不同卸荷措施下深覆土特大跨度明洞受力特性研究及衬砌结构变形预测

    Study on mechanical characteristics of deep soil-covered supper-span open cut tunnel under different unloading measures and deformation prediction of lining structure

    • 摘要: 为探明可有效降低深覆土特大跨度明洞结构内力和变形的卸荷方式,通过开展模型试验研究了EPS板和混凝土柱单独或组合使用时产生的卸荷效果,分析土压力、衬砌结构内力和位移后探明了卸荷机理,使用破损阶段法评估了衬砌结构的安全性,基于多元线性回归原理求得了衬砌结构薄弱部位(拱顶和拱腰)位移预测方程。研究结果表明:无卸荷措施时明洞顶部会出现土压力集中现象,明洞顶部和两侧铺设EPS板与混凝土柱相结合的卸荷方式可最大限度的减小明洞周围土压力,平均竖向和水平土压力可分别减小40.01%,79.34%。然而,此种卸荷措施会大幅减小水平土压力,削弱土体对衬砌结构的约束作用,导致衬砌结构内力和位移不能降至最小。仅在明洞顶铺设EPS板,可在减小竖向土压力增幅的同时增大水平土压力增幅,加强土体对衬砌结构的约束作用,达到最优卸荷效果。填土完成后,无卸荷措施时明洞顶位移为29.15 mm,拱顶和拱腰的弯矩分别为4111.88 kN·m,-3988.51 kN·m,在明洞顶铺设EPS板后,明洞顶位移减小了50.15%,拱顶和拱腰的弯矩分别减小了77.48%,75.71%,且相较于其他卸荷措施,该措施可更有效提升结构安全性。以土压力为变量,基于多元线性回归原理,所得位移预测方程求得的位移预测值与实际值间最大和最小误差分别为7.30%,0.28%,位移预测方程可有效应用于深覆土特大跨度明洞工程卸荷措施研究及卸荷参数优化。

       

      Abstract: In order to find out the unloading method that can effectively reduce the internal force and deformation of the super-span cut-and-cover tunnel in deep overburden, the unloading effect of EPS slab and concrete column used alone or in combination is studied through model test, the unloading mechanism is found out after analyzing the soil pressure, internal force and displacement of the lining structure, and the safety of the lining structure is evaluated by using the damage stage method. Based on the principle of multiple linear regression, the displacement prediction equation of the weak parts (vault and haunch) of the lining structure is obtained. The results show that the earth pressure will be concentrated on the top of the cut-and-cover tunnel without unloading measures, and the combination of cut- and-cover tunnel with concrete columns can reduce the earth pressure around the cut-and-cover tunnel to the maximum extent, and the average vertical and horizontal earth pressures can be reduced by 40. 01% and 79. 34%, respectively. However, this kind of unloading measure will greatly reduce the horizontal earth pressure and weaken the constraint effect of the soil on the lining structure, resulting in the internal force and displacement of the lining structure can not be reduced to the minimum. When the EPS is only laid on the top of the cut-and-cover tunnel, the horizontal earth pressure can be increased while the vertical earth pressure is reduced, and the constraint effect of the soil on the lining structure is strengthened to achieve the optimal unloading effect. After the completion of filling, without unloading measures, the displacement of the top of the cut-and-cover tunnel is 29. 15 mm, and the bending moments of the crown and haunch are 4111. 88 kN · m and 3988. 51 kN · m, respectively. After laying EPS board on the top of the cut-and-cover tunnel, the displacement of the top of the cut-and-cover tunnel is reduced by 50. 15%, and the bending moments of the crown and haunch are reduced by 77. 48% and 75. 71%, respectively. And compare with other unloading measure, that measure can effectively improve the structural safety. Taking the earth pressure as the variable, based on the principle of multiple linear regression, the maximum and minimum errors between the predicted value and the actual value of the displacement are 7. 30% and 0. 28%, respectively.The displacement prediction equation can be effectively applied to the study of unloading measures and the optimization of unloading parameters of super-span cut-and-cover tunnel in deep overburden soil.

       

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