Coefficient Of Earth Pressure Research Articles

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

Underground space is being utilized due to the saturation of surface ground. The box culvert, as a representative infrastructure that has moved underground, is installed to protect such fixtures as electricity and gas. Because buried box culverts are necessarily affected by soil, it is important to study the earth pressure according to soil type. Herein, the horizontal earth pressure of the buried box culvert was analyzed. Accordingly, a precisely simulated centrifuge model test was performed. Additionally, the coefficient of earth pressure was analyzed. The results had significant variability because, in the existing theory, the horizontal earth pressure acting on the side of the box culvert was only calculated using the coefficient of earth pressure and the friction angle of the soil. Therefore, a correction factor was deemed necessary for calculating the horizontal earth pressure acting on the side of the box culvert.

Novel adaptation of Marston's stress solution for inclined backfilled stopes

In underground mining, it is crucial to consider the arching phenomenon, especially for inclined backfilled trenches and mine stopes. That phenomenon decreases the vertical stress of the fill material, so, the in-site stress has already redistributed itself to the hanging- and foot-walls when the stope was excavated. In such cases, the mobilized resistance due to friction between the granular backfill material and the inclined walls can substantially reduce the pressure at the bottom of the stope, which could have a major impact on the stability of the backfill medium and consequently also on economic aspects. Most of researchers used numerical analysis or Lab. tests to predict both of vertical and lateral stresses in inclined stopes. However, there is a need to investigate analytical solution to describe the behaviour of those stresses in inclined stopes. Based on Marston’s formula, this research provides a new approach to predicting vertical stresses at any depth in inclined backfilled stopes. The proposed approach introduces a new parameter, η, to account for the contribution of backfill arching. This parameter specifies the ratio of normal stresses on the hanging wall and foot wall of the inclined backfilled stope. This differs from previous approaches, which assumed that the normal stress on the inclined backfilled stope's hanging wall and foot wall was equal. To validate the proposed approach, results obtained are compared with numerical, analytical, and experimental results from previous research. It is found that if the proposed parameter, η, is modified to 0.2 for the lateral earth pressure coefficient at rest with an angle of inclination of 60° to 80°, good agreement with experimental data is achieved.

Appraisal of the hypoplastic model for the numerical prediction of high-rise building settlement in Neogene clay based on real-scale monitoring data

This article presents the finite element modeling (FEM) based settlement analysis of two high-rise buildings founded on the stiff raft foundations 12.0 m below the ground level in Neogene clay using a modified hypoplastic model with the concept of intergranular strains. The numerical prognoses of the settlement for different phases i.e., deconsolidation, short term and long-term consolidation deformations pertaining to excavation, construction, and operation, respectively, were compared with the real-scale geotechnical monitoring (GTM) data acquired through deformeter installed in a borehole below the foundation. The results showed that the prediction of the settlement of high-rise buildings in stiff Neogene clay using the hypoplastic model can be equitable to the actual values given that calibration of model based on precisely performed laboratory tests, i.e., triaxial oedometer, simple shear and small strain element tests, high coefficient of earth pressure (K0 > 1.0) and appropriate design loads are considered for the analysis. The optimization of intergranular strain parameters showed that mR value in conjunction with r parameter affected the predicted deformation in the excavation, construction and operational phases of high-rise buildings, whereas, βr only affected the deformations during excavation and construction phases. Overall, the predictions of deformation of excavation and short-term consolidation phases using the hypoplastic model were close to the GTM as compared to that of the long-term consolidation phase, which was found to be sensitive to the contact load, σol. Moreover, in comparison to Mohr Coulomb's and cam clay models, the hypoplastic model yielded more reliable subsoil deformation for high-rise buildings based on directly calibrated parameters, proving to be a more value-added model for meticulous numerical analysis. The difference between the predictions of total settlement using the hypoplastic model for all optimization schemes was observed to be in a reasonably good range of 16–29% in comparison to the real-scale settlement.

