旁压试验在黄土地区地基勘察中的应用

在介绍了旁压试验原理及试验方法的基础上,结合西北黄土地区某工程的旁压试验,对黄土地基旁压试验P-V曲线的特点和相关特征指标进行了分析。由旁压曲线推求了土的变形模量、压缩模量、地基承载力等力学和工程特性指标,为评价该工程的地基条件提供了依据。     

旁压试验在广州地铁勘察工程中的应用

通过分析在广州轨道交通某支线地铁勘察中所得到的旁压试验数据,获得了其沿线不同区间内典型控制地层的P-V曲线,并由这些曲线确定相应的总静止土压力、临塑压力、极限压力及其旁压模量等岩土体力学参数,为地铁设计与盾构施工提供了相关参数,对相关工程有借鉴意义.     

旁压试验在某高层建筑场地原位测试中的应用

回顾了旁压试验的发展历程,详细介绍了旁压试验的原理及典型旁压曲线,简述某高层建筑场地的工程地质概况,分析了基床反力系数随着深度及土类的变化规律,为工程设计提供了科学的勘测数据。     

基于Excel-VBA的旁压试验数据自动处理程序开发

旁压试验是原位测试的主要手段之一。旁压试验数据处理一般是绘制试验曲线,以人工绘辅助线或者主观目测的方法确定旁压曲线特征压力及其对应的特征体积。传统方法不能提供曲线的表达式,准确确定旁压曲线的特征压力有一定的困难,确定的岩土体参数存在较大误差。针对这些弊端,本文利用Excel自带的VBA环境编写了旁压试验数据自动处理程序,包括弹性膜约束力及仪器综合变形校正、旁压曲线直线段识别、旁压曲线特征点坐标确定、地层参数计算和试验报告自动生成四个模块。其中,旁压曲线特征点坐标确定模块中,采用Bézier曲线方程,准确计算出旁压曲线特征点坐标,实现了精确确定三个特征压力及两个特征体积的功能,可准确地计算出岩土体的变形参数以及承载力等力学指标。     

依据旁压试验结果估算地基土载荷试验沉降量

本文提出一种依据旁压试验结果估算地基土载荷试验沉降量的方法。由于本方法考虑了土体剪切变形引起的沉降和土的应力-应变的非线性反应,在某些土类的范围内,对整个载荷试验过程的P-S曲线的估算,与实际试验结果符合较好。通过这项研究为直接利用旁压试验结果估算建筑物的沉降打下了基础。     

用旁压试验结果预估单桩性能的新发展

本文介绍了法国道桥试验中心在深基础领域中应用旁压试验所取得的一些新成果,简述了梅那标准旁压仪(以下简称为PM)试验和自钻式旁压仪(以下简称为PAF)试验的快速试验工艺。介绍了用大量的足尺桩的原位静载试验结果来重新修正用旁压试验结果预估轴向荷载作用下桩的承载力的计算方法和安全系数取值。对用旁压试验预估轴向或横向荷载作用下的位移,提出了土阻力发挥曲线的取定方法,并对其作了评价。     

自钻式旁压试验中邻近腔壁土的应力路径分析

 采用剑桥自钻式旁压仪对邻近膨胀腔壁土的应力–应变进行研究。根据自钻式旁压试验的特点和腔室膨胀理论,假设试验过程中土只发生小变形,土为弹性–完全塑性材料。基于以上假设,对试验过程的应力路径进行理论推导,并与试验得到的应力路径对比分析,结果表明：两者在弹性阶段差异较大,塑性阶段较为一致;非线性和线性两种理论分析方法相比,前者推导的应力路径理论曲线与试验确定的应力路径更为接近。此外,根据试验确定的应力路径曲线,可以分析土的应力变化,判定土的应力历史,推导土性参数。     

非饱和土土水特征曲线特性研究

土水特征曲线是岩土工程界的热点问题。土水特征曲线是土的含水率或饱和度随基质吸力变化的一个特征曲线。饱和土是由气态、液态、固态三相比例指标组成。饱和土体土水特征曲线研究基本成熟,非饱和土体土水特征曲线特性研究还有不足。文章利用英国欧美GDS三轴仪测得围压值不变但基质吸力变化下的非饱和土土水特征曲线的试验数据,并绘制土水特征曲线,结果表明,基质吸力小于100 kPa,粘聚力与基质吸力是非线性增长,增长曲线逐渐变缓;基质吸力大于100 kPa,粘聚力与基质吸力呈线性增长。     

