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Large settlement and lateral deformation during construction of a rubble mound, such as a breakwater, over a soft clayey foundation are a challenge. Different mechanisms contribute to excessive settlement of marine clay, including consolidation, the size of the rubble particles, the penetration of individual rock particles and the flow of sludge through the rock pores. Placing a geotextile layer or sand mattress can restrict the amount of material loss caused by these mechanisms. To accurately assess the performance of a geotextile under a rubble mound, eight geotechnical centrifuge tests were conducted. The shear strength of the foundation and the type of the separator layer were the variables considered. The results indicate that the use of a geotextile as basal reinforcement reduced settlement at the breakwater crest and increased stability. In addition, the horizontal displacement of the rubble mound and the clayey foundation decreased remarkably.

In this study, dynamic compaction in sandy soil has been simulated using a three-dimensional numerical model, considering a cap plasticity model and the large deformation effects. Two different app...

For the design of rubble mound breakwaters on soft soil, it is essential to predict the behavior of soft soil and large deformations phenomena occurring in the course of construction of the rubble mound breakwater. Large deformations in various problems can be well simulated using the coupled Eulerian–Lagrangian (CEL) method. In this study, the CEL method has been used to simulate the rubble mounds construction on soft soil and predict the resulting settlements. To validate the numerical model, the results of three experiments conducted in the physical modeling laboratory at Kharazmi University were used. Also, two case studies of real rubble mound breakwaters constructed on soft seabeds were numerically simulated and the results of the numerical model were compared with the recorded data. According to the obtained results, the finite element analysis by the CEL method is able to predict the deformations and settlement occurred during construction of rubble mound breakwaters on soft soils with a reasonable accuracy. In very soft soils with undrained shear strength less than 10 kPa, the CEL simulation outperformed the Lagrangian formulation. Then, parametric study was performed and the effects of height, crest width, breakwater slope and thickness and strength of the soft soil on the amount of rubble mound settlement were investigated.

The construction of rubble mound structures such as a breakwater or access road on a very soft seabed is essential to the development of maritime transportation. This process can result in significant settlement that causes the rock particles to sink into the seabed, leading to loss of material. In the current study, several case studies on breakwaters facing large settlements, which resulted in the use of excessive amounts of rubble, were surveyed. A series of physical models were developed to study the deformation and volume loss of rubble mound breakwaters on very soft clayey soil during construction. It was found that most deformation occurred early in construction. The primary mechanisms influencing settlement were rock penetration into the soft bed, flow of clay material into the porous body of the rubble mound, and lateral deformation of the soil beneath the breakwater, which is associated with soft bed heave at the breakwater toe. During testing of very soft beds, the ratio of material loss to the design weight of the rubble mound increased up to 27%, and the proportion of penetration to total material loss was as high as 56%. The results of the experiments and case studies were used to develop an empirical relation with which to predict settlement.

The construction of rubble-mound breakwaters on soft sea beds is problematic, but is necessary in many coastal areas. The issues faced include the penetration of the rock particles into the very so...

Assessment of liquefiable soils strength is a challenging task in engineering practice especially when a structure is founded on top of the liquefied soil. While it has been addressed and studied i...

Purpose The purpose of this paper is to study the distribution of active earth pressure in retaining walls with narrow cohesion less backfill considering arching effects. Design/methodology/approach To this end, the approach of principal stresses rotation was used to consider the arching effects. Findings According to the presented formulation, the active soil pressure distribution is nonlinear with zero value at the wall base. The proposed formulation implies that by increasing the frictional forces at both sides of the backfill, the arching effect is increased and so, the lateral earth pressure on the retaining wall is decreased. Also, by narrowing the backfill space, the lateral earth pressure is extremely decreased. Originality/value A comprehensive analytical solution for the active earth pressure of narrow backfills is presented, such that the effects of the surcharge and the characteristics of the stable back surface are considered. The magnitude and height of the application of lateral active force are also derived.

