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"Earth pressure."
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Analytical solution for displacement-dependent 3D earth pressure on flexible walls of foundation pits in layered cohesive soil
This paper proposes a calculation method of displacement-dependent three-dimensional (3D) earth pressure on flexible walls of the foundation pits, further considering spatial effects, layered cohesive soil, and seepage effect on earth pressure. Based on improved Coulomb’s earth pressure theory, the displacement-dependent 2D earth pressure model for flexible walls is established. By introducing the concepts of spatial influence factor and plane strain ratio (PSR), the calculation model of displacement-dependent earth pressure on flexible walls of foundation pit considering spatial effects is further proposed. And the displacement-controlled solutions of earth pressure under different boundary conditions are obtained. The proposed solution is verified by numerical simulations and reported test data of foundation pit and shows good agreement. The traditional 2D earth pressure theory underestimates and overestimates the active and passive earth pressure in the corner effect area of the excavation, respectively. Through parameter analysis and discussion, the parameter effects on 3D earth pressure are ranked as soil cohesion > soil friction angle > wall friction angles. The results of the study provide an important theoretical basis for the 3D design calculation of foundation pits.
Journal Article
An experimental study of the active failure mechanism of narrow backfills installed behind rigid retaining walls conducted using Geo-PIV
A new visual model was used to study the failure mechanism and earth pressure of cohesionless narrow backfill installed behind a rigid retaining wall. The experimental system can simulate the different displacement modes of the retaining wall, inclinations of the retaining wall and widths of the backfill. Using a HD camera, displacement transducers and earth pressure cells, the deformation of the backfill, displacement of the retaining wall and earth pressure on the wall were recorded. Image data were post-processed using geo-particle image velocimetry. The shear strain contours and displacement vector diagrams of the soil were obtained. The test results showed that under the translation mode of the retaining wall, a sliding surface develops as a reflection between the walls to reach the ground. As the backfill width decreases, the number of reflective sliding surfaces increases. The active earth pressure on the wall is less than that obtained from calculations performed using classical theories and has a nonlinear distribution. The number of reflective sliding surfaces can be reduced by increasing the retaining wall inclination. When the retaining wall was under a rotation displacement mode, the backfill exhibited progressive failure, and no reflective sliding surface was produced. The tests help to understand the special failure mechanism and earth pressure distribution of narrow backfills and provide a basis for theoretical research.
Journal Article
Verification Analysis of the Relationship Between Soil Pressure and Displacement of Retaining Structure
Variation laws of earth pressure accounting for the displacement of are taining wall can be well described by mathmatical fitting in the study of the relationship between earth pressure and retaining wall displacement. The common mathematical function expressions of earth pressure displacement of retaining wall can be divided into sinusoidal function model, exponential like function model, hyperbolic function model, fitting function and semi-numerical and semi-analytical model function, etc. The characteristics and shortcomings of the current expression of earth pressure displacement function are summarized. Then combined with the field test and model test, the applicability and characteristics of various mathematical functions in predicting the displacement of earth pressure with retaining structures are analyzed. The results show that when the displacement is small, the sinusoidal function model and the quasi-exponential function model are close to the measured results. When the displacement of retaining structure is large, the fitting results of hyperbolic model and semi-numerical and semi-analytical model are better. For the prediction of earth pressure displacement relationship in passive area, the buried depth has a great influence. And the error between the theoretical value and the actual value has a great influence on the fitting result of the model.
Journal Article
Earth Pressure of Partially Saturated Over-Consolidated Collapsible Soils
Collapsible soils are known as unsaturated soils that exhibit high strength when dry, while experiencing a drastic volume reduction when inundated. Due to the constant growth in construction and urban development, dealing with these types of soils has become unavoidable. Collapsible soils are exposed to water during deep excavations, rising the groundwater table, irrigation activities, heavy rainfalls, broken sewer pipes, etc., which results in excessive settlement of foundations, landslides, embankments or slope failures. In most of these structures, retaining walls and earth pressures dominate the design. Numerical models were developed to simulate the case of walls retaining over-consolidated, partially saturated collapsible soils. The models used the finite element technique and the commercial software “ABAQUS” to model walls subjected to at-rest or passive earth pressure. The theory of unsaturated soil mechanics was employed to evaluate the soil parameters at a given degree of saturation. It is of interest to report that for a given collapse potential, the coefficient of the at-rest earth pressure increases with the increase of the degree of saturation up to a maximum value for each over-consolidation ratio, beyond which it decreases with the increase of the degree of saturation, while the coefficient of passive earth pressure decrees with the increase of the degree of saturation. Design charts are presented to estimate the coefficients of at-rest and passive earth pressures for a given collapse potential, over-consolidation ratio, and degree of saturation.
Journal Article
Evaluation of the Active and Passive Pseudo-dynamic Earth Pressures using Finite Element Limit Analysis and Second-order Cone Programming
This paper presents a numerical model for the evaluation of the active and passive seismic earth pressure coefficients against the retaining structures subjected to pseudo-dynamic loading using the lower bound limit analysis coupled with finite element discretization and second-order cone programming. The active and passive pseudo-dynamic earth pressures are formulated as functions of the earthquake non-dimensional wavelength as well as the local site effects originated from the backfill damping characteristics and the elastic properties of the underlying foundation. Results generally show that the retaining wall tends to instability by increasing the seismic intensity. In particular, it is shown that when the input acceleration at the base of the wall increases, the active and passive lateral earth pressure coefficients undergo increment and decrement, respectively. Moreover, the pseudo-dynamic active and passive earth pressures are bounded between their static and pseudo-static equivalents. Indeed, it is revealed that when trivial wavelengths are encountered, the influence of seismic loading vanishes due to the counteracted inertia force increments and the static solution is reached. On the contrary, when very high wavelengths are assumed, especially for shorter walls, the acceleration fields become homogeneous lending support to the contention that the pseudo-dynamic earth pressure starts from the pseudo-static asymptote values. The soil-wall interface friction angle is also observed to considerably affect the limit earth pressure coefficients due to the augmented shear resistance provision. Furthermore, foundation elasticity is shown to be as important as the backfill damping characteristics in the pseudo-dynamic site response analysis.
