Key Consrtuction Technology Of Two-Stage On The Open-Cut Subway Station In Hefei Expansive Soil Layer

The open-cut subway station in Hefei crosses expansive soil layer with the engineering properties of water swelling and dehydration shrinkage, which often cause adverse effect on the excavation and construction of the main structure in deep foundation pit. To guarantee the stability and safety of deep foundation pit in its excavation stage and its main structures construction stage, many safety measures were used in its design and construction stage, which always lead to tedious construction process and slow down the construction progress. Based on the Wanghucheng open-cut station of Heifei subway line one, and combined with two-stage construction technology of open-cut subway station in expansive soil layer, research had been done mainly in following aspects:(1) According to Rankine soil pressure and equivalent method, the calculated method of soil pressure in the excavation stage of deep foundation pit was obtained. Based on the analysis of filed measurement data, the revised calculated method of deep foun dation pit in Hefei expansive soil was put forward.(2) Analyzed on the whole stability of foundation pit in excavation stage, the analysis feasibility of horizontal support’s erection time was put forward. And combined with numerical simulation technology, the author analyzed on the erection time of horizontal support in different excavation step, also put forward the erection time of horizontal support in the excavation stage of deep foundation pit.(3) Compared with the advantages and disadvantages of constructing support-exchange method on main structures, no-support-exchange construction method was put forward. Also its application condition was obtained by calculating and analyzing the envelop stiffness and construction time of tunnel floor. Based on the research on different no-support-exchange construction methods and filed experiments, the minimum construction method was obtained.(4) Combined with results obtained in the two-stage construction of open-cut subway station which crosses Hefei expansive soil layer, two-stage monitoring and measurement scheme are advanced, which can provide reference for filed construction.