Vertical Earth Pressure Research Articles

Experimental study of face stability for shield tunnels in sandy cobble strata of different densities

This paper aims to study the influence of relative density on the working face stability of shield tunnel in sandy cobble stratum. A series of geomechanical model tests were conducted for shield tunnels excavating through loose sample (LS), medium dense sample (MS) and dense sample (DS), respectively. Relative densities of LS, MS and DS are 0.35, 0.55, and 0.75. The method of continuous rotation of spiral excavators while shield excavators stop tunneling is adopted to simulate the instability of tunnel face. Experimental results effectively reveal the variation characteristic of vertical and horizontal earth pressure and lateral pressure coefficient of shield tunneling. The evolution of the failure zone and soil arch height of strata with different densities was explored. The failure area and collapse range obtained from the model test were compared with the existing method. The effect of relative density on the horizontal earth pressure in the instability stage of the tunnel face in the sandy cobble strata is greater than that of the vertical earth pressure. In addition, increasing the relative density can effectively increase the lateral pressure coefficient as well as the stability of the tunnel face. The existing methods have deviations in analyzing the instability area of the tunnel face in the sandy cobble strata with different relative densities. The research in this paper provides a reference for the construction and theoretical analysis of sandy cobble strata shield tunnel engineering.

Determining performance of two-tiered GRS walls subjected to traffic cyclic loading

This study evaluates the performance of two-tiered geogrid-reinforced soil (GRS) walls subjected to traffic cyclic loading considering several influencing factors. These factors herein include the offset distance (D) of walls, the number (N), amplitude (Pmax), and frequency (f) of applied cyclic loading. Seven GRS walls with a reduced scale of 1 : 3 were prepared in the laboratory and employed to investigate their (i) vertical foundation pressures during construction, (ii) load-induced settlements, (iii) facing lateral displacements, (iv) vertical and horizontal earth pressures, and (v) geogrid strains under the action of cyclic loading. Experimental results demonstrate that GRS walls constructed in tiered configurations can effectively reduce vertical foundation pressures. The increasing D, as well as the decreasing N and Pmax, introduces a reduction to the above five mechanical and deformation properties. However, increasing f results in the decrease of wall settlements and facing lateral displacements, and in the increase of others. Performance of several empirical equations for predicting the vertical foundation pressures, location of maximum geogrid strains, and failure surfaces inside walls was examined using the experimental data obtained in this study. Comparisons were also performed to describe the deformation and failure surface modes of the walls after loading.

Earth Pressure of the Trapdoor Problem Using Three-Dimensional Discrete Element Method

Load transformation from the yielding part of the soil to the adjacent part is known as the soil arching effect, which plays an important role in the design of various geotechnical infrastructures. Terzaghi’s trapdoor test was an important milestone in the development of theories on soil arching. The research on earth pressure of the trapdoor problem is presented in this paper using the three-dimensional (3D) discrete element method (DEM). Five 3D trapdoor models with different heights are established by 3D DEM software PFC 3D. The variation of earth pressure on the trapdoor with the downward movement of the trapdoor, the distribution of vertical earth pressure along the horizontal direction, the distribution of vertical earth pressure along the vertical direction, the distribution of lateral earth pressure coefficient along the depth direction, the magnitude and direction of contact force chain are studied, respectively. Related research results show that the earth pressure on the trapdoor decreases rapidly after the downward movement of the trapdoor, and then reaches the minimum earth pressure. After that, the earth’s pressure will rise slightly, and whether this phenomenon occurs depends on the depth ratio. For the bottom soil, due to the stress transfer caused by the soil arching effect, the ratio of earth pressure in the loose area decreases, while the ratio of earth pressure in the stable area increases. With the trapdoor moving down, the vertical earth pressure along the depth in the stable zone is basically consistent with the initial state, which shows an approximate linear distribution. After the trapdoor moves down, the distribution of earth pressure along with the depth in the loose area changes, which is far less than the theoretical value of vertical earth pressure of its self-weight. Because of the compression of the soil on both sides, the lateral earth pressure coefficient of most areas on the central axis of the loose zone is close to the passive earth pressure coefficient Kp. The existence of a ‘soil arch’ can be observed intuitively from the distribution diagram of the contact force chain in the loose zone.

