Soil Deformation Research Articles

Research on mining-induced surface soil cracking mechanism and development depth of downward fracture

In order to reveal the cracking mechanism of surface soil layer caused by coal seam mining, and explore theoretical methods for predicting the development depth of downward fractures during mining. Based on the background of the No. 1–2 upper coal seam mining in Daliuta Coal Mine, combining with fracture mechanics, soil mechanics, physical similarity simulation and numerical calculation methods. The mining-induced cracking mechanism and criterion of surface soil layer were analyzed, the crack development pattern and expansion mechanism were revealed, and the prediction formula of downward crack development depth of surface soil layer was put forward. The research results show that surface cracks mainly occur in the tensile zone, the concentrated tensile stress produced by the subsidence of overburden in the tensile zone can lead to soil cracking. When the surface maximum horizontal tensile deformation exceeds the limit horizontal deformation of soil, the soil layer cracks, and the cracking criterion of the surface soil layer was given accordingly. The soil crack of coal seam mining belongs to the mixed mode crack, and the soil cracks tip starts cracking and expanding along the direction of the maximum principal stress, therefore, the initiation crack angle of soil crack tip was obtained, and the fracture criterion of soil crack was proposed. With the crack propagation and development, the microcosmic crack becomes the macroscopic downward fracture. When the horizontal stress of the soil decreases to the cohesive force of the soil, the downward fracture stops develop, and the calculation formula for the development depth of mining-induced downward fracture was proposed. The development and evolution law of downward fracture was revealed, after the surface cracks, with the advance of the longwall face, the downward crack continues to extend and develop to the deep. Downward fracture develops on the ground surface at the open cut side, the mined-out area and in front of the longwall face, the maximum development depth of downward fracture tends to be stable when the longwall face advances to a certain distance. According to the physical simulation, numerical calculation and theoretical calculation, the development depth of downward fracture in No 1–2 upper coal seam mining is 8.11 m, 8.21 m and 8.14 m respectively. The theoretical prediction formula is reliable, and the results can provide a new method for the research of the development depth of mining-induced surface downward fracture.

Investigation of the liquid water content in composite saline soil containing chloride and sulfate ions

Different salt types have different effects on the liquid water content of saline soil, resulting in differences in the physico-mechanical properties and water/salt migration process of saline soil. In order to investigate the phase transition process and the change of the liquid water content in composite saline soil, saline soils with the same total salt content and different ratios of sodium chloride and sodium sulfate were taken as the objects. The results indicated that two phase transitions occur in the saline soil with single salt type, while three phase transitions can be found in the composite saline soil with two salt types. Mirabilite crystallization contributes to the 1st phase transition, mirabilite and ice precipitate together in the 2nd phase transition process, and mirabilite, ice, and hydrohalite precipitate simultaneously in the 3rd phase transition process. The liquid water is reduced in the phase transition process during cooling, and the pore characteristic has been changed significantly. The change of the liquid water content reflects the processes of salt crystallization and ice formation in saline soil, then the amounts of ice and hydrated salt were calculated at different temperatures, and the mechanism of inhibiting the deformation of sulfate saline soil was examined by adding sodium chloride. The results have reference value for those seeking understanding of the deformation in natural composite saline soil, and these findings can provide theoretical basis for the phase transition mechanism of saline soil in cold regions.

Investigation on shakedown response-behavior of thawed subgrade soils under long-term traffic loading

The shakedown state of the subgrade is crucial for the sustainable design and long-term stability evaluation of pavement structures. In order to characterize the plastic deformation and shakedown behavior of subgrade soil in seasonal frozen regions, cyclic triaxial tests were conducted on the thawed subgrade soil after seven cycles of freeze-thaw. The influences of the numbers of cycle loading, the amplitude of cyclic deviator stress, and the confining stress were considered variables. The evolution features of accumulative plastic strain, accumulative plastic strain rate, and critical dynamic stress were experimentally analyzed. Based on the shakedown theory, the ensuing discoveries were that the accumulative plastic strain response-behavior of thawed subgrade soil was typically divided into plastic shakedown, plastic creep, and incremental collapse under the long-term cyclic loading. Furthermore, the shakedown standard for thawed subgrade soil was also proposed based on the evolution of the accumulative plastic strain rate. The critical dynamic stresses can be obtained by the proposal formula to determine the different plastic deformation ranges.

