Soil Arching Effect Research Articles

A frictional arch model for pile-cap-beam-supported embankment

The pile-cap-beam-supported (PCBS) system can strength the soil arching effect of embankment, increase the lateral stiffness, bending resistance and vertical bearing capacity of the rigid pile, however there is no frictional soil arch model of PCBS embankment. In this paper, first a frictional arch model for PCBS embankment modified from Russell’s frictional arching model was proposed. The proposed model in this paper considers the algorithm of lateral pressure coefficient k and a changing critical height of soil arch. In this new method, the influence of pile spacing, filling properties, height and pile spacing on critical height soil arch was comprehensively considered. Second, a series of numerical cases were performed to verify the effectiveness of the proposed model and study the arching effect of PCBS embankment. By comparing the vertical stress and settlement between the theoretical and simulation results, the rationality of the proposed method to estimate the stress and critical height of arch was validated. The effectiveness of the proposed method was further validated by comparing loading efficacy to a reported case. Last, the stress and deformation of PCBS and pile-cap-supported (PCS) embankment were analyzed and the superiority of PCBS system in improving the performance of embankment was observed finally.

An analytical solution to ground stresses induced by tunneling considering ground surface boundary conditions and gravity

Accurately predicting the stress distribution around the tunnel is crucial for designing safe and economical support systems. The stress distribution is closely related to the ground stress release induced by tunneling, as well as the initial gravity stress and boundary conditions. In this study, a two-dimensional analytical model considering the ground surface boundary conditions and gravity is presented to investigate the stress field around the tunnel. Then, a numerical model was developed to validate the proposed analytical model. Finally, parametric analyses were conducted, and the limitations of the load calculation method of the code for design of shield tunnel in China were discussed. The results indicate that: (a) Tunnel excavation induces stress redistribution in the soil, resulting in a soil arching effect around the tunnel. This arching effect causes nonlinear load changes around the tunnel. (b) The soil mass around the tunnel can be divided into undisturbed and disturbed zones. Above the tunnel, the disturbance range is C-2D(C and D represent the burial depth and the tunnel diameter), while below and on both sides of the tunnel, the disturbance ranges are 4D and 1.5D, respectively. (c) Once the stress release rate reaches 0.6, a combined arching effect zone, consisting of both major and minor principal stresses, is formed in the disturbance zone above and below the tunnel. (d) The load distribution pattern calculated by the code for design of shield tunnel in China is gourd-shaped, and this calculation method is insufficient for accurately evaluating the load around the tunnel. The research results can provide a reference for the design of the shield tunnel.

Discrete element analysis of geosynthetic-reinforced pile-supported embankments

A discrete element trapdoor model was established using the MatDEM software, and the effects of different embankment and reinforcement heights on the soil arching effect of embankments under reinforced conditions were investigated by introducing a biaxial geogrid. The outcomes demonstrated that the inclusion of a geosynthetic reinforcement could enhance the load transfer efficacy of the embankment and thereby reduce the differential settlement of the embankment surface. The differential settlement could be reduced by approximately 50 % when the reinforcement height and the pile cap were close. The inclusion of the geosynthetic reinforcement helped reduce the development of the slip surface within the embankment above the reinforcement and prevented the vertical slip surface from continuing to move upwards, thus ensuring that the soil arching effect did not degrade too quickly and continued to play a role. In the case of a low embankment reinforcement, the soil arching effect was largely nonfunctional because of the rapid development of the vertical slip surface, and the load on the embankment in the soft soil was mainly transferred to the piles through the tensioned membrane effect of the geosynthetic reinforcement. For a high embankment with a low reinforcement height, the soil arch structure of the embankment was well maintained, the soil arching effect did not degrade, and the load on the embankment in the upper part of the soft soil was transferred to the piles via the soil arching effect along with the tensioned membrane effect. In the case of a high embankment with a high reinforcement, the reinforcement blocked the vertical slip surface only for the soil above the reinforcement height, whereas the vertical slip surface below the reinforcement height developed in line with that of the same height, when the tensioned membrane effect and soil arching effect worked together in the embankment above the reinforcement height, and the soil arching effect below the reinforcement height degraded and hardly played a role.

