Equal Settlement Research Articles

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.

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.

Pricing and service effort strategy in live streaming commerce supply chain under the equal proportion settlement mode.

Investigating novel collaboration modes is imperative for enhancing the cooperative ties between brand retailers and anchors as live streaming commerce moves progressively towards standardization. In this paper, we study a live streaming commerce supply chain system composed of a brand retailer and an Internet celebrity anchor. We also develop the pricing and live streaming service effort decision models under the equal proportion settlement mode of pit fee for the brand retailer and anchor. The research results show that under certain conditions, there is an optimal joint decision on price discount and live streaming service effort. In addition, the equal proportion settlement mode provides security for brand retailers but tends to expose the anchor's capabilities of live streaming sales. Consequently, anchors can only obtain a higher proportion of the pit fee by putting in more effort. Finally, through numerical analysis, we presented the impact of key parameters on the optimal decisions, demand, and profits of brand retailers and anchors. Based on these findings, we provided relevant managerial insights, offering valuable guidance and reference for the live streaming commerce industry.

Effects of cyclic loading on soil arching within pile-supported embankment with artificial crust: A coupled DEM-FDM approach

This study endeavors to investigate the evolution of soil arching within pile-supported embankments featuring artificial crusts under cyclic loading. A quasi-three-dimensional (quasi-3D) model was formulated utilizing the Discrete Element-Finite Difference coupled method (DEM-FDM) and validated by in-situ vibration tests. The mechanism underlying the soil arching weakening due to cyclic loading was elucidated, and the impacts of artificial crust moduli and thicknesses on soil arching were consolidated. The findings demonstrate that the equal settlement section moves upwards, and the lower limit of the settlement trough resulting from cyclic loading extends downward with an escalation in axle load, but these remain relatively consistent as the loading velocity increases. Additionally, the transmission of dynamic stress from the pavement surface to the outer surface of the arch approximately adheres to the Boussinesq formula, whereas the stress propagation from the outer surface to the top of the pile cap conforms to the prescribed dynamic pile-soil stress ratio. Furthermore, increasing the thickness and the elastic modulus of the artificial crust contributes to diminished pile-soil differential settlement, alteration in the pile-soil stress ratio, lowered susceptibility of artificial crust deflection to cyclic loading, reduced anisotropy coefficient, and a counterclockwise rotation in the primary direction of the normal contact force exerted on particles within the arch region.

Improved analytical solution of lateral soil restraint for pipes buried in dry sand considering arching effects

Abrupt transverse ground movements induced by landslide, strike-slip offset, and excavation can exert excessive soil restraints on buried pipes and threaten the pipe safety. The determination of lateral soil restraint is, therefore, a key factor for the evaluation of buried pipes in such areas. However, effective analysis solutions to assess the area of failure zone of surrounding soils and to estimate the soil resistance on pipes are still limited. In this work, an improved implicit limit equilibrium model is proposed to calculate the ultimate lateral soil restraint of buried pipes in dry sand, in which the effect of active soil wedge is considered, and the heights of equal settlement plane in both passive and active wedges can be estimated. Comparisons are made between collected physical modeling results and calculations from different methods. Results show that the proposed method yields a better approximation to the measured data. Parametric studies are subsequently conducted, which illustrate that the ultimate soil lateral restraint is influenced by the pipe diameter, internal friction angle, and constrained modulus of soil. The influence of effective soil unit weight is minimal. The proposed method is beneficial for safety evaluation of buried pipes subject to lateral dragging.