Reinforcement placement on mechanics and deformation of stepped reinforced retaining wall experimental study of characteristics

Abstract Three sets of indoor model tests of reinforced retaining walls were conducted to study the effects of reinforcing material placement on the displacement of reinforced retaining walls, wall top settlement, earth pressure distribution, and potential failure surface. The test results show that under different reinforcement laying conditions, the maximum horizontal displacement of the lower wall panel appears at the top of the lower retaining wall, and the maximum horizontal displacement of the upper wall panel appears at 0.6H. The settlement of the top of the wall decreases by about 9.1% when the reinforcement is laid in the lower layer. Under the condition of 160 kPa, the maximum horizontal and vertical earth pressures increase by about 19.2 and 12.4%, respectively, and the position of the potential fracture surface of the lower wall moves up to the back of the wall with the position of the reinforcement laying. When the reinforcement is laid in the upper layer, the fracture surface of the upper wall is furthest away from the panel.

Investigation of the Static Characteristics of a Geogrid-Reinforced Embankment

The research object of this paper is a geogrid-reinforced embankment. Through numerical simulation and data monitoring, the characteristics of vertical displacement, horizontal displacement, vertical earth pressure, horizontal earth pressure, and internal force in a geogrid-reinforced embankment are studied. The results show that: (1) According to the analysis of monitoring data, the cumulative horizontal displacement decreases and the cumulative vertical displacement increases with time. Additionally, the cumulative vertical displacement is greater than the cumulative horizontal displacement. (2) The vertical pressure of the fill and tensile stress of the geogrid are largest at the center of the structure section, and the horizontal earth pressure is also largest on both sides of the structure. (3) The numerical simulation value and actual monitoring value of the project are compared with the design value. It is found that the tensile force, horizontal pressure, vertical pressure, horizontal displacement, and vertical displacement of the geogrid are less than the design value. The simulated characteristic value is greater than the actual monitored characteristic value. The research results provide a reference for the design of similar geogrid-reinforced embankments.

Model Test and Numerical Simulation Research of Reinforced Soil Retaining Walls under Cyclic Loads

The stress diffusion characteristics of reinforced soil retaining walls (RSW) with concrete-block panels under cyclic loads are studied. The distribution of the vertical dynamic earth pressure caused by an external load and the analysis of stress diffusion angles were studied using a model test and the numerical simulation model of the reinforced soil retaining wall was established to analyze the change in the stress diffusion angle. We then changed the parameters to investigate the influencing factors of the stress diffusion characteristics. The results showed that: the average value of the peak vertical dynamic earth pressure caused by an external load at the loading position of the RSW was a nonlinear distribution, decaying from top to bottom and increasing with the increase in the loading amplitude, while the change in the loading frequency number of loading cycles had no obvious rule. The results of model test and numerical simulation agree with each other. The diffusion angle of the stress caused by the external load of the reinforced body was basically between 50° and 65° in the range from 1.8 m to 1.2 m, the diffusion angle at the top was slightly larger than the middle, and the diffusion angle away from the wall was larger than the diffusion angle close to the wall. The main factors affecting the stress diffusion in reinforced soil retaining walls are the coefficient of reinforcement of the soil and the dynamic stress amplitude; the stress diffusion angle increased with an increase in the coefficient of the reinforcement of the soil and the dynamic stress amplitude. The conclusion of this paper can provide a reference for the design of reinforced soil structures.

