Soil Displacement Research Articles

Shear failure analysis of slip zone soil with different coarse particle shapes: Visualized shear test and PIV technology

Coarse particle shape in slip zone soil influences the mesoscopic structure of the soil, which in turn affects soil shear strength and failure behavior. In order to investigate the effect of particle shape on the shear characteristics of coarse–fine-grained mixed slip zone soil, three types of coarse particles (spheroidal, rounded, and angular) were selected for mixing and matching, and a total of 10 sets of medium-scale shear tests were designed for this paper. To quantify the shear deformation and failure process of slip zone soils, particle image velocimetry (PIV) technology and the hanging hammer method were used to obtain mesoscopic data of the soil (displacement vector data of soil particles and elevation data of the shear failure surface), which were used to calculate shear band thickness, shear dilatation, and roughness coefficient of the shear failure surface. The results indicate that coarse particle shape can considerably affect the macroscopic mechanical properties (internal friction angle and shear strength) and mesoscopic deformation characteristics (shear band thickness, shear dilatation, and shear surface morphology) of soils. Angular coarse particles have higher interlocking strength than spheroidal and rounded coarse particles, allowing angular coarse-grained slip zone soils to develop large shear band thickness and rough shear failure surfaces. In addition, mesoscopic damage analysis suggests that the damage rate of slip zone soils decreases with increasing coarse particle shape complexity. These findings enhance comprehension of the failure characteristics of soil-rock mixture slopes and serve as a good reference for the stability analysis of similar slopes.

Study on dynamic response and long-term settlement of silty soil around Shanghai metro tunnel

At present, the method for calculating long-term tunnel settlement predictions under metro loading considers only one working condition of passenger loading, which is inconsistent with actual working conditions. To establish a tunnel settlement model that accounts for variations in passenger flow, this study uses data mining methods to categorize metro operation into three working conditions: "peak period, secondary period, and low period." The impact of these passenger flow conditions on the dynamic response of the soil around the tunnel is analyzed. Then, based on the principles of calculus, a calculus-based prediction model is established to consider the changing patterns of metro passenger flow. The model is applied to analyze the long-term settlement characteristics of Shanghai Metro Line 10. The results indicate that, under identical conditions, soil displacement and dynamic deviatoric stress around the tunnel increase with passenger capacity. The calculus prediction model aligns more closely with actual working conditions than the conventional model. The predicted tunnel settlement of Shanghai Metro Line 10 after 20 years of operation is approximately 37.07 mm, with most settlement occurring in the early stages, primarily due to cumulative plastic deformation of the soil.

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.

Analysis of Offshore Wind Turbine by Considering Soil-Pile-Structure Interaction: Effect of Sea-Wave Load Duration

ABSTRACT Offshore Wind Turbines (OWTs) confront different types of environmental loads during their lifetime. One of the most significant loads is the cyclic sea-wave load which affects the OWT system during the approximate 25 years of design life. This lateral cyclic load can influence the response of the OWT system because of accumulated permanent displacement and excess pore water pressure generation in soil. This procedure can change pile-soil stiffness. However, the behavior of OWT and its foundations is mostly studied under short-term cyclic loading, and the effects of duration of the cyclic loads on pile-soil interaction and performance of the foundation are not well understood and documented. Therefore, there is a lack of guidance in codes for the duration effects of cyclic loads on the structural and geotechnical response of OWTs. In this regard, the current study considers the effects of duration of the cyclic loads on serviceability and performance of the OWT system by considering soil-foundation-structure interaction using a 2-D finite element method. The behavior of the OWT system is evaluated based on the internal forces and deformation of the monopile foundation, shear strain, and excess pore water pressure ratio in the surrounding soil. Besides, liquefaction susceptibility in the sandy soil layer at the vicinity of the monopile and its effect on the performance of the foundation is investigated. Finally, the results can provide guidance on estimation of the dynamic performance of the OWT system during long-term cyclic loads. They can be used to specify the need for consideration of the duration of cyclic lateral loads for the design of OWT structures.