Influence of Foundation Pit Excavation on Tunnels at Different Locations

To evaluate the tunnel deformation law and soil stress distribution between foundation pit excavation and tunnel in different locations, numerical analyses using the hypoplastic model are conducted based on reported centrifuge model tests. Two cases are designed to investigate the effects of the foundation pit excavation on the deformation of existing tunnels. In case C, an existing tunnel is directly located underneath the foundation pit; in case S, the tunnel is located at one side of the foundation pit. Three-dimensional tunnel deformation mechanisms along the tunnel axis are observed through the variation of stresses change in the soil circumambient tunnel. It is found that compared with case C, there are minor Earth pressure changes in case S. The different Earth pressure changes around the tunnel lead to different modes of tunnel deformation. The maximum additional tunnel bending strain appears at the crown and invert, while the minimum value appears at the spring lines in case C. In case S, the maximum values appear in the right shoulder and left knee, while the minimum values appear on the left shoulder and right knee. The additional tunnel bending strain and stress reduction at different tunnel cross sections in case S is much smaller than those in case C. In case C, after the excavation, lateral Earth pressure coefficient changes ΔKxz and ΔKyz rise to 70% and 150%, respectively, of their initial value at shoulders, while little changes can be found at spring lines. However, in case S, the maximum absolute value of both ΔKxz/(Kxz)0 and (ΔKyz/(Kyz)0) is no more than 10%.

Active earth pressure against flexible retaining wall for finite soils under the drum deformation mode

A reasonable method is proposed to calculate the active earth pressure of finite soils based on the drum deformation mode of the flexible retaining wall close to the basement’s outer wall. The flexible retaining wall with cohesionless sand is studied, and the ultimate failure angle of finite soils close to the basement’s outer wall is obtained using the Coulomb theory. Soil arch theory is led to get the earth pressure coefficient in the subarea using the trace line of minor principal stress of circular arc after stress deflection. The soil layers at the top and bottom part of the retaining wall are restrained when the drum deformation occurs, and the soil layers are in a non-limit state. The linear relationship between the wall movement’s magnitude and the mobilization of the internal friction angle and the wall friction anger is presented. The level layer analysis method is modified to propose the resultant force of active earth pressure, the action point’s height, and the pressure distribution. Model tests are carried out to emulate the process of drum deformation and soil rupture with limited width. Through image analysis, it is found that the failure angle of soil within the limited width is larger than that of infinite soil. With the increase of the aspect ratio, the failure angle gradually reduces and tends to be constant. Compared with the test results, it is shown that the horizontal earth pressure reduces with the reduction of the aspect ratio within critical width, and the resultant force decreases with the increase of the limit state region under the same ratio. The middle part of the distribution curve is concave. The active earth pressure strength decreases less than Coulomb’s value, the upper and lower soil layers are in the non-limit state, and the active earth pressure strength is more than Coulomb’s value.

Extending Mononobe-Okabe theory to account for arbitrary backfill topography and variable density of surcharge

Coulomb proposed a formula for the static earth pressure acting on a rigid gravity retaining wall supporting a soil. Many researchers have generalized this theory and several analytical studies were achieved regarding the evaluation of seismic action. Following the work of Mononobe and Okabe, investigations have considered cohesive backfill, and with some restrictions the topography of the backfill and the pattern of surcharge acting on its surface. In this work an extension of the Mononobe-Okabe theory was proposed to deal with the most general case of backfill having an arbitrary shape and also vertical surcharge acting with variable density at the ground level. Equilibrium of Coulomb wedge was applied to express the active earth pressure coefficient related to a given orientation of the failure plane. Then, numerical optimization was performed to fix the critical angle providing its maximum value. Parametric studies were conducted after that. It was found that both the upward and downward vertical seismic acceleration should be considered. The obtained results indicate that the backfill surface shape and surcharge density have a significant effect on seismic action. The maximum relative variation of the pressure coefficient with regards to the reference case is however limited to 20%.