Using expanded polystyrene geofoam and tire-derived aggregate in different forms to reduce vertical earth pressure on high-filled cut-and-cover tunnels

Using expanded polystyrene geofoam and tire-derived aggregate in different forms to reduce vertical earth pressure on high-filled cut-and-cover tunnelsAll authorsShamil Ahmed Flamarz Arkawazi & Mohammad Hajiazizi https://doi.org/10.1080/23311916.2022.2138100Published online:27 October 2022Display full sizeUsing the high-filled cut-and-cover tunnels (HFCCTs) provides a typical solution for the possibility of using valuable lands with plateaus terrain. Because of the high quantities of backfill soil above the HFCCT, at present, the existing estimating methods of the vertical earth pressure (VEP) may not suit the HFCCTs construction. The ability to estimate the load or pressure on the HFCCTs is essential. As a principle, the soil column pressure equation can be used to estimate VEP on the HFCCTs. This study presents a numerical investigation of the effect of using expanded polystyrene (EPS) and tire-derived aggregate (TDA) in different forms on the relative vertical displacements and VEP reduction on the HFCCTs. The results showed a significant VEP reduction on the HFCCTs, especially with the use of TDA in different forms. Also, a comparison is made between the calculated and estimated VEP values on the top of the HFCCT study model with the base conditions using the soil column pressure equation, Li et al. (2019) modified equation, and Abaqus CAE 2019 software. The calculated and estimated VEP values on the top of the HFCCT study model with the base conditions showed that the calculated value using Li et al.’s (2019) modified equation is 27.942% lower than the calculated value using the soil column pressure equation, which is a high percentage of difference. While the estimated value using Abaqus CAE 2019 is 0.156% higher than the calculated value using the soil column pressure equation, which is a low percentage of difference.

Study on Dynamic Response Characteristics of Stepped Reinforced Retaining Wall

In order to further explore the influence of reinforcement materials laying position on the dynamic characteristics of reinforced retaining walls, based on FLAC3D finite difference methods for solving nonlinear problems, established with the same size of the retaining wall in practical engineering, the reinforcement material’s relative position in the retaining wall for the normalized processing, under seismic load, and the panel under the conditions of different reinforcement arrangement were analyzed, and the horizontal displacement of slope, the vertical and horizontal earth pressures behind the wall, and the distribution of potential sliding surface were calculated. The relationship between the maximum horizontal displacement of the panel and the laying position of the reinforcement was fitted by MATLAB. The results show that the horizontal displacement of the panel is about 40% smaller when the upper layer of the reinforcement is arranged than that in the lower layer for step 1, and the horizontal displacement of the reinforcement in step 2 is about 30% lower than that in other conditions when the reinforcement is arranged at the top of the slope. The reinforcement arranged in the lower layer of step 1 and the upper layer of step 2 can minimize the wall top displacement. In step 1, the vertical earth pressure and horizontal earth pressure are 19% and 5% smaller than those in other conditions when the reinforcement is arranged near the middle and lower layer of the step. In step 2, the difference between vertical and horizontal earth pressure is not obvious, and the difference between the two conditions is controlled within 5%. At the same time, soil liquefaction and uplift occur under the action of earthquake. The position of sliding crack surface has no obvious regularity with the position of reinforcement, but the position of reinforcement at the step classification is obviously better than other conditions. The fitting formula can describe the relationship between the panel displacement and the position of the reinforcement well. The conclusions can provide a point of reference for practical engineering.

Load bearing mechanism and simplified design method of hybrid monopile foundation for offshore wind turbines

The hybrid monopile foundation for offshore wind turbines demonstrates an enhancement of bearing capacities. This innovative foundation is composed of an embedded pile and a gravity footing (namely wheel). In this study, centrifuge tests are conducted to investigate the lateral capacity of hybrid monopile foundation in cohesionless soil. Pile-wheel-soil interactions are studied through validated finite element models. Load transfer mechanisms between the wheel and the pile and failure modes of each component in a hybrid monopile foundation are demonstrated. Functions of wheel are categorized into a friction resistance and additional rotational constraints at the pile head, which are quantitively assessed in terms of the vertical earth pressure generated beneath the wheel. A reduction factor is suggested to determine the effective contact area. The addition of the wheel effectively reduces bending moments at the embedded pile, and the maximum earth pressure of the equivalent monopile is similar to an original monopile. A simplified calculation method is proposed to estimate the lateral capacity of hybrid monopile foundation in ultimate condition. Previously reported tests were used to calibrate the analytical method, demonstrating good consistency. This method is applicable for performing an initial design for hybrid monopile foundation and enhancing calculation accuracy.