Numerical Simulation of Double-Row Retaining System with Different Piers

With the rapid expansion of foundation pit excavation areas due to the burgeoning underground transportation networks in large cities, spatial combined double-row retaining structures have become indispensable for ensuring stability and minimizing deformation. Integrating piers into these structures enhances stiffness; however, the research on this topic is limited. This study investigates the Chisha Metro project, which utilizes a double-row support structure with added support piers to improve overall stiffness. Numerical simulations are employed to model the foundation pit and analyze the stress distribution and deformation of double-row retaining systems with T-shaped, cross-shaped, or square-shaped piers. The results demonstrate that the retaining system, after the introduction of piers, exhibits reduced maximum horizontal displacement and surface settlement of soil, and indicates spatial characteristics and the transformation from a planar problem to a spatial problem. Furthermore, in specific geological conditions, the T-shaped support pier proves to be more effective in connecting the front and rear support structures compared to the cross-shaped and square-shaped support piers, which mainly reinforce the soil without connecting the support structures. This research provides valuable insights for improving design and construction practices in foundation pit engineering.

Centrifuge model tests on an anchor pile under cyclic oblique pullout load using transparent sand

Cyclic load on anchor piles of single point mooring systems is an important issue, and the cyclic behavior of anchor piles has a connection with the surrounding soil displacement. Based on transparent sand and particle image velocimetry (PIV) technique, centrifuge model tests on the pile subjected to oblique pullout load were conducted. The cyclic pile performance and the soil displacement field under various cyclic load characteristics were studied. The mechanism for the cyclic response of anchor piles was investigated. It can be observed by transparent sand that the failure mode of the pile is a combination of vertical and lateral translation without rotation. The post-cyclic pullout bearing capacities are decreased with the increasing of the cyclic amplitude and number of cycles, but the pile vertical displacement and the soil displacement are increased at the same post-cyclic reload. During the cyclic load period, the pile produces cumulative displacement due to soil particle movement, especially vertical displacement that can reduce embedment depth and bearing capacity. However, the shakedown behaviors of the cumulative displacement and post-cyclic bearing capacity of the pile occur, because the increasing rate of the soil displacement is decreased with loading cycles.

Bearing and deformation characteristics of monopile foundation under monotonic and cyclic horizontal loads.

The bearing and deformation characteristics of monopile foundation under the monotonic and cyclic loads are key factors to consider in the design of the transmission tower structure or offshore wind energy converters. The model tests and numerical simulations of monopile foundation under monotonic and cyclic horizontal loads were performed in sand to explore the bearing characteristics and the deformation characteristics of pile. The potentially affected factors including loading height, relative density of soil, displacement amplitude were analyzed. The results show that with the loading height varies from 1D to 4D, the horizontal static bearing capacity of the pile under different the soil relative density decreased by 1.63-1.9 times, and the peak bending moment increased by 22.9%-36.8%. Under the cyclic loads, the peak load on the pile top increased by 31.7%-56.1% for each 1 mm increase in displacement amplitude. The stiffness of soil around pile varies as the number of cycles increases with the development trend of decreases first and then increases gradually. As the horizontal load and cycle number increase, the range of the displacement of soil extends towards the bottom of pile, until it covers the entire lower part of the model.

Method of settlement calculation for underlying layer of soft soil composite foundation based on load transfer mechanism

The mechanical properties of soil in soft soil area are poor, and the settlement of the underlying layer in the composite foundation accounts for a large proportion of the total settlement. At present, most of the research focuses on the settlement of the reinforced area, and the research on the settlement of the underlying layer is of great significance for the settlement of soft soil composite foundation. The differences in load transfer modes of soil and pile are analyzed, and based on the Boussinesq solution and Mindlin solution, a calculation method for the stress and settlement of the underlying layer in flexible and rigid pile composite foundation is proposed. The relative displacement of soil and pile in flexible pile composite foundation is small, and the negative friction can be ignored, but the influence of effective pile length should be considered. The relative displacement of soil and pile in rigid pile composite foundation is large, so the negative friction should be considered. Part of soil top stress is transmitted to the pile via negative friction, and then the pile axial force is transmitted back to the soil via positive friction. In addition to effective pile length, the change of stress transfer path caused by negative friction should also be considered in settlement calculation.

