为了解决软土城市开展国内首条类矩形盾构隧道工程勘察遇见的技术难题，从勘察执行的技术标准及等级的确定、勘察的重难点、勘察方案、高流变性软土工程地质特征、场地水文地质条件、工程措施建议等方面进行分析。主要得出以下结论： 1）按现行《城市轨道交通岩土工程勘察规范》3.0.8条文及说明、7.3.5条文分别确定软土地区场地复杂程度等级、类矩形盾构隧道工程勘探孔深度，结果往往会偏于保守、安全，势必会造成勘察工作量浪费问题； 2）在第四纪松散海相沉积软土地区建设类矩形盾构隧道，按中等复杂场地控制勘探孔间距，以分别进入隧道底以下不小于2H（一般性孔，H为隧道高）、3H（控制性孔）控制勘探孔孔深是经济合理且满足工程需求的； 3）本工程勘察方案对今后类矩形盾构隧道工程勘察及相关勘察规范标准修编具有一定的参考价值。

In order to solve the technical difficulties in the development of the first quasirectangular shield tunnel in urban soft soil in China, the determination of technical standards and grades, key and difficult points of investigation, investigation program, geological characteristics of high rheological and soft soil, hydrogeological conditions of construction site and suggestions on construction technology are analyzed. Some conclusions are drawn as follows: 1) The complexity grade of construction site in soft soil and the depth of investigation drilledhole of quasirectangular shield tunnel of relevant standards and criteria are conservative, which will definitely lead to work waste. 2) The investigation drilled holes with depths of 2H to 3H, where H is tunnel height, under tunnel bottom are rational and economical when quasirectangular shield tunnel is located in Quaternary marine sedimentary soft soil area. The investigation program abovementioned can provide reference for the future revision of engineering investigation of quasirectangular shield tunnel and relevant standards.