海相沉积软土广泛分布于我国沿海地区，是典型的结构性土，具有灵敏度高、承载能力低等特点。通过自钻式旁压试验调查软土场地的原位力学特性，获得了29.0 m深度范围软土层的原位水平应力、临塑压力、不排水抗剪强度、剪切模量等力学指标。结果表明，软土的旁压试验曲线可分为应力平衡阶段、弹性阶段、塑性阶段和破坏阶段4个阶段；破坏阶段之前软土的卸载会造成有效应力的显著降低，在工程实践中对软土卸载过程的稳定性应予以关注；软土的剪切模量具有明显的非线性特征，采用非线性分析法得到的剪切模量较为合理。通过对试验结果的拟合，建立了原位水平应力和临塑压力随深度变化的经验公式，可为工程中该两类参数的确定提供参考依据。

Marine sediment soft soil is one kind of typical structure soil with high sensitivity and low bearing capacity, widely distributed in the coast area of China. The In-situ mechanical properties of soft soil site are tested in the depth range of 29 meters through self-boring pressuremeter test. The in situ horizontal stress, critical plastic stress, undrained shear strength and shear modulus, etc. are obtaind. The curves of pressuremeter test show four stages of soil, including stress balance stage, elastic stage, plastic stage and failure stage. Unloading reduces the effective stress of soft soil significantly before the last stage; much attention should be paid to the stability of soft soil during unloading process in engineering practice. Based on the obvious nonlinear characteristic of soft soil’s shear modulus, it is more reasonable to get shear modulus by using nonlinear analysis method. On the basis of the experimental results, using fitting methods to set up empirical formulas of in situ mechanical properties and critical plastic stress varying with depth, so as to provide a reference instruction for the determination of the parameters in engineering.