层状土场中冲刷作用下部分埋置单桩动力响应分析

桩周土场受冲刷作用的变化是部分埋置单桩结构失效的主要原因之一。工程中土场多呈层状,此类场地中桩基的力学特性研究日益受到关注。为精确揭示冲刷作用对层状土场中部分埋置单桩动力响应的影响,基于改进Vlasov地基模型,利用Hamilton原理建立层状土场中横向受荷单桩的动力学模型。利用有限差分法求解受冲刷作用单桩的固有频率,实现对冲刷作用下土−结构相互作用系统的准确建模,进而用Green函数法求得单桩受迫振动的解析解。通过数值计算和参数分析,研究了层状土场的物理特性对受冲刷作用部分埋置单桩动力响应的影响。结果表明：基于改进Vlaosv地基模型建立的层状土场中部分埋置单桩动力学模型可精确预测冲刷作用对桩基动力学特性的影响。随冲刷程度加剧,层状土场中单桩的第一阶固有频率显著降低,改进Vlasov地基模型中各层土体的地基反力系数均减小,剪切系数则增大。当冲刷至非埋置段桩长 （ 为桩长）时,部分埋置单桩在动荷载作用下出现横向失稳现象。随底层土体厚度增加,各冲刷等级下单桩的第一阶固有频率均增大。如果第1层土的弹性模量增大了约0.43倍、1.14倍、1.86倍,则冲刷等级为0时单桩第一阶固有频率分别增大了约8.9%、19.5%、27.1%。     

饱和软土成层地基一维非线性固结解析解

假定土体在固结过程中压缩性和渗透性的变化成正比,基于 - 及 - 关系,推导出饱和软土成层地基一维非线性固结解析解,分别给出了按沉降定义和按有效应力定义的每层土平均固结度及整个土层总固结度的计算公式。采用Fortran语言编制了相应的计算程序,将计算得到的结果与已有双层地基一维非线性固结解析解计算结果进行比较,验证该解析解的正确性。利用该程序分析成层地基一维非线性固结性状,分别讨论了初始竖向渗透系数、初始体积压缩系数、荷载值及土层厚度对地基固结性状的影响。分析结果表明：在成层地基一维非线性固结过程中,初始竖向渗透系数对超静孔压的影响较为复杂,对上下层地基固结速率影响不同;初始体积压缩系数增大,超静孔压增大,固结速率变小;所加荷载值越大,超静孔压消散越慢,固结发展越慢;超静孔压消散速率不仅取决于土层厚度,同时取决于各层土渗透性的相对大小。     

Bearing Capacity of Two-Layered Artificial Ground with Firm Crust and Weak Subgrade Under Circular Pressure

Classical bearing capacity expressions can not afford variant engineering requests, since they were deducted under hypotheses of strip footing on homogeneous soil. An often met case was taken into account that circular footing on two-layered ground, which has firm crust and weak subgrade. Weighted method and layered method were used in capacity deduction, respectively. The former counts layered soils as single layer of weighted structure and material parameters. But it is restricted to conditions with close strength to each layer. The latter is preferred in engineering calculation, which regards the whole bearing capacity as subgrade’s capacity under the influence of the upper layer. Thus the issue is transformed to K. Terzaghi model plus stress reduction and dispersion effects. At last, the expressions gained from both methods and finite element analysis (FEA) were used in an example calculation, respectively. It approves layered calculating method and suggests the corresponding security coefficient based on elastoplastic FEA results.     

层状土重力释水机制初步探讨

地下水位下降时,土体中粗细不等的孔隙通道释水不同步而在细孔隙中形成悬挂毛细水,这是重力疏干释水减量与滞后的一个重要原因。文中用模型解释了孔隙通道大小愈悬殊,水位降速愈大,均质土给水度愈小,释水愈滞后的原因。分析了层状土中给水度与水位变动带及毛细水带的岩性,厚度及其配置情况,以及水位下降速率的关系。     

