Numerical Simulation Of Differential Settlement Among Diaphragm Wall And Upright Column In Top-Down Construction Method

Compared with the traditional down-top method, top-down method has the basement floors and upright columns belong to permanent structure which can be used as supporting structures during the pit excavation. To prevent slabs from cracking caused by uneven settlement of upright columns and diaphragm wall, uneven settlement must be given enough attention.By treating the connection of vertical structures and soil as sliding contact, numerical simulation of the whole construction processes for the engineering case was conducted, and a comparative analysis was made to estimate the impact weather to set sliding contact or not.By taking the pit engineering of Changfeng mall as a design reference, feasibility of top-down method for the pit engineering of Majiaying in Kunming, was conducted. According to the geological survey report, the parameters of modified Cambridge model were calculated. The design parameters including length of upright column and diaphragm wall, spacing of upright columns, and the soil properties including resilient modulus, distribution range of the reinforced passive soil, distribution of soft soil were considered to analyze the rebound of diaphragm wall, average settlement of upright columns and differential settlement between the side upright column and diaphragm wall. The main contributions of this thesis are described in the following:(1) As for the pit engineering of Majiaying in Kunming, considering the upper structures simultaneously constructed with the basement structures, the plan that three layers of upper structure is cast when one underground structure is cast. The different settlement gets19.8mm, which is lose to the specification limit of20mm.(2) When digging the soil above the bottom plates, differential settlement and the uplift of diaphragm wall attain their maximum. By the load of single floor, the settlement of diaphragm wall is less than the side upright column, and the settlement of the side upright column is less than the average settlement of the whole upright columns. For soil unloading can affect the uplift of the vertical support structures, the uplift of the side upright column is less than the diaphragm wall, and the uplift of the diaphragm wall is less than the average settlement of the whole upright columns.(3) Economically, the best depth of the diaphragm wall is about42m, and the ratio of the depth of excavation and the depth of penetration of pillar pile is1:2.2; when the spacing of upright columns is8.5m, the differential settlement can be ensured and the soil can be digged out smoothly.(4) Consolidating the passive soil inside of the foundation pit can significantly inhibit the bottom soil resilience, the ground settlement outside the pit and the lateral displacement of the wall; However this method can’t always reduce the differential settlement, which can always raise the position of the top of the diaphragm wall.