Journal Article
Experimental study on the adjustments of servo steel struts in deep excavations
Recently, servo steel struts have been increasingly used in deep foundation pits that require strict control over the deformation of the surroundings induced by excavation. However, the effects of strut length and axial force adjustments of servo struts on wall deflection and lateral earth pressure behind the wall are still unclear. In this study, a model excavation support system was constructed, and several model tests were conducted to investigate the effects of strut adjustments in which the axial forces and lengths of the struts were adjusted to various values. The strut axial forces, lateral earth pressure, and wall deflection were monitored and analyzed. The results show that: (i) the effects of the strut length and axial force on the lateral wall deflection vary with the depth of the adjusted struts. Adjustments of the struts at lower levels can reduce lateral wall deflections and effectively control the deformations. (ii) Increments in both the axial force and length of the struts result in lateral earth pressure changes between the at-rest and passive earth pressures in the vicinity of the adjusted struts. Neutral points can be observed during strut adjustments where the lateral earth pressures remain relatively constant. The locations and number of these neutral points varied depending on the depth of the adjusted struts. (iii) Simultaneous adjustments of the axial forces on multiple layers of struts are more effective in controlling lateral wall deflection than single-layered strut adjustments.
Journal Article
A New Pseudo-dynamic Approach for Seismic Active Soil Thrust
A critical review of the existing pseudo-dynamic approach is provided and a new pseudo-dynamic approach is proposed based on a visco-elastic behavior of backfill overlying rigid bedrock subjected to harmonic horizontal acceleration. Considering a planar failure surface, closed form expressions for seismic active soil thrust, soil pressure distribution and overturning moment are obtained. The results of this study indicate that the existing pseudo-dynamic method can strongly underestimate the soil active thrust especially close to the fundamental frequency of the backfill, where the soil response is more sensitive to the damping ratio. The acting point of the total seismic active thrust is always found to be higher than that predicted by the traditional pseudo-dynamic approach. The effect of the shear resistance angle and wall friction angle on the acting point increases as the amplitude of the base acceleration increases, whereas their effect is generally small far from the natural frequencies of the backfill.
Journal Article
Calculation of nonlimit active earth pressure of retaining walls based on curved sliding surface
The shape of the sliding surface and the displacement of the wall have important effects on the earth pressure of retaining walls. Taking the cohesive backfill behind the inclined retaining wall as the research object, the relationship between the displacement ratio of the wall and the internal friction angle, the external friction angle, the cohesion and the wall-soil adhesion were build up. The potential slip surface behind the wall was assumed to be a cycloid curve, establishing the force balance and moment balance equations of the horizontal differential soil element, the distribution of the non-limit active earth pressure was obtained. The reliability of the proposed method is verified by two model tests and some theoretical results. The parametric research indicates that with the increase of displacement ratio and internal friction angle, the range of potential sliding body decreases gradually, and the non-limit active earth pressure decreases accordingly, presenting a convex curve distribution with the peak value in the middle and lower part of the wall; With the increase of cohesion, the range of potential sliding body increases slightly, and the non-limit active earth pressure near the wall bottom gradually transitions from positive value to negative. With the increase of the inclination of the wall back, the range of potential sliding body increases, and the shape of non-limit active earth pressure curve gradually transitions from convex curve to concave curve. The theoretical method proposed in this paper can provide reference for the research of earth pressure of retaining walls under translational mode.
Journal Article
Mechanical characteristics of counterfort-relief shelf composite retaining wall
A counterfort–relief shelf composite retaining wall is capable of reducing lateral earth pressure. With its relief shelf and T-shape variable section beam as tension member, this wall is effective for high fill slope engineering; however, research on this type of retaining wall is limited. Moreover, investigating the lateral earth pressure distribution law and the mechanical and deformation characteristics of this composite structure is necessary. In this study, three models (a counterfort structure, structure with short relief shelves, and structure with long relief shelves) were tested. Moreover, lateral earth pressure, bending stress, and structural displacement were measured. The measurements revealed that the lateral earth pressure, bending stress in the buttress, and displacement of composite structures were less than those of the counterfort retaining wall under the same conditions. The present study reveals that relief shelves can reduce the total lateral force, maximum bending moment, and maximum displacement at the top of the structure by 33%, 30%, and 33%, respectively, compared with those of the counterfort wall. The lateral earth pressure acting on the structure with long relief shelves is significantly lower than that on the structure with short relief shelves. However, in terms of bending stress and displacement, the difference is not evident. The lateral earth pressure under each relief shelf starts from zero and follows a certain distribution law. Although the relief shelf can reduce the magnitude of lateral earth pressure, it raises the point of application of the total lateral force. Thus, the length and position of the relief shelf are important governing factors of the bending moment of a composite structure. Due to variations in the bending moments derived from the tests, theoretical lateral earth pressures, and calculated bending stresses in the buttress, this study hypothesizes that a certain force is exerted on the lower part of the unloading zone, thus requiring further research. The displacement curve of the composite retaining wall is similar to that of the counterfort retaining wall; it conforms to the bending deformation of the cantilever beam.
Journal Article