drainage condition.

Prediction of the axial strain development curve of soft clay under dynamic triaxial conditions based on LSTM

The dynamic triaxial test results of soft clay show that a long-term cyclic traffic load lead to significant deformation of soft clay. Considering that the dynamic triaxial test data of soft clay under cyclic loading have apparent time series characteristics, the long short-term memory (LSTM) model can be used to predict the deformation law of soft clay. Through a dynamic triaxial test of Shanghai soft clay, time series data, such as axial stress, pore water pressure, and axial strain were obtained to establish the sample data of the LSTM model. The LSTM model is then used to predict the axial strain development curve. The results showed that the LSTM model had a good fitting precision for the sample data under different dynamic stresses and frequencies, and its accuracy was above 97% in all conditions. The prediction results can reproduce the fluctuation law of the axial strain under cyclic loads and can be used to study elastic and plastic strains. The research results can provide technical support for disaster prevention and control in soft clay.

Numerical investigation on the effect of repeated surface surcharge loading on soil deformation and tunnel displacement in structured soft clay

Shanghai soft clay is a typical marine clay with specific structural characteristics. The tunnel and overlying soft clay may undergo repeated surface surcharge loading, such as the temporary soil stacking. Assessing the extent of structured soft clay deformation and tunnel displacement caused by repeated surface surcharge loading is of great significance for evaluating of the safety of ground structures and underground tunnels. In this study, the effects of repeated surface surcharge loading on the soil and tunnel displacement were numerically investigated. The finite element code DBLEAVES with an elasto-plastic constitutive model (Shanghai model) that describes the mechanical properties and structural characteristics of natural clay was used to simulate the soil response. The parameters of the constitutive model were obtained through geotechnical testing. The effects of the soil structural characteristics, seepage conditions, and loading conditions on the soil response and tunnel displacement were analyzed. The numerical results show that the maximum excess pore pressure of clay decreased as the number of loading cycles increased. The effects of the structural characteristics cause greater displacement, whereas the effects of the degradation parameters of the structure are more significant than the initial degree of the structure. The differences in the vertical displacement of the tunnel and overlying soils owing to the structural characteristics become apparent with an increase in surface surcharge loading. However, the effects of structural characteristics become less significant as the depth increases. The seepage conditions and loading method primarily affect the build-up of excess pore pressure and the development of effective stress paths. For soils inside the surcharge area, a flexible surcharge produces a greater vertical displacement than a rigid surcharge. As the burial depth increased, the effects of the seepage conditions and loading method showed a declining tendency.

Deformation Characteristics of Lime Stabilized Marine Clay Using Finite Element Method

The coastal area is one of the environmentally vulnerable areas, with soil characteristics such as weak soil and marine clay, which is classified as hazardous soft soil. Because marine clay has poor mechanical and physical properties, foundation conditions such as pad footing were unstable and prone to corruption. As a result, the lime column will be used to stabilize marine clay in this study. The purpose of this research is to investigate the deformation of marine clay with lime to increase shear strength and reduce excessive settlement by analyzing data from previous studies and conducting a review of the literature, as well as to investigate the deformation of untreated and treated marine clay with lime columns and PLAXIS software projection. Compared to the traditional method, PLAXIS 2D software is one of the most cost-effective ways to test a foundation, such as the pad footing. At the same time, PLAXIS 2D was able to shorten the time required to achieve an analytical result. The results of the settlement and stress value have been taken after the computation and analysis from PLAXIS 2D. The greatest percentage difference between untreated and treated marine clay for stress and displacement is 81.82 percent and 7.98 percent, respectively.

The Effect of Soluble Sugar Degradation on the Evaporation of Compacted Clay

In arid climates, evaporation and water loss in surface soil can lead to the development of shrinkage cracks in the soil. The crack network in contaminated soil sites can become a rapid pathway for the infiltration and transport of contaminations, thereby increasing the range of soil contamination. Dense contaminated clay samples were prepared by using glucose as a representative soluble sugar of domestic source contaminations. Through indoor evaporation simulation tests, the effect of soluble sugar anaerobic degradation on the water loss, deformation, and crack growth of compacted clay was analyzed, and the mechanism of this effect was revealed. The results showed that glucose increased the water-holding capacity of clay, while the anaerobic degradation of glucose decreased the water-holding capacity of clay. Although glucose anaerobic degradation reduced the overall deformation of dense clay, it promoted the development of evaporative cracks on the surface of dense clay. Soluble sugar anaerobic degradation mainly affected the evaporative cracking of clay by “forming hydrogen bonds to reduce the rate of evaporative water loss in clay” and “generating CO2 to alter the structure of the clay”.