Influence of soil amplification and backfill angle on seismic earth pressure coefficients by pseudo dynamic method

ABSTRACT The knowledge of earth pressure concepts plays a major role to design a retaining wall. The most traditional pseudo-static methodology as proposed by Mononobe–Okabe gives the direct approximation of earth pressure in seismic condition. This paper utilised the pseudo-dynamic methodology to figure out the seismic earth pressure on rigid wall with cohesion less backfill along with considering the effects of time, phase difference, soil amplification factor along with the variation in seismic velocities. The main contribution is the soil amplification and backfill inclination which is not given much attention before. By considering the above factors coefficients the seismic earth pressure against retaining wall is determined. The coefficient of seismic passive earth pressure decreases with the increase of soil amplification keeping other properties as standard values. The value of coefficient of seismic active earth pressure increases with increase of soil amplification. The comparison is also done without taking backfill angle for both coefficients of seismic earth pressures. The influence of all the soil properties like backfill angle, wall friction angle, soil friction angle, non-dimensional parameters are shown in tabular format as well as in the graphical with respect to the soil amplification which is more realistic towards the design.

Seismic Active Earth Pressure of Limited Backfill with Curved Slip Surface Considering Intermediate Principal Stress

The traditional method for seismic earth pressure calculation has certain limitations for retaining structures under complex conditions. For example, when the soil width is small, the results obtained by the traditional method will be much larger. Therefore, this paper assumes that the soil slip surface is a logarithmic spiral. Based on the plane strain unified strength theory formula, while also considering the soil arching effects and tension cracks, the analytical solutions of the lateral earth pressure coefficient and the active earth pressure under the earthquake action were deduced. The mechanism and distribution of seismic active earth pressure with limited width were discussed in terms of some relevant parameters. The results indicated that the seismic active earth pressure presented a “convex” nonlinear distribution along the retaining structure. As the contribution of the intermediate principal stress increased, the strength limit of the material was effectively utilized, and the earth pressure was reduced by 22.96%. The resultant force increased as the horizontal seismic coefficient increased. However, this effect was no longer evident when the wall–soil friction angle was close to the internal friction angle. The resultant force action point increased with the wall–soil friction angle, and it should be noted that ha>H/3 was true when δ/φ0>0.55. Finally, by drawing a comparison with previous studies, we verified that the method proposed in this paper is reasonable and can provide a new idea for subsequent 3D seismic earth pressure research.

Physical modeling of the long-term behavior of integral abutment bridge backfill reinforced with tire-rubber

The primary objective of this study is to investigate the benefits of adding tire rubber as an inclusion to backfill behind integral bridge abutments. In this respect, four physical model tests that enable cyclic loading of the backfill-abutment are conducted and evaluated. Each test consisted of 120 load cycles, and both the horizontal force applied to the top of the abutment wall and the pressures along the wall-backfill interface is measured. The primary variable in this study is the tire rubber content in the backfill soil behind the abutment. Results show adding tire rubber to the backfill would be beneficial for both pressure and settlement behind the abutment. According to results, adding tire rubber to soil decreases the equivalent peak lateral soil coefficient (Keq-peak) up to 55% and earth pressure coefficient ({K}^{*}) at upper parts of the abutment up to 59%. Moreover, the settlements of the soil behind the wall are decreased up to 60%.

An attempt to apply the kinematic method of rigid solids in the study of bearing capacity of shallow foundations

Abstract In the geotechnical engineering field, shallow foundations are frequently needed to ensure good fieldwork stability. They are also intended to permanently and uniformly transmit all load pressure on the seating floor. However, numerous mechanical constraints, such as bearing capacity of foundations, durability, stability, design of shallow foundations, lead, unfortunately, to a serious realization challenge. Finding an adequate solution presents the main goal and effort of both scholars and professionals. Indeed, the corresponding drawback is observed through the high number of reported damages that occurred in the structure of foundations and the punching failure. The failure mechanisms of shallow foundations, verified in full size or on scale models, show “sliding surfaces” and rigid (solid) blocks, which can be described with the kinematic method of rigid solids. The main objective of this study is the application of the kinematic method of rigid solids in the study of the stability of shallow foundations with respect to punching, the purpose of which is to determine the bearing capacity factors Nc, N γ, and the passive earth pressure coefficient Kp of foundations. In this context, two mechanical models have been proposed with 5 and 7 rigid solids, and a program developed via the MathCAD environment is applied to check the validity of the two previous models. The kinematic method of rigid solids gives results very close and comparable with that of Caquot/Kerisel for the factors of the bearing capacity and passive earth pressure coefficient - the ratio Kp - according to the five- and seven-solid model.

