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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.

This work reports that the use of a high-performance and low-cost micron carrier material with abundant load-bearing pores and stable conductive networks for silicon/carbon (Si/C) nanoparticles (NPs) could be an effective strategy to increase the practical use of Si/C anode materials for lithium-ion batteries (LIBs). It proposed for the first time mildly expanded graphite microspheres (MEGMs) as a micron carrier for yolk–shell structured Si/C (Si@void@C) nanospheres to construct a Si@void@C-MEGMs nano/microcomposite. Si@void@C nanospheres disperse on the nanosheets and pores of MEGMs, which is like bunches of grapes hanging between the branches and leaves of the grape. Accordingly, compared with Si@void@C nanospheres, this nano/microcomposite electrode exhibits a reversible specific capacity of 851.2 mAh/g after the rate test and the following 135 cycles at 100 mA/g. The microstructure and composition analysis indicates that the great electrochemical properties could be because the abundant pores and excellent conductivity of the MEGM carrier effectively improve the structure and cycling stability of Si@void@C nanospheres. This work has not only provided a high-performance Si@void@C-MEGMs nano/microcomposite but also verified that MEGMs are an effective and low-cost carrier for the Si@void@C NPs, which will benefit the commercial use of Si/C anode materials for LIBs.

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