Analysis of Load Transfer and the Law of Deformation within a Pile-Supported Reinforced Embankment

In this paper, the load-transfer mechanism and settlement behaviors of the pile-supported reinforced embankment are reviewed by laboratory model tests, and a series of finite element method (FEM) modellings are conducted to analyze the soil-arching geometry and embankment deformation patterns of the pile-supported reinforced embankment. The results show that: the embankment load distribution is significantly impacted by the filling cohesion because of the effect of cohesion on the interaction between particles. The soil pressure difference between the center and corner of the pile caps decreases with the increase of filling cohesion. The pile-subsoil stress ratio decreases with the increase of filling cohesion. The embankment deformation behavior and soil-arching geometry are less affected by the change in filling cohesion compared with the influence of pile spacing. That may because of the fact that although the cohesion of the embankment filling has been increased, the granular material’s properties have not been fundamentally changed. Pile-subsoil different settlement decreases with the increase of embankment filling cohesion, and the different settlement at the mid-span between four piles decreases by 4.09% and 6.34%, respectively, as filling cohesion increases from 0 kPa to 11 kPa and 25 kPa. The height of the soil-arching crown decreases with the increase of filling cohesion, and the height of the soil-arching crown between horizontal adjacent piles decreases by 3.85%, 7.69%, and 9.62%, as filling cohesion increases from 5 kPa to 15 kPa, 25 kPa and 45 kPa. The rate of decrease in soil-arching height gradually decreases with increasing cohesion. The height of the soil-arching between the horizontal adjacent piles is about 1.0 (s−a). The height of soil arching between the diagonal adjacent piles is about 1.02 (s−a). The differential settlement at the same height inside the embankment decreases with the increase of filling cohesion, and the height of the equal settlement plane is basically the same as the height of soil arching.

Multiple arching in cohesion–friction soils: Insights from deformation behavior and failure mechanisms using FEM-SPH approach

Soil arching is a common phenomenon in many underground engineering problems. This paper develops a coupling approach involving the Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH) method to investigate the multiple soil arching effects of cohesive–frictional soils. This approach is proved to be successful in capturing multiple soil arching by comparing the numerical results with experimental observations. Then, a sensitivity analysis is carried out to reveal the influence of geometric and material parameters on load transfer, deformation behaviors, and failure mechanisms. From a microscopic point of view, the mobilization of soil particles is analyzed to explain the formation of multiple soil arches. The failure mechanisms are characterized by two types of failure surfaces formed above the trapdoors and the rigid bases, respectively. The key factors that influence the interaction between adjacent soil arches are identified by analyzing the inclinations of the failure surfaces. The evolution of the equal settlement plane and failure surfaces during the arching process is also discussed.

An Iterative Computing Method for Load Effect of Bidirectional Reinforced Embankment

Bidirectional reinforced embankment (BRE) technology, pile supporting in vertical and geosynthetic reinforcement in horizontal, has been widely adopted in engineering practice to control total and/or differential settlement. In design, the load distribution of BRE is essential for determining pile size (i.e., diameter and length), pile spacing, pile cap details (if any), and properties of geosynthetic reinforcement, et al. Several methods have been proposed in previous studies to investigate the load bearing mechanism in the BRE platform. However, resistance of foundation soil is typically neglected, which implies that the load on piles would be overestimated if the resistance of foundation soil is neglected or over weakened. The reason for this overestimation is that larger geosynthetic deflection would be expected without the reaction of foundation soil, which would cause a more significant soil arching and thus more load would be transferred to piles. To minimize this overestimation, a method for analyzing load transfer mechanism in the BRE was proposed, considering the subsoil resistance as well as the existence of neutral plane (i.e., zero skin friction). An equal settlement was assumed for soils at the embankment bottom and the foundation top. The iteration process was adopted to solve equations to determine the load shared by piles and soils. In derivation, the soil arch height in the embankment was calculated instead of being assumed in existing methods. A flow chart was developed to solve equations of the proposed method and two case histories from literatures were used to compose the rationality verification. Compared with the field measurement and numerical calculation, this study can be more effective in calculating loads shared by piles and soils in the BRE for the working condition with better pile end bearing stratum.