PurposeThe purpose of this study is to present a diagram for the lateral earth pressure of c–φ soils exerted on anchored walls in presence of surcharge.Design/methodology/approachTo this end, two-dimensional plane strain modeling of anchored wall was carried out in Plaxis software. To validate the numerical model, two excavations with different specifications were simulated and the model results were compared with the available results. Subsequently, a parametric analysis was done and based on its results, a diagram was proposed for the lateral earth pressure of c–φ soils including the surcharge effects.FindingsThe proposed diagram without the surcharge and cohesion effects is a trapezoidal with zero value at the ground surface that is linearly approaching the apparent earth pressure of sand according to Terzaghi and Peck (1967) at 0.1H (H: wall height). The surcharge and cohesion effects at the ground level is 4 Ka*q and 0, respectively, and below 0.1H, they are treated as the same way for lateral earth pressure of a retaining wall. It should be emphasized that the apparent pressure diagram for design does not resemble the real distribution of earth pressure against the wall and it is for calculating the values of the anchors loads.Originality/valueThe available diagrams to determine the earth pressure exerted on the anchored walls are related to sandy or clayey soils and do not take the presence of surcharge into account. Thus, the proposed diagram is quite original and different from the previous ones.

PurposeAnchorage with concrete bearing pad is commonly used in Iran for stabilization of excavations because of the ease of construction, less costs and less time consumption than the soldier pile method. In this method, a wall facing which includes the concrete bearing pads at the location of the anchors and a shotcrete layer between the bearing pads is constructed parallel to the excavation operation similar to the nailing method.Design/methodology/approachIn this paper, using the finite element software Abaqus, a three-dimensional model of the above-mentioned type of wall is constructed, and the effect of spacing and size of bearing pads on the wall behavior is discussed.FindingsAccording to the obtained results, the size of the concrete bearing pads has little effect on wall deformations, but the internal forces and bending moments developed in the shotcrete layer between the bearing pads are greatly influenced by the bearing pads dimensions and spacing.Originality/valueOwing to the discrete elements of the wall facing, the behavior of this system is completely three-dimensional.

In this study, a fully coupled dynamic finite element model was employed for numerical simulation of the response of level to gently sloping saturated sand layers subjected to cyclic loading. This model utilized a critical state two-surface-plasticity constitutive model to simulate the cyclic behavior of sandy soil. Moreover, a recently proposed variable permeability function was implemented in the numerical model to reflect the effects of soil permeability variations during the liquefaction phenomenon. The numerical model was validated by simulating a number of well-documented geotechnical centrifuge tests with different relative density of sand, base acceleration time history, and surface slope of the sand layer. The obtained results confirmed that the developed model was capable of simulating the behavior of saturated sand under cyclic loading for both level and gently sloping conditions. RESUMEN En este estudio se presenta un modelo parejo dinámico de los elementos finitos para la simulación numérica del nivel de respuesta de las capas de una cuesta arenosa saturada objeto de una carga cíclica. Este mecanismo utiliza un modelo constitutivo de plasticidad de dos superficies en estado crítico para simular el comportamiento cíclico de los suelos arenosos. Además, se implementó una función de permeabilidad variable recientemente propuesta en el modelo numérico para reflejar los efectos de estas variaciones durante el fenómeno de licuefacción. El modelo numérico ha sido validado al simular varias pruebas bien documentadas de centrifugación geotécnica con diferentes densidades relativas de arena, línea de tiempo de aceleración base, e inclinación superficial de la capa arenosa. Los resultados obtenidos confirman que el modelo desarrollado es capaz de simular el comportamiento de las capas arenosas bajo cargas cíclicas en condiciones planas y de ligeramente empinadas.

In many cases, the construction of rubble mound structures such as breakwaters over soft beds is inevitable in coastal areas. The common problems arising from these structures include sinking of the rubble into the seabed, shear failure, general seabed instability, severe settlement, and soft material flow into the rock pores. The present study investigated the use of sand mattress and geotextile as separation layers through physical-model testing. The results of the model without a separation layer showed that the individual penetration of aggregates into the soft bed and flow of soft clay into the rubble mound pores is the effective mechanisms in wasting rock materials. The results are suggestive of the 25% share of penetration in total material loss. Further, mud flow accounted for a 49% share compared to foundation settlement. It was shown that placing a separation layer under the rubble mound can help significantly reduce material loss and offers control over deformations. Using a sand mattress or a geotextile layer enabled a considerable reduction in material loss—26 and 39%, respectively—by controlling penetration and mud flow. The better performance of geotextile over the sand mattress can be attributed to its capacity for withstanding tension and its reinforcing role, helping reduce lateral deformations.