Numerical tests on dynamic response of pile-supported reclaimed embankment for high-speed railway in saturated soft ground using soil–water coupling elastoplastic FEM

High-speed train (HST) running in the saturated soft ground induces significant vibration that may threaten the running safety and serviceability of high-speed railway (HSR). Extensive studies have been conducted on the dynamic responses of HSR, yet, the soil–water coupling and plastic behavior in the saturated soft ground are rarely considered, and thus the build-up of excess pore water pressure (EPWP) and displacement cannot be accurately calculated. In this study, 2D soil–water coupling elastoplastic FEM was employed to investigate HST induced vibration in the pile-supported embankment using FE code called DBLEAVES. Dynamic soil stress, EPWP, acceleration and displacement under different cases were numerically analyzed in detail. Numerical tests confirm that liquid phase in soft ground plays important influence on the dynamic responses that vertical acceleration and displacement will be overestimated while the horizontal acceleration and displacement as well as EPWP will be underestimated if soil–water coupling is not considered. Single-phase analysis also exaggerates the acceleration attenuation and underestimate the vibration amplification in soft ground. The existence of piles can induce significant soil arching effect in the embankment, the distributions of vertical acceleration and EPWP are partitioned sharply by the piles while vertical displacement in soft ground becomes more uniform along the depth direction within the pile reinforced area. The existence of piles also induces stronger vibration beneath the pile end so that larger EPWP is generated below the pile end than around the pile body. The main influence area due to HST vibration for pile-supported embankment is overall 20 m away from the centerline of HSR track, therefore, it is reasonable to improve the ground by properly increasing the number of pile within this area. When the number of pile is determined, increasing the length of pile or reducing the pile spacing are two effective ways to mitigate the dynamic response.

The Performance of a Circular Excavation Supported by a Prefabricated Recyclable Structure in a Full-Scale Test

Excavations for underground structures, such as working shafts, underground grain silos, and parking garages, are characterized by uniformity, consistent dimensions, large quantities, and strict timelines. Prefabricated recyclable supporting structures (PRSS) are gaining attention over traditional retaining structures due to their standardized design, efficient construction, and reusability, which suit such excavations better. To validate their performance, full-scale tests are conducted to analyze the deformation and stress characteristics of PRSS. The results show that the average maximum lateral displacement of supporting pile is 0.07% of the excavation depth (He), roughly half that of steel plate. Differences in ground surface settlement behind steel plates and the supporting piles are not as significant as those in their lateral displacements. While the displacement of the supporting piles is insufficient to induce soil movement into the active limit state on the non-excavation side, the circular excavation’s arching effect reduces the earth pressure on this side of the supporting piles below the active earth pressure limit. Furthermore, the earth pressure acting on the steel plates is lower than that acting on the supporting piles, suggesting the presence of a soil arching effect between two adjacent piles. These findings offer valuable insights for guiding the construction of PRSS.

A method for calculating the lateral earth pressure on rigid anti-slip piles with EPS inclusions

Expanded polystyrene (EPS) inclusions are placed between rigid anti-slip pile-free sections and slopes, causing soil displacement and transforming the lateral earth pressure from a static to an active state. This study proposes a calculation method for estimating the lateral pressure on rigid anti-slip piles with EPS inclusions based on the deformation coordination of the rigid pile–EPS geofoam–soil composite system and soil-arching effect behind the pile using the polar coordinate translation and oblique differential-unit methods. A FLAC3D numerical model, designed to verify the theoretical results and analyse the effect of load reduction due to EPS inclusions, confirmed the validity of the proposed calculation method. The load-reduction effect of EPS inclusions were positively and negatively correlated with the thickness and elastic modulus of the EPS specimen, respectively. Finally, three EPS-inclusion design methods are proposed; specimens manufactured by the first two methods facilitate both the load-reduction effect and poor economic efficiency, whereas those manufactured by the third method show excellent load reduction with economic efficiency. The results of this study contribute significantly towards research on EPS inclusions that could facilitate high-performance engineering and construction applications.

Settlement and stress analysis in stabilized slab- and pile-supported embankment based on double-equal settlement plane

PurposeThe soft stabilized slab and pile-supported (SSPS) embankment is an improvement technique to increase the efficiency of resources in road construction. To capture the effects of stabilized slabs on the stress transfer mechanism, the differential settlements and the lateral displacement of the embankment completely. A theoretical model of SSPS is proposed by considering the effect of soil arching and the interaction between the embankment fill, stabilized soil, pile, foundation soil and bearing stratum.Design/methodology/approachIn the theoretical model, the stress and strain coordination relationship of the system was analyzed in view of the minimum potential energy theory and equal settlement plane theory. Subsequently, the theoretical method was applied to field tests for comparison. Finally, the influence of the elastic modulus and the thickness of the stabilized slab on the stress concentration ratio and foundation settlement were examined.FindingsIn addition to the experimental findings, the method has been revealed to be reasonable and feasible, considering its ability to effectively exploit the stabilized slab effect and improve the bearing capacity of soil and piles. An economical and reasonable arrangement scheme for the thickness and strength of stabilized slabs was obtained. The results reveal that the optimum elastic modulus was chosen as 28 MPa–60 MPa, and the optimum thickness of the stabilized slab was selected as 1.5 m–2.1 m using the parameters of field tests, which can provide guidance to engineering design.Originality/valueAn optimization calculation method is established to analyze the load transfer mechanics of the SSPS embankment based on a double-equal settlement plane. The model’s rationality was analyzed by comparing the settlement and stress concentration ratios in the field tests. Subsequently, the influence of the elastic modulus and the thickness of the stabilized slab on the stress concentration ratio and settlement were examined. An economical and reasonable arrangement scheme for the thickness and elastic modulus of stabilized slabs was obtained, which can provide a novel approach for engineering design.

