Numerical Simulation of Seepage and Deformation in Excavation of a Deep Foundation Pit under Water-Rich Fractured Intrusive Rock

Abstract

Water is one of the major risk sources in the excavation of deep-large foundation pits in a water-rich area. The presence of intrusive broken diorite porphyrite in the stratum aggravates the risk level of deep foundation pits. Based on a geological survey report and design documents of parameter information, MIDAS/GTS software was used to perform the numerical simulation of an engineering example of a deep foundation pit project of ultradeep and water-rich intrusion into the broken rock station of subway line 4 in a city. The simulation results show the characteristics of seepage path evolution, seepage aggregation areas and points, and the effect of seepage on the deformation of a deep foundation pit during the whole construction of this deep foundation pit. The results show that with the precipitation-excavation of the deep foundation pit, the pore water pressure at the bottom of the foundation pit follows a distribution of three “concave” shapes. High-permeability pressure zones are found around the foundation pit, intruding broken diorite porphyrite zones, and middle coarse sand zones. With further excavation of the foundation pit, the seepage pressure in the middle part of the foundation pit gradually decreases, and the two “concave” distributions in the middle gradually merge together. After excavation to the bottom of the pit, the pore water pressure at the bottom is distributed in two asymmetrical “concave” shapes, and the maximum peak of pore water pressure is found at the intrusion of fractured porphyrites prone to water inrush. The four corners of the foundation pit are prone to form seepage accumulation zones; therefore, suffosion and piping zones are formed. The surface settlement caused by excavation is found to be the largest along the longitudinal axis of the deep foundation pit, whereas the largest deformation is found near the foundation pit side in the horizontal axis direction of the foundation pit. With the excavation of the deep foundation pit, the diaphragm wall converges to the foundation pit with the maximum deformation reaching about 25 mm. After the first precipitation-excavation of the deep foundation pit to the silty clay and the bottom of the pit with the largest uplift, with further precipitation-excavation of the deep foundation pit, the uplift at the bottom of the deep foundation pit changes only slightly.

Comparison and Economic Envelope Structure Schemes for Deep Foundation Pit of Subway Stations Based on Fuzzy Logic

“…He used MIDAS/GTS software to carry out numerical simulation on the example of subway deep foundation pit engineering. The results show that the deeper the water in the deep foundation pit, the greater the danger [ 5 ]. Bian et al found that in the excavation of deep foundation pits in subway stations, if the protective measures are not perfect, the safety of subway tunnels will be seriously threatened.…”

Foundation Settlement Response of Existing High-Speed Railway Bridge Induced by Construction of Undercrossing Roads

“…According to the actual project, Yu [14] used Abaqus finite element software to simulate the construction steps for excavation of the foundation pits supported by large diameter ring beams and obtained the influence law of the foundation pit support system on the surrounding environment. Yuan [15] used MIDAS/GTS software to conduct a numerical simulation of a deep and large foundation excavation in a water-rich area and analyzed the distribution law of seepage in a deep foundation pit and the surface settlement law of the soil around a foundation pit during construction.…”

Causation Identification and Control Measures of Deformation by Integrated Dewatering-Excavation Process Simulation of a T-Shaped Deep Foundation Pit

“…The excavation process had been studied by simulation method extensively. However, most of the case studies only focused on one aspect, accounting for either the rock and soil mechanical deformation of the foundation pit excavation [14][15][16] or ground surface settlement caused by the drawdown of groundwater level [17][18][19][20]. Few cases consider both types of deformation.…”