The current study was undertaken to study the effect of soil arching on active earth pressure distribution in retaining walls with c–φ backfill. An analytical approach is presented to develop a gen...

An anchored soldier pile wall is used for deep excavation stabilisation in the vicinity of buildings which are sensitive to displacement. In the current study, a three-dimensional model of anchored soldier pile wall was created in Abaqus software to estimate displacement and internal forces, especially due to surcharge. The effects of soil type, wall height, spacing of anchors and soldier pile rigidity were analysed. The results indicate that the surcharge had great effect on the wall deformation and the bending moment of the soldier piles; however, the bending moment of the lagging was less influenced by the surcharge.

In performance-based geotechnical earthquake engineering, the required degree and spatial extent of ground densification for mitigation of liquefaction beneath a structure should be determined based on the acceptable levels of performance of foundation. Currently, there is no solution for evaluation of the amount of settlement and tilt of footings constructed on a densified ground which is surrounded by a liquefiable soil. This implies the need for numerical procedures for simulation of seismic behavior of shallow foundations supported on both liquefiable and densified subsoil. In this paper, the dynamic response of shallow foundations on a densified ground is studied using a 3D fully coupled dynamic analysis. For verification of the numerical model, simulation of a series of centrifuge experiments has been carried out and the results were compared with the experimental measurements. After verification of the numerical model, a comprehensive parametric study has been performed to develop a methodology for estimating the effectiveness of subsoil densification in reducing liquefaction-induced settlement of shallow foundations. Range of problem variables were considered in a way that the possibility of bearing capacity failure is low enough. The proposed methodology can be utilized for development of a performance-based design procedure for liquefaction hazard mitigation by soil densification.

The construction of a rubble mound breakwater over a soft clayey seabed is a challenging issue in marine engineering. Excessive settlement and the sinking of such structures into the seabed sludge impose high costs on a project and can cause operational problems. The present study evaluated the mechanisms contributing to the large deformation that can occur during the construction of a breakwater using the results of four centrifuge tests. The result showed that the penetration of individual pieces of rubble and the flow of soft clay into the rubble pores were the leading mechanisms contributing to material loss during the construction of the breakwater. According to the conducted tests, the amount of material loss contributing to the penetration of individual rock particles for Cu = 3.2, 4.1, 11.2 kPa, equal 10.3, 7.6 and 2% of the initial breakwater section respectively. Also, the amount of material loss caused by the flow of sludge into rock pores for the three mentioned undrained shear strengths are equal to 15.1, 10.4 and 5.9% of the initial section respectively. So current study indicates that failing to account for these two mechanisms can lead to considerable underestimation of the required material for construction.

Liquefaction phenomenon is usually accompanied by large amounts of settlement owing to disruption of soil structure. In addition to that, large settlement also occurs by a significant increase in soil permeability during seismic excitation. To properly simulate the post-liquefaction settlement, it is important to take the compressibility properties of the liquefied sand as well as the permeability increase into account. Using initial permeability coefficient in the course of simulation of liquefaction leads to underestimation of settlement. In addition to that, using unrealistic values for permeability may cause erroneous predictions of other aspects of soil behavior. Therefore, an accurate simulation of pore pressure generation and dissipation and consequent settlement during liquefaction requires incorporating the actual variation of permeability in the numerical model. In this paper, variation of soil permeability during liquefaction and its effects on soil seismic response is studied using a fully coupled dynamic analysis. Having a realistic mechanism for simulation of soil skeleton response using a well-calibrated critical state two-surface plasticity model, the focus of attention in this paper is on the effects of permeability variation on the behavior of liquefied grounds. Numerical simulations are performed using parts of Modified OpenSees Services (MOSS) library, a set of coupled finite elements, constitutive integration procedures, and material models from the UC Davis toolset along with a novel implementation of variable permeability. Two relationships are proposed for considering the variations of permeability coefficient in the process of liquefaction. The proposed relationships have been implemented into the model and applied for simulation of a centrifuge experiment. Comparison of the numerical results and experimental measurements reveals that there is a direct relationship between (variable) permeability coefficient and excess pore pressure ratio in all build-up, liquefaction, and dissipation phases.