Two-dimensional soil arching evolution in geosynthetic-reinforced pile-supported embankments over voids

Soil arching and tensioned membrane effects are two main load transfer mechanisms for geosynthetic-reinforced pile-supported (GRPS) embankments over soft soils or voids. Evidences show that the tensioned membrane effect interacts with the soil arching effect. To investigate the soil arching evolution under different geosynthetic reinforcement stiffness and embankment height, a series of discrete element method (DEM) simulations of GRPS embankments were carried out based on physical model tests. The results indicate that the deformation pattern in the GRPS embankments changed from a concentric ellipse arch pattern to an equal settlement pattern with the increase of the embankment height. High stiffness geosynthetic hindered the development of soil arching and required more subsoil settlement to enable the development of maximum soil arching. However, soil arching in the GRPS embankments with low stiffness reinforcement degraded after reaching maximum soil arching. Appropriate stiffness reinforcement ensured the development and stability of maximum soil arching. According to the stress states on the pile top, a concentric ellipse soil arch model is proposed in this paper to describe the soil arching behavior in the GRPS embankments over voids. The predicted heights of soil arches and load efficacies on the piles agreed well with the DEM simulations and the test results from the literature.

New insights into soil arching behaviour in column-supported embankments

The observation of failure surfaces within column-supported embankments is critical to understanding how the embankment stresses are transferred towards the column heads. In this study, finite element simulations utilising a strain-softening constitutive model, nonlocal regularisation, and the Arbitrary Lagrangian–Eulerian formulation are used to examine these failure surfaces over various embankment geometries. This methodology offers insights into the nature of the failure mechanism, the development of a plane of equal settlement, and the influence of the subsoil settlement profile. Depending on the embankment geometry, the results indicate a punching failure, inverted general bearing failure, or a localised failure develops. The transition between punching and inverted general bearing failure is found to be closely related to the establishment of a plane of equal settlement within the embankment. The height of the plane of equal settlement and the range of failure mechanisms that develop were largely insensitive to the nature of the subsoil settlement profiles simulated. These findings have implications for the practical design of efficient embankments and the effective design of future experimental studies.

Soil Arching of Piled Embankment in Equal Settlement Pattern: A Discrete Element Analysis

Soil arching, which occurs in the piled embankments, plays an important role in stress redistribution between the relatively soft subsoil and the stiffer piles. The formation of the soil arching depends on the differential settlement of the embankment fill above the pile and the subsoil. The soil arching effect is barely investigated in the literature from the perspective of differential settlement of piles and soils. Based on the discrete element method (DEM), this paper develops a classic trapdoor test model to investigate the differential settlement in piled embankment during the downward movement of the trapdoor, and to explore the formation mechanism of soil arching in equal settlement pattern by changing the width of the pile cap and the height of the embankment. Due to symmetry, only one section of the laboratory test model is simulated herein. It was found that the soil arching formed under the equal settlement pattern remained unchanged after a certain degree of development, and the height of the equal settlement did not change at 0.7(s-a), where s is the pile spacing, and a is the width of the pile cap. The height of the embankment (H) and the width of the pile cap (a) have a significant influence on the formation of the equal settlement pattern when the width of the trapdoor is kept constant. Both the decrease in “H” and the increase in “a” facilitate the differential settlement of the soil between the piles and the pile-soil, enabling the slip surface to develop upward gradually, thereby hindering the formation of the equal settlement pattern.

Model Test on the Soil Arching Effect of Pile-Supported Embankments Using Transparent Soil

Abstract Pile-supported embankments have been widely used in subgrade engineering for highways and high-speed railways. Soil arching has an important effect on the deformation characteristics of pile-supported embankments. In this study, a new model testing apparatus and its test method for the soil arching effect were developed based on the transparent soil method and particle image velocimetry technique. The composition of the apparatus and the test steps were elaborated in detail. The development of the soil arch with the settlement of foundation soil was explored. The variations in the settlement of the embankment at different elevations and distances from the pile center were analyzed, and afterwards, the effect of pile spacing on the embankment settlement was discussed. The results revealed that a basin-shaped soil arch gradually formed in the embankment, with the settlement of the soil between the piles. The settlement below the arch boundary was larger, and the settlement above the arch boundary was relatively small. An equal settlement plane appeared in the embankment. The elevation of the equal settlement plane increased with increased pile spacing. The maximum settlement occurred at the center of the soil between the piles on the pile cap top plane. The settlement of the embankment increased as the pile spacing increased. This study provides a new solution for understanding the spatial effect of soil arching in pile-supported embankments.