围压对土动剪模量和阻尼比影响的简化计算方法

围压对土的初始动剪模量、阻尼比、动剪模量比和阻尼比随剪应变的变化关系（G/Gmax-λ 和h-λ等性质产生明显的影响.通过总结分析已有研究和经验模型,确认围压对初始动剪模量和阻尼比的影响.以M.B.Darendeli的研究为基础,得出了由常规围压状态下土动剪模量和阻尼比与剪应变的关系曲线来分析任意围压状态下其关系曲线的简化计算方法,在不考虑围压引起G/Gmax-λ 和h-λ 曲线形状变化的条件下,直接由剪应变值计算动剪模量和阻尼比.通过试验结果的统计回归分析,提出了砂土和黏性土的主要参数建议值.与已有经验模型和试验结果的分析对比表明,所获得的围压状态下的土性质曲线具有足够的工程精度.将该方法与等效线性化方法结合可方便地进行考虑围压影响的一维场地地震反应分析.上海地区典型深厚场地的地震反应分析表明,由基岩反应谱计算地表反应谱时,在大震作用下宜考虑围压对土性质的影响.     

温控下高压实膨润土持水特性及预测研究

高庙子膨润土是我国核废料深地质处置的首选材料。作为缓冲密封材料,在使用过程中,会受到核素衰变放热的影响而改变土的持水特性、渗透性和力学特性,其工作性能也随之改变。为研究高温下高庙子膨润土的持水特性,文中采用在80℃侧限条件下进行实验研究。实验采用渗析法和水汽平衡法来控制吸力,测得在不同吸力点的含水量,从而得出土水特征曲线。对于特定吸力点的土样进行压汞试验,分析不同吸力点的孔隙特点,并由压汞试验得到PSD曲线来预测其土水特征曲线,并在PSD预测中考虑温度影响。最终将PSD预测曲线与实测曲线对比研究,发现考虑温度的PSD预测比较接近于真实的土水特征曲线。     

Identification of Bonded Clay Parameters in SBPM Tests: A Numerical Study

A bonded elasto-plastic soil model is adopted to simulate self-boring pressuremeter tests. Calibration of the model with results from several natural clays identifies a meaningful parameter range for the simulations. Then a systematic sensitivity analysis of the loading SBPM test curve is carried out with an infinite cylindrical cavity analogue, focusing on the variables and parameters that are specific to the bonded material. This analysis reveals that the effects of mechanical overconsolidation and bonding on the pressuremeter loading curves are very similar. Unloading and strain-holding phases of the test show a greater capability to separate mechanical overconsolidation from bonding. The limited effects of finite pressuremeter length and partial drainage on the simulated curves do not change those conclusions.     

城市生活垃圾抗剪强度参数的测试与分析

对某城市生活垃圾填埋场取得的原状垃圾土样进行室内大尺寸直剪试验，根据试验结果，初步分析了影响垃圾土抗剪强度参数的诸因素，在垃圾填埋场进行现场旁压试验，给出了一种利用旁压曲线推求强度指标的方法。     

旁压试验反演邓肯-张模型参数方法研究

研究了联合室内模拟试验和现场旁压仪试验综合确定邓肯 -张E-B 模型有关参数的方法。内容包括 :①采用邓肯 -张E-B 模型和有限元方法 ,对旁压试验机理进行数值模拟 ;②研制采用阻尼最小二乘法非线性优化理论 ,依据实测旁压曲线 ,进行土体本构模型参数反演的方法和计算机程序 ;③在对模型各参数敏感性分析基础上 ,以室内试验结果为初值 ,对某工程地基覆盖层现场旁压试验实测曲线进行E-B 模型参数的反演分析。为实际工程的计算分析提供了更为可靠依据     

Stiffness decay characteristics and disturbance effect evaluation of structured clay based on in-situ tests

