Coefficient Of Earth Pressure Research Articles

Dynamic Stability for Seismic-Excited Earth Retaining Structures Following a Nonlinear Criterion

Based on the upper bound limit analysis, the multi-log spiral failure mechanism for earth retaining structures under horizontal seismic loads was constructed, which could introduce the nonlinear strength criterion into stability analysis without any linearization technique. By calculating various external work rates and the internal energy dissipation, the energy balance equation was established, and the active earth pressure formula required for the retaining structure to be in a critical stable state was derived. With the application of a genetic algorithm and particle swarm optimization, the optimal upper bound solutions of active earth pressure coefficients were obtained. The validity of the research results was verified through comparative analysis. This paper provided diagrams of the active earth pressure coefficients required for earth retaining structures to maintain a critical stability state under different parameters. The influences of seismic load, slope inclination angle, soil strength tension cutoff (TC), and the δ/ϕ ratio were investigated. By investigating the design charts, the active earth pressures applicable to practical engineering can be obtained, which provide a theoretical basis for the preliminary design of retaining structures in earthquake-prone areas.

Evaluation of Face Stability for Mega Tunnel Under Varying Ground Strength Parameters

Abstract Transportation demands in developing countries necessitate the use of underground infrastructure, notably tunnels, which also serve as storage spaces for vehicles and military equipment, expanding their utility. Mega Tunnels, defined as those with a diameter exceeding 10m, offer diverse functionalities, including facilitating the storage and movement of large equipment and establishing comprehensive operational systems for urban areas. However, ensuring the stability of these tunnels’ faces poses a significant challenge due to their larger diameter, making it a crucial research focus. This study investigates the impact of various geological strength variables, such as Young’s modulus and coefficient of lateral earth pressure, on Mega Tunnel face stability. Employing the numerical analysis-based computational tool Midas Gts Nx, three-dimensional modelling was conducted to analyze Mega Tunnels. A parametric study involving approximately 40 models was undertaken, focusing on key locations including the crown, invert, and vertical sidewalls. Variable parameters such as critical cover-to-diameter ratio (C/D), Young’s modulus, and coefficient of lateral earth pressure were examined. The findings highlight the significant influence of geological strength characteristics on tunnel face stability prediction. This research offers valuable insights for the planning and design of Mega Tunnels in urban areas during the preplanning phase, enhancing their efficiency and effectiveness.

Ground Behavior of Parallel Tunnels in Response to Variations in Groundwater Flow

With the steady expansion of urban development, the importance of tunnel design and construction has increased, particularly with respect to changes in the groundwater level. Excavation without considering groundwater variations can destabilize tunnels; and this problem has been exacerbated by recent climate change-induced groundwater level fluctuations. This study evaluates the impact of various factors, such as filler width, lateral earth pressure coefficient, and groundwater flow, on tunnels by analyzing the ground behavior around parallel tunnels in Korea. The findings reveal that an increase in filler width reduces settlement and displacement, while the coefficient of lateral earth pressure affects convergence displacement to a higher degree than other settlements. Moreover, steady flow conditions are observed to wield a more pronounced impact on ground behavior than unsteady ones. These findings emphasize the importance of thoroughly evaluating groundwater flow characteristics during tunnel excavation and provide essential data for the future design and construction of parallel tunnels.

The Coefficient of Earth Pressure at Rest K0 of Sands up to Very High Stresses

The mechanical behaviour of soils subjected to any stress path in which deviatoric stresses are present is heavily characterised by non-linearity, irreversibility and is strongly dependent on the initial state of stress. The latter, for the majority of geotechnical applications, is normally determined by the at-rest earth pressure coefficient K0, even though this state is valid, strictly speaking, for axisymmetric conditions and for zero-lateral deformations only. Many expressions are available in the literature for the determination of this coefficient for cohesive and granular materials both for normal consolidated and over-consolidated conditions. These relations are available for low to medium stress levels. Results of an extensive experimental investigation on two sands of different mineralogy up to very high stress (120 MPa) are reported in the paper. For reach very high vertical stresses, a special oedometer has been realised. In the loading phase (normal consolidated sands), the coefficient K0n depends on the stress level. It passes from values of about 0.8 to values of about 0.45 in the range of effective vertical stress σ′v = 0.5–4 MPa. Subsequently, K0n is about constant and varies between 0.45 to 0.55 up to very high vertical effective stresses (120 MPa). For the sands employed in the tests, Jaki’s relation did not lead to reliable results at relatively low pressures, while at high pressures, the same relationship seems to lead to reliable predictions if it refers to the constant volume angle of shear strength. For the over-consolidated sands, K0C strongly depends on the OCR, and for very high values of OCR, K0C could be greater than Rankine’s passive coefficient of earth pressure, Kp. This result is due to the very locked structure of the sands caused by the grain crushing, with intergranular contact of sutured and sigmoidal, concavo-convex and inter-penetrating type, that confer to the sand a sort of apparent cohesion and make it similar to weak sandstone.

