## 1 Introduction
[17] studied the stress changes and deformation patterns of the three-pile and two-anchor support systems for deep foundation pits, as well as the stability of deep foundation pit supports. The results demonstrated that the lateral pressure of the formation gradually increased with the increasing excavation depth of the foundation, and the pre-stress of the anchor rod gradually increased until the excavation ended and tended to stabilize. The maximum horizontal displacement of the pile body was less than the design value, and the maximum horizontal displacement was not at the top of the pile. The axial force of prestressed anchor rods varied with variations in layer pressure and surrounding loads; the pulling force of the lower anchor had a certain impact on the axial force of the upper anchor. [PERSON] and [PERSON] et al. [18; 19] studied the resistance of diaphragm wall-to-wall deflection, the maximum wall deflection rate, the stress development of diaphragm walls, support axial force, etc. Based on the measured data, a general apparent earth pressure envelope of earth pressure was proposed, as was an optimization scheme of diaphragm wall construction and design. [PERSON] et al. [20] proved that changes in surface settlement, the axial force of anchor cables, and the horizontal displacement of piles during the spring thawing process can provide a certain reference for the engineering of deep foundation pits in high-altitude and cold regions. [PERSON] et al. [21] believes that changes in the water level have a significant impact on the stability of the foundation pit, and has analyzed and optimized the grouting reinforcement parameters. If piles are connected to form a group of piles, the position of the connecting beam and the axial force generated by the load also affect the synergistic effect between multiple piles. The transfer of load can cause plastic damage to the beam, which requires consideration of the beam's position and construction excavation sequence to reduce the internal force of the beam structure and ensure the effectiveness of the support structure [22; 23; 24]. When the supporting structure is complex, using numerical simulation methods to study foundation pit excavation is easier to achieve than using on-site experimental methods [25; 26; 27; 28; 29]. The research conducted by the aforementioned scholars has significance for the design and construction of deep and large foundation pit-support structures, but complex on-siteconditions remain a challenge for foundation pit design. Owing to the large foundation pit area along a subway project in Shenzhen, separate excavation is required in order to reduce its impact on the subway tunnel, and the row of piles cannot be made into the form of opposite bracing. This article proposes a new type of internal support row pile support structure, namely, the \"T\" type composite pile support system, introduces its basic design concept, and uses the finite element numerical simulation method to simulate the support effect of this new type of support structure, obtaining its deformation law. This design scheme can effectively solve the problem of unconditional support beams for foundation pits, and has good stability. This provides a new design approach for similar subway tunnel projects in the region.