Mechanical Behavior of Reinforced Embankment with Different Recycling Waste Fillers

The application of construction and demolition (C&D) waste and used tires in geotechnical engineering contributes to the demand of the sustainable development. This study mainly compared the mechanical behavior of pure sand embankment (PSE), C&D material embankment (CDME), sand-tire shreds mixture embankment (STSME) through a scale model test. Effects of tire shreds content, the first layer geocell reinforcement burial depth, geocell reinforcement depth and compaction degree on the bearing capacity of embankments were investigated. Moreover, embankment load-settlement ratio, the reinforced bearing capacity ratio, the bearing capacity improvement factor (IF), the embankment surface deformation, and the vertical earth pressure distribution inside the embankment were discussed. Results indicate that both C&D material fillers and sand-tire shreds mixture can improve the bearing capacity and stability of embankment slopes. However, C&D material is better than sand-tire shreds mixture in the improvement. The optimum value of tire shreds content is 5%. The reinforcement effect of geocell decreases with the increase of reinforcement depth. With the increase of the buried depth of the first layer, it first increases and then decreases. With the increase of compaction degree increases. The minimum earth pressure appears near the slope. The bearing capacity of CDME is greater than STSME. The ultimate bearing capacity of CDME under the action of the geocell is twice that of the unreinforced embankment.

Effect of tunnelling-induced ground loss on the distribution of earth pressure on a deep underground structure

This paper investigated the stress-transfer mechanisms in soil around a circular tunnel (CT) and a rectangular tunnel (RT) using the finite element method (FEM). Compared with the CT, there was a self-weight stress zone in the local soil above the RT, and the shear stress was concentrated only near the sliding surface, which caused the trajectory of the minor principal stress in this area to take an inverted arch shape. Then, a multi-arch model consisting of the end-bearing arch and the friction arch was proposed for estimating the distribution of the vertical earth pressure on a deep RT in dry sand. Unlike the CT, the friction arch in the RT was based on the assumption that the minor principal stress was a circular arc. The distribution factor of the vertical earth pressure on the RT was obtained. Note that a modified coefficient in the distribution factor was introduced, which was obtained by numerical simulation at different cover depth ratios and internal friction angles. Finally, the theoretical, experimental and numerical results were compared to evaluate the validity of the proposed model. The theoretical results in this paper were in good agreement with the experimental and numerical results.

Experimental study on the mechanical behavior of shored mechanically stabilized earth walls for widening existing reinforced embankments

Shored mechanically stabilized earth (SMSE) walls have been increasingly applied in embankment widening projects because of their good mechanical performance, simple construction, low cost, and low site requirements. In this paper, several large-scale model tests were conducted to explore the mechanical behavior of the composite structures with different connection forms and relative densities, and the wall deformation, earth pressure, reinforcement strain, potential failure surface and the effects of the connection forms behind SMSE walls were also analyzed. The results show that the deformation of SMSE walls is mainly concentrated on the upper middle part, showing a “bulging” failure trend. The deformation of the SMSE walls can be effectively controlled by improving the relative density and adopting a “sandwich” connection behind the walls. The horizontal earth pressure against the SMSE wall facing shows a “K”-shaped distribution, and the vertical earth pressure is large in the upper part and small in the lower part. The potential failure surface originated at the junction of the old and new retaining walls, forming a “double-line” failure surface. For a “sandwich” connection, the failure surface moves forward and occurs where the primary and secondary reinforcements overlap, and this connection form is recommended in engineering practice.

