深埋3孔小净距隧道围岩压力计算方法及其工程应用

基于普氏理论,考虑开挖顺序以及中岩柱主要具有的承载松散岩土体和抑制围岩变形作用,提出3孔小净距隧道围岩压力的计算方法,并分析净距和开挖跨度对围岩压力分布规律的影响。通过与八达岭长城站3孔小净距隧道围岩压力实测值对比,验证计算方法的合理性和有效性。结果表明:中洞受力状态最为不利,边洞内侧围岩压力显著大于外侧;净距一定时,中洞或边洞跨度增大不仅导致各自洞室围岩压力增大,且会导致相邻洞室围岩压力增大;随净距增大,围岩压力逐渐降低并接近规范计算单洞值;Ⅴ级围岩段实测围岩压力约是Ⅲ级围岩段实测值的3倍,净距相同时,Ⅴ级围岩比Ⅲ级围岩更易形成极限承载拱;围岩压力理论计算值的偏差率在10%~25%。根据围岩压力的理论值和前期监测值,主动对隧道采取超前加固与加大锚杆长度,使实测围岩压力减小30%,可保障隧道施工安全。

Calculation Method for Surrounding Rock Pressure of Deeply Buried Closely Spaced Triple Tunnels and Its Engineering Application

Based on the Protodyakonov\s theory,considering the excavation sequence and the main roles of the middle rock pillar in bearing loose rock and soil mass as well as restraining the deformation of surrounding rock,the calculation method of the surrounding rock pressure of closely spaced triple tunnels was deduced.The influence of clearance and excavation span on surrounding rock pressure distribution was analyzed.Then,the comparative analysis was made between theoretical values and monitoring data measured from closely spaced triple tunnels of Badaling Great Wall Station,and the rationality and validity of the calculation method were verified.Results show that the stress state of the middle tunnel is the most unfavorable,and the surrounding rock pressure on the inner side of the side tunnels is significantly greater than that on the outer side.When the clearance is constant,the increase of the span of a single tunnel not only increases its own surrounding rock pressure but also increases the surrounding rock pressure of the adjacent tunnels.As the clearance increases,the surrounding rock pressure of each tunnel gradually decreases and approaches the value of a single tunnel prescribed in the code.The measured value of surrounding rock pressure of grade V surrounding rock is about 3 times higher than that of grade III surrounding rock.When the clearance is constant,the ultimate bearing arch is more likely to form in grade V surrounding rock than in grade III surrounding rock.The deviation rate between the theoretical calculation value and the measured value of surrounding rock pressure is 10%~25%.According to the theoretical value and early monitoring data of surrounding rock pressure,advance reinforcement measures for tunnel are actively taken,the length of the anchor bolt is increased,the measured value of surrounding rock pressure is reduced by 30%,and the safety of tunnel construction is guaranteed.