Simulation Research of Motion of Lightweight Wheeled Mobile Robot on Various Types of Soft Ground – a Case Study

A problem of influence of three types of soft ground on longitudinal motion of a lightweight four-wheeled mobile robot is considered. Kinematic structure, main design features of the robot and its dynamics model are described. A numerical model was elaborated to simulate the dynamics of the robot's multi-body system and the wheel-ground interaction, taking into account the soil deformation and stresses occurring on the circumference of the wheel in the area of contact with the deformable ground. Numerical analysis involving four velocities of robot motion and three cases of soil (dry sand, sandy loam, clayey soil) is performed. Within simulation research, the motion parameters of the robot, ground reaction forces and moments of force, driving torques, wheel sinkage and slip parameters of wheels were calculated. Aggregated research results as well as detailed results of selected simulations are shown and discussed. As a result of the research, it was noticed that wheel slip ratios, wheels’ sinkage and wheel driving torques increase with desired velocity of motion. Moreover, it was observed that wheels’ sinkage and driving torques are significantly larger for dry sand than for the other investigated ground types.

Modelling of Multi-Storey Cross-Laminated Timber Buildings for Vibration Serviceability

In this study, the vibration serviceability of multi-storey timber buildings is addressed. The core of this study pertains to the preparation of a comprehensive finite element model to predict modal properties for an accurate vibration serviceability checking. To that end, findings obtained from studying three multi-storey timber buildings are summarized and discussed. Two of the buildings (of seven and eight storeys) consist entirely of cross-laminated timber (CLT), while the third is a five-storey hybrid CLT-concrete building. Thanks to the detailed finite element models and modal testing results, one has the capability to conduct sensitivity analyses, classical and Bayesian model updating, and uncertainty quantifications. With these methodologies, influential modelling parameters as well as the sources of modelling error were identified. This allowed for conclusions to be drawn about the in-plane shear stiffness of the constructed walls (whose higher value causes the natural frequencies to increase by up to 25%), the soil deformability (which may cause the natural frequencies to drop by up to 20%), and the perpendicular-to-the-grain deformation of floor slabs (which may lead to an overestimation of a fundamental frequency by up to 8%).

The Effect of Soil-Structure Interaction (SSI) on Structural Stability and Sustainability of RC Structures

The issue of SSI involves how the ground or soil reacts to a building built on top of it. Both the character of the structure and the nature of the soil have an impact on the stresses that exist between them, which in turn affects how the structure and soil beneath it move. The issue is crucial, particularly in earthquake regions. The interaction between soil and structure is an extremely intriguing factor in increasing or reducing structural damage or movement. Structures sitting on deformable soil as opposed to strong soil will experience an increase in static settlement and a decrease in seismic harm. The engineer must take into account that the soil liquefaction problem occurs for soft ground in seismic areas. A reinforced concrete wall-frame dual framework's dynamic reaction to SSI has not been sufficiently studied and is infrequently taken into consideration in engineering practice. The structures’ seismic performance when SSI effects are taken into account is still unknown, and there are still some misconceptions about the SSI idea, especially regarding RC wall-frame dual systems. The simulation study of the soil beneath the foundations significantly impacts the framework's frequency response and dynamic properties. Therefore, the overall significance of SSI in the structural aspect and sustainability aspects will be reviewed in this research.