Effect of large-span three-sided culvert configuration on its performance at service and ultimate loading conditions

The configuration of large-span reinforced concrete (RC) three-sided culverts (TSCs) with flat top slab can affect their geo-structural performance. Therefore, the measured responses of an instrumented 13.5-m-span TSC under 3.0 m of backfill were analyzed to elucidate the effect of its configuration on the pressure distribution along the top slab and sidewalls as well as underneath the footing. The field monitoring data were utilized to validate two-dimensional (2D) nonlinear finite element models (FEMs) that were then employed to analyze the culvert response at service loading conditions. The validated nonlinear 2D FEM was then extended to analyze the ultimate limit state (ULS) response at deeper backfill heights. In addition, the influence of the culvert sidewall and footing pedestal heights on the footing-culvert system performance was investigated. To further examine the effect of sidewall height on the structural capacity of the precast culvert unit, 3D nonlinear FEMs were developed to simulate a laboratory load testing for the precast unit of the subject TSC with different sidewall heights. The results from the 2D FEMs demonstrated non-uniform vertical earth pressure distribution on the top slab at all backfill heights. The height of the culvert sidewall was found to influence the location of failure surface and the maximum backfill height at failure. Moreover, the results clearly demonstrated significant influence of sidewall configuration on the performance of the footing-culvert system. Relatively short sidewall with long footing pedestal performs better than long sidewalls with short pedestals. The 3D FEMs showed that the precast unit structural capacity could decrease by up to 18% due to increased sidewall height.

Vertical Earth Pressure Behavior and Shear Band Propagation on Cyclic Loading Mode in Trap-door

Vertical Earth Pressure Behavior and Shear Band Propagation on Cyclic Loading Mode in Trap-door

Analysis of Vertical Earth Pressure Acting on Box Culverts through Centrifuge Model Test

Due to the lack of surface space, most structures are heading underground. The box culvert is underground infrastructure and serves to protect the buried structure from the underground environments, but it has a different characteristic from other structures in that the inner space is empty. Therefore, in this study, the vertical earth pressure which is the most significant effective stress acting on a box culvert was measured by conducting a geotechnical centrifuge model test. A box culvert was installed following the embankment installation method, and the vertical earth pressure acting on it was measured considering the cover depth, gravitational acceleration, and loading and unloading conditions. The soil pressure measured was greater than the existing theoretical value under high cover depth and the unloading condition, which is considered as the variability of many soils or the residual stress acting under the loading condition. Finally, a goodness-of-fit test was conducted as a part of variability analysis. The measured earth pressure was found to be considerably larger than the existing theoretical value, and the variability was large as well. This means the existing theoretical equation is under-designed, which should be reflected in future designs.

Design guidelines for reinforced concrete three-sided culverts

A comprehensive parametric study is conducted to investigate the structural performance of reinforced concrete (RC) three-sided culverts (TSCs) and the applied earth pressures. Nonlinear finite element models were established for a range of TSCs configurations and were validated using full-scale field measurements of three TSCs with spans of 7.3, 10.4, and 13.5 m. The parametric study covered a wide range of main design factors, including backfill height, installation method, backfill soil type and compaction level, and concrete compressive strength. The results demonstrated that embankment installation method resulted in slightly higher earth loads on the culvert top slab and sidewalls compared to trench installation method. The results revealed that vertical arching factors (VAFs) stipulated in the CHBDC (CSA, 2019) for B1 and B2 standard installations consistently overestimated the vertical earth pressure on the top slab. Therefore, the equation proposed by AASHTO (AASHTO LRFD, 2014) for evaluating VAFs was modified and proposed to evaluate vertical earth pressures for TSCs. It was found that culvert installation involving dumped soil or moderately compacted sidefill along with compacted backfill on the top slab significantly increased the vertical earth loads on the top slab, and adversely affected the structural performance of TSCs and their ultimate capacity. Therefore, these compaction scenarios should not be used in the construction of TSCs. The results also demonstrated that the predicted maximum backfill height at failure could increase by up to 50% when concrete with higher compressive strength (i.e., 60 MPa instead of 40 MPa) is used in manufacturing the RC TSCs. Finally, midspan vertical deflection limits are proposed to ensure that the crack width of the RC culvert satisfies the allowable limits considering soil-structure interaction effects.