成层地基中倾斜偏心荷载下单桩计算分析

针对工程中地基土性质变化的具体情况,假定地基系数满足(mz+C)的线性增长规律,考虑P-Δ效应并计入桩身自重和桩侧摩阻力的影响,采用矩阵计算方法,分别得到单层土中倾斜偏心荷载作用、桩段顶端倾斜偏心荷载作用以及桩身水平分布荷载共同作用下的竖向单桩计算分析的幂级数解答。并在此基础上,利用上述两幂级数解答对成层地基中倾斜偏心荷载下单桩的受力进行了分析计算,列出了具体的计算步骤;最后,结合某具体实例,对上述方法进行了验证,结果表明,该解答与实际吻合较好,具有一定的应用价值。     

ANALYSIS OF PILED RAFT SYSTEMS IN LAYERED SOIL

This paper presents a method of analysis for piled raft systems constructed in layered soils. The method presented takes account of the interactions of the raft, piles and soil without the cost of a full three-dimensional rigorous analysis. This is done by the use of finite layer methods for the analysis of the soil and finite element methods for the raft. Examples are provided in the paper for piled rafts constructed on layered soils, and results are presented for bending moments in the raft and loads in the piles.     

Analytical solution to 1D coupled water infiltration and deformation in two‐layer unsaturated soils

An analytical solution to 1D coupled water infiltration and deformation in layered soils is derived using a Laplace transformation. Coupling between seepage and deformation, and initial conditions defined by arbitrary continuous pore‐water pressure distributions are considered. The analytical solutions describe the transient pore‐water pressure distributions during 1D, vertical infiltration toward the water table through two‐layer unsaturated soils. The nonlinear coupled formulations are first linearized and transformed into a form that is solvable using a Laplace transformation. The solutions provide a reliable means of comparing the accuracy of various numerical methods. Parameters considered in the coupled analysis include the saturated permeability (k_s), desaturation coefficient (α), and saturated volumetric water content (θ_s) of each soil layer, and antecedent and subsequent rainfall infiltration rates. The analytical solution demonstrates that the coupling of seepage and deformation plays an important role in water infiltration in layered unsaturated soils. A smaller value of α or a smaller absolute value of the elastic modulus of the soil with respect to a change in soil suction (H) for layered unsaturated soils means more marked coupling effect. A smaller absolute value of H of the upper layer soil also tends to cause more marked coupling effect. A large difference between the saturated coefficients of permeability for the top and bottom soil layers leads to reduced rainfall infiltration into the deep soil layer. The initial conditions also play a significant role in the pore‐water pressure redistribution and coupling effect. Copyright © 2011 John Wiley & Sons, Ltd.     

Consolidation analysis of saturated multi‐layered soils with anisotropic permeability caused by a point sink

This paper presents the analytical layer‐element method to analyze the consolidation of saturated multi‐layered soils caused by a point sink by considering the anisotropy of permeability. Starting from the governing equations of the problem, the solutions of displacements and stresses for a single soil layer are obtained in the Laplace–Hankel transformed domain. Then, the analytical layer‐element method is utilized to further derive the solutions for the saturated multi‐layered soils in the transformed domain by combining with the boundary conditions of the soil system and continuity conditions between adjacent layers. The actual solutions in the physical domain can be acquired by the inversion of Laplace–Hankel transform. Numerical results are carried out to show the accuracy and stability of the proposed method and evaluate the influence of sink depth and anisotropic permeability on excess pore pressure and surface settlement. Copyright © 2011 John Wiley & Sons, Ltd.     

三维横观各向同性成层地基的传递矩阵解

通过解耦变换推导出三维直角坐标系下横观各向同性地基的非耦合状态方程;利用双重Fourier变换以及Cayley-Hamilton定理得到了单层地基的传递矩阵;结合边界条件和层间连续条件进而得其传递矩阵解。编制了相应程序并进行了数值计算与分析,结果表明：数值结果与已有文献结果十分吻合,地基的横观各向同性性质与成层性质对受荷地基中竖向位移和应力的影响较为显著。     

壳内低速层与地震活动关系

本文根据华北、扬子地台、青藏高原等地区的速度结构、介质特征、地震活动分布等特征,认为地壳中的低速层是在地壳中的弱化层,它与壳内低阻或高导层相对应,在地质构造上反映中地壳大型层间韧性剪切带,与地震活动的层状分布深度范围相对应,粘滑机制是壳内地震活动非常重要的机制,反映了岩石变形呈脆韧性过渡状态。