For the problem of inaccurate value of the safety factor of the middle rock pillar in the calculation of the surrounding rock pressure in deep buried neighborhood tunnels,this paper calculated the ultimate bearing capacity of the middle rock pillar from the state that the excavation and support of the first tunnel was completed while the later one was not supported integrality yet,and the strength reduction method was used to calculate the safety reserve factor of the middle rock pillar,deduced the expression of the sharing effect of the middle rock pillar on the surrounding rock pressure of the neighborhood tunnels,and the method of calculating the surrounding rock pressure in deep buried neighborhood tunnels considering the safety reserve of the middle rock pillar was established.The reasonableness of the calculation method of the surrounding rock pressure in this paper was verified by examples,and the influence of the distance on the surrounding rock pressure of the tunnel was analyzed with the calculation method.The results showed that the proposed method of calculating the surrounding rock pressure took into account the influence of rock parameters,tunnel span,excavation method and other factors on the safety reserve factor of the middle rock pillar,which could more accurately reflect the sharing effect of the middle rock pillar on the surrounding rock pressure of neighborhood tunnel than the calculation method of determining the safety factor of the middle rock pillar based on the experience of the current specification;the corrected load capacity of the middle rock pillar in the four-lane tunnel with grade Ⅳ surrounding rock was 10 324 kN/m,the maximum vertical surrounding rock pressure of the vault was 264 kPa,the corrected load capacity of the middle rock pillar in the two-lane tunnel with grade Ⅴ surrounding rock was 2430 kN/m,the maximum vertical surrounding rock pressure of the vault was 251 kPa,achieving the envelope of the measured value and reducing 6%and 29%respectively compared with the specifications value.The critical distance for the four-lane,three-lane and two-lane tunnel in the grade-Ⅲ section were 0.6B4lanes,0.7B3lanes and 0.7B2lanes respectively,in the grade-Ⅳ section were 1.2B4lanes,0.9B3lanes and 0.9B2lanes respectively.The critical distance for the three-lane and two-lane tunnel in the grade-Ⅴ section were 1.8B3lanes and 1.2B2lanes.
tunnel engineeringdeep buried neighborhood tunnelsurrounding rock pressuremiddle rock pillarstrength reduction method
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