Calibration of Hypoplastic Parameters for Danube Sand

Abstract The relationship between stress and strain tensors in soil is described by the soil constitutive equation, which depends on the soil type and deformation conditions. The development of various constitutive models has enabled a better understanding of the macromechanical properties of soil. One such model is hypoplasticity, which was discovered more than three decades ago. The purpose of this study is to determine whether hypoplasticity could accurately represent the behavior of Danube sand, a specific type of sand. The researchers conducted laboratory measurements to obtain the eight basic hypoplastic parameters of Danube sand and employed the intergranular strain concept as an extension of hypoplasticity to achieve a more precise material behavior. All the parameters were then utilized to simulate the cyclic triaxial test using the SoilTest Module of PLAXIS. The results showed that the hypoplastic constitutive simulation model for Danube sand was capable of making relatively accurate predictions for accumulative settlement.

A frictional contact algorithm in smoothed particle method with application in large deformation of soils

A frictional contact algorithm in smoothed particle method with application in large deformation of soils

Micromechanical analysis of pipeline-soil interaction in unsaturated granular soil undergoing lateral ground movement

The micro- to macro-scale pipeline-soil interaction mechanism in unsaturated granular soil remains unclear. This study investigates the unsaturated suction effect on the pipeline-soil interaction undergoing lateral ground movement using coupled discrete element method and finite element method (DEM-FEM) simulations. The Johnson-Kendall-Roberts (JKR) adhesive model was used to simulate the interparticle suction while the pipe segment was simulated with finite element meshes. The findings reveal that discontinuity and large deformation occurrences in unsaturated sandy soil in model tests can be successfully modelled by the DEM-FEM method. Besides, the interparticle suction effects on contact forces, particle collision behaviours, and special soil pressure distributions near the pipeline-soil interfaces were discovered and successfully explained. Additionally, progressive soil deformation and failure behaviours in dry and unsaturated soils were compared while the partial similarity between the suction effect and buried depth effect on pipeline-soil interaction was discussed. Finally, several conclusive pipeline-soil interaction failure patterns in different interparticle-suction conditions were identified after analysing a series of particle-scale behaviours including particle trajectories, particle contacts, and particle rotation distributions. The study indicated that neglecting the unsaturated effect can result in severely underestimating the intensity of pipeline-soil interaction and misjudging the soil failure patterns.

Arching development above active trapdoor: insight from multi-scale analysis using FEM–SPH

AbstractUnderground excavation is usually accompanied by complex soil-structure interaction problems in practical engineering. This paper develops a novel multi-scale approach for investigating the soil arching effect through trapdoor tests. This approach adopts the finite element method (FEM) and smoothed particle hydrodynamics (SPH) method to handle the particle-rigid body interaction in the trapdoor tests, incorporating a micromechanical 3D-H model to derive the nonlinear material response required by the SPH method. The variation of the earth pressure on the trapdoor in simulations exhibits good agreement with those of the experiments. Extensive parametric analyzes are performed to assess the effects of soil height and inter-particle friction angle on the evolution of load transfer and soil deformation. Three deformation patterns are observed under different buried conditions, including the trapezoid, the triangle, and the equal settlement pattern. Results indicate that the planes of equal settlement develop progressively with the trapdoor movement and then enter the range of experimentally observed values. Additionally, three failure mechanisms are identified that correspond to the three deformation patterns. Due to the advantages of the micromechanical model, mesoscale behavior is captured. The anisotropy of stress distribution in the plastic region is found during the arching process.

An efficient fully Crouzeix-Raviart finite element model for coupled hydro-mechanical processes in variably saturated porous media