Passive earth pressure coefficients prediction using deep learning techniques

Predicting passive earth pressure coefficients is crucial for the design of retaining structures, as these coefficients, dependent on soil properties and wall geometry, they impact wall stability. In a practical context, the experimental and analytical approaches are often inaccurate and complex. In this paper, we have developed and tested three Recurrent Neural Networks: RNN, LSTM, and GRU models to predict passive earth pressure coefficients 〖(K〗_pγ, K_pq and K_(pc )) using datasets with 1147 observations, including key parameters such as the ratio of wall width to height (b⁄(h)), the soil-wall interface friction angle to internal friction angle ratio (δ⁄(ϕ)) and the soil friction angle (ϕ). The results demonstrate that our deep neural network models perform better in terms of accuracy and reliability when compared to previously models. As a result, the LSTM model outperformed the RNN, and GRU models in terms of prediction accuracy, exhibiting the best MSE performance (K_pγ = 0.0014, K_pq = 0.0020, K_pc = 0.0020).

An Alternative Approach to Dynamic Earth Pressure Coefficients to Improve the Seismic Limit State Design of Earth-Retaining Structures

An Alternative Approach to Dynamic Earth Pressure Coefficients to Improve the Seismic Limit State Design of Earth-Retaining Structures

Deformation-related earth pressure within grid wall-pattern foundation under adjacent surcharge

This study investigated the deformation-dependent earth pressure evolution on the periphery of the grid wall-pattern foundation fully embedded into soft ground. The numerical modelling was performed using the embedded Modified Cam Clay Constitutive model in the FLAC3D software platform and numerical results were validated using centrifuge results. The induced effective vertical and horizontal stresses acquired from the numerical modelling were used to compute the corresponding deformation-dependent earth pressure at different buffer zone distances and surcharge loading. Thereafter, the parameters that influence the determination of the lateral displacement, induced effective vertical stress and deformation-dependent earth pressure coefficient were investigated using machine learning and genetic programming was used to establish the physical equations that could be used to estimate parameters for similar problems. Moreover, for the deformation-dependent earth pressure to be within Rankine's active and passive earth pressure the buffer zone distance/depth ratio should be 10% of the grid wall-pattern foundation embedment into the ground. Furthermore, it was also discovered that the structure fully embedded into the ground under adjacent loading cannot only be designed based on Rankine's active and passive earth pressure investigation on the periphery but the evaluation should be done within the entire location of the grid wall foundation.

Joints mechanical characteristics of prefabricated subway station considering bending stiffness difference

In prefabricated subway stations, the presence of joints leads to an uneven circumferential distribution of structural stiffness. However, there has been limited research focusing on the variability in bending stiffness of joints so far. Therefore, this paper proposes a theoretical framework to study deformation characteristics considering the differences in bending stiffness. This study aim to analyze the deformation characteristics of prefabricated structures, with a specific focus on the impact of variations in bending stiffness on the overall structural behavior. The research scope includes the calculation methods for the bending stiffness of joints, predicting maximum settlement of the top plate, and analyzing the influence of key parameters such as joint positions, geometric shapes, and dimensions, overburden density γ, lateral earth pressure coefficient λ, overburden thickness hf, and concrete density ρ on the joint bending stiffness. Results validate the reliability of the proposed method for calculating joint bending stiffness and demonstrate the key factors contributing to differences in bending stiffness.