Characteristics of Cantilever Retaining Wall Composed of Upper Wall and Lower Wall by Physical Testing

Based on the finite element method, the earth pressure and deformation of the cantilever retaining wall composed of upper wall and lower wall are compared and analyzed. The results show that the maximum lateral displacement of the fill occurs near the top of the upper wall, the lower wall has the tendency of overturning to the free surface, while the upper wall has a certain deviation from the free surface. The vertical earth pressure acting on the heel plate of the upper wall and the lower wall presents non-linear characteristics. When the cantilever retaining wall composed of upper wall and lower wall is unstable, there are two slip surfaces in the filling. The first slip surface runs through the filling based on the heel plate root of the lower wall, and the second slip surface runs through the upper filling based on the heel plate root of the upper wall.

Study on earth pressure of deep-buried tunnel in layered ground with centrifuge modelling

Deep-buried tunnels have been increasingly used for transportation infrastructure and underground space development in major metropolitan areas around the world. Evaluation of the earth pressure on deep-buried tunnels is crucial in the design of such urban infrastructure. This paper presents an experimental study using a series of centrifuge model tests undertaken in a beam centrifuge at 150g to provide insight into the earth pressure distribution on deep-buried tunnels after the construction in layered soil strata. The experimental and comparative results indicate the earth pressure at the invert of the deep-buried tunnel is slightly greater than the earth pressure at the crown of the tunnel, and the earth pressure at the springline is less than that at the crown. These results also show that the full overburden theory can reasonably predict the vertical earth pressure of a deep-buried tunnel in the clay layer. However, in the scenarios when sand layers are dominant in the overburden soil, the vertical earth pressure values calculated by the Terzaghi loosening earth pressure theory are more consistent with measured values from centrifuge tests. The insights obtained from this study can provide useful references for improved methods in the load consideration of deep-buried tunnel design.

Model Test on the Influence of Surcharge, Unloading and Excavation of Soft Clay Soils on Shield Tunnels

In view of the influence of symmetrical surcharge, unloading and excavation of soft clay soils on shield tunnels, the surface settlement, tunnel settlement, vertical additional earth pressure and tunnel additional confining pressure are measured by an indoor model test. The changes of confining pressure, tunnel settlement, surface settlement and vertical earth pressure caused by surcharge, unloading and excavation are studied and analyzed. The results show that, in soft clay, surcharge will cause tunnel settlement, and unloading and excavation will generally cause tunnel uplift. There is hysteresis in surface settlement and tunnel settlement above the shield tunnel caused by surcharge and unloading; the change of additional confining pressure of the shield tunnel caused by surcharge is mainly concentrated in the three directions of 3, 5 and 7 of the radar chart. These points belong to weak points. Unloading and excavation can effectively reduce the additional confining pressure of the tunnel in these three directions; excavation will cause the increase of vertical cumulative additional earth pressure and tunnel confining pressure in local directions. The influence range of surcharge in soft clay is wider than that in sand, but the depth is relatively shallow.

Calculation of earth pressure distribution on the deep circular tunnel considering stress-transfer mechanisms in different zones

It is of great significance for ensuring the lining safety to reasonably determine the earth pressure on the tunnel, especially the deep-buried tunnel. In this study, the stress-transfer mechanisms of soils in different zones above the tunnel were analyzed firstly. A multi-arch model for calculating the distribution of the vertical earth pressure on a deep tunnel in dry sand was then proposed based on the limit equilibrium method. The model is composed of three parts: the upper end-bearing arch, the stability zone and the lower friction arch. The key parameters (i.e., width and height of friction arch zone, thickness of end-bearing arch zone and lateral stress ratio in friction arch zone) in the proposed model were suggested according to the existing literature, and a formula for predicting the height of the friction arch zone was deduced. The experimental and numerical results and Terzaghi’s solution were adopted to assess the validity of the proposed model, which indicates that the proposed model not only coincide with the test results of average vertical earth pressures on the tunnel, but also describe the nonuniform distribution characteristics of vertical stress on the circular tunnel, namely, the minimum vertical earth pressure is located at the centreline of the tunnel, and then gradually increases as it moves away from the centreline. Finally, the impacts of geotechnical and geometrical parameters on the earth pressure were discussed.