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1.
Three-dimensional (3D) finite element analyses have been performed to study the behaviour of a single pile and 3 × 3 and 5 × 5 pile groups during open face tunnelling in stiff clay. Several governing factors, such as tunnelling-induced ground and pile settlement, axial pile force changes and shear transfer mechanism at the pile–soil interface, have been studied in detail. Tunnelling resulted in the development of pile head settlement larger than the free-field soil surface settlement. In addition, axial force distributions along the pile change substantially due to changes in the shear transfer between the pile and the soil next to the pile, which triggers tunnelling-induced tensile forces in the piles with tunnel advancement. It was found that the relative displacements and the normal stresses at the pile–soil interface drastically affected shear transfer. The extent of slip length along a pile increased as the tunnelling proceeded. The apparent allowable pile capacity was reduced by up to approximately 42% due to the development of tunnelling-induced pile head settlement. Shear stress on the pile was increased for most of the pile depth with tunnel advancement, which was associated with changes in soil stresses and ground deformation, and hence, the axial pile force was gradually reduced with tunnel advancement, indicating the development of tunnelling-induced tensile pile force. The maximum tunnelling-induced tensile force on the pile was approximately 0.33Pa, where Pa is the allowable pile capacity applied to the pile head prior to tunnel excavation. The range affected by tunnelling in the longitudinal direction may be identified as approximately −2D ∼ +(1.5–2.0D), where D is the tunnel diameter, from the pile centre (behind and ahead of the pile axis), in terms of pile settlement and axial pile force changes based on the analysis conditions assumed in the current study. Larger pile head settlements and smaller changes in axial pile forces were computed for piles that were part of groups. It has been found that the serviceability of piles experiencing adjacent tunnelling is more affected by pile settlement than by axial pile force changes, in particular for piles inside groups. The magnitude of the tunnelling-induced excess pore pressure was small and may not substantially affect pile behaviour. 相似文献
2.
In densely built areas, the development of underground transportation systems often involves twin tunnels, which are sometimes unavoidably constructed adjacent to existing piled foundations. Because soil stiffness degrades with induced stress release and shear strain during tunnelling, it is vital to investigate the pile responses to subsequent tunnels after the first tunnel in a twin-tunnel transportation system. To gain new insights into single pile responses to side-by-side twin tunnelling in saturated stiff clay, a three-dimensional coupled-consolidation numerical parametric study is carried out. An advanced hypoplasticity (clay) constitutive model with small-strain stiffness is adopted. The effects of each tunnel depth relative to pile are investigated by simulating the twin tunnels either near the mid-depth of the pile shaft or adjacent to or below the pile toe. The model parameters are calibrated against centrifuge test results in stiff clay reported in literature. It is found the second tunnelling in each case resulted in larger settlement than that due to the first tunnelling with a maximum percentage difference of 175% in the case of twin tunnelling near the mid-depth of the shaft. This is because of the degradation of clay stiffness around the pile during the first tunnelling. Conversely, the first tunnelling-induced bending moment was reduced substantially during the second tunnelling. The most critical location of twin tunnels relative to the pile was found to be the tunnels below the pile toe. This is because the entire pile was located within the major influence zone of the twin tunnelling. Two distinct load transfer mechanisms can be identified in the pile, namely downward load transfer in case of tunnels near mid-depth of the pile shaft and next to the pile toe and upward load transfer in case of twin-tunnelling below the pile toe. These two transfer mechanisms can be useful for practitioner to assess the pile performance due to twin tunnelling. 相似文献
3.
This paper presents the results of three-dimensional, finite element analyses performed with an advanced, two-surface-plasticity, constitutive sand model to investigate the response of non-displacement piles to axial loading. The analysis domain is carefully meshed such that the formation and evolution of shear bands next to the pile shaft and near the pile base can be properly captured. Analyses considering various soil profiles and pile geometries show that the mobilized lateral earth pressure coefficient K along the pile shaft increases with increasing relative density and decreasing initial confining stress. The ultimate unit base resistance is independent of pile diameter, increasing with increasing relative density and increasing initial confining stress at the pile base. Based on the analysis results, design equations are proposed to estimate the limit shaft resistance and ultimate base resistance of non-displacement piles in sandy soil. In proposing these relationships, the pile slenderness ratio is considered. The effect of layer proximity to the base of the pile or pile base embedment in a layer is also considered. 相似文献
4.