Effect of Loading Direction on Deformation and Strength of Heterogeneous Paleo Clay Samples

Landslides result from weak surfaces with varying rock-soil properties, posing a significant concern for engineering and accurate deformation analysis. This study investigated the macroscopic physical and mechanical properties of paleo clay specimens during triaxial compression testing, aiming to elucidate the deformation mechanisms exhibited by these specimens under varying loading directions at both the loading and unloading ends, and numerical simulation methods were carried out to simulate actual engineering scenarios. The analysis encompasses deformation patterns, stress–strain relationships, Mohr stress circles, and numerical simulation failure cloud diagrams for soil samples under different loading directions. The results showed that the loading end of heterogeneous specimens exhibited noticeable deformations. Alteration of the loading direction induced variations in the failure mode. The position and size of the deformations for the only iron-manganese clay, loading end iron-manganese clay, and loading end reticulated clay samples changed with the clay layer at the loading end of the sample. Moreover, the stress–strain curves under different loading directions were different, with strain hardening and strain softening appearing in the two loading directions, respectively. The results of this study contribute to an in-depth understanding of the impact of the loading direction on the deformation and strength of paleo clay, thereby providing a foundation for landslide prevention and control measures.

A simplified algorithm for predicting creep settlement of high fills based on modified power law model

The calculation and prediction of creep settlement is an important basis for judging whether the settlement of high fills is stable and arranging subsequent construction. In this study, a modified power law model is established based on Hypothesis B and Bjerrum's classification of creep deformation. The modified model can uniformly describe the one-dimensional creep deformation of clay, sand and soil-rock mixture, and satisfies the requirement that the one-dimensional creep deformation tends to a constant value over time rather than increasing indefinitely. Then a simplified algorithm for predicting creep settlement is proposed based on the modified model. The simplified algorithm has only three parameters with explicit physical meaning, which are determined by settlement monitoring data. By the settlement monitoring data from high fills at Chengde Airport, Chengchi Expressway and Panzhihua South Railway Station, the fitting and predicted results of the simplified algorithm were compared with other three prediction algorithms commonly used in geotechnical engineering. The results show that the proposed simplified algorithm can predict the creep settlement of high fills more effectively and accurately.

Cyclic stress–strain characteristics of red clay treated with permeable water-soluble polyurethane

Red clay, a globally distributed type of chemical weathering soil, is commonly utilized as a road base in road infrastructure. However, due to its susceptibility to water and vibrations, it is prone to settlement and formation of potholes during operation, consequently leading to damage in the pavement structure. This paper employs a dynamic triaxial apparatus to simulate realistic traffic loads and investigates the dynamic properties of red clays treated with permeable water-soluble polyurethane (PSP). Additionally, a series of microscopic tests are conducted to elucidate the microstructural mechanisms of using PSP for improving red clay, as well as the microscopic deformation mechanisms of the PSP-treated red clay (PSP clay) under cyclic loading. The results provide detailed insights into the influence of soil moisture content and PSP content on key parameters, including the resilient modulus, damping ratio, permanent deformation, and strength of PSP clay after repeated loading. Moreover, the overall performance of PSP clay is evaluated under varying loading amplitudes and confining pressures. These results are complemented and interpreted in conjunction with the findings from the microscopic tests. The findings reveal that the inclusion of PSP improves the strength of the soil skeleton by enveloping and interlocking with the clay particles. Furthermore, it is observed that the engineering properties of high-moisture-content red clay soils can be significantly improved with low levels of PSP. Under specific conditions, repeated loading further compact the PSP clays, thereby enhancing their mechanical properties. The experimental findings presented in this study are of utmost importance for the improvement and application of red clays through the utilization of rapid solutions, such as PSP.