Numerical analysis of soil arching effect in piles-reinforced airport foundation

The soil arching effect is the key mechanism for load transfer in pile-supported reinforced road (runway) foundations. To investigate the formation and evolution process of soil arching effect in the whole process of embankment filling and soft soil foundation consolidation, a three-dimensional hydro-mechanical coupled numerical model of pre-fabricated high-strength concrete (PHC) pile-reinforced soft soil runway foundation was established based on the foundation treatment project in Pudong Airport. The laws of variation of soil settlement, pore water pressure and pile soil stress were analysed, and the influence of pile spacing was considered. These data from both numerical simulation and field test indicate the soil arching effect in the foundation reinforced by PHC piles and preliminarily reveal the evolution of soil arching in the process of embankment filling and soft soil foundation consolidation. The preliminary results encourage the authors to continue this research to investigate the evolution of soil arching under aircraft dynamic loads through adding a more suitable constitutive model or subroutine in this numerical model.

Evaluation of sand subgrade seepage erosion caused by buried pipeline leakage

Leakage from buried pipelines can lead to an increase in the water content of the subgrade soils and a rise in the water table, leading to soil loosening, erosion and ultimately the formation of hidden voids and roadway collapses. This study presents a discrete-element method and validates its accuracy by utilising cavity data from model experiments. It investigates the mechanism of seepage erosion resulting from pipe leakage and analyses the development of the soil arch effect. Furthermore, it discusses the influence of sand void ratio and particle size on sand seepage erosion. The results indicate that the erosion area is primarily affected by the void ratio and particle size. In comparison to soil particles ranging from 0.1 to 5 mm and from 2 to 5 mm, those with sizes between 0.1 mm and 2 mm generate areas of erosion and loosening that are approximately 40% larger. The proposed model offers a precise analysis of the developmental process and the extent of seepage erosion, thereby contributing to the prediction of potential road cavity areas based on dynamic changes in key factors such as subgrade soil type and groundwater level.

Study on pile-soil contact effect of anti-sliding piles in swelling soil landslides

In recent years, it is not uncommon for swelling soil landslides to occur again after treatment, which has seriously affected the safe operation of highways and railways. The degree of consolidation and cementation of swelling soil is poor, and its fractures are developed and it has a certain expansibility. Under the action of expansion force, its shear strength is obviously reduced. Thus, anti-slide pile support is used to control swelling soil landslides in this study. Based on the geological conditions and genetic mechanism of swelling soil landslide, a three-dimensional geological model with a width of 40 m is established to simulate the interaction mechanism and influencing factors between soil and pile in the process of anti-slip pile support. The results show that the larger the cohesion and internal friction angle, the stronger the soil arch effect, but the sensitivity is higher when the value is small. Therefore, attention should be paid to the weakening effect of soil arch effect in soil with low shear strength. The larger the pile spacing, the less obvious the soil arch effect. The swelling force also has a great influence on the soil arch effect from scratch. With the increase of the expansive force, the soil arch effect is weakened and completely disappears. Therefore, the adverse effects of expansive force should be considered, when designing anti-slide piles in swelling soil areas.

Laboratory experimental study of the forming and failure mechanisms of soil arching during EPBS tunnelling in sand

The effect of soil arching often leads to delayed ground collapse disasters when the tunnelling instability of earth pressure balance shields (EPBS) in sand. To reveal the formation and evolution of soil arching in sand, a laboratory-scale EPBS tunnelling model test was conducted. This EPBS tunnelling system simulated the entire process of shield tunnelling, which includes stable tunnelling, tunnel face instability, and ground collapse. The application of multi-field monitoring and three-dimensional scanning has revealed the influence of soil arching on sand layer collapse. The results indicate that: (1) Controlling the actual sand discharge rate to approach the theoretical rate can achieve stability of the tunnel face during the excavation process; (2) Maintaining higher soil pressure on the cutterhead can alleviate the loosening of the sand layer ahead; (3) The loosening zone in the vertical direction of the excavation section is significantly larger than that in the horizontal direction; (4) After the loose zone develops to the surface, each failure of the soil arching will cause significant surface subsidence, which can serve as a precursor to sudden ground collapse. The study provides a reference for the safe construction of tunnel engineering in sand.