在膨胀土地基中进行隧道对群桩影响的三维离心模型试验研究,目标地层损失比为2%,着重研究引起的地基沉降槽、桩的附加沉降、附加弯矩、轴力的变化规律。试验得出：隧道开挖沉降槽空间效应明显;隧道开挖从-0.75D至1.25D时,桩附加沉降呈线性增长,隧道开挖至1.25D以后,桩依然沉降明显。前桩与后桩沉降值不同,桩帽会出现倾斜;前桩上部出现负附加弯矩而下部出现正附加弯矩,而后桩仅在下部出现正附加弯矩;前桩附加弯矩最大值出现在隧道轴线附近,且比后桩附加弯矩大得多;前桩附加轴力随着隧道的开挖而增加,且每步最大值在隧道轴线附近。后桩的轴力也随隧道的开挖而增加,但每步最大值出现在桩顶附近。 相似文献
5.
Although simplified numerical methods are reliable for evaluating the response of a single pile under horizontal load, their application is questionable for assessing the response of pile groups. The notion of “p–y” curves has been considered with the aim of establishing a transformation relationship able to provide the “pG–yG” curves of soil resistance around a pile in a group from the well-known curves of soil resistance around the single pile.This transformation extends the applicability of the “p–y” method to pile groups, without the need for time consuming numerical computations, rendering the proposed method efficient and attractive. Comparative examples demonstrated the applicability and the effectiveness of the proposed method. In addition, the method can be straightforwardly extended to account for varying soil resistance, according to the particular location of a pile in a group. It can therefore be used to estimate accurately force and bending moment distributions along the characteristic piles of a group, which are required for the efficient design of foundations. 相似文献
6.
《Computers and Geotechnics》2006,33(4-5):234-247
For shield-driven tunnels, the influence of the soil and grout material properties and of the cover depth on the surface settlements, the loading and deformation of the tunnel lining and the steering of the TBM is investigated numerically. To this end, comparative numerical simulations of a mechanised tunnel advance in homogeneous, overconsolidated, soft, cohesive soil below the ground water table are performed and sensitivities are evaluated. The advancement of the step-by-step tunnel construction process is modelled using a three-dimensional finite element model, which takes into account all relevant components of shield tunnelling. The material behaviour of the saturated soil and the tail void grout is modelled by a two-field finite element formulation in conjunction with an elasto-plastic Cam-Clay model for the soil and a hydration-dependent constitutive model for the grout. The analyses provide valuable information with regard to the significance of the investigated parameters and demonstrate the complexity of the various interactions in shield tunnelling. 相似文献
7.
Pile group interaction effects on the lateral pile resistance are investigated for the case of a laterally loaded row of piles in clay. Both uniform undrained shear strength and linearly increasing with depth shear strength profiles are considered. Three-dimensional finite element analyses are presented, which are used to identify the predominant failure modes and to calculate the reduction in lateral resistance due to group effects. A limited number of two-dimensional analyses are also presented in order to examine the behaviour of very closely spaced piles. It is shown that, contrary to current practice, group effects vary with depth; they are insignificant close to the ground surface, increase to a maximum value at intermediate depths and finally reduce to a constant value at great depth. The effect of pile spacing and pile–soil adhesion are investigated and equations are developed for the calculation of a depth dependent reduction factor, which when multiplied by the limiting lateral pressure along a single pile, provides the corresponding variation of soil pressure along a pile in a pile row. This reduction factor is used to perform p–y analyses, which show that, due to this variation of group effects on the lateral soil pressures with depth, the overall group interaction effects depend on the pile length. Comparisons are also made with approaches used in practice that assume constant with depth reduction factors. 相似文献
8.
