中心应力法"应力泡"作图与分析方法

针对城市地质学中"天际线"地质规划工作需要,讨论城市建筑或大型工程建筑"应力泡"(或称建筑应力场)的几何学研究方法.在地层均质弹性假设条件下,针对圆形载荷构建"中心应力法"绘制简易的"应力泡"及图形速查法相关图版,实现对地下空间"应力场"的规划,从几何学上实现"应力泡"和地下空间"沉积地质模型"对接.讨论了"建筑载荷应力场"的内涵及应用意义,应力场存在两种"场"的表达方法,一个是应力迹线,一个是等应力线."应力泡"的理论内涵和功用涉及到地下空间沉积体的物性禀赋、全生命期建筑和地下应力场之间相互作用、(外加)"应力泡"和原位应力场的复杂的动态场变、地震动载荷与"应力泡"的相互作用、斜坡区地应力破坏、"应力泡"和流体场耦合动态变化等问题."应力泡"分析既可以用于已经建设城市的建筑应力场(包络线)空间结构,也可以预测规划城市或工程的理论建筑应力场.     

日本MW 9.0级大地震前后华北和东北地区现今构造应力作用调整过程与研究意义探讨

为了探讨日本M_W 9.0级大地震前后华北和东北地区现今构造应力作用调整过程与研究意义,对华北和东北地区进行原位现今地应力绝对测量与实时监测、GPS测量,结果表明：日本大地震在山东半岛、华北北部地区和东北地区所诱发同震位移引起的张性效应调整周期分别约为6个月(即调整结束时间大约在2011年9月)、15个月(即调整结束时间大约在2012年6月)和26个月(即调整结束时间大约在2013年5月),张性效应调整周期与同震位移大小成正比。在这种调整过程中,往往表现出区域现今构造应力作用方式和构造应力场转换,并可能伴随重大地质事件(如地震等)的发生。2012年5月28日和29日、6月18日、8月26日及2013年1月11日在唐山及其周围地区分别发生的4.8级、3.2级、4.0级、3.3级和3.0级地震与华北北部地区构造应力作用方式和构造应力场转换有关,而2013年10月31日以来在吉林省松原市发生的地震群应与东北地区构造应力作用方式和构造应力场转换有关,而非一个大地震前的小震群。     

桩-土-承台共同作用的简化分析方法

从桩与承台下地基土共同分担荷载的基本条件出发,提出了一种从单桩荷载沉降曲线入手的桩-土-承台共同作用简化分析方法。在给定单桩荷载水平下,假定承台下桩间土的变形量等于此时单桩沉降量,求解相应的板底应力,从而可以得到任意桩荷载水平下的承台荷载分担量,而不必将桩的受荷水平限制在极限荷载。将基础沉降分为桩间土变形量及桩端下卧土层的整体压缩量两部分进行分析。桩间土变形量等于单桩在给定荷载水平下的沉降量,而桩端下卧土层的整体压缩量则由承台与桩两部分荷载引起,可以相对准确地预测基础沉降量。工程实例分析与实测结果的比较表明该方法是可行的。     

A simplified analytical method for soil penetration analysis

A new one-dimensional model for penetration analysis of a rigid projectile into a soil target is presented. The soil medium is represented by a set of discs of constant thickness, responding in the radial direction under plain strain regime. When penetration through a typical disc occurs, the projectile displaces soil material and a radial plastic shock wave propagates in the disc. The interaction pressure between the projectile and soil material is compatible with the motion of the contact boundary, between them. The instantaneous resistive force is obtained by summation of the contributions of all the discs which are in contact with the nose surface of the projectile. Soil is considered as a ‘floating’ ideally locking material, in which the locking volumetric strain is adjusted to the physical stress–strain properties of the soil material. Friction between projectile and soil is assumed to be negligible. Comparison is made with both twodimensional computer program results and experimental data, and very good agreement is observed. Comparison with other analytical methods reveals that the present model most closely resembles existing experimental results and permits further analysis of the problem as predictions of target response and of stress distribution on the projectile nose. The calculations require very small amounts of computer time. Analysis with the present model yields an efficient and comprehensive means to analyse penetration and perform parameter analysis.     

改进的排水孔解析解和有限元耦合计算方法

在分析詹美礼、速宝玉等提出的排水孔解析解和有限元耦合计算方法的基础上,针对三维六面体单元,提出了改进的排水孔排水流量准解析式,并将此解析式与有限元渗流计算耦合, 算例说明了改进的解析计算式的合理性。     

考虑桩土差异沉降影响的桩网复合地基桩土应力比分析方法

桩土应力比是桩网复合地基或路基设计的重要控制参数,受土拱效应、拉膜效应和桩土相互作用及其耦合作用的综合影响,为此,本文首先引入几何同心拱模型,考虑桩土差异沉降与土拱发挥程度的关系,建立了新型桩网复合地基土拱效应分析模型,并根据水平加筋网变形特征将水平加筋网变形曲面视为球面与柱面的组合,建立了反映桩土差异沉降影响的拉膜效应分析模型。然后,考虑桩土相互作用及桩土差异沉降,建立了考虑路基填土、网、桩土加固区耦合作用的桩网复合地基荷载传递分析模型,进而提出了其桩土应力比分析新方法。该方法不仅能反映土拱效应、拉膜效应和桩土相互作用对桩土应力比的影响,而且还能反映桩土差异沉降对三者发挥程度的影响。最后,通过工程实例计算以及与现有同类相关方法的比较分析,表明了本文分析模型与方法的可行性与合理性。     