Seismic behaviour of a micropile-reinforced cut slope behind a cantilever retaining wall

The micropile-cantilever retaining wall (CRW) combined retaining structures are widely used in slope reinforcement design. While the landslide thrust distributed between the micropiles and the CRW remains unclear. In this work, the seismic response of a micropile-reinforced cut slope behind a CRW are studied by means of a centrifuge shaking-table model test. The proportion of slope sliding force borne by CRW and micropiles under multistage earthquakes is revealed. When the backfill has a large slope angle and loads are applied to the upper part of the slope crest, the dynamic earth pressure coefficient is much larger than that when the backfill surface is horizontal and no additional loads are applied. The current data show that the residual bending moment accumulates significantly on the CRW and micropiles after an earthquake, which must be considered during the seismic design of the micropile-CRW combined retaining structures.

Modeling of Initial Stresses and Seepage for Large Deformation Finite-Element Simulation of Sensitive Clay Landslides

AbstractGroundwater seepage and an increased lateral earth pressure coefficient at rest (K0) increase the potential for triggering large-scale landslides in sensitive clays. After the failure is tr...

Comparative Analysis of Two cell and Three cell Box Culvert for Different Aspect Ratio

Abstract: Culverts serves primarily as the hydraulic conduits conveying water from one side of a roadway or similar traffic embankment to the other; therefore, culverts serves the dual purposes of functioning as hydraulic structures as well as acting as traffic load bearing structures. They are normally cheaper than bridges, which make them the natural stream passes through channels. Box culvert are most stable and safe among various types of culverts. It can be constructed for soft soil conditions also. Therefore these are the best alternative to the major bridges for the small span and for cross drainage situation. In this work, we analyze the R.C. box culvert of two cell and three cell with different L/H ratio with the use of STAAD Pro software. In this study, we consider the span of culvert bridge as 10 m and we done the analysis for two cell and three cell culvert on the same span and varies the height with respect to span of the culvert bridge for different aspect ratio. Here we considered the traffic loading of Class AA loading as per IRC:6 2014 and also consider all the loading conditions as per IS codes. The structure designing includes the considerations of pressure cases (Box empty, Full, surcharge load) and factors such as Impact load, Braking force, Dispersal of load through fill, Effective width, Coefficients of earth pressure, Live load etc. The analysis of structure as per limit state method IS 800-2007. The IS standard requirements in the design manual for roads and bridges (IRC6-2014, IS 112-2011) is used in the structural designing of concrete box culverts. The structural elements of two cell and three cell Box culverts are compared with respect to its maximum moments respectively for the different L/H ratio on the same span of the culvert. In the results we conclude that the moments are less than the two cell Box culvert with comparison to three cell Box culvert for the constant span of both the cases of culverts. In the present study, this paper provides full discussion on the provisions in the codes, considerations and justifications of all the above aspects of design. Keyword: Box culvert, aspect ratio, Staad pro, IRC codes.

Application of a critical state model to the Merriespruit tailings dam failure

The use of stress–deformation analyses to evaluate the characteristics of possible static liquefaction events is rapidly becoming the norm for tailings dams exposed to such risk. Ideally, those analyses should be based on constitutive models that incorporate the fundamental mechanics of the problem, are able to perform robustly in commercial numerical platforms and are simple to calibrate. A model that aims to fulfil that specification is proposed. The model is a new implementation of a previously proposed model based on critical state concepts that is able to represent static liquefaction. The model formulation is elaborated to show that all the required inputs can be related to familiar concepts such as the critical state line, the state parameter, the normalised undrained peak strength or the coefficient of earth pressure at rest. The methodology is illustrated by analysing the failure of the Merriespruit tailings dam, which occurred in South Africa in 1994 and was instrumental in the recognition of how widespread liquefaction risk might be in saturated tailings. Numerical analysis of the case showed how a large static liquefaction failure might have been triggered by a relatively small slope erosion caused by overtopping.