Influence of synchronous grouting on surrounding sandy cobbles during shield tunnelling process: Insights from a scaled model test

Substantial soil deformation around tail-grouting activity is frequently observed during the shield tunnelling process in the sandy cobble strata, which is attributed to the convergence and potential collapse of the soils around the tail-void left behind the shield machine. The stability of the underlying strata is significantly impacted by synchronous grouting inside the tail-void. This study examines four-opening synchronous grouting, which is frequently used in shield tunnelling of metro-tunnels, to analyze the grout-spreading mechanism and soil displacement generated by the synchronous grouting in the sandy cobble layer. Laboratory tests are used to determine the characteristics of grouting mortar and soils in accordance with the similarity theory. The model experiment outcomes show that a rise in the GVR (Grouting-Volume Ratio) can cause the settlement at the ground surface. However, as the GVR improves, the pace of settlement growth diminishes. Additionally, the expanding cover depth of the tunnel contributes to the stability of the soil after synchronous grouting. As observed in the model test, when GVR achieves its maximum amplitude (i.e., GVR = 200 %), the grout mortar cannot spread to the crown of the tail-void, necessitating secondary grouting after the synchronous grouting during tunnelling practice. After grout hardening process, it was discovered that grout material above the tunnel waist was concentrated near the upper grout openings, implying a seepage spreading mode of the grout-mortar at these locations. In contrast, grout material below the tunnel waist was evenly distributed along the periphery of the tail void. The model test outcomes may be utilized as a guide for tail-grouting while shield tunneling in sandy cobble strata.

Experimental investigation of dynamic behaviour of pile-supported bridges in sandy deposits

This paper presents the results of centrifuge tests performed on reinforced concrete (RC) pile–supported simply supported girder bridge models in non-liquefiable (unsaturated) and liquefiable (saturated) slightly inclined sandy soil sites. The main objectives were to investigate the dynamic response characteristics of RC pile–supported simply supported girder bridges in non-liquefiable and liquefiable soils, examine the mechanisms causing beam collapse and damage to pile–pier yielding, and verify the effectiveness of cable restrainers. The centrifuge tests were conducted in non-liquefiable and liquefiable sites, each consisting of a three-span RC pile–supported simply supported girder bridge model and a control model with a superstructure equipped with a cable restrainer. First, the dynamic characteristic parameters of the soil and structural models in both sites were obtained. Subsequently, the conventional test results were interpreted, including the excess pore pressure ratio, acceleration, and displacement. The analysis included examining the moment demand of the pile–pier structure and seismic damage mechanisms. Finally, a correlation analysis was performed to evaluate the inertial and kinematic effects on the moment demand of the pile–pier structure. The results show that the acceleration response after soil liquefaction at the inclined sites is amplified unilaterally in the downslope direction and spikes appear. The liquefiable foundation is displaced to the downslope. However, major earthquake induces foundation displacement, and liquefaction leads to a longer duration and more significant soil displacement. The installation of cable restraints significantly increased the acceleration response of the superstructure. Still, it effectively reduced the relative displacement of the superstructure and prevented the beam from collapsing. Soil liquefaction decreases the bending moment of the pile–pier structure, and the cable restrainer causes the damage mode of the pile–pier structure to shift from the pile head to the pier bottom. In the non-liquefiable scenario, the bending moment demand at the pile head has a more significant influence on the inertial effect. Additionally, using the cable restrainer system can increase the kinematic effect after liquefaction. The test results can be used to validate numerical models and provide a reference for pile foundation design.

