DESIGN CONCEPT OF TUNNEL SUPPORT STRUCTURE

在隧道支护结构设计中，采用了“特征曲线法”。该方法由两条曲线组成，一条是考虑围岩情况的收敛曲线，另一条是基于薄环或厚环理论的围护曲线。这项研究是关于CCS的。研究的目的是给出新的支承约束曲线(即支承刚度)。为此，隧道被理想化为一个完全圆柱形的薄壳，两端有两个加劲钢环。本文的主要研究结论如下：(1)提出了一种估算隧道支座(支座刚度)的简单闭合解析表达式。此外，该公式还有助于更好地了解隧道围护结构的特性。(2)用该公式计算的隧道围护结构的刚度结果小于CCS的计算结果，最大误差为20%。(3)钢圈加劲效应可用有效宽度L^*(=αL)来表示，其中L为两环之间的长度，在所考虑的几何和材料特性范围内，系数α大于或等于0.35。因此，在α≦1的情况下，可能会出现隧道支护的临界状态。(4)喷射混凝土的弹性模数和厚度对α值有很大影响。

In the design of tunnel support structure, the method called "Characteristic Curve Method" is used. The method consists of two curves ; one is convergence curve for surrounding ground and the other is confinement curve for support (CCS) based on the thin or thick ring theory. This study is concerned with the CCS. The purpose of the study is to present the newly confinement curve for support (namely stiffness of support). To this end, the tunnel is idealized as a perfectly cylindrical thin shell with two stiffening steel rings at ends. The principal conclusions of this study are summarized as follows.(1)A simple closed-form analytical expression for estimating the tunnel support (stiffness of support) is presented. In addition, this equation is useful for a better understanding of the characteristics of the tunnel support.(2)The results for the stiffness of support obtained by the present equation are less than the CCS result ; the maximum error is 20 percent.(3)The effect of stiffening steel ring may be presented in terms of an effective width L^* (=αL), where L is the length between two rings and the coefficient α is greater than or equal to 0.35 within the range of geometric and material properties considered. Thus, in the case of α≦1,a critical state may be occur in tunnel support.(4)The elasticity modulus and thickness of the shotcrete has a major effect on the value ofα.