The structure of the sedimentary clay influences its mechanical behavior in non-negligible ways. This paper proposes an effective approach for investigating the in-situ stiffness characteristics from shear modulus and strain decay curves (G–γ curves) based on self-boring pressuremeter and seismic dilatometer tests. To evaluate the excavation disturbance effects on the structured clay, the stiffness parameters from pre-bored pressuremeter tests are compared with the results of self-boring pressuremeter tests. The result indicates that the complete in-situ G–γ curves can be acquired by integrating the strain-dependent tangent shear modulus G_t from self-boring pressuremeter tests and the small-strain modulus G₀ from seismic dilatometer tests. Simultaneous observations of the G–γ curves with hyperbolic shapes in semi-logarithmic coordinates at the same strain scale show the similarity of the stiffness decay mode of the soil at different depths. The increase in the measured values of G_t and G₀ with depth can be attributed to the improved consolidation pressures and cemented strength in the structured clay. Additionally, the G/G₀–γ curves measured by the in-situ tests generally agree well with the results predicted by the Stokoe model. The excavation disturbance weakens the stiffness of the structured clay, as evidenced by G_t from the pre-bored pressuremeter data being significantly smaller than that from self-boring pressuremeter tests at the same depth. Based on quantitative analysis, the disturbance degree computed from the measured results has a low sensitivity to the soil depth and a strong negative correlation with the strain level of the soil. This study provides an effective method for predicting the stiffness parameters of structured soil based on in-situ tests.     

利用旁压试验分析设计横向受荷桩

本文从理论上导出如何通过旁压曲线确定桩的P-y曲线。对地基土的反力函数提出双曲线模型P(z,y)=y/[a(z)y+b(z)]的假设,并考虑其系数a(z),b(z)随深度z成线性变化。以这一模型拟合桩的P-y曲线族,求出系数a(z),b(z),得到地基土反力P(z,y)的数学表达式。对横向受荷桩的求解问题则采用弹性地基梁的微分方程,用有限差分法,并考虑边界条件进行求解,编制了单桩受横向静荷载作用下的分析求解程序,供饱和粘性土中的单桩计算应用,并通过一个实例进行计算对比,表明理论结果与实测结果相当吻合。     

Characterization of a Cohesive Soil Bed using a Cone Pressuremeter

A new cone pressuremeter has been developed at the University of Engineering and Technology, Lahore-Pakistan. The new device is called the Akbar Pressuremeter (APMT). This paper is based on the APMT testing of a cohesive soil deposit comprised of low plastic lean clay (CL) to sandy silty clay (CL-ML). The APMT testing, using a full-displacement technique, standard penetration tests and undisturbed samples, was carried out at two locations. The soil strength and type were determined using the undisturbed samples. The applied pressure-cavity strain curves of the APMT tests performed at different levels were analysed to determine soil strength and stiffness. The undrained shear strength of the undisturbed samples was determined in the laboratory by unconfined compression tests. This paper provides a comparison of the parameters interpreted from the pressuremeter and those determined from other field and laboratory methods.     

冻土原位旁压蠕变试验粘弹性模型分析

研究高温高含冰量冻土的蠕变特性,采用Menard旁压仪在青藏高原多年冻土区开展了大量的旁压蠕变试验,利用Merchant粘弹性模型对蠕变曲线进行回归分析并得到模型参数。结果表明,温度对高温冻土力学性质的影响要大于含水量。随着压力的增加,每级压力下冻土的瞬时应变在总应变中所占的比例逐渐减小。回归分析发现,瞬时剪切模量与负温的绝对值呈线性关系,而延迟剪切模量和粘滞系数与负温的绝对值之间为幂函数关系;当冻土的含水量达到46%时,各参数均出现峰值,而后缓慢减小,此结果与低温冻土有所差别。     

High quality and cost effective drilling system for prebored pressuremeter testing

A prebored pressuremeter test (PMT) requires a predrilled vertical smooth surface borehole of a constant diameter. Two methods for the preparation of predrilled boreholes are included in ASTM D4719. The first method is drilling a borehole using a rotary rig. While this method provides a constant diameter and a vertical borehole, it is costly and time consuming. The second method is the drilling of a borehole by a hand auger (Iwan type). While this is a low cost, rapid method, it may not provide a vertical borehole of constant diameter in a variety of soils.An innovative mechanical drilling system (MDS) has been developed for the preparation of vertical smooth surface borehole of constant diameter for the pressuremeter testing. The PMT was conducted in boreholes drilled by MDS, rotary rig (RR) and hand auger (HA) at a site that comprised clayey silt (CL-ML) and sandy silt (ML) deposits. The PMT curves thus obtained were compared in terms of quality, cost and time. The comparison indicates that good quality and cost effective PMT curves can be obtained by using MDS in broader strain range (up to 40%) for the stiffness and limit pressure determination.     

预钻式旁压试验结果分析

介绍了预钻式旁压试验的原理及试验注意事项,通过对旁压试验实测数据分析得到旁压模量、旁压剪切模量、地基土的力学参数等,为评价所在土层的地基条件提供依据。