The mechanics of arching in induced trench construction – a new theoretical formulation

Full-scale experimental case studies have shown that the induced trench construction method effectively reduces the vertical earth load that is exerted on culverts installed beneath high embankments. Induced trench culverts are traditionally designed on the basis of Marston’s theory; however, various theoretical shortcomings of this formulation have recently come to light. In this paper, a new induced trench theoretical formulation is presented. The proposed analytical model employs inclined shear planes within the embankment fill; such geometry is consistent with experimental findings reported in the literature and leads to positive arching resulting from a reduction in vertical stress and an increase in horizontal stress (thus increasing the lateral earth pressure coefficient within the induced trench zone). A series of parametric studies is performed using finite element software. The proposed theoretical formulation is shown to be in good agreement with the numerical results, and correlations are developed to provide guidance in selecting the appropriate values of (i) the induced trench lateral earth pressure coefficient and (ii) the height to the plane of equal settlement. Two instrumented full-scale induced trench case studies are discussed, and the proposed theoretical formulation is shown to produce results that are in good agreement with the experimental data.

Evaluation of geosynthetic-encased column-supported embankments with emphasis on penetration of column toe

Geosynthetic-encased stone column (GESC)-supported embankments are environmentally friendly methods and are increasingly being used for highways over soft soil. Based on a load-transfer mechanism of a GESC-supported embankment, a solution was obtained by considering the nonlinear elastic behaviours of the GESC and penetration of the column toe. The radial stress equilibrium of the GESC and the vertical load transfer mechanism were taken into consideration. By applying the deformation and stress continuity at the bottom of the embankment fill and the surface of the underlying soil layers, the deformations and stresses of the embankment fill, the surrounding soil, and the GESC were compatible. The equal settlement planes, the column efficacy, the skin friction along the GESC, and the differential settlement at the bottom of the embankment can be computed by the proposed method. Compared with field data and a numerical method, the proposed method has been proven reasonable. The bearing type of the column with different underlying soils is between floating column and end-bearing column. The deformations and stresses affected by the stiffness of the underlying soil were analysed.

Study on characteristics of pile–net composite foundation at 500 kV substation in China

The overall requirements of substation engineering are very high, and the differential settlement control of substation engineering is relatively strict. On the soft foundation of the tidal flats at the Zhenhai 500 kV substation in China, a field test was carried out to study the working characteristics of the pile–net composite foundation during the soil filling and consolidation stage. Variation laws of the settlement, earth pressure, pile–soil stress ratio, geogrid tension and axial force of pile were obtained and analysed. When the height of the filled soil increased to 2 m, a plane of the equal settlement was formed. Because of the soil arch effect, the earth pressure on the pile top was always higher than that between the adjacent piles. The pile–soil stress ratio rapidly increased from 1.2 at the stage of soil filling to 6.0 at the initial stage of consolidation. The ability of the geogrid to transfer the load was limited, and the soil arch effect was the main reason that the load was transferred to the pile top. Due to the lateral negative friction resistance of the pile in the shallow soil, the axial force of the pile first increased and then decreased along the depth.

2D and 3D discrete numerical modelling of soil arching

In this study, 2D and 3D soil arching phenomena associated with piled embankments were evaluated by performing a series of discrete numerical analyses using the particle flow code (PFC3D) software. After validating the micro-parameters with experimental results, we compared the stress-displacement distribution, force chain evolution, maximum vertical displacement of particles, and deformation characteristics induced by 2D and 3D arching effects. Additional analyses were carried out to understand the influence of the fill height, pile clear spacing, friction coefficient, and porosity on soil arching with respect to the stress concentration ratio (SCR) and settlement along the elevation at various sections. The numerical results indicated that a plane soil arch in a 2D embankment overestimates the degree of load transfer and underestimates the settlement at the crest and within the embankment along the elevation in a 3D embankment. A lower equal settlement plane can be found in a 2D embankment. Furthermore, an increase of fill height and friction angle, and a decrease of pile clear spacing and porosity can help to improve the degree of reduction in load transfer and settlement in both 2D and 3D embankments. However, for partially mobilized soil arching in the 3D condition, the increase of fill height reduces the settlement of soils mainly in the portion above the square subsoil area, but has less influence over the portion above the rectangular subsoil area.