Coupled hydro-mechanical processes in variably saturated porous media can be encountered in several applications in geosciences and soil mechanics. They are ruled by highly nonlinear and strongly coupled equations of fluid flow in unsaturated porous media and quasi-static mechanical deformation. In this work, we develop an efficient and robust numerical scheme for unsaturated poroelasticity that allows for balancing computational requirements and accuracy. The spatial discretization is based on the Crouzeix-Raviart (CR) finite element method for both the displacement field and the hydraulic head. The CR method is locally mass conservative and uses low-order approximation, which alleviates the computational burden. The time discretization of the coupled nonlinear hydraulic mechanical equations is performed using high order time integration methods and efficient time stepping schemes via the method of lines (MOL).Four test cases are investigated to highlight the efficiency and accuracy of the developed numerical scheme. The first test case deals with the settlement induced by gravity in the case of saturated and unsaturated soils. A new semi-analytical solution is developed for the settlement in the unsaturated case and used for the validation of the numerical scheme. The second test case is the Cantilever bracket problem, extended here to variably saturated media and studied to investigate the nonphysical oscillations of the pressure variable with different numerical schemes. The results are compared to finite element solutions obtained with COMSOL with either linear or quadratic approximation of the displacement field. The third test case deals with the deformation of an unsaturated soil under partial infiltration and surface load. This test case is simulated to investigate the accuracy and efficiency of the CR scheme for the challenging problem of infiltration into dry soils. The last test case is simulated to show the applicability of the developed model to a realistic problem dealing with the stability of a hillslope under intense rainfall periods.Results of the numerical experiments show that the CR scheme coupled with high order time integration methods allows for significant gain in both computational requirements and accuracy.

LSTM-based deformation forecasting for additional stress estimation of existing tunnel structure induced by adjacent shield tunneling

A redistribution of stress is caused by the excavation of a new tunnel within the soil surrounding the existing shield tunnel structure. This stress redistribution results in alterations to the soil and water loads around the existing tunnel structure, ultimately impacting its stress and deformation. The deformation response of existing tunnels is primarily focused on in most existing studies, with limited research conducted on the coupling system of new tunnel excavation, soil stress state, and deformation and stress of existing tunnels. This paper proposed an innovative methodology to predict deformation in existing tunnel structures and estimate additional stress during the excavation of a new shield tunnel. The reliability of the suggested calculation method was verified using measured internal force and convergence data of the structures. The results demonstrated that the Long Short-Term Memory (LSTM) model could more effectively establish the temporal correlation between the excavation parameters of new tunnels and the deformation of existing tunnels. Compared to the Recurrent Neural Network (RNN) model, the R2 of the LSTM model increased by 11.81% in the prediction of the tunnel waist and 9.38% in the prediction of the tunnel crown. The Light gradient boosting machine (LightGBM) algorithm was used to analyze the crucial factors of deformation of the existing tunnel structures during shield tunneling, and the results showed that the relative position and the average earth pressure were the essential factors. Furthermore, a calculation method for the additional stress of existing tunnel structures was proposed based on the load structure model. The method assumed that the additional load was distributed rectangularly at the top and bottom of the existing tunnel, and triangularly at the waist of the tunnel. The comparison between the calculated results and the measured results indicated that the phased characteristics of the internal force changes in the existing tunnel structure during the construction of a new tunnel could be accurately reflected by this method.

A stress-controlled soil column test equipment for investigating water seepage-consolidation characteristics of the compacted soil

For deep-filled building site, it is not acceptable to neglect water seepage and land settlement caused by the coupling effect of wetting and loading. However, previous soil column tests employed in investigating the water seepage always failed to consider the vertical stress. In this article, a stress-controlled soil column test was conducted to investigate the effect of vertical stress on water seepage and deformation of the compacted soil. The soil column was equipped with a vertical loading device and a water-recharge device to control the boundary conditions and water sensors, tensiometers, dial indicators and a data collector to monitor the displacement and water movement. The soil column test was utilised to perform seepage tests on compacted loess with vertical stresses of 0 and 400 kPa. The time-history data of wetting front depth, volumetric water content (VWC), suction and vertical displacement have been monitored directly. The VWC and suction profiles, soil–water characteristic curves and hydraulic conductivity curves were then obtained with the monitored data. The test results demonstrated that the vertical stress affected the water seepage and consolidation of the compacted soil, but this effect gradually decreased as the depth of the soil column increased. Moreover, the reliability of the proposed test method was verified by the comparison of some available test results. The findings of this study contribute to a better understanding of water seepage and consolidation characteristics of the compacted soil subjected to vertical stress.

