Kinematic Pile Response to Vertical P-wave Seismic Excitation

An analytical solution based on a rod-on-dynamic-Winkler-foundation model is developed for the response of piles in a soil layer subjected to vertical seismic excitation consisting of harmonic compressional waves. Closed-form solutions are derived for: (1) the motion of the pile head; (2) the peak normal strain in the pile, and (3) the group effect between neighboring piles. The solutions are expressed in terms of a dimensionless kinematic response factor Iv, relating pile-head motion and free-field soil surface motion, a dimensionless strain transmissibility factor Iε, relating pile and soil peak normal strains, and a pile-to-pile interaction factor α measuring group effects. It is shown that a pile foundation may significantly reduce the vertical seismic excitation transmitted to the base of a structure.     

利用高钙粉煤灰做软粘土固化剂

通过室内试验和微观分析，从材性的角度说明用高钙为煤灰做软粘土的固化剂是一种经济可行的办法，为软土地基的加固提供了一条新途径．     

Universal Intelligence: A Definition of Machine Intelligence

A fundamental problem in artificial intelligence is that nobody really knows what intelligence is. The problem is especially acute when we need to consider artificial systems which are significantly different to humans. In this paper we approach this problem in the following way: we take a number of well known informal definitions of human intelligence that have been given by experts, and extract their essential features. These are then mathematically formalised to produce a general measure of intelligence for arbitrary machines. We believe that this equation formally captures the concept of machine intelligence in the broadest reasonable sense. We then show how this formal definition is related to the theory of universal optimal learning agents. Finally, we survey the many other tests and definitions of intelligence that have been proposed for machines.     

Settlement Ratio of Pile Groups in Sandy Soils from Field Load Tests

This note studies settlement ratio, Rs, of pile groups in sandy soils, defined as the ratio of the settlement of a pile group to that of a single pile at the same average load per pile. 31 cases of field pile-group load tests and the corresponding field single-pile load tests were collected for this study. More than one-half of the cases consist of 3-diameter spaced, 9-pile groups. Based on the field test data, statistical analyses of Rs at different load levels were conducted for pile groups with cap-ground contact (PGCs) and pile groups with freestanding caps (PGFs), respectively. The mean of Rs decreases with the load level for both PGCs and PGFs, whereas the coefficient of variation of Rs increases with the load level. The influence of cap-ground contact on Rs does not appear to be significant based on a comparison of the mean Rs values of these PGCs and PGFs. In addition, a comparative study on Rs and group resistance ratio Rr, which is defined as the ratio of the average resistance of a pile in a group to that of a single pile at the same settlement, was conducted to clarify possible misunderstanding between Rs and pile group efficiency factor η for driven pile groups in sandy soils. The value of Rs compares settlement at the working load and is often larger than unity. The value of η compares failure loads, which occur at different settlements for pile groups and their respective single piles. η is usually larger than unity due to soil densification and additional contributions from the cap-ground contact for PGCs.     

Evaluation of Building Stiffness for Building Response Analysis to Excavation-Induced Ground Movements

A major element in the design and construction of tunnels and braced excavations in urban areas is the control of ground movements and protection of adjacent or overlying structures, which are often constructed with masonry and set on shallow foundations. Initial evaluation of potential building damage is obtained by assuming that building distortion is compliant with the imposed ground movements. Further investigations take into consideration the reduction in building distortion that occurs as a result of building stiffness. Presented in this paper are the results of numerical analyses for evaluating the equivalent bending and shear stiffness of masonry structures taking into account the anisotropy of the masonry units and the percentage of window openings. The distinct element code, UDEC, has been used to model each masonry block and the mortar between blocks for masonry walls in plane stress conditions. Parametric studies, conducted for a range of window opening percentage and brick/mortar joint stiffness, show that the equivalent shear stiffness for buildings with windows are low, typically in the range of 1/10–1/20 of the equivalent bending stiffness. Thus, for most masonry buildings, the shear deformation is dominant for a building subjected to excavation-induced ground movements. Equivalent bending and shear stiffness evaluated by the numerical analyses is compared with field data and analytical calculations, which may be available only for the case of no window openings.     

