Adaptability Evaluation of Rotary Jet Grouting Pile Composite Foundation for Shallow Buried Collapsible Loess Tunnel  
[PERSON]  
1 School of Civil Engineering, Weifang University, Weifang 261061, China 1, [PERSON]  
2 School of Highway, Chang an University, Xi'an 710064, China 2, [PERSON]  
2 School of Highway, Chang an University, Xi'an 710064, China 2, [PERSON]  
2 School of Highway, Chang an University, Xi'an 710064, China 2, and [PERSON]  
2 School of Highway, Chang an University, Xi'an 710064, China 2,3,*  
At present, academia has carried out a lot of research on tunnel base reinforcement, and the foundation reinforcement measures are diverse [6; 7]. To improve the bearing capacity of the highway tunnel foundation, according to the characteristics of the surrounding rock of a highway tunnel, [PERSON] et al. (2009) adopt horizontal pile jet grouting for pre- support at the portal section [8]. [PERSON] et al. (2022) simulated four tunnel reinforcement schemes (the right tunnel annular reinforcement, the left tunnel annular reinforcement, the double tunnel annular reinforcement, and the cement wall reinforcement between left and right tunnels). Through a series of three-dimensional numerical analysis, the interaction mechanism of double tunnels in the construction process was revealed, including surface settlement, tunnel deformation, convergence deformation of tunnel lining, and internal force of tunnel lining [9]. [PERSON] et al. (2018) applied a three-dimensional finite element model to the Fujiayao tunnel in the loess stratum to deeply understand the consolidation settlement after jetted grouting pile reinforcement of tunnel foundation [5]. In order to study the influence of base reinforcement on the tunnel, [PERSON] et al. (2019) conducted a finite element analysis based on the previously reported centrifuge model test without base reinforcement and analyzed the influence of [PERSON]'s modulus and depth of reinforced soil on the tunnel deformation [10]. In many reinforcement measures, pile foundation, as one of the commonly used forms of base reinforcement, has been widely studied by scholars. Among them, pile length, pile diameter, and pile stiffness are the key factors to be considered when strengthening the loess tunnel base. [PERSON] et al. (2020) takes a subway tunnel as an example and use finite element software to simulate the influence of four reinforcement methods on foundation settlement, namely, deep hole grouting reinforcement, deep hole grouting combined with radial grouting reinforcement, bolt reinforcement, and tension bolt deep hole grouting reinforcement under different gap conditions [11]. [PERSON] et al. (2010) used Plaxis 3D tunnel finite element software to study the distribution law of pile foundation lateral deformation and settlement change along the pile shaft during the whole tunnel crossing process and analyzed the influence of pile length on pile foundation deformation [12]. For loess tunnel, the base is a weak surrounding rock with low strength, and the deformation is large during construction. To explain the progressive failure of roof collapse in deep tunnels, [PERSON] (2018) studied the progressive collapse mechanism and collapse block shape of a deep circular tunnel under plane strain conditions. Based on the nonlinear power law failure criterion considering the change of dilatancy angle and separation velocity, the analytical solution of the collapse block shape curve of circular tunnels is derived. In addition, the variable dilatancy angle criterion for the progressive failure of deep tunnels is also obtained [13]. Based on a new three-dimensional limit equilibrium