Kinematics of soil arching in piled embankments

The transfer of embankment stresses towards pile heads in piled embankments is attributed to the mechanism known as soil arching. Three-dimensional physical models of piled embankments were built to simulate this mechanism. The progressive settlement of subsoil beneath an embankment was modelled and paused at increments of displacements to allow synchrotron X-ray computed tomography to be performed on the models. Image correlation techniques were then applied to the reconstructed volumes to obtain evolving three-dimensional displacement and strain fields. The strain fields show localised (shear bands) and diffuse failure modes occurring above pile heads within the embankment fill. These failure surfaces are seen to progressively develop as the subsoil undergoes settlement. The displacement fields also show the formation of a plane of equal settlement developing at a height above the pile heads, known as the critical height. The critical height is dependent on the height at which the failure surfaces propagate into the embankment fill, and a method is proposed to calculate the maximum height of failure surfaces based on the observed kinematics. The full-field kinematics provide fundamental insight into the soil arching mechanism that develops within piled embankments.

Double-leg reinforced concrete columns of one-storey frame buildings for seismic countries

characteristics, a technique of prototypes and results of pilot studies of the bearing ability and a deformationof knots of reinforced concrete double-legcolumns of one-storeyedframe industrial buildings are provided inarticle at action of low-cyclic sign-variable loadings of type of seismic. Knots were tested sign-variable cyclesquantity not less than 30, at coefficient of asymmetry of a cycle, ρs=-1. The size of loading of a cycle was accepted by equal settlement seismic. Valuesof the skilled ultimate loads experienced knots, both single unilateral, and low-cyclic sign-variable by loadings exceeded values of settlement seismic loads of 50-87%. At the sametime, decreasein the bearing ability of the knotstested by low-cyclic sign-variable loading of average and high levels in comparison with the bearing ability of the reference samples tested by single loading reached 20%.Materials with recommendationsabout tests of knots were used when developing a standard series of columns for applicationin seismic countries to 9 points

Soil Arching Effect Analysis via a Modified Finite Element Model Based on a Field Test

Abstract Soil arching is a special physical phenomenon in piled embankments that plays a significant role in load distribution between the pile and the subsoil. A modified finite element model, in which the interaction among the embankment fill, pile, and subsoil is simulated by a series of springs, is used in this study to analyze the mechanical behavior of soil arching. The proposed model is easily implemented and time saving compared with traditional models. A field test is conducted to verify the suitability of the numerical model. Results show that the arch-shaped appearance of the maximum principal stress distribution is caused by the composition of the horizontal and vertical stresses. The stress caused by the load changes from the vertical to the horizontal directions with the increase in the embankment fill depth. Soil arching occurs after differential settlement because the height of the equal settlement plane is inconsistent with that of the critical arch height. The maximum intensity of soil arching could be determined by reasonably setting the pile spacing value.

Laboratory model tests about the sand embankment supported by piles with a cap beam

ABSTRACTPiled embankment is widely used in soft soil areas. Most researches focused on effects of embankment height-net pile spacing ratios and equal settlement plane; there are limited publications paying attention to the shape of slip surfaces occurring in the embankment. In some extreme conditions, such as the ground being quite soft or embankment height needed to be restricted, to reduce the differential settlement and lateral displacement, piles are usually installed in several rows and cap beams or isolated caps are placed on the heads of piles. In this paper, five laboratory tests were carried out to investigate the effect of embankment height on the slip surfaces and stress exerted on the subsoil. Based on the observation of the slip surface’s shape within the embankment fill, a new calculation model is proposed to predict the stress exerted on the subsoil. In comparison with the experimental results, the accuracy of this new method is verified. From the perspective of reducing the differential settlement and cost savings, the embankment height is about four times net pile spacing according to this calculation model, since continuing to increase the embankment will not make an obvious difference to the reduction of soil stress exerted on the subsoil.