黄土地区高填土明洞土拱效应及土压力减载计算

 基于涵洞减载基本原理，结合明洞结构特点，通过室内缩尺模型试验，研究不同减载方案下高填方明洞土压力随填土高度变化的规律及土拱效应。试验结果表明，随着填土高度的增加，土拱效应逐渐显现但不稳定，使明洞顶土压力小于理论土压力。根据明洞顶土压力变化规律及明洞减载结构力学模型，利用朗肯土压力理论，提出铺设单层土工格栅减载结构土压力计算公式，包括格栅顶部土柱土压力、格栅底部土体支撑力、明洞顶土压力的计算公式，并针对实际工程中广泛采用的多层土工格栅结构类型，推导其明洞顶土压力的计算公式。结合现场明洞试验，证明土工格栅减载的良好效果及本文计算方法的准确性，可为高填土明洞顶土工格栅减载结构设计及施工提供理论参考。

EARTH PRESSURE AND SOIL ARCH EFFECT FOR HIGH FILL OPEN CUT TUNNEL IN LOESS AREA UNDER DIFFERENT LOAD REDUCTION SCHEMES

The soil arch effect of the open cut tunnel and the variations of the earth pressure with the heights of the filled soils under the different load reduction schemes were studied with the model tests of reduced scales. The experimental results showed that the earth pressures on the top of open cut tunnel increased nonlinearly and the soil arch effect occurred when the filled height was up to a certain level. The soil arch effect was not stable and the soil stresses measured at the crest of the tunnel were smaller than the calculated ones. A single layer of geogrid was thus proposed to be placed above the tunnel and a corresponding method of calculation of the earth pressures at the top of the geogrid，under the geogrid and on the crest of the open cut tunnel was presented on the basis of Rankine?s theory of earth pressure. In addition，an expression of earth pressures for multiple layers of geogrid was also derived. The field experiment of an open cut tunnel demonstrated that the load reduction by geogrid was effective and the calculation method was appropriate.