应力路径对重塑黏土有效抗剪强度参数的影响

为探讨应力路径对黏土有效抗剪强度参数的影响,即临界状态线的惟一性问题,在确保试样的初始状态、应力历史、排水条件、加荷速率、试验仪器、破坏取值标准均一致的前提下,进行了常规三轴压缩与等p三轴压缩应力路径下同种重塑黏土的固结排水剪切试验.得到了两种应力路径下的有效抗剪强度参数和临界状态线参数,试验结果证实不同应力路径下重塑黏土有效抗剪强度参数有较大差别,临界状态线不惟一.定性分析表明:相对于常规三轴压缩路径,重塑黏土在等p三轴压缩路径下具有较低、有效内摩擦角的原因是剪切过程中围压的降低造成侧向卸荷引起的土体抗剪能力下降;产生凝聚力的原因是在排水剪切过程中存在超固结效应.

内撑式支护控制变形设计的关键问题

本文提供软土层中建筑基坑的带内支撑的围护桩按控制变形设计的简明计算方法 ,其成果与工程实测资料基本相符。对受水平力时的“长桩”和“短桩”的桩身变形提供不同的算法。另对确定坑底软土的“m”值的预设位移和超固结影响也提出了新见解。

Secondary settlement estimation in surcharge preload subject to time effect of secondary consolidation coefficient

In order to eliminate the settlement underestimation in surcharge preload engineering, a study based on Bjerrum's creep diagram and the tangent slope definition of secondary consolidation coefficient was carried out to analyze the time effect of secondary consolidation coefficient of over consolidated soil, and a time–growth model for it was formulated. As Bjerrum's creep diagram is an idealized model, oedometer tests were performed to improve the above time–growth model of secondary consolidation coefficient for the purpose of achieving a better agreement with the actual ground situations. It is found that secondary consolidation coefficient of over consolidated soil not only decreases with the ratio of historical maximum to current effective stress of soil(OCR), but also increases with the development time of secondary consolidation. No matter how large OCR is, the long-term time effect of secondary consolidation coefficient of over consolidated soil is all significant. Based on the above results, a model for settlement estimation was formulated and a case study to estimate it indicates that the settlement estimated by our method is 2–5 times larger than that estimated by the previous method. Moreover, the larger the OCR is as well as the longer the service life is, the larger the difference between our method and the previous method is. Thus, the post-construction secondary settlement in surcharge preload engineering will be underestimated when neglecting the time effect of secondary consolidation coefficient in over consolidated state.

室内地下空间基础补偿原理初探

讨论将补偿基础用于室内建造地下空间的原理与方法,提出考虑活荷载影响的室内地下空间补偿原理及相应的活荷载地基应力影响系数,根据该原理,增建地下室新增荷载将被基坑开挖移去的土重和以地坪活荷载影响为主的先期固结压力的一部分所补偿。初步研究和应用实例显示,将补偿法应用于既有建筑室内地下空间开发是可行的,适当控制开挖深度和新增荷载,室内基坑开挖和地下空间建造引起的地基扰动和变形可以被控制在较小范围内,从而降低对既有建筑造成损害的风险。