Estimating relative density from shallow depth CPTs in normally consolidated and overconsolidated siliceous sand

Current interpretation of relative density (<i>D<sub>r</sub></i>) based on CPT end resistance (<i>q<sub>c</sub></i>) data in sand relies on empirical expressions established from calibration chamber studies for which a deep failure penetration mechanism is attained. These expressions are mainly based on stress normalised <i>q<sub>c</sub></i> data. Previous studies have highlighted the importance of performing the normalisation procedure with respect to the mean effective stress (<i>p'</i>) in overconsolidated (OC) sand deposits instead of the vertical effective stress (<i>σ'<sub>v</sub></i>) that has been used in normally consolidated (NC) deposits. Due to a large variation in the coefficient of earth pressure at rest (<i>K<sub>0</sub></i>), on which <i>p'</i> depends, in the uppermost (3-5) m of OC sand, a recent study has demonstrated a rigorous unified approach for estimating a varying <i>K<sub>0</sub></i> with depth. However, the surficial shallow failure penetration effects are not accounted for, and consequently, interpretation of the upper (0.5-1.5) m of sand is still erroneous. This depth range is very important for low stress geotechnical applications such as offshore flowlines and mudmats. With a reinterpretation of previously published data, a new global model is presented that enables estimation of <i>D<sub>r</sub></i> from shallow CPTs in siliceous sand by taking into account both the shallow failure penetration effects (important in the uppermost 0.5-1.5 m) as well as the varying <i>K<sub>0</sub></i> with depth for OC sand (important in the uppermost 3-5 m).

Integrated Plug High-Strength Geocell Reinforcement in Foundation Design for Square Footing

This paper develops an analytical model to calculate the ultimate bearing capacity of the integrated plug high-strength geocell (IPGC)-reinforced foundation under a square footing. The high strength and stiffness of the geocell wall and the typical failure of the integrated plug-in joint tearing were considered. The ultimate bearing capacity of the IPGC-reinforced foundation was calculated in two separate parts. The ultimate bearing capacity of an unreinforced foundation was calculated using the modified Terzaghi equation. The increased bearing capacity of the IPGC was calculated as the function of the tearing force of the geocell wall, the height and the diameter of a geocell, the empirical static earth pressure coefficient, and the vertical additional stress coefficient under uniformly distributed rectangular loading. The results showed that the maximum error between the experimental and the theoretical results is less than 18%. The ultimate bearing capacity of IPGC-reinforced foundations decreases with larger geocell diameters. When the diameter of the geocell exceeds 1.8 times the foundation width, the confinement effect of IPGC becomes negligible. The findings of this study offer a robust analytical equation for predicting IPGC-reinforced foundations, along with valuable insights into the efficacy of IPGC reinforcement in enhancing foundation stability.

Passive earth pressure due to surcharge loading under three modes of wall movement

ABSTRACT Passive earth pressure behind retaining walls under rotational movements has been widely investigated recently. However, the behavior of surcharge loading under rotational movement has not been fully explored in the literature. This paper numerically investigates the impact of different types of wall movement; translation, rotation about the top and rotation about the bottom, on the two and three-dimensional passive earth pressure due to uniform surcharge loading. Results prove that the limit pressures under rotational mode are significantly lower than those in translational mode, ranging from 63% to 98% of those used in the literature. Overestimating coefficients in the design of retaining structures can lead to insecurity and instability. Furthermore, the distribution of passive earth pressure with depth is no longer rectangular. Shape factors are then evaluated to facilitate the practical application of passive earth pressure coefficients under rotational wall movements.

Improved Liquefaction Resistance with Rammed Aggregate Piers Resulting from Increased Earth Pressure Coefficient and Density

Improved Liquefaction Resistance with Rammed Aggregate Piers Resulting from Increased Earth Pressure Coefficient and Density

