# A Novel Strutless Double-Row Structure for Deep Excavation: Working Mechanism Study and Analysis
## 1 Introduction  
The stability of deep foundation pits, which are intricate engineering systems, is subject to the influence of various factors. These factors include soil shear strength [1], stress history [2], stress level [3, 4], geotechnical properties [5], excavation depth [6], as well as the characteristics of the surrounding environment [7]. In recent years, the rapid pace of urbanization in China has led to a growing scarcity of urban land. As a result, a rising number of excavations are encroaching upon adjacent buildings [8]. Excavation projects are advancing towards deeper excavations, stricter control of deformation, a variety of support methods, and the use of advanced digital technologies in construction processes [9]. The single-row pile wall (SPW), though commonly used, faces limitations with increasing excavation depths. SPWs often struggle to meet new support requirements, particularly in soft soils where foundation pit failures can cause significant destruction and pose risks to human lives [10]. This challenge highlights the need for more effective and adaptable support systems. Retaining structures such as diaphragm walls with internal struts have been widely adopted in excavation engineering, especially in soft soils [11, 12]. However, these systemscan significantly increase construction difficulty and costs for large excavation geometries due to the extensive installation of bracing. Anchored retaining wall systems, which are unsupported, can secure sufficient working space. Nevertheless, they are unsuitable for soft soil strata and require careful attention when applied at depths of 10 m below the groundwater level in coarse-grained soil [13]. The need to balance support effectiveness with environmental and site management considerations remains a significant challenge. The use of anchor bolts may pose risks of underground disturbance, particularly if they pass through neighboring areas. The double-row pile wall (DRPW) system, comprising front-row piles, rear-row piles, and connecting crossbeams, is gaining popularity in urban construction due to its independence from adjacent underground structures [14]. The system has been implemented in various applications, such as foundation pits [8], side slopes [6], and cofferdams [15]. Research by [PERSON] et al. [16] and [PERSON] et al. [17] has validated the DRPW's effectiveness in earth retention, particularly in clayey soils, through finite element analysis and field investigations. The DRPW system is suitable for medium to dense sandy soils, medium to stiff clayey soils, and for excavations of limited depth. Additionally, studies by [PERSON] et al. [18] investigated the impact of row spacing on DRPW performance, finding that optimal spacing significantly influences pile behavior. They found that the optimal row spacing was three to four times the diameter of the pile. However, their study did not consider the influence of pile tilt on the performance of double-row piles. Recent studies by [PERSON] [19] further explored how flexural stiffness and surcharge loading affect the stability of DRPWs in foundation pits, revealing that surcharge loading can adversely impact stability, with deformations inversely related to the proximity of the surcharge load. Physical scale model tests were performed to analyze the effect of the inclination angle on the pile head displacements and bending moments during excavations and step loadings. Numerical simulations were also conducted to verify the effectiveness of the inclination angle adjustment in optimizing the double-row piles. These findings underline the need for enhanced front-row pile stiffness and more refined design considerations. [PERSON] et al. [14] used PLAXIS3D to establish a real 3D finite element model of double-row piles, and their spatial effects on the entire foundation pit were considered. The results showed that the soil pressures among the piles and below the excavation face are close to Rankine's active and static earth pressures, respectively.