基于滑移线场理论斜坡条基极限承载力解析解

在工程建设领域,经常需要把基础设置在斜坡地基上,但在现行成果中,对斜坡地基极限承载力的确定并没有给出具体计算方法。为合理确定斜坡地基极限承载力,从而为斜坡地基上的基础设计提供理论依据,并有效降低基础工程的建设成本,本文基于滑移线场理论,建立了斜坡地基的滑移破坏模型,进而根据斜坡地基坡前、坡后土体的塑性边界条件,推导了无重土斜坡地基极限承载力解析公式。同时,提出了采用有限差分方法获取斜坡地基滑移线场及应力分布场的方法。实例计算表明,滑移线解小于极限平衡解及有限元解,主要误差来自于地基土自重的影响,但总体误差在10%以下,本文所述解析法可用于斜坡地基极限承载力的快速估算。     

Simplified Lateral Analysis of Deep Foundation Supported Bridge Bents: Driven Pile Case Studies

A simplified approach for modeling soil and foundation system supported bridge bents is applied to three bridges that represent three pile types and three superstructures. This point-of-fixity approach is applied by modeling the bridge bent substructure as an elastic frame. The models are compared with more refined analyses in FB-MultiPier, with SAP as an independent verification tool, using pile sections with nonlinear soil, pile, and pile cap material properties. The results for simple pile bents show that an equivalent frame model provides similar moment, shear, and displacement values as those obtained from both the SAP and MultiPier nonlinear analyses. Analysis results also indicated that the equivalent frame model parameters are particularly sensitive to the comparable selection of both axial and lateral loads. If lateral loads used to develop the equivalent model are higher than experienced, the axial and lateral deflections and moments will also be higher. For design purposes, this is conservative.     

大直径钢管桩非连续打桩过程中拒锤原因的分析研究

 在大直径超长钢管桩施工过程中,往往会因为接桩或施工调配等原因出现停锤,实际工程中,由于各种原因造成停锤后桩体无法继续顺利打入的情况屡屡发生,因此对这一问题的解决就成为决定打桩工程是否成功的关键。采用有限元动力分析方法对连续打桩过程中砂土中的孔压和有效应力的变化进行研究,对停锤所造成的后续打桩困难的机制进行探讨。同时利用工程实测数据对有限元分析得到的结论进行进一步讨论和验证。动力有限元分析的结果显示,连续打桩会造成桩周土残余孔压的明显累积;如果出现停锤,砂土中超静孔隙水压力消散速度很快,导致桩端1～2倍桩径范围内的有效应力的显著变化,造成桩端阻力的明显提高,而打桩对桩侧摩阻力的影响主要集中在振源附近区域。工程实测数据证实,停锤3个月后,砂土中的土阻力增长明显,尤其是桩端处的砂土层。而处于黏土层中间的薄砂层固结程度明显降低。在进行打桩预测时,对于停锤造成的侧摩阻力的提高应该考虑打桩的影响范围和固结时间,对于桩端阻力的提高应该考虑复打过程的影响。     

深长嵌岩桩承载力计算方法研究

 基于收集的120根嵌岩桩试验数据,应用于大型公路桥涵及其他重大工程中的深长嵌岩桩(嵌岩深度大于5倍桩径)承载力的计算,沿用设计规范[1]的形式及思路,对计算公式中岩层端阻发挥系数和侧阻发挥系数的取值进行分析研究,确定不同桩端岩石强度下岩层端阻发挥系数和侧阻发挥系数的取值,并引入到承载力计算公式。对西堠门大桥、青岛海湾大桥、荆岳长江公路大桥、坝陵河大桥等大型桥梁工程的试桩极限承载力进行验算,并将计算值和实测值进行比较,结果显示计算值和实测值吻合很好,能满足工程设计要求。     

基于二维弹性变形的碎石桩复合地基固结分析

首先对超静孔压影响下的复合地基二维弹性变形性状进行分析,给出复合地基土体和桩体的体积应变、应力及位移等的解析表达式;然后,基于二维变形分析的结果,给出考虑外部荷载瞬时施加、土体内径竖向组合渗流以及扰动区土体水平向渗透系数3种变化模式的复合地基固结解;最后,对二维变形条件下的复合地基固结性状进行分析。分析结果表明:(1)考虑二维变形特性的复合地基固结解给出的固结度小于同等条件下只考虑一维变形的复合地基固结解答给出的固结度;(2)本文解给出的复合地基桩-土应力比随着地基固结逐渐增大,但和以往一维变形解预测结果不同的是,其值增大到一定程度即停止增长,并不会增大到桩-土压缩模量比之值;(3)跟传统一维变形解不同,本文考虑二维变形的复合地基固结解给出的桩-土应力比在初始时刻并不等于0。