Upward soil arching effect under unloading: mechanism, theory and engineering application

Upward soil arching effect under unloading indicates the unloading part moves in a vertically downward direction, generating the arching zone and the loosened zone towards an upward direction. This study presents a summary of definitions, characteristics, theoretical models and engineering applications for the upward soil arching effect under unloading. The evolution of the upward soil arching effect is highly related to the unloading/differential displacement. The characteristics of the upward soil arching effect under unloading are comprehensively interpreted in terms of the normalized height of arching, the minimum soil arching ratio (at which state the maximum arching is developed) and the normalized unloading displacement to reach the maximum arching state. Two deformation-dependent theoretical models are introduced, to appropriately interpret and predict the variation of the soil arching ratio with the normalized unloading displacement (i.e., the ground reaction curve). Using the research findings for the upward soil arching effect under unloading, the settlement of the geosynthetic-reinforced pile-supported embankment as well as the face stability and ground settlement during tunnelling are proven to be precisely predicted and well controlled.

Numerical simulation of three-dimensional soil arch effect between h-type pile-based discrete element method

Numerical simulation of three-dimensional soil arch effect between h-type pile-based discrete element method

Model Test and Numerical Simulation for Tunnel Leakage-Induced Seepage Erosion in Different Strata

Leakage in underground structures, especially tunnels, may cause seepage erosion in the surrounding soil, which in turn leads to ground subsidence, posing a great threat to urban safety. The current literature mainly focuses on seepage erosion in the sand but lacks a systematic study on the development process of seepage erosion induced by tunnel leakage in different strata. To investigate the different seepage erosion modes induced by tunnel leakage in different stratum types, a series of reduced-scale model tests were carried out. A coupled fluid–solid numerical model was further established to analyze the fine-scale characteristics of different seepage erosion modes. The results show that (1) the soil seepage erosion modes can be divided into three categories: no soil cave, unstable soil cave, and stable soil cave; (2) the adopted coupled fluid–solid numerical model based on DEM, which takes into account the degradation of clay during seepage erosion, can effectively simulate the erosion process of soil with different seepage erosion modes; (3) the phenomena of the three erosion modes are different in the process of erosion development; and (4) the micro-mechanisms of the three seepage erosion modes are different, which are manifested in the erosion range, soil arching effect, and displacement.

Dynamic soil arching effect in pile-supported embankment due to train passages at high speeds

Pile-supported embankment has been widely adopted for high-speed railways constructed over soft soils to reduce post-construction settlement. The role of soil arching effect in stress distribution inside pile-supported embankment under static weight load has been extensively studied, while the dynamic soil arching effect due to train moving loads has been paid little attention. In this paper, a sophisticated three-dimensional (3D) track-embankment-pile-subsoil finite element model (FEM) has been developed to analyze dynamic stress responses due to train passages at high speeds. The numerical model has been validated by experimental results on a full-scale pile-supported railway embankment model. The numerical analyses reveal that the dynamic soil stress distribution in the embankment near the track is almost consistent with the Boussinesq solution, but the presence of piles underneath the embankment leads to the redistribution of dynamic soil stresses inside the embankment due to the dynamic soil arching effect. The soil arch height under train load is 2 m (2.5 times of the clear space of piles), higher than the height 1.6 m (2 times of the clear space of piles) under embankment self-weight. Besides, the pile efficacy (ratio of load borne by the pile cap to the total applied load) caused by moving train load at 100 m/s is 0.6, which also is higher than the pile efficacy 0.57 caused by embankment weight. Train passage at high speeds significantly amplifies the dynamic stress intensity in the embankment but barely changes the pile efficacy.

Asymmetric instability damage patterns of curved shield tunnels based on transparent soil visualization model tests

With accelerated urbanization, underground structures have imposed significant restrictions on underground spaces. Urban shield tunnels must be designed using curved lines to avoid existing tunnels, pile foundations, and other structures. Over-excavation on the inner side of a curved tunnel during tunneling and the difference between the inner and outer jacking forces complicate research on excavation surface stability. In this study, a combination of transparent soil visualization model tests and numerical simulation methods was used to investigate the spatially asymmetric distribution patterns, focusing on the progressive destabilization damage of the soil and the soil arching effect in front of the excavation during construction of curved shield tunnels. Furthermore, the effect of the radius of curvature on the soil arch morphology in sandy soils was analyzed in detail. The results show that the soil displacement in front of the working face of the curved tunnel exhibited a crescent-shaped deflection toward the over-excavation side. The settlement tanks in the curved tunnel exhibited an asymmetric distribution along the center of the tunnel and were deflected to the over-excavation side. The smaller the radius of curvature, the greater was the deflection of the soil in front of the curved tunnel to the over-excavation side.

