全吸力范围内渗透系数快速测定方法研究

非饱和土渗透系数函数跨越多个数量级,传统的测量方法动辄耗时数月,且难以实现全吸力范围内渗透系数的测量。为了实现全吸力范围内渗透系数的快速测量,将湿润锋前进法与瞬时剖面法相结合（简称联合测定方法）,利用自行研制的土柱入渗装置,开展了不同干密度条件下青海粉质黏土全吸力范围内渗透系数测量试验。试验结果表明：在联合测定方法中,湿润锋前进法适用于高吸力段（基质吸力ψ > 25 kPa）渗透系数的测量,瞬时剖面法则适用于低吸力段（基质吸力ψ ≤25 kPa）渗透系数的测量,且两种方法在吸力重叠范围内渗透系数测量结果基本一致。联合测定方法可将全吸力范围内渗透系数的测量时长压缩至一周左右,且精度良好。此外,还对两种试验方法的误差来源进行了分析与讨论。研究结果表明：联合测定方法能够实现全吸力范围内渗透系数的快速测量,有望使得非饱和土渗透系数的测量成为土力学的常规试验。     

干湿过程中花岗岩残积土抗拉强度变化研究

利用自制的土体直拉强度测试仪,研究了重塑花岗岩残积土在不同含水率下、增湿过程和干燥过程中抗拉强度的变化规律,并从胶结力和湿吸力的角度讨论了抗拉强度变化规律的微观机制。结果表明：不同含水率条件下抗拉强度随含水率增加呈现先增后减,峰值两侧呈较好的指数规律;增湿过程中抗拉强度随含水率增加呈先增后减趋势,峰值两侧为一次函数规律;干燥过程中抗拉强度随含水率降低出现指数增加阶段、平稳阶段和小幅降低阶段3个阶段,其抗拉强度峰值为不同含水率条件下抗拉强度的4倍。花岗岩残积土在不同含水率和增湿过程中的抗拉强度的变化主要受湿吸力控制,而干燥过程中抗拉强度变化的同时受湿吸力和胶结力的控制,且胶结力对抗拉强度的贡献超过70%。土体的干燥开裂过程对应干燥过程中抗拉强度变化的几个阶段,干燥时湿吸力是土体内部拉应力的来源,这说明湿吸力既是抗拉强度的贡献者,同时也是抗拉强度的破坏者。该研究结果从另一种角度解释了土体抗拉强度的形成来源及其变化的主控因素。     

寒区高吸力非饱和土的破坏准则研究

针对北方寒旱区路基边坡时常因拉剪强度不足而发生浅层滑坡的现象,通过常规三轴试验探究了冻融和高吸力对非饱和土的强度特性影响。结果表明：随着冻融次数的增加,非饱和土的土-水特征曲线逐渐下移,抗拉强度与抗剪强度逐渐减小;随着基质吸力的增加,抗剪强度逐渐增大,抗拉强度逐渐降低。鉴于传统的抗拉抗剪联合公式不能很好地反映经冻融作用之后高吸力非饱和土抗拉区破坏包线的实际情况,通过引入“界值”概念,提出一种新的抗拉区绘制破坏包线的方法对传统公式进行修正,修正后的公式具有很好的适用性,可以为寒旱区非饱和土边坡稳定性计算提供可靠的理论依据。     

An integrated approach for validating unsaturated soil parameters in seepage analyses

Soil–water characteristic curves (SWCCs) and soil permeability functions (SPFs) for a silty sand were validated based on soil suction and soil water content measurements in calibration box and constant-head seepage tests. Transient seepage analyses using finite element method (FEM) were performed to examine the accuracy of the derived SWCCs and SPFs, with a special focus on the wetting front propagation. Results show that the proposed new integrated system consisting of experimental and analytical techniques works well, in the sense that the soil moisture responses at specific depths of soil mimic those measured in constant-head seepage tests.     

海上风电塔架基础的新型吸力锚研发

海上风电作为一种清洁能源,其开发利用越来越受到世界各沿海国家的重视.吸力锚基础是海洋工程中的一种新型基础型式,广泛应用于海洋平台、海洋浮动式结构等.近年来,也被作为海上风电工程塔架的基础,此海上风电塔架的基础部分是整个工程结构的重要组成部分,它涉及到整个风电结构的安全性,是工程可靠运行的前提.在深入研究已有塔架的基础上...     