Thermomechanical Analysis of Energy Piles Using a Load-transfer Approach Considering Soil Coupling Effects

Energy piles are inevitably subjected to thermomechanical loads due to their dual role of utilizing geothermal energy and supporting structural loads. The load-transfer approach is a suitable predictive method for addressing the analysis and design of energy piles, but it generally does not properly consider the continuity and deformation behavior of the soil mass. This study presents experimental and analytical investigations on the thermomechanical behavior of full-scale energy piles. A new thermomechanical load-transfer approach allowing consideration of the soil coupling effects was proposed by involving the soil deformation and the soil-pile interface behavior. Through comparative analysis with experimental data, the proposed method (with soil coupling effects) demonstrated superior predictive accuracy compared to the existing method (without soil coupling effects). In this field condition, ignoring soil coupling effects could result in an underestimation of nearly 48.8% of pile head settlement. The validated method was further used to analyze the thermally induced cyclic behavior of energy piles under various mechanical load levels. The results indicated that the thermally induced response of energy piles was directly associated with the level of the head load. The energy piles under higher axial loads may show irreversible thermomechanical behavior when subjected to cyclic thermal loading.

Study on the Mechanical Characteristics of Large Shear Deformation of Lightweight Soil Solidified by Blowing and Filling with High Moisture Content

Study on the Mechanical Characteristics of Large Shear Deformation of Lightweight Soil Solidified by Blowing and Filling with High Moisture Content

Simulation of Draught Reduction Performance of Subsoiling with Upcutting Belt Motion Using Discrete Element Method

Conventional subsoiling has the problem of excessive draught resistance, which has long been a major concern. A great reduction in draught is urgently required to make better use of the subsoiling technique with many agronomic benefits. In this study, an attempt was made to test the draught reduction performance of a series of tools with continuous belt motions. Comparative simulations between regular tools and belt tools were carried out using the discrete element method (DEM) to investigate the effects of belt motion on tool force, soil disturbance characteristics, particle velocity distribution, and soil deformation and movement patterns. The results indicated that the belt motion reduced the draught force by 13.18%, 25.21%, 37.98%, and 44.64% for the rake angles of 30°, 45°, 60°, and 75°, respectively, and caused acceptable increases in downward vertical force. The changes in soil disturbance, particle velocity distribution, and soil deformation and movement patterns contributed to the reduction in draught force. Negative effects on soil disturbance were acceptable considering the 13.18% to 44.64% reductions in draught force. The present study suggests that the belt motion has a great application potential for draught reduction in subsoiling. Also, this can serve as a theoretical foundation for future studies.

Mechanical response and numerical simulation of liquid soil abutment backfill

The application of a new liquid soil material and the treatment effect of backfilling an underpass tunnel in an airport are studied. The deformation and mechanical properties of liquid soil and conventional soil under load are comprehensively compared and analyzed via a numerical simulation with finite element software. The effects of the buried depth of overlying fill, tunnel height, and traffic load on the backfilling of liquid soil abutment are analyzed. The research results show that under the action of load, the overall deformation and stress distribution of the liquid soil and conventional soil show similar laws. However, liquid soil backfilling has great advantages over conventional soil backfilling in all aspects. Liquid soil backfilling can reduce the deformation and the compressive stress at the corner of the backfilling area by approximately 13% and 15%, respectively. The overburden buried depth has a great impact on the subgrade deformation. In the actual construction, the overburden buried depth should be 1.5 m. Overburden depth has a greater impact on the vertical deformation of the road, the self-weight of the overburden will act as an additional load on the overall roadbed, compared to conventional soil backfill, the overburden depth of 2.0 m conventional soil backfill overall deformation of the overburden depth is about equal to the overburden depth of 1.5 m liquid soil backfill, the use of liquid soil backfill is equivalent to the overburden fill to reduce the additional load of 0.5 m. The height of the box culvert has a greater impact on the stress, but this change is not linear, the actual construction in the case of meeting the specific requirements of use, should try to control in the vicinity of 8.4 m, and at the same time the use of liquid soil backfill can reduce the compressive stress of about 14%. The compressive stress increases first and then decreases with the increase in liquid soil modulus. The liquid soil modulus should be controlled to 180 MPa. Moreover, liquid soil backfilling can reduce the compressive stress in the backfilling area by approximately 25%. The trapezoidal slope of the backfill area is proportional to the deformation amount. Although an obvious correlation with compressive stress exists, the regularity is not strong. Thus, the trapezoidal slope should be set to 1:1 during construction. Traffic load slightly affects the overall deformation and compressive stress of the road. However, the distribution trend of deformation and stress changes obviously under the action of aircraft load. In the actual design, only one load form of aircraft load should be considered.

