从土的基本工程性质出发，提出了考虑土的应变软化特性的线性弹塑性模型，并用以解析桩孔扩张条件下桩孔周边土体的应力应变及位移，分析了应变软化状态到塑性流动的残余状态的强度准则的变化特征以及两个塑性区的存在方式，从理论上分析了桩孔扩张的反例──桩孔开挖应力释放条件下的桩孔壁土体状态与存在条件。 Based on the basic engineering properties of soil, a linear elasto-plastic model considering the strain-softening behavior of soil is proposed. It is used to analyze the stress, strain, and displacement of soil around the pile hole in the condition of pile hole expansion. The state of strain softening to plastic flow is analyzed. The variation characteristics of the strength criterion of the residual state and the existence of the two plastic zones theoretically analyzed the counter-example of the expansion of the pile hole--the condition and existence conditions of the soil in the pile hole wall under the condition of stress release from pile hole excavation.