小净距隧道设计荷载的确定

Determination of designing load of small clear space tunnel

为了提高小净距隧道的设计理论水平，分析了小净距隧道的受力情况．塌落拱的高度一般在3～4m（隧道宽度15m），小净距隧道中夹岩墙宽度只有5～7m，在施工过程中，2个隧道的松动圈会出现重叠，使中夹岩墙产生较大的垂直向下位移，从而增加了塌落拱的跨度，中夹岩墙上部的应力相应增加．基于双塌落拱理论，认为小净距隧道松动压力的计算值应在单个隧道宽度与整个隧道开挖宽度相应的松动压力之间取值，根据中夹岩壁下沉的大小，在双塌落拱压力上乘以0．5～0．8的系数，来确定小净距隧道的荷载，建立了深、浅埋小净距隧道荷载模式．将该方法确定荷载与福州国际机场高速公路鹤上隧道（小净距）的监测数值进行对比，两者有较好的吻合．

Force analysis to small clear space tunnel was conducted in this study. It has already been studied that the height of slumping arches could be over 3 to 4 m if the width of tunnel approaches 15 m. For small clear space tunnel, because the width of middle-rock wall is as small as 5 to 7 m, the loosening zone of two tunnels could be overlaid during the process of construction which results a large vertical displacement of middle-rock wall and leads to the augment of span of slumping arch and stress raising of the up part of middle-rock wall. Based on the two slumping arches assumption, a new load-design method of small clear space tunnel was put forward which considered that the value of loosening pressure of small clear space tunnel was between the value of single tunnel excavation and that of two tunnels. A correction factor was adopted by multiplying the pressure of two slumping arches to get the final load confinement of small clear space tunnel. The values range of correction factor was suggested between 0. 5-0. 8 which based on the vertical displacement of middlerock wall. The load modes of deep and shallow small clear space tunnel were presented. For comparison purpose, a case study of small clear space tunnel, Heshang tunnel of Fuzhou international airport highway was conducted. The results showed that the pressure calculated by the method presented in this study was consisted with the site-monitoring data.