Evaluation of deformation for two-dimensional (2D) and three-dimensional (3D) braced excavation in clays with centrifuge modelling and numerical analysis

This study presents an improved in-flight strutting system for centrifuge modelling. Based on the centrifuge model test data, the mobilizable strength design (MSD) method was revised. The modified MSD method extends to the prediction of three-dimensional (3D) deformations in retaining walls due to excavation activities. Initially, an improved in-flight excavation tool used in centrifuge tests was employed to investigate the impacts of staged excavation on the characteristics of wall displacement and ground settlement in two-dimensional (2D) braced excavation. Subsequently, 2D and 3D finite element analyses, calibrated against the centrifuge test data and considering the small strain effect, were conducted to assess the performance of wall displacement, ground settlement, and movement of the underground soil induced by the braced excavation. Moreover, this research proposes a straightforward predictive model based on the modified MSD, specifically for calculating the deformation along the length of retaining walls in 3D braced excavations. The insights and the modified MSD method given in this study may facilitate the design of foundation pit projects, especially when the 3D effects are an essential detail to be considered in these projects.

Observed soil arching-induced ground deformation and stress redistribution behind braced excavation

This paper presents observed arching-induced ground deformation and stress redistribution behind braced excavation using the top-down construction method. The soil properties around the excavation were determined by laboratory and field tests. The ground deformation, soil displacement vector, strain path, principal strain, maximum shear strain, lateral earth pressure, pore water pressure, and effective stress path are presented based on the measured data. The majority of soil behind the wall is under volumetric expansion, indicating consolidation, creep behavior, or a combination of both. Besides, two periods of increases in pore pressure are observed, due to stress transfer from the lower to the upper parts (i.e., soil arching effect). The deep inward movement of the wall and the nearby soil accounts for the distribution of lateral earth pressure acting on the wall. The soil located behind the area of maximum wall deformation and adjacent to the wall, as well as the soil below the excavation base intersected by the shear plane, is in an active stress state. The lateral earth pressure at 5 m from the left excavation wall showed minimal changes, due to the combined effects of soil arching from lateral excavation and shield tunneling.

An Improved Winkler Foundation Modulus for a Beam in a Full Space

The Winkler foundation modulus is key to evaluating the response of underground structures using the elastic foundation beam model. In this paper, an improved formula of the Winkler foundation modulus for a beam embedded in a full space is proposed to overcome the limitation of inconsistent assumptions in previous studies. To achieve this goal, the bending responses of the beam are obtained using the elastic foundation beam model and three-dimensional elastic continuum model, respectively, wherein a consistent assumption is proposed that tangential interactions at the beam–ground interface are ignored in the two models. In addition, as deformation of the site is an important source of the underground structure response, the beam is applied to standard soil displacement of the free field on the Winkler foundation to improve the accuracy of the Winkler modulus obtained by fitting solutions based on the concentrated force on the beam. The formula for the Winkler foundation is obtained by equating the first zero of the bending moment in the two models. The Winkler foundation modulus is verified by comparing the results with numerical solutions and previous studies.

A numerical investigation of the role of basements on tunnel-frame interaction in sandy soil

This paper investigates the role of basement depth on the response of framed buildings to tunnel construction in sandy soil using finite element modelling. Six frames are considered to explore the influences of tunnel cover depth, building width, eccentricity, and the number of storeys on the role of basement depth. The numerical models adopt the hypoplastic constitute model to simulate the behaviour of the sand. The results suggest that basement depth plays an important role in determining the settlements of the raft foundations and soil displacements due to tunnelling. Its effect on the structural shear distortion primarily depends on the ratio of tunnel depth to building width (C/B); an increase in basement depth decreases and increases building maximum shear distortion for C/B<0.3 and for C/B>0.35, respectively. The basement considerably increases the shear distortion of short eccentric structures by preventing tilt of the building, causing a divergence from existing empirical envelopes and modification factors for shear distortion. The applicability of the meta-model is extended to the embedded structures by linking the building tilt freedom coefficient with the basement depth parameter, achieving good agreement between the predicted results and calculated data. Limitations and practical implications of the research are briefly discussed.