Upper bound stability analysis of tiered geosynthetic-reinforced soil wall

The tiered geosynthetic-reinforced soil (GRS) walls have been increasingly applied in the high and steep retaining soil structures. However, very little is known about the design method for the tiered GRS wall in practice. This study is aimed at proposing an upper-bound stability analysis method of a tiered GRS wall. The proposed method was firstly validated by the existing results from the centrifuge test and the numerical method, and then a parametric study was performed to investigate the effects of the cohesionless backfill friction angle ϕ1 and the wall geometric parameters including the offset distance, the total wall height, the batter angle δ, the number of tiers n, and wall height ratio of adjacent tiers on the dimensionless equivalent earth pressure coefficient KT. The analysis results demonstrated that as the ϕ1 increases, the shear strength of backfill is enhanced and thus the KT or the total reinforcement tensile force decreases, and the KT decreases with the increase of the offset distance at the initial stage and then becomes stable when it reaches a certain critical value. For a fixed offset distance, the KT or the total reinforcement tensile force decreases with the increase of the δ. For the two-tiered GRS walls having the offset distance less than the critical value, the wall with the smaller wall height ratio has a larger KT. Further, the variation of the location of the critical failure surfaces of tiered GRS walls was presented in this study with the variation of the ϕ1 and the wall geometry.

A method for estimating coefficient of lateral earth pressure based on cone penetration tests

The coefficient of lateral earth pressure at rest (K0) is a key state soil variable for the design of foundations and underground structures, characterizes in-situ stress state and soil condition. In this study, a method for the in-situ estimation of K0 using the cone penetration test (CPT) is proposed considering vertical and inclined cone resistances (qc). For this purpose, a series of laboratory CPTs in a soil chamber were conducted to obtain and characterize vertical and inclined qc values at various inclination angles (θ) and relative densities (DR). It was observed that the values of qc increased as θ increased, which was more pronounced at higher DR. Coupled Eulerian-Lagrangian (CEL) finite element analyses were performed to quantify the values of inclined qc at various cone penetration and soil conditions. Based on results from laboratory CPTs and CEL analyses, a CPT-based K0 correlation model was established, which was given as a function of vertical and inclined qc values. The model parameter for the proposed method was evaluated and quantified. The validity of the proposed method was confirmed from the comparison with case examples.

Design of the Nant Ffrwd mainline bridges with flexible integral frame abutments

As part of the A465 Head of the Valleys sections 5 and 6 project, two integral bridges with a maximum span of 70 m across the Nant Ffrwd valley were designed to support the new mainline carriageway construction. The topography and founding rock levels were such that abutment walls up to 19 m high were required. To provide significant material and carbon dioxide efficiencies, the abutments were designed to be slender with their flexibility accounted for in the design. For full-height integral frame abutments, UK guidance presents a limit equilibrium/simplified method to determine K* (enhanced horizontal earth pressure coefficient generated from strain ratcheting), where the values of earth pressures generated are based on the full height of the abutment and do not consider abutment flexibility. For slender abutments, this can be conservative for the design and unrealistic to the soil–structure interaction. Where the foundation is rigid and the abutment flexible, there will be parts of the abutment that will not deflect or rotate from expansion of the bridge deck and will thus not generate earth pressures that approach the limiting K* values. This paper discusses the design of the Nant Ffrwd bridges and the methods used to determine the magnitudes of earth pressures and their distribution based on the stiffnesses of the foundation and the structural elements.

An extended graphical solution for undrained cylindrical cavity expansion in K0‐consolidated Mohr–Coulomb soil

AbstractThis paper develops a general and complete solution for the undrained cylindrical cavity expansion problem in nonassociated Mohr‐Coulomb soil under nonhydrostatic initial stress field (i.e., arbitrary values of the earth pressure coefficient), by expanding a unique and efficient graphical solution procedure recently proposed by Chen and Wang in 2022 for the special in situ stress case with . It is interesting to find that the cavity expansion deviatoric stress path is always composed of a series of piecewise straight lines, for all different case scenarios of K0 being involved. When the cavity is sufficiently expanded, the stress path will eventually end, exclusively, in a major sextant with Lode angle θ in between and or on the specific line of . The salient advantage/feature of the present general graphical approach lies in that it can deduce the cavity expansion responses in full closed form, nevertheless being free of the limitation of the intermediacy assumption for the vertical stress and of the difficulty existing in the traditional zoning method that involves cumbersome, sequential determination of distinct Mohr–Coulomb plastic regions. Some typical results for the desired cavity expansion curves and the limit cavity pressure are presented, to investigate the impacts of soil plasticity parameters and the earth pressure coefficient on the cavity responses. The proposed graphical method/solution will be of great value for the interpretation of pressuremeter tests in cohesive‐frictional soils.

