Abstract: To guarantee the rock stability between the underground diaphragm wall and the karst cave during the concrete pouring stage in the karst area, the form of force on the castinplace concrete underground diaphragm wall is analyzed. In addition, the lateral pressure calculation formula of castinplace concrete is established based on Jassen theory. Then, the simple analysis of the lateral pressure influencing factors is presented. Moreover, on the basis of the nonlinear lateral pressure calculation equation for castinplace concrete, the local linearization of the sidewall load of the underground diaphragm wall is carried out and the determination method of the safety factor for the local linear calculation is proposed. A method for calculating the maximum bending moment of the castinplace underground diaphragm wall and the minimum safe thickness of the karst cave sidewall bending resistance is obtained. Accordingly, the stability analysis of the underground diaphragm wall and karst cave sidewall is carried out. Finally, the analysis of the influencing factors is carried out through typical engineering data, revealing the variation of the minimum safe thickness of the karst sidewall with the vertical span of the cavern form, rock tensile strength, burial depth, concrete slump, and casting time. The basic principles of karst stability analysis of the lateral part of the karst sidewall of the underground diaphragm wall are determined. The results of the study show that the minimum safe thickness of the karst sidewall increases with increasing burial depth, span, and concrete slump, and decreases with increasing rock tensile strength and casting time. Based on the survey and construction data, the stability of the rock formation should be analyzed during the engineering design and stability evaluation, so that the evaluation results can be more relevant to the actual situation.

Key words: foundation pit engineering, local linearization; safety thickness, karst sidewall, tensile strength