In this paper, a numerical simulation method for evaluating tunnelling-induced ground movement is presented. The method involves discrete element simulation of TBM slurry shield advancement and considers explicitly soil excavation from the face, effects of varying face support pressure, and the influence of tunnel cover depth. For the cases studied, it is found that for tunnel cover depths (C/D) between 0.7 and 2.1, ground deformations inducing by the tunnelling can be controlled within a certain extent and tunnel face stability can ensured, provided the support pressure ratio (N) lies between 0.8 and 1.5. The proposed method is reasonably benefited to modeling the face stability in shield-driven tunnels in soft soils. 相似文献
9.
The study investigates the disturbance to piles and pile groups caused by multiple nearby drives of a large diameter slurry shield-driven tunnelling machine in Shanghai. The minimum distance between the slurry shield tunnel (with diameter D = 15.43 m) and the adjacent pile groups of Metro Line 3 and Yixian Elevated Road is 1 m. The nonlinear finite element (FE) software program ABAQUS was used to analyse the movement of the pile groups caused by the process of shield tunnelling. A field investigation was conducted before the multiple crossings to study the impact (movement and excess pore water pressure) on the surrounding soil and piles caused by the tunnelling process. The field investigation is divided into two sections: (i) free-field tunnelling, and (ii) tunnelling close to trial piles pre-installed in the section. For the full-scale test, tunnelling variable, including slurry pressure and grouting pressure, are adjusted during construction to reduce the disturbance during tunnelling close to pile groups supporting two elevated bridges. The FE simulation of the multiple crossings includes two steps: (a) shield tunnelling along the south bound tunnel approaching the working shaft at the western bank of the Huangpu River, and passing separately between two adjacent pile groups of each bridge; (b) return tunnel passing again between the pile groups of the two bridges along the north bound tunnel. Three different FE models are generated: (1) free-field tunnelling process, (2) tunnelling close to trial piles, and (3) multiple tunnel passes adjacent to pile groups supporting the two elevated bridges. Most of the relevant factors in tunnelling are taken into consideration in the FE models including (a) slurry pressure, (b) grouting pressure, (c) grouting material hardening, and (d) soil-pile interaction. 相似文献
10.
The influence of the gravity and inertia of a concentrated mass attached to the top of a single pile on the pile’s dynamic response was investigated in this study. Based on Muki’s fictitious pile method, the static initial axial force of the pile caused by the gravity of the concentrated mass was calculated first. Using the obtained initial axial force of the pile and taking into account the influence of the inertia of the concentrated mass, the second kind of Fredholm integral equations describing the dynamic response of the preloaded single pile were established via the fictitious pile method. Using the obtained integral equations, the dynamic response of the preloaded single pile to an incident Rayleigh wave was calculated. The influence of the pile–soil Young’s modulus ratio, the frequency of the incident Rayleigh wave and the pile length on the dynamic response of the preloaded pile was examined. The numerical results of this study show that the concentrated mass attached to the top of the pile will affect both the dynamic axial and shear forces of the pile. Generally, the concentrated mass attached to the pile top has a greater influence on the shear force of the pile than on the axial force. 相似文献
11.
The pre-bored grouted planted pile is a new type of composite pile foundation that consists of a precast concrete pile and the surrounding cemented soil. A series of shear tests were conducted in a specific shear test apparatus to investigate the shaft capacity of the different pile–soil interfaces. The test results show that the frictional capacity of the cemented soil–sand interface is controlled mainly by the sand properties, while the strength of the cemented soil slightly influences the interface properties by affecting the normalized roughness coefficient Rn. The frictional capacity of the concrete–sand interface is similar to the frictional capacity of the cemented soil–sand interface, and the existence of mud cake layer virtually hampers the frictional properties of the interface. The maximum skin friction of the concrete–cemented soil interface increases approximately linearly with the increasing cemented soil strength, and the value of the maximum skin friction is much larger than that of the cemented soil–sand interface of identical cemented soil strength, which demonstrates the integrity of the pre-bored grouted planted pile in the load transfer process. 相似文献
12.
