Janbu tangent modulus method for settlement and determination of parameters
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摘要: 港珠澳大桥沉管隧道埋置深度较深,地基回弹再压缩沉降及其变化的准确评估对结构受力安全尤为重要。隧道初步设计与施工图设计阶段,开展了大量的原位孔压静力触探（CPTu）和室内固结试验。如何利用这些原位和室内试验数据准确评估隧道的回弹再压缩沉降及其变化规律,成为一个迫切需要解决的问题。在综合比较各类沉降计算方法基础上,采用了改进的Janbu切线模量法进行沉管隧道的沉降计算,推导了不同土层、不同应力状态下的土体竖向应变计算公式。并依据室内固结试验和原位CPTu试验对该方法的计算参数（模量数m、回弹再压缩模量数mr、应力指数j和回弹再压缩应力指数jr等）进行了分析和探讨。最后通过算例说明了方法的计算过程。Janbu切线模量法具有公式形式简单、反映围压影响及卸载再加载特性等优点。但由原位试验获取计算参数方面,还有待深入研究。Abstract: Due to the deep embedment depth of the immersed tunnel of Hong Kong-Zhuhai-Macao Bridge, accurate assessment of rebound re-compression settlement and its variation is particularly important to the safety of tunnel structure. During its preliminary design and detail design, a large number of in-situ tests (CPTu) and high-quality oedometer tests are carried out. How to use these test data and accurately assess the re-compression settlement and its variation of the tunnel becomes an urgent problem to be solved. Based on the comprehensive comparison of various types of settlement calculation methods, the improved Janbu tangent modulus method is adopted to calculate the settlement of the immersed tunnel. The formulae for vertical strains of different soil layers under different stress states are derived. Besides, the parameters (modulus m, re-compression modulus mr, stress exponent jand rebound re-compression stress exponent jr) are analzsed and discussed. The calculation processes are illustrated through examples. The Janbu tangent modulus method has the advantages of simple shape, considering effect of confining pressure and unloading load characteristics. But the parameters obtained by in-situ tests should be future studied.
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