Occurrence of liquefaction in saturated sand deposits underlying foundation of structure can cause a wide range of structural damages starting from minor settlement, and ending to general failure due to loss of bearing capacity. If the bearing capacity failure is not the problem, reliable estimation of the liquefaction-induced settlement will be of prime importance in assessment of the overall performance of the structure. Currently, there are few procedures with limited application in practice for estimation of settlement of foundations on liquefied ground. Therefore, development of a general relationship is important from the practical viewpoint. In this paper, the dynamic response of shallow foundations on liquefied soils is studied using a 3D fully coupled dynamic analysis. For verification of the numerical model, simulation of a centrifuge experiment is carried out and the analysis results are compared with the experimental measurements. The results of centrifuge experiment are taken from the literature for the purpose of comparison and the experiment has not been performed by the authors. After verification of the numerical model, a practical relationship for estimation of liquefaction-induced settlement of rigid footings on homogeneous loose to medium fine sand is proposed based on the results of a comprehensive parametric study. In the interpretation process, the soil layer thickness in which the liquefaction takes place is found to be a key parameter, since by normalization with respect to this parameter, effects of a number of other parameters can be eliminated.

Dynamic compaction is a widely used method for improvement of loose granular deposits. Its applicability in saturated layers generally considered to be less effective because of the fact that part of the applied energy is absorbed by pore water. Up to now the majority of numerical simulations have focused on the analysis of dynamic compaction in dry/moist soils. In this paper, a fully coupled hydro-mechanical finite element code has been developed and employed to evaluate the dynamic compaction effects on saturated granular soils. After verification of the results by comparing the numerical results with those measured in a real field case of DC treatment in a highway, some sensitivity analyses have been performed to evaluate the effect of water phase on the dimensions of the zone of improvement in the soil beneath the tamper. The results indicate that in the DC process the soil demonstrate two different behaviors. At the very early stage after impact, the soil behaves in an undrained manner and high oscillation of pore pressure occurs. After this phase, consolidation begins during which the pore-water-flow out of the soil mass takes place. The numerical analysis reveals that most of the DC improvement occurs during the undrained phase. The main mechanism responsible for the densification of soil during the undrained phase seems to be the compressibility of pore water. The simulation results indicate that the improvement zone diminishes when the degree of saturation increases.

Dynamic compaction (DC) is a common soil improvement technique, used extensively worldwide. DC treatment design is usually based upon empirical relations and past experience. The common problem with all empirical relations is oversimplification of the mechanisms, and the use of parameters that are highly dependent on engineering judgement. In this paper, a developed finite-element code is used for modelling the impact behaviour of dry and moist sandy soil. The code is verified against the results of centrifuge tests. Then the validity of the popular Menard empirical relation for determination of improvement depth in DC design is investigated. The effect of initial relative density, tamper radius, number of drops, and the impact energy are studied using the developed numerical model. It was found that Menard's empirical relation yields suitable results when tamper weight and falling height are both in the ordinary ranges. However, for higher impact energies, Menard's relation overestimates the depth of improvement. The obtained results also indicate that the value of the empirical coefficient in Menard formula depends strongly on the applied energy and tamper radius. Based on this finding, a new relation for predicting the improvement depth is proposed and applied to a number of DC projects. The results show that the new relation provides better results than the old formula.

Numerical analyses of liquefiable sand are presented in this paper. Liquefaction phenomenon is an. undrained response of saturated sandy soils when they are subjected to static or dynamic loads. A fully coupled dynamic computer code is developed to predict the liquefaction potential of a saturated sandy layer. Coupled dynamic field equations of extended Biot's theory with u-P formulation are used to determine the responses of pore fluid and soil skeleton. Generalized Newmark method is employed for integration in time. The soil behavior is modeled by two constitutive models; a critical state two-surface plasticity model, and a densification model. A class 'B' analysis of a centrifuge experiment is performed to simulate the dynamic response of level ground sites. The results of the numerical analyses demonstrate the capability of the critical sate two-surface plasticity model in producing pore pressures that are consistent with observations of the behavior of liquefiable sand in the centrifuge test. (c) 2006 Elsevier Ltd. All rights reserved.