Stiffness Determination of Backfill-Rock Interface to Numerically Investigate Backfill Stress Distributions in Mine Stopes

Numerical modeling is an effective and efficient method to investigate the stress distributions of backfill in stopes, which should be well understood in underground mining. Interface elements between backfill and rock in simulated stopes had been proved to be essential components, for which the stiffness parameters need to be assessed and assigned. However, few reports have revealed the effects of interface stiffness on backfill stress distributions, and there is not yet a clear solution to determine the interface stiffness to simulate stresses in backfilled stopes, except an empirical method for simply applying a high value suggested in FLAC manual. In this study, a new solution is first proposed to determine the normal stiffness and shear stiffness of interface elements, respectively, in numerical modeling of backfill stresses. The applicability of the solution has been verified by investigating backfill stress distributions in mine stopes of two widely used mining methods with variable stiffness values. The results show that the newly proposed method leads to totally the same backfill stress distributions with models applying the interface stiffness by the method in FLAC manual based on a “rule-of-thumb” but will save at least 20%–30% calculation time to improve modeling efficiency under the same simulation conditions and will carry much clear physical meanings corresponding to the interaction between backfill and rock walls in mine stopes. In addition, the vertical and horizontal stresses show good agreements with the analytical stresses predicted by the Marston equation under the at-rest state, which validates the reliability of the proposed solution for interface stiffness. Moreover, the plotting methods of stress distributions and the coefficient of lateral earth pressure of backfill in simulated stopes with proposed interface stiffness were discussed to further clarify the reasonable methods to investigate the backfill stresses in mine stopes, especially after considering the effects of the convergence from rock walls, which is a very significant and common phenomenon in practical mining engineering.

Application of ANN in Predicting the Cantilever Wall Deflection in Undrained Clay

The main objective of this study is to propose an artificial neural network (ANN)-based tool for predicting the cantilever wall deflection in undrained clay. The excavation width, the excavation depth, the wall thickness, the at-rest lateral earth pressure coefficient, the soil shear strength ratio at mid-depth of the wall, and the soil stiffness ratio at mid-depth of the wall were selected as the input parameters, whereas the cantilever wall deflection was selected as an output parameter. A set of verified numerical data were utilized to train, test, and validate the ANN models. Two commonly used performance indicators, namely, root mean square error (RMSE) and mean absolute error (MAE), were selected to evaluate the performance of the proposed model. The results indicated that the proposed model can reliably predict the cantilever wall deflection in undrained clay. Moreover, the sensitivity analysis showed that the excavation depth is the most important parameter. Finally, a graphical user interface (GUI) tool was developed based on the proposed ANN model, which is much easier and less expensive to be used in practice. The results of this study can help engineers to better understand and predict the cantilever wall deflection in undrained clay.

Neural network application in forecasting maximum wall deflection in homogenous clay

An attempt was carried out by using a neural network to predict the maximum deflection and its position caused by braced excavation in homogeneous clay. Six input variables, including excavation depth, Ratio of EI wall/EI of brace, the vertical distance between bracing, Length to width ratio of an excavation, shear strength, and the coefficient of lateral earth pressure, were adopted. Two models were developed, one is to estimate the maximum deflection and the other one to estimate the position of maximum deflection. The ANN models were developed and verified using a database of (169) cases of actual measured and presumptive cases using the analysis with the Finite element of maximum deflection. A sensitivity analysis was accomplished, to examine the relative significance of the parameters that influence the maximum deflection of the wall and its position; it indicates that the Ratio of EI wall/EI of brace has the most significant effect on the maximum wall deflection, while the properties of the soil have the most considerable effects on the position. The results show that the ANN can reasonably forecast the magnitude of the maximum deflection of the wall, as well as its position. Design charts are developed based on the ANN model.