This paper presents an embedded beam formulation for discretization independent finite element (FE) analyses of interactions between pile foundations or rock anchors and the surrounding soil in geotechnical and tunneling engineering. Piles are represented by means of finite beam elements embedded within FEs for the soil represented by 3D solid elements. The proposed formulation allows consideration of piles and pile groups with arbitrary orientation independently from the FE discretization of the surrounding soil. The interface behavior between piles and the surrounding soil is represented numerically by means of a contact formulation considering skin friction as well as pile tip resistance. The pile–soil interaction along the pile skin is considered by means of a 3D frictional point‐to‐point contact formulation using the integration points of the beam elements and reference points arbitrarily located within the solid elements as control points. The ability of the proposed embedded pile model to represent groups of piles objected to combined axial and shear loading and their interactions with the surrounding soil is demonstrated by selected benchmark examples. The pile model is applied to the numerical simulation of shield driven tunnel construction in the vicinity of an existing building resting upon pile foundation to demonstrate the performance of the proposed model in complex simulation environments. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
13.
Tapered piles represent a more equitable distribution of the pile material in several respects. In order to study their efficiency over piles of uniform section with the same material input, a three-dimensional finite element analysis is developed. The numerical procedure accounts for the non-linear elastic behaviour of both the soil and the pile-soil interface. In order to include the latter, which involves relative slip and debonding, zero/non-zero thickness interface elements are used. Three shapes of cross-section, viz. circular, square and triangular, have been attempted for the piles. The load-settlement behaviour under axial load predicted by the analysis is compared with laboratory test results obtained on instrumented model piles, installed as ‘replacement’ piles, and the fit obtained is found to be reasonably good. Also examined are interface shear and axial force in the pile, displacement and stress fields in the medium and the progression of failure in the latter. 相似文献
14.
In this paper, a numerical procedure based on the finite element method is outlined to investigate pile behaviour in sloping ground, which involves two main steps. First a free-field ground response analysis is carried out using an effective stress based stress path model to obtain the ground displacements, and the degraded soil stiffness and strength over the depth of the soil deposit. Next a dynamic analysis is carried out for the pile. The interaction coefficients and ultimate lateral pressure of soil at the pile–soil interface are calculated using degraded soil stiffness and strength due to build-up of pore pressures, and the soil in the far field is represented by the displacements calculated from the free-field ground response analysis. Pore pressure generation and liquefaction strength of the soil predicted by the stress path model used in the free-field ground response analysis are compared with a series of simple shear tests performed on loose sand with and without an initial static shear stress simulating sloping and level ground conditions, respectively. Also the numerical procedure utilised for the analysis of pile behaviour has been verified using centrifuge data, where soil liquefaction has been observed in laterally spreading sloping ground. It is demonstrated that the new method gives good estimate of pile behaviour, despite its relative simplicity. 相似文献
15.
Hossain Md. Shahin Teruo Nakai Kenji Ishii Toshikazu Iwata Shou Kuroi 《Acta Geotechnica》2016,11(3):679-692
To investigate the realistic ground behavior during tunneling, a new device has been developed. With the new device, model tests of tunnel excavation considering an existing tunnel and an existing building were carried out. Non-linear finite element analyses corresponding to the model tests were also conducted using FEMtij-2D software where an elastoplastic subloading t ij model was used to describe the mechanical behavior of soil. Earth pressure distribution around the tunnels and ground movements during tunnel excavation depend on the distance and position between the twin tunnels. There is a significant effect of tunneling on the existing foundation of building even in the case where the tunnel is constructed in deep underground. The numerical analyses capture well the results of the model tests. 相似文献
16.
Negative skin friction (NSF) along a pile caused by soil consolidation is of great concern to engineers. The development of NSF is time-dependent because soil consolidation is also time-dependent. In this paper, a numerical solution is provided for the development of negative skin friction of a pile in nonlinear consolidated soil under different loads on a pile top. A hyperbolic interface model is also developed. This model considers the development of shear strength during soil consolidation and loading–unloading scenarios at the pile–soil interface. One-dimensional nonlinear consolidation theory is invoked to estimate the soil settlement and shear strength. The distributions of NSF and the axial force along the pile are obtained using the differential quadrature method (DQM). The influences of soil consolidation and different pile loads on the negative skin friction of a pile are discussed. 相似文献
17.
