Ground surface settlement analysis of shield tunneling under spatial variability of multiple geotechnical parameters

This paper presents an efficient method of shield tunneling reliability analysis using spatial random fields. We introduced two stochastic methods into numerical simulation. The first one computes the maximal ground surface settlement using classical statistics, in which the response surface method is utilized to calculate the failure probability by first-order second moment. Cohesion, internal friction angle, Young's modulus and mechanical model factor are considered as random variables. The second method is the spatial random fields of aforementioned three key geotechnical parameters. Using these two methods, similar multiple soil layers are converted into a stationary random field by local regression as the first step, and then the process is followed by the spatially conditional discretization of multivariate. Failure probability of maximal ground surface settlement is calculated by a subset Monte-Carlo Algorithm. This approach is applied into the four-overlapping shield tunnels of the 5^th and 6^th metro lines intersecting at Huanhu W Rd station, Tianjin China. The failure analysis results indicated that classical statistics of geotechnical parameters showing higher variability than spatial random fields, which substantially support the complex shield tunneling project.

Study on soil reinforcement param in deep foundation pit of marshland metro station

In this paper, the reinforcement method outside the deep foundation pit of a subway station in marshland under a high water level was proposed, and the reinforcement parameters were studied. The influence of reinforcement measures outside the deep foundation pit on deformation and the anti-overturning stability coefficient of the diaphragm wall under high water levels was analyzed. According to the economic law of diminishing marginal returns, the grouting reinforcement parameters were analyzed and optimized. The effects of different reinforcement measures on the safety control of deep foundation pits was analyzed based on field-measured data. The results show that the change in the water level has a significant impact on the stability of the foundation pit, and it is necessary to adopt reinforcement measures for the foundation pit at 10 m below the surface; the change in the reinforcement depth has a more significant impact on the stability of the foundation pit; and the optimized reinforcement parameters can reduce the grouting volume by 45%.