Seismic responses analysis of monopile offshore wind turbines in clays considering the long-term cyclic degradation effect

In marine environment, the monopile offshore wind turbines (MOWTs) are subjected to long-term horizontal cyclic loads caused by wind, waves and currents, which will lead to the stiffness degradation and plastic cumulative deformation of clays. The decrease of clays bearing capacity caused by long-term cyclic degradation effect is a threat to the safe use of MOWTs in earthquake-prone countries (such as some countries in the circum-Pacific seismic belt). A three-dimensional finite element model is established to research the seismic response analysis of MOWT in clays considering the long-term cyclic degradation effect. The cumulative deformation of pile-soil system after long-term cycle are obtained by adopting the stiffness degradation of clays through the USDFLD subroutine. On this basis, the dynamic response analysis of MOWT system under the combined action of seismic and environmental loads is carried out. The influence of long-term horizontal cyclic load number, long-term horizontal cyclic load amplitude, seismic intensity, soil strength, environmental loads and cyclic degradation parameter on the dynamic response of MOWT is analyzed. In the seismic design of MOWTs, the effects of long-term degradation and random wind, waves and other environmental loads should be considered.

Accumulative plastic strain of freezing–thawing subgrade clay under cyclic loading and its particle swarm optimisation–back-propagation-based prediction model

Accurate evaluation of cumulative plastic strains in subgrade soil is crucial for road designs and maintenance. Roads in seasonally frozen regions undergo several freeze–thaw (F–T) cycles annually, resulting in considerable deterioration of soil properties. Under the repeated cyclic loading of moving vehicles, distinct residual deformation occurs in the thawed subgrade. To study the influence of F–T cycles on the cumulative strain characteristics, cyclic triaxial tests were conducted on subgrade clay under the most unfavourable conditions and in situ measured dynamic stress amplitudes. The test results revealed that the cumulative strain (εap) increased with the dynamic stress amplitude. When the dynamic stress amplitude increased from 46 kPa to 70 kPa, εap of unfrozen and F-T specimens increased by more than 14 and five times, respectively. The axial deformation of clay is sensitive to the number of F–T cycles. The freeze-thaw effect was greatest in the first cycle, with εap increasing from 1.42% to 5.63% at the end of the test (dynamic stress amplitude of 46 kPa). In subsequent cycles, relatively small deformations accumulated. A particle swarm optimisation–back-propagation-based (PSO-BP) model for predicting the accumulative plastic strain of clay was developed based on experimental results. In this model, the influences of the F–T process and loading cycles were considered. The prediction performance of the proposed model was validated and compared with that of traditional regression models. The predictions were in good agreement with the experimental data and satisfied the deterioration law for clays subjected to F–T cycles. The maximum error of the PSO–BP model was 2.75%.

Equivalent seismic behaviors of artificial frozen-thawed soft clay with a new reduction factor of shear stress

The artificial ground freezing (AGF) technique is widely used in the construction of underground structures, and the deformation of soft clay is more significant after freezing-thawing cycles. Moreover, many earthquake disasters indicate that the engineering in soft soil areas experience huge risks to seismic fortification. In this paper, the inversion formula of seismic acceleration time history for different peak ground accelerations (PGAs) in the frequency domain was derived. The maximum peak acceleration and maximum dynamic shear stress in the undisturbed and frozen-thawed soft clay sites were analyzed by DEEPSOIL. The reduction factor of dynamic shear stress suitable for the clay field was calculated to provide basic parameters for the cyclic triaxial tests considering different confining pressures, dynamic stress amplitudes and loading frequencies. The ground motion acceleration of soft clay sites has an amplification effect, and that of frozen-thawed soft clay sites is more obvious. The reduction factor of shear stress for the clay site is overestimated by the liquefaction resistance shear stress method. The axial strain of the frozen-thawed clay reaching failure is less than that of the undisturbed clay. Under the same seismic shear stress, the development of the excess pore water pressure in frozen-thawed clay is more significant than that in undisturbed clay.

An empirical formula for the accumulative deformation of saturated clay under different cyclic loading frequencies

Road and subway tunnels in soft clay soils subjected to traffic loading often cause lager settlement. It can pose danger to the surrounding buildings and structures. Hence, it is necessary for engineers to correctly predict the long-term deformation of saturated clay foundations under cyclic loading. In this paper, a series of dynamic triaxial tests were carried out on Nanning clay to investigate the effect of loading frequency and cyclic stress on axial strain accumulation of clay under undrained condition. Results show that loading frequency has a great effect on the axial strain accumulation of clay. Based on the experimental results, an empirical formula for calculating the accumulated deformation of saturated clay under cyclic loading was presented.

