一、前言众所周知,隧道洞口地层结构松散、胶结弱、地压大,围岩稳定性差,再加之覆盖薄成洞条件差,施工中极易发生坍塌。以往洞口施工,为了减少对围岩的扰动,保证施工安全,曾使用过加固山坡上导进洞法;接长明洞进洞法;侧向进洞法和下导引进翻井退出施工法。这些方法有其共同特点,一是临时支护都是采用木支撑,二是先用小导坑 I. Preface It is well-known that the stratum of the tunnel entrance is loose and has weak cementation, large pressure and poor stability of the surrounding rock, together with the poor conditions of covering the thin cavities, and the collapsibility in the construction. Previous hole construction, in order to reduce the disturbance to the surrounding rock to ensure construction safety, has been used to reinforce the hillside on the introduction of the hole method; then Chang-ming hole into the hole method; These methods have their common characteristics, one is the temporary support wood support, and second, first with a small pilot hole