Method for calculating the surrounding rock pressure in loess tunnels

To propose a calculation method for surrounding rock pressure applicable to loess tunnels, analyzed the formation mechanism of surrounding rock pressure in loess tunnels, based on a large amount of field test data of surrounding rock pressure, extracted the impact factors, explored the sensitivity and variation patterns of different impact factors on the surrounding rock pressure of loess tunnels, a calculation formula for surrounding rock pressure was constructed based on the multi-factor coupled regression analysis method, then, the method for calculating the surrounding rock pressure of loess tunnels considering multiple influencing factors was proposed by using the sample enveloped method combined with the trial algorithm. The results show that: (1) The surrounding rock pressure in loess tunnels is the deformation pressure mainly, the methods used commonly for calculating the surrounding rock pressure cannot truly reflect the load situation of loess tunnels; (2) The surrounding rock pressure in loess tunnels is affected significantly by the grade of surrounding rock, which has a good exponential function correlation with the burial depth, the span and the height-span ratio of excavation; (3) Compared with the commonly used Terzaghi's formula, the formula of "Code for Design of Highway(Railway) Tunnels", and the Caquot's formula, the formula proposed in this paper has a better envelope for the surrounding rock pressure of loess tunnels, and the calculation results are closer to the measured values.