Mechanical mechanism of soft soil foundation improved by geosynthetic-reinforced pile-supported technology based on field experiment

Geosynthetic-reinforced pile-supported (GRPS) technology is an effective method for improving soft soil foundations. Conducting field tests is crucial for accurately assessing the mechanical behavior of GRPS technology. Based on the fourth expansion project at Pudong Airport, field tests were conducted to investigate the effects of GRPS technology on soft-foundation treatment. Specifically, the tests examined the changes in the pile and soil settlement, pore water pressure, and pile and soil stress. The results showed that the settlement of the GRPS foundation mainly occurred during the loading period, accounting for approximately 65% of the total foundation settlement. Increasing the pile modulus and reducing the pile spacing decreased the total foundation settlement. The filling load was mainly transferred to the piles through the soil arching effect, resulting in a large excess pore water pressure in the soil layer near the pile tip. In addition, when the filling height was low, the load transfer relied predominantly on the tensile membrane effect of the geogrid, which was more pronounced near the piles. However, as the filling height increased, the soil arching effect surpassed the tensile membrane effect and played a key role in load transfer.

Numerical Simulation Study on the Spacing of Landslide Anti-slip Piles Based on Strength Reduction Method

In landslide control engineering, anti-slip piles are the most commonly used means. This article established a numerical model of the interaction between fully weathered granite landslides and anti-slip piles based on the strength reduction method. Firstly, five pile-soil interaction models with different pile spacing were established using Abaqus software, and individual components were generated and assembled using the stretching function. The friction surface is used between the pile and soil, and the normal and tangential contact characteristics are both Penalties. Secondly, the strength reduction method based on displacement criteria is used to reduce the rock and soil parameters to the unstable stage before failure, while calculating the slope safety factor. Then, the influence of anti-slip pile spacing on slope stability, pile shear force, bending moment, and soil arch effect are studied. The strength reduction method and pile-soil interaction model used in this article can effectively avoid single pile effects and have high accuracy in characterizing soil arching effects. The results afford certain application and promotion values by providing theoretical references and technical guidance for similar anti-slide pile reinforced slope projects.

Experimental and numerical investigation on soil erosion under different pipeline-leaking locations

In recent years, cave-in ground failures have become increasingly common worldwide. The leakage of defective pipelines buried below ground level has been identified as a significant contributor to these failures. This study utilized experimental seepage-erosion tests to characterize ground collapses resulting from pipeline leakage and examined the impacts of leakage locations on soil and water losses. Subsequently, discrete element method-finite difference method (DEM-FDM) coupling analyses were conducted to elucidate the mesoscopic mechanisms of pipeline leakage, including changes in seepage force, effective stress, and soil pressure on the pipeline during leakage. The findings include: (1) The locations of leaking spots on pipelines significantly influenced soil and water losses; (2) Leaking spots closer to the pipe bottom led to more severe ground collapses due to larger seepage forces; (3) Soil pressure exhibited decreasing trends near the leaking spot and increasing trends at other locations due to the soil arching effect. These insights provide valuable guidance for preventing pipeline leakages.

Influences of number of geosynthetic reinforcement layers on soil arching under cyclic loading

Geosynthetic-reinforced pile supported (GRPS) embankments have been widely used in highways and railways on soft subsoil. During the operation period, these embankments are often subjected to cyclic loading, such as traffic loading. Considering that soil arching is a key load transfer mechanism in these embankments, the development of soil arching under cyclic loading is vital important to operational safety of these embankments. Conventional trapdoor system cannot represent actual conditions of soil arching in GRPS embankments because it have a forcibly-moved trapdoor and cannot simulate load-induced subsoil settlement. Hence, this paper used a self-moving trapdoor supported by compression springs that moved up and down dependent on its overburden pressure. To investigate influences of number of geosynthetic reinforcement layers on soil arching under cyclic loading, two self-moving trapdoor tests were conducted, including a single layer and two layers, where the total reinforcement stiffness were approximately same. The trapdoor test results show that the inclusion of two reinforcement layers with a fill layer of a certain height in between reduced surface settlement of the fill and tensile forces of reinforcement, as compared with a single reinforcement layer. It also enhanced soil arching effect and improved the stability of soil arching under cyclic loading.