大跨分岔式隧道结构设计关键技术研究

以深圳市东部过境高速公路莲塘隧道为工程背景,对大跨分岔式隧道结构设计中的关键技术进行研究。通过有限元计算,对＂2＋2车道＂和＂2＋3车道＂分岔的断面形式,连拱段结构设置的必要性,钢支撑的选型以及系统锚杆的布设方案进行分析和对比。主要结论：1）在满足交通功能的前提下,应尽量选取＂2＋2车道＂的设计形式;2）小净距段隧道受力状态及施工工法前后转换方面均较连拱段有优势,建议取消连拱段;3）大跨分岔式隧道分岔部一般设置在隧道工程地质较好地段,以方便大跨分岔结构的实施,如莲塘隧道将分岔部设置在Ⅲ级围岩段,而对于开挖跨度接近30m的大跨段,初期支护一般应设置钢格栅,此时应优先选用＂钢筋格栅＋喷锚＂的初期支护形式;4）莲塘隧道分岔部位于Ⅲ级围岩段,系统锚杆设计长度以5 m为宜,应于拱部、侧墙均匀布设。

Study on Key Technologies for Structural Design of Large-span Forked Tunnel

The key technologies for the structural design of large-span forked tunnel are studied,with Liantang tunnel on East Transit Highway in Shenzhen as an example.The cross-section modes of the forked tunnel,the necessity to arrange the double-arch section,the selection of steel support types and the layout of the systematic anchor bolts are analyzed by means of finite element calculation.Conclusions drawn are as follows： 1） Cross-section of ＂2＋2 driveway＂ mode shall be adopted as far as possible,provided that the traffic requirements can be satisfied;2） Small-spaced tunnel is superior to double-arch tunnel in terms of the stress conditions and the transition among the construction methods,therefore it is suggested that the double-arch tunnel section should be cancelled;3） The forked section of large-span forked tunnel is usually arranged at positions with good geological conditions,so as to facilitate the construction of the large-span forked structure.The forked section of Liantang tunnel is arranged at the position with Grade Ⅲ rock mass.For tunnel sections with the excavation span being close to 30m,the primary support consisting of rebar lattice girder,shotcreting and bolting shall be preferred.4） The forked section of Liantang tunnel is located in Grade Ⅲ rock mass,therefore the systematic anchor bolts should be 5m long and should be installed uniformly on the arch and side walls.