Prediction of the nonlinear behavior of laterally loaded piles in unsaturated soils

This paper proposes an analytical method for estimating the load versus displacement curves for laterally loaded rigid piles in unsaturated soils taking account the influence of matric suction. The distribution of lateral soil resistance along the pile in this method considers three distinct states: (i) pre-tip yield state; (ii) post-tip yield state; and (iii) ultimate limiting state. The lateral earth pressure coefficient, Kc required in this method is derived by extending the three-dimensional (3D) effect factor for drained loading. A numerical technique is also proposed which incorporates a user-defined subroutine (USDFLD) into ABAQUS for simulating the behavior of laterally loaded piles extending 3D finite element analysis taking account of nonlinear behavior of shear strength and modulus of elasticity with respect to matric suction. The proposed analytical method and numerical techniques were validated, respectively using the results of seven field studies and two laboratory tests published from the literature. In addition, close agreement was observed between the predictions of the proposed analytical method and numerical technique for a single pile example problem placed in a soil with varying groundwater table conditions. The summarized studies are promising for use in practice for the rational design of laterally loaded piles in unsaturated soils.

Experimental research of the conditions for the transfer of rock pressure by saliniferous rocks to the casing

The analysis of field data from casing failure on the fields of the Borislav and Dolinsky oilfield regions has been carried out. It has been found that the most significant negative factors that have a bearing on the preservation of the integrity of the casing strings are the presence of saliniferous rock intervals in the borehole log and not taking into account the possible impact of rock pressure when designing casing strings in these rocks. In saliniferous rocks, under certain conditions, rock pressure can be transferred to the column. To study the thermobaric conditions of the external pressure transfer to the casing from the saliniferous rock, experimental tests have been carried out on the core materials of the rocks of the Vorotyshchensk floor, sampled at different depths of the Oriv-Ulychniansk field. For this purpose, a special laboratory installation was made, which allows to study the stress conditions and rock flowage on exposure to formation temperature and rock pressure. Because it was difficult to directly measure the radial pressure transmitted to the pipe and the temperature inside the chamber during the experiments, the installation was calibrated by pressure and temperature. This made it possible to determine the temperature inside the chamber by the value of the voltage supplied to the heating element, and the value of the radial pressure supplied to the pipe - by the value of the pressure inside the pipe. Based on the results of experimental research, the depen-dences of the lateral earth pressure coefficient of saliniferous rocks on temperature were obtained at various values of normal stresses. It was found that when the temperature rises to 70 ° C and higher, the value of the lateral external pressure on the pipe approaches the vertical component of the pressure. According to the results of the experimental research, the temperature and pressure conditions for accounting for rock pressure were recommended when calculating casing strings for external overpressure in the intervals of occurrence of saliniferous rocks of the Carpathian fields.

Analytical solution for displacement-dependent passive earth pressure on rigid walls with various wall movements in cohesionless soil

Current design practice of retaining wall is generally based on Rankine’s and Coulomb’s earth pressure theories that are subjected to some important limitations. In the present study, an analytical solution for displacement-dependent passive earth pressure on rigid walls is proposed by assuming a linear relationship between the passive earth pressure coefficient and displacement. Based on Coulomb’s theory, the passive ultimate earth pressure coefficient is modified in order to adapt the earth pressure model to various wall movements. The proposed solution is verified with reported experimental data and shows good agreements. Based on the observed experimental data, the normalized passive ultimate displacements (sp/H) are obtained and found to be related to the n value which indicates the location of rotation center. By performing curve fitting, an exponential function of sp/H and the parameter n is proposed. Further, the influence of n value on the distribution of the proposed displacement-dependent passive earth pressure under various wall movements are studied. The proposed analytical model provides an effective approach to calculate the distribution of displacement-dependent passive earth pressure on rigid walls with various wall movements in cohesionless soil.