深海吸力锚水平极限承载力研究

深海吸力锚基础的极限承载能力是海洋工程锚固系统的一个关键问题。基于Coulomb摩擦接触对原理,给出一种模拟吸力锚承载能力的有限元模型。在该数值模型基础上,利用通用有限元分析软件ABAQUS,研究系泊点位置、吸力锚长径比对极限承载力的影响,并给出深海吸力锚失稳模式。结果表明,系泊点位置极大地影响着吸力锚的极限承载力与稳定性,系泊点位置的变化会导致吸力锚出现前倾转动、平移滑动和后仰转动失稳模式,同时吸力锚失稳模式受长径比的影响。为工程实际和理论分析提供了技术支持和理论指导。     

An evaluation of the osmotic method of controlling suction∗

Experimental techniques of testing the mechanical properties of unsaturated soils are complex and difficult to conduct. As a consequence, complete sets of parameters that characterise the behaviour of unsaturated soils remain scarce and necessary. In this context, it has been found useful to gather the information obtained after some years of practice of the osmotic technique of controlling suction. As compared to the more documented axis-translation technique, the osmotic technique has its own advantages and drawbacks that are discussed in this paper, together with some potential future developments.

The osmotic method has been developed by soil scientists in the 1960s and adapted to geotechnical testing in the early 1970s. This paper presents the osmotic technique and comments on its advantages (including suction condition close to reality and higher suctions easily attained) and drawbacks (including some concern with the membrane resistance and some membrane effects in the suction/concentration calibration). Various applications to geotechnical testing are presented such as the determination of the water retention curve, oedometer and triaxial testing procedures and the determination of the permeability of unsaturated soils. Recent developments, that include the extension of the method up to high suctions (10 MPa) are also described, together with some recent and novel applications such as data from high controlled suction oedometer compression test and the determination of the oil/water retention properties of oil reservoir chalks.     

天津高新区117大厦超长桩钻孔施工技术

天津高新区中央商务区117大厦桩基设计为超长桩,质量要求高,施工难度大。施工过程中通过对孔口护筒埋设、泥浆质量、孔内液面高度、孔位偏差、钻孔垂直度和孔底沉渣的有效控制,不仅钻孔质量达到设计要求,而且钻孔效率高,成本较低。介绍了117大厦超长钻孔灌注桩工程的施工情况,其经验可供类似工程借鉴。     

非饱和黄土基质吸力的变化

天然状态下存在大量的非饱和黄土。因此,非饱和黄土中存在的基质吸力在很大程度上可以控制抗剪强度。本次研究的非饱和黄土土样采自中国兰州市,用以展开室内试验,探讨黄土中基质吸力的变化规律以及其脱离含水量的影响因素。结果显示:结构性、矿物成分以及可溶盐含量是控制非饱和黄土基质吸力变化的最重要的三个影响因素。其中,残余含水量和土样密度有相反的相互关系。土样中存在大量的蒙脱石和伊利石的互层(I/S),以及土样中存在的可溶盐也在某种程度上影响着基质吸力的变化。     

A unified bounding surface plasticity model for unsaturated soils

A unified constitutive model for unsaturated soils is presented in a critical state framework using the concepts of effective stress and bounding surface plasticity theory. Consideration is given to the effects of unsaturation and particle crushing in the definition of the critical state. A simple isotropic elastic rule is adopted. A loading surface and a bounding surface of the same shape are defined using simple and versatile functions. The bounding surface and elastic rules lead to the existence of a limiting isotropic compression line, towards which the stress trajectories of all isotropic compression load paths approach. A non‐associated flow rule of the same general form is assumed for all soil types. Isotropic hardening/softening occurs due to changes in plastic volumetric strains as well as suction for some unsaturated soils, enabling the phenomenon of volumetric collapse upon wetting to be accounted for. The model is used to simulate the stress–strain behaviour observed in unsaturated speswhite kaolin subjected to three triaxial test load paths. The fit between simulation and experiment is improved compared to that of other constitutive models developed using conventional Cam‐Clay‐based plasticity theory and calibrated using the same set of data. Also, the model is used to simulate to a high degree of accuracy the stress–strain behaviour observed in unsaturated Kurnell sand subjected to two triaxial test load paths and the oedometric compression load path. For oedometric compression theoretical simulations indicate that the suction was not sufficiently large to cause samples to separate from the confining ring. Copyright © 2005 John Wiley & Sons, Ltd.