一种填方路堤反压护道断面设计的解析方法研究

针对软弱地基上的高速公路填方路堤稳定性问题,利用整体圆弧法稳定性分析原理,推导了同时考虑滑动面上黏聚力 和内摩擦角 联合作用的平衡方程;并将滑面上内摩擦角 在滑面切向方向上的作用等效为黏聚力作用,提出在此条件下的等效黏聚力概念;进而利用平衡方程和等效黏聚力讨论了合理反压护道宽度和高度的确定方法。以某高速公路反压护道工程为背景,进行了护道断面尺寸的设计计算和分析,并将安全系数和滑体特征与规范推荐方法进行了对比分析。结果表明：相对只考虑黏聚力的计算结果,综合考虑黏聚力 和内摩擦角 联合作用的分析方法更接近大部分软弱地基内摩擦角非零的工程实际条件,且在获得相同安全系数时具有更优的断面尺寸（节约用地和土方量）;该方法与规范推荐方法计算的安全系数有紧密的联系,其值取1.05时与规范容许值较为吻合;该方法能避免设计中依靠经验反复试算确定护道尺寸的盲目性,可减少设计工作量。     

A modified analytical solution of soil stress distribution for XCC pile foundations

X-section cast-in-place concrete pile (XCC pile) is a new type of pile foundation, which has an X-shaped cross section. Compared to the traditional circular pile of the same cross-sectional area, the bearing capacity of an XCC pile is higher due to increased cross-sectional perimeter. Since Geddes solution is based on St. Venant’s principle, leading to the results independent of the cross-sectional geometry and size, large differences are induced when estimating the soil stress distribution for XCC pile foundations. This paper derives a modified analytical solution, which is dependent on the cross-sectional geometry of XCC pile, from Geddes solution. Validation of this modified solution was conducted through three-dimensional numerical analysis and proven more suitable for XCC pile foundations. Parametric study on three geometrical parameters is conducted using this modified solution. The results indicate that the stress in founding soil due to skin friction decreases with increasing pile radius and central angle of concave, but increases with increasing length of flat side. The stress due to end-bearing decreases with increasing pile radius and length of flat side, but increases with increasing central angle of concave. From the parametric studies, the recommended dimensions of XCC pile radius, length of flat side, and central angle of concave are recommended ranges from 200 to 600 mm, 30 to 60 mm, and 90° to 150°, respectively.     

An analytical approach for cased borehole stress calculation in general anisotropic formations

We present an explicit analytical approach for calculating the distribution of stress around a circular cased borehole in a general anisotropic formation. This approach is developed based on a pure elastic cased borehole model, which can include multiple cemented concentric casing strings that are surrounded by a homogeneous anisotropic medium. The wall of the innermost casing is under the compression of borehole internal fluid pressure, and the formation can be subjected to arbitrary far‐field stresses. Every casing–cement boundary is assumed to be welded, so as the cement–formation boundary. The derived analytical solution can be applied to an arbitrary wellbore trajectory in an arbitrary anisotropic formation and is also applicable to degenerate isotropic formations. Accuracy and robustness of the analytical solution is validated through comparing its results with those calculated from the classical Kirsch solution for an isotropic example that has identical elastic properties for all materials and from a finite element method for an anisotropic cased borehole example.     

Proposed nonlinear 3-D analytical method for piled raft foundations

The load distribution and deformation of piled raft foundations subjected to axial and lateral loads were investigated by a numerical analysis and field case studies. Special attention is given to the improved analytical method (YSPR) proposed by considering raft flexibility and soil nonlinearity. A load transfer approach using p–y, t–z and q–z curves is used for the analysis of piles. An analytical method of the soil–structure interaction is developed by taking into account the soil spring coupling effects based on the Filonenko-Borodich model. The proposed method has been verified by comparing the results with other numerical methods and field case studies on piled raft. Through comparative studies, it is found that the proposed method in the present study is in good agreement with general trend observed by field measurements and, thus, represents a significant improvement in the prediction of piled raft load sharing and settlement behavior.     

预应力锚杆复合土钉墙支护体系增量解析方法

以预应力锚杆复合土钉支护体系受力变形为分析对象,假定潜在滑裂面为平面,并考虑土体分层开挖过程,将施加预应力作为一个施工工况,建立了预应力锚杆复合土钉支护体系受力变形的增量解析方法。锚杆预应力和设置位置影响分析表明,随着锚杆预应力值的增加,潜在滑裂面的倾角逐渐减小,对基坑整体稳定性的贡献先增大后减小;锚杆设置越低,增加预应力对基坑整体稳定性的贡献越大。通过实际基坑支护工程的数值模拟分析与施工过程监测结果的对比分析,验证了考虑预应力锚杆施工过程特点的复合土钉支护体系增量解析方法的合理性。