Research On Soil Displacement Prediction Method Caused By High-pressure Jet Grouting Pile Group Construction Under Adjacent Pile Response

This paper analyzes the soil displacement effect during high-pressure jet grouting pile construction by simplifying the construction process as a series of pressure-controlled spherical cavity expansions in a semi-infinite soil medium. Based on the elastic-plastic solution of pressure-controlled spherical cavity expansion theory, a calculation method is proposed to estimate the soil displacement caused by high-pressure jet grouting pile construction. Non-linear contact theory between the pile and soil is introduced, and the finite difference method is employed to determine the internal forces and deformations of the pile. The proposed method is applied to field construction cases, and its validity is verified by comparing the results with on-site monitoring data. The research findings reveal that the soil displacement effect decreases with depth and primarily occurs in shallow soil layers during the construction of individual high-pressure jet grouting piles. The lateral displacement at the ground surface increases first and then decreases with the increase in horizontal distance, while the ground uplift exhibits an exponential decay trend.

Experiment on the performance of high-speed railway subgrade with tire debris mixed filling

As an important component of railway track, railway subgrade bears a huge dynamic load from trains. To explore the feasibility and dynamic characteristics of mixed filling of railway subgrade soil with tire debris, a series of large-scale indoor model tests were conducted to compare and analyse the magnitude and distribution of earth pressure, and the cumulative settlement displacement of sleepers, under two different loading conditions (i.e., single-stage cyclic loading and multi-stage cyclic loading). The results demonstrate that under all conditions, the vertical displacement at the sleeper ends is greater than that at the sleeper middle, the vertical displacement at the sleeper end decreases with the increase of static load and frequency, but increases with the increase of amplitude. Additionally, adding tire debris can help reduce the settlement and displacement of the subgrade soil, and the same amount of tire debris has the best effect when mixed in two layers. Moreover, multi-stage cyclic loading can significantly reduce the cumulative settlement of the subgrade soil. Under multi-stage cyclic loading, the settlement displacement at the end of the subgrade soil sleeper is larger than that at the middle of the sleeper, but the difference gradually decreases as the static load increases. It is revealed from the research that tire debris can significantly improve the performance of railway subgrade soil.

Study on the effect of tunneling and secondary grouting on the deformation of existing pipelines in bedrock raised strata

Shield crossing the bedrock raised strata easily leads to large deformation of the soil, resulting in deformation and damage of the upper pipelines. To investigate the law of pipeline deformation caused by shield underpassing in bedrock raised strata, the changes in the action range of the additional thrust of the cutter head (p1), the friction resistance of the shield shell (p2), and the additional grouting force (p3) were analysed. A convergence model of the excavation face suitable for bedrock raised strata was proposed. The calculation formula of soil displacement at the axis of the pipeline was derived by using Mindlin’s solution and stochastic medium theory. The solutions of the vertical displacement, bending moment and strain of the pipeline were obtained by the energy variational method and the principle of minimum potential energy. Pipeline deformation analysis and reliability verification were carried out by an engineering case in Hangzhou, China. The influence of bedrock distribution and secondary grouting behind the pipe wall on pipeline deformation was studied. The results show that the calculated results are similar to the measured data with a high degree of coincidence, and the degree of agreement is higher compared to the existing method. When the shield tunneling direction is well controlled, the settlement and bending moment of the pipeline caused by the shield crossing the raised bedrock stratum will be reduced, and the reduction increases with increasing bedrock length and intrusion depth. The secondary grouting behind the pipe wall can reduce the settlement of the pipe line, but it is necessary to reasonably control the three parameters of grouting amount per unit length (Vinj), grouting ring length (Lh), and grouting ring angle (δ). Lh should not be too long and can be controlled below 30 m, δ should be controlled within 60°, and Vinj can be adjusted according to the deformation size of the pipeline to prevent excessive or insufficient correction.