Analytical Method for the Deformation-Based Design of Retaining Walls in Asymmetric Excavation

Conventional methods for designing retaining structures are not applicable to asymmetric excavation or deformation-based designs. This study proposes a quadruple-line displacement-dependent earth pressure coefficient model. Based on the proposed model, an analytical solution was developed to facilitate the deformation-based design of the asymmetric length of retaining walls propped at the crest. Furthermore, the effects of the soil internal friction angle, strut stiffness, excavation asymmetry level, and deformation control value on the embedment ratio (Re) of retaining walls were investigated. The results showed that Re determined by the classical equivalent-beam method is unsafe due to its basis on the ultimate-state earth pressure theory. The Re value of the shallower side exhibited greater sensitivity to asymmetric excavation than that of the deeper side. The retaining structure’s required Re decreased with an increase in the excavation asymmetry level. The required Re on either side of the retaining structure decreased as the deformation control values increased. The controlled deformation had a more obvious effect on the Re value of the retaining structure on the deeper side. The proposed method can be used for the deformation-based design of asymmetric wall lengths of retaining structures propped at the crest, considering the different excavation depths on both sides.

Deformation characteristics and creep behaviour of rigid particulates-EPS beads composites

The compression behaviour of the mixture of glass beads (representing rigid particles) and EPS beads (representing deformable particles) during the loading-unloading process is systematically examined through performing two sets of large-size oedometer experiments, including incremental step-by-step and one-step loading scenarios. At each step during the loading-unloading cycle, the void ratio (e) and the at-rest coefficient of lateral earth pressure (K0) are measured for pure rigid samples and rigid-soft particle mixtures. To consider the creep effect, the overburden pressure at the final loading step is maintained on the sample for 24 h prior to unloading. The results show that at a given overburden pressure, with the addition of soft particles to the pure rigid aggregates, the values of e and K0 decrease. Additionally, for both pure rigid samples and rigid-soft particle mixtures, with increasing the overburden pressure, e decreases whereas K0 augments. Moreover, due to the creep behaviour during the constant loading step, K0 decreases over time for both samples; a phenomenon which is observed to be more pronounced for pure rigid aggregates compared to rigid-soft particle mixtures. Finally, a well-established creep model is used to simulate the creep behaviour of pure rigid samples and rigid-soft particle composites.

Estimation of coefficient of earth pressure at rest for coral sand considering the effect of density and stress

Estimation of coefficient of earth pressure at rest for coral sand considering the effect of density and stress

Numerical Simulation of Polymeric Strap Material Reinforced Walls Under Seismic Excitation

This paper presents a comparison between the two-dimensional finite element and experimental results of shaking table tests on six one-third-scale polymeric strap or polymeric geostrip reinforced walls performed under seismic excitation at given peak ground accelerations [Formula: see text]. The effects of initial tangent stiffness or the stiffness of polymeric strap material [Formula: see text] and the slope angle of the cohesionless backfill material [Formula: see text] on the maximum relative displacement, [Formula: see text], of the reinforced earth wall, the values of the horizontal incremental dynamic earth pressure [Formula: see text] with distributions, acceleration responses, horizontal dynamic active earth pressure coefficient [Formula: see text] and maximum dynamic tensile forces [Formula: see text] were assessed in this study. Moreover, the vertical dynamic active earth pressure coefficients [Formula: see text] and the angles of the resulting dynamic active force with horizontal [Formula: see text] were predicted from the numerical analysis. Closely matched responses between the experimental and numerical studies were attained. Data obtained from experimental and numerical studies illustrated that increasing the slope angle of the cohesionless backfill material resulted in an increase in the values of horizontal displacement in the walls, and in dynamic earth pressure and root mean square acceleration [Formula: see text]. Increasing the stiffness of the reinforcement material caused a decrease in horizontal reinforced earth wall displacement and increases in dynamic earth pressure. In addition, the conventional pseudostatic limit equilibrium methods overestimated [Formula: see text] values, whereas they underestimated [Formula: see text] values, and the recommended [Formula: see text] values by current design codes were not found to be compatible with the numerical and experimental results.