In this paper a typical soil–structure interaction problem is considered, the case of a vertical pile installed in sand and submitted to an axial compression loading. Results from two full scale pile tests are analysed and the tests are reproduced by numerical simulations via finite elements method (FEM). The choice of the mechanical parameters for the soil and the sand–pile interface and the modelling approach are first described. A new numerical strategy is outlined to account for pile installation effects due to jacking and driving via FEM. The proposed approach is based on the application of existing empirical correlations available for the quantification of residual radial and shear stresses along the pile shaft as well as residual pressures around the pile base after the installation. This approach is proposed as an alternative to more complex methods based on the numerical modelling of the pile penetration problem. The role of the constitutive modelling of the interface is also discussed. Finally, comparative analyses of pile loading tests using FEM are provided and the comparisons between numerical and experimental results are presented and discussed. 相似文献
18.
基于砂土中隧道开挖引起的土体竖向位移经验公式,分析隧道开挖对邻近桩基础的竖向影响。采用两阶段计算方法,将邻近桩基础视为竖向被动桩,依据砂土中隧道开挖引起地表及地表以下土体产生的沉降槽,考虑桩土相互作用的非线性,得到砂土中隧道开挖对邻近桩基础轴力影响的简化计算方法,并与土工离心试验结果进行对比,验证了该方法的合理性。在研究过程中,分析了隧道覆盖层厚度、隧道直径、隧道与桩之间的距离、隧道土体损失率、桩长、桩径等因素。研究结果表明,桩身轴力随着覆盖层厚度的增加而减小,随隧道直径和土体损失率的增大而增加;隧道与桩之间距离为2.5倍隧道直径时对轴力的影响最大;随着桩长、桩径的增加,桩身轴力逐渐增加。 相似文献
19.
N. M. Sa’don M. J. Pender A. R. Abdul Karim R. Orense 《Geotechnical and Geological Engineering》2014,32(4):1053-1064
This paper presents an elastic continuum model using an extended nonlinear Davies and Budhu equations, which enables the nonlinear behavior of the soil around the long elastic pile to be modeled using a simple expression of pile-head stiffness method. The calculated results were validated with the measured full-scale dynamic field tests data conducted in Auckland residual clay. An idealized soil profile and soil stiffness under small strain (i.e. shear modulus, G s and shear wave velocity, V s of the soil) determined from in situ testing was used to model the single pile tests results. The predictions of these extended equations are also confirmed by using the three-dimensional finite-element OpenSeesPL (Lu et al. in OpenSeesPL 3D lateral pile-ground interaction: user manual, University of California, San Diego, 2010). A soil stiffness reduction factor, G s /G s,max of 0.36 was introduced to the proposed method and model. It was found to give a reasonable prediction for a single pile subjected to dynamic lateral loading. The reduction in soil stiffness found from the experiment arises from the cumulative effects of pile–soil separation as well as a change in the soil properties subjected to cyclic load. In summary, if the proposed method and model are accurately verified and properly used, then they are capable of producing realistic predictions. Both models provide good modelling tools to replicate the full-scale dynamic test results. 相似文献
20.
盾构隧道施工对邻近承载桩基影响研究 总被引：5，自引：0，他引：5
针对苏州轻轨1号线成层非均质土地基,选用Mohr-Coulomb弹塑性本构模型,建立三维有限元数值模型,研究非均质土中盾构隧道施工对邻近承载桩基工作性状的影响规律。数值计算结果表明,随着成层非均质土中各土层软硬程度差异的增大,隧道开挖会在邻近承载单桩引起明显反弯点,且桩体沉降亦随之增大;位于上软下硬成层土中的承载单桩桩身正弯矩更大,且该正弯矩出现在桩身中上部的反弯点部位,而上硬下软成层土中的承载单桩下部出现更大的负弯矩;与均质土中同位置承载单桩相比,位于上软下硬成层土中承载单桩桩顶及桩端轴力均更大,而位于上硬下软成层土中承载单桩桩顶轴力则更小。不同竖向集中荷载作用下,非均质土中盾构隧道开挖引起的承载群桩中前桩水平位移沿桩身分布与同位置承载单桩重合,后桩挠曲程度小于承载单桩;盾构隧道施工对承载群桩内力的影响明显高于对变形的影响。 相似文献