Influence of water content on clay deformation characteristics subjected to periodic intermittent loading

The influence of clay's drainage and reconsolidation behavior during the intermittent period on clay's deformation needs to be further studied. Dynamic loads, such as traffic and earthquake, etc., have a certain intermittent period during the loading process. This study examined the deformation behavior of the clay obtained from Nanchang under various cyclic stress ratios (CSR) and water content conditions. The results demonstrated that minor strain rebound occurs in all intermittent periods. Aside from that, drainage reconsolidation during intermittent periods alters the pattern of strain accumulation during subsequent loading periods, and cyclic stress levels and water content conditions can impact the intermittent effects. In contrast, the development of strain in the samples under intermittent loading is more negatively impacted by high CSR and low water content (deviation from optimal water content). The hysteresis curve continued to change throughout the test, the accumulation and dissipation of excess pore water pressure changed, and it was found that the samples' resilient modulus had increased, indicating an improvement in the samples' resistance to deformation.

Softening and deformation characteristics of Tianjin soft soil under principal stress rotation induced by traffic loading

The vibration caused by moving traffic loading can create additional shear stress in the soil element, thereby resulting in the rotation of the principal stress axis, which can, in turn, accelerate soil softening and increase the cumulative deformation of soft clay. Nevertheless, the designed parameters are often obtained by the cyclic triaxial test (i.e., the rotation of the principal stress axis cannot be considered), or the cumulative axial plastic strain prediction is inaccurate, and these are some of the main reasons for geotechnical engineering problems. In this study, cyclic triaxial and cyclic torsional shear tests were performed to understand the softening and deformation characteristics of soft clay. The influences of the cyclic stress ratio, shear stress ratio, and loading frequency on the softening index and cumulative axial plastic strain of soft clay were analyzed. When the rotation of the principal stress axis was considered, the softening index decreased by 19.57%–51.09%, or the cumulative axial strain increased by 35.49%–74.39%, and failure occurred under higher cyclic stress ratios and shear stress ratios. Additionally, increasing the cyclic stress ratio and shear stress ratio and reducing the loading frequency will cause a surge in the softening index and cumulative axial plastic strain of soft clay. A cumulative axial plastic strain prediction equation considering the influences of cyclic stress ratio, shear stress ratio, and loading frequency was established and verified on the basis of literature. The availability of the prediction equation was verified by comparison with monitoring data. The relevant results can provide a theoretical reference for the prevention of urban engineering geological disasters.

Experimental study on creep wetting of silty clay

To study the wetting of a silty clay subgrade in an expressway, many laboratory tests were carried out. The test results show that the creep deformation of silty clay under water immersion cannot be ignored, but it is different from the deformation caused by wetting. The creep properties of soil mass are affected by many factors. Under different stress conditions, the soil mass will show different properties. In order to study the creep characteristics of silty clay in Chongqing under water wetting and different stress levels, a series of triaxial water wetting creep tests were carried out. The Singh-Mitchell creep equation was introduced to establish the creep model of silty clay drainage in Chongqing, and the parameters of the model were discussed.

Study on the wetting effect of the silty clay reservoir bank sub-grade

In this paper, the deformation characteristics of silty clay after immersion in water were studied. The wetting test of silty clay in a stratum in Chongqing under different confining pressures and different stress levels was carried out by using multi functional triaxial apparatus. Through the single line method and double line method experiments, the law of wetting deformation of silty clay was obtained and a new curve formula was fitted.

Bearing capacity and soil deformation around modified suction caisson in clay under monotonic horizontal loading

Suction caissons for offshore wind turbine (OWT) are required to withstand larger horizontal load resulting from wind and wave. In order to increase the horizontal bearing capacity, the modified suction caisson (MSC) was proposed. Experimental studies were conducted to investigate the bearing behavior and soil deformation around MSC in clay under horizontal loading. Influence factors such as the undrained shear strength and installation methods were studied. Results show that the horizontal bearing capacity of the MSC increases by 20–40% compared with the regular suction caisson (RSC). The horizontal bearing capacity of the MSC increases with increasing the undrained shear strength. In addition, the horizontal bearing capacity of the MSC installed by jacked force is higher than that installed by applied suction. The rotation center was found to move downwards with the increase of the suction caisson deflection. In the limit state, upward deformation of clay and cracks within the deformed clay were observed in the loading direction. However, a gap between clay and the suction caisson edge opposite the loading direction was found. The deformation range around the MSC is larger than that around the RSC, indicating that the MSC can mobilize more soil to resist the horizontal load.