Janbu tangent modulus method for settlement and determination of parameters

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 m_r, stress exponent jand rebound re-compression stress exponent j_r) 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.