Design of Conical Foundations with Increased Bearing Capacity in Areas of Undermined Soils

This article discusses the foundations of a conical shape directed with their apex downwards to increase the cross-sectional area and, accordingly, the bearing capacity during settlement and under the influence of horizontal tensile strains in undermined areas. To simulate the deformability of undermined and seismically exposed foundations, a three-dimensional expandable box was manufactured and assembled. Models of a conical foundation with an aperture angle of the cones at 90° and 80° were buried into the soil at 0.75 of its height, in order to provide a safety margin for further loading due to an increase in the bearing area when the cone is immersed deeper into the ground. Laboratory and field tests were performed on the vertical loading of single cones before and after horizontal soil displacement. Numerical modeling of the interaction between soil and foundation was carried out for conical foundation models that were considered for laboratory and field testing using the Plaxis 2D (Version 8.2) program. To compare the bearing capacity, isolated shallow foundations with a diameter equal to the cross section of the conical foundation at the intersection with the ground surface were tested. The isolated shallow foundations lost their bearing capacity after 0.15 kN in laboratory tests and after 75 kN in the field tests, while the ultimate bearing capacity of conical foundations with the similar cross section at the soil surface was not achieved, even after 0.2 kN during laboratory tests with horizontal soil displacement and at a load of 100 kN in field tests.

Case Study on Instrumenting and Monitoring Geosynthetic-Reinforced Pile-Supported Mechanically Stabilized Earth Wall Built over Soft Soil

This paper presents a case study on instrumenting, monitoring, and finite element modeling (FEM) of geosynthetic-reinforced pile-supported (GRPS) mechanically stabilized earth (MSE) walls. The GRPS-MSE wall was monitored using various instruments such as piezometers, earth pressure cells, shape-acceleration arrays (SAAs), and strain gauges. The performance criteria included efficacy, stress concentration ratio (SCR), differential settlement, and reinforcement tension. Collected data, such as excess pore-water pressures, contact pressures on pile and soft soil, differential settlements, and lateral displacement of MSE wall, were analyzed thoroughly. A 3D FEM was also developed to simulate the GRPS MSE wall, and the results are in good agreement with field data. The results demonstrated significant load transfer from soil to piles as a result of soil arching, yielding 30–32 SCR. The field efficacy was measured at 37.69 %, while the FEM efficacy was estimated as 42.4. Strains in geogrids within the geosynthetic-reinforced load transfer platform (GLTP) system were under 1%, less than the 5% maximum recommended by FHWA. The maximum differential settlement measured between pile cap and soft soil from SAAs is 7.1 mm, while it is estimated to be 8.3 mm from FEM. The MSE wall exhibited low lateral displacement (&lt;25 mm), indicating enhanced stability because of GLTP. The comparison between five analytical GLTP design methods showed that the CUR226 methods gave the closest results to field measurements and FEM results. This study offers crucial insights into leveraging GLTP and MSE walls in highway construction.

A Study on the Potential of Sand Liquefaction Hazard at Chukai Sentral, Terengganu Using Plaxis 2D

An earthquake is classified as a natural disaster of mother nature. Sometimes, it cannot be predicted when it will occur and difficult to estimate the striking force values and the period of incident. The effect of the earthquake may catastrophic if the magnitude is more than 6 Richter. It had been proved by previous event, an earthquake could cause a huge impact towards the soil condition especially when the saturated soil is soft or loose since the propagation of shear wave and compression could induced the soil liquefaction and gave an effect towards excess pore pressure and effective stress of the soil that may affect the stability of infrastructure such as dam, embankment, and bridge. This study was conducted to analyse the horizontal displacement of soil due to earthquake and to evaluate the possibility of liquefaction at Chukai Sentral, Kemaman, Terengganu, Malaysia. The study was conducted using Plaxis-2D software based on Mohr-Coulomb soil model at magnitude of 5.4 Richter. The Mohr-Coulomb model was selected as its failure occurs when the shear stress acting on the soil reaches a critical value and the shear strength is related to the effective stress acting on it. The analysis was concentrated on the mesh deformation and horizontal displacement. The result shows the mesh deformation and horizontal displacement obtained in the boreholes not more than 6 mm. It is considered as a small deformation and will not trigger to the potential of liquefaction to that area. It can be concluded that the earthquake magnitude of 5.4 Richter is unable to disturb the natural resistance of the soil and structure due to their stiff layer proportion.