Effects of moisture content and soil suction on the permanent deformation of tropical subgrade soils: experimental investigations and modelling

This study presents the effects of moisture variation and the influence of matric suction on the permanent deformation (PD) of three tropical soils with different geological-geotechnical characteristics used in road subgrades in southern Brazil. The experimental programme consisted in determining the soil-water characteristic curves and in dynamic triaxial tests to obtain the PD in different compaction and post-compaction moisture contents. The variation of compaction moisture content caused microstructural changes, influencing the plastic behaviour of soils: the higher the initial moisture content, the greater their accumulated permanent deformations. As expected, the post-compaction moisture variation (wetting process) tended to increase the plastic deformation of materials, evidencing the influence of the suction variation on the performance of the soils studied. In addition, matric suction proved to be the best variable to represent the effects of moisture variation on the plastic behaviour of soils subjected to cyclic loading. Thus, a PD prediction model for tropical soils with the inclusion of this parameter was proposed. The model proved to be highly predictive and may become an important tool to be incorporated into current mechanistic-empirical design methods.

Micromechanical Analysis of Lateral Pipe–Soil Interaction Instability on Sloping Sandy Seabeds

The micromechanical mechanism of pipe instability under lateral force actions on sloping sandy seabeds is unclear. This study investigated the effects of slope angle and instability direction (upslope or downslope) on pipe–soil interaction instability for freely laid and anti-rolling pipes using coupled discrete element method and finite element method (DEM–FEM) simulations. The numerical results were analyzed at both macro- and microscales and compared with the experimental results. The findings revealed that the ultimate drag force on anti-rolling pipes increased with slope angle and was significantly larger than that on freely laid pipes for both downslope and upslope instabilities. Additionally, the rotation-induced upward traction force was proved to be the essential reason for the smaller soil deformation around freely laid pipes. Moreover, the shape differences in the motion trajectories of pipes were successfully explained by variations in the soil supporting force distributions under different slope conditions. Additionally, synchronous movement between the pipe and adjacent particles was identified as the underlying mechanism for the reduced particle collision and shear wear on pipe surfaces under a high interface coefficient. Furthermore, an investigation of particle-scale behaviors revealed conclusive mechanistic patterns of pipe–soil interaction instability under different slope conditions. This study could be useful for the design of pipelines in marine pipeline engineering.

A Multiscale Method to Develop Three-Dimensional Anisotropic Constitutive Model for Soils

A multiscale method is presented to develop a constitutive model for anisotropic soils in a three-dimensional (3D) stress state. A fabric tensor and its evolution, which quantify the particle arrangement at the microscale, are adopted to describe the effects of the inherent and induced anisotropy on the mechanical behaviors at the macroscale. Using two steps of stress mapping, the deformation and failure of anisotropic soil under the 3D stress state are equivalent to those of isotropic soil under the triaxial compression stress state. A series of discrete element method (DEM) simulations are conducted to preliminarily verify this equivalence. Based on the above method, the obtained anisotropic yield surface is continuous and smooth. Then, a fabric evolution law is established according to the DEM simulation results. Compared with the rotational hardening law, the fabric evolution law can also make the yield surface rotate during the loading process, and it can grasp the microscopic mechanism of soil deformation. As an example, an anisotropic modified Cam-clay model is developed, and its performance validates the ability of the proposed method to account for the effect of soil anisotropy.