高填方黄土明洞顶EPS板和土工格栅共同减载计算及土拱效应分析

Load Reduction Calculation and Soil Arch Effect Analysis for High Fill Open Cut Tunnel in Loess Area under Joint Action of EPS and Geogrid

基于土压力减载机理,推导高填方黄土明洞顶铺设EPS板和土工格栅共同减载的明洞顶土压力计算公式。利用ANSYS软件模拟不同弹性模量EPS板和土工格栅共同减载时高填方黄土明洞顶的土压力,采用荷载等效方法将数值模拟的"波浪形"分布的土压力转化为均布荷载,将其与公式计算结果进行对比。结果表明:明洞顶土压力均随内外土柱沉降差的增大而减小,公式计算结果与数值模拟结果最大相对误差为3.59%,验证了计算公式的正确性。取EPS板的弹性模量为0.5 MPa,数值模拟明洞顶土体的竖向位移、最小主应力和竖向应力。结果表明:EPS板变形导致明洞顶最小主应力方向发生旋转,指向外土柱,在0.83倍洞高处出现明显的"应力拱";"应力拱"下部竖向、横向土压力均减小;内外土柱沉降差越大,"应力拱"横向应力越大,承担上部荷载越大,土拱效应越明显。

Based on the load reduction mechanism of earth pressure,the computational formula for earth pressure with the load reduction measures of laying EPS board together with geogrid on the top of high fill open cut tunnel in loess area was derived.The earth pressures on the top of high fill open cut tunnel in loess area under the common load reduction of EPS board and geogrid with different elastic modulus were simulated by ANSYS software.The load equivalent method was adopted to convert the earth pressure of the ＂wavy＂distribution obtained by numerical simulation to the uniform distributed load,and was compared with the calculation results of the computational formula.Results show that the earth pressure on the top of open cut tunnel decreases with the increase of the settlement difference between the inner and outer soil columns.The maximum relative error between the formula computational results and the numerical simulation results is 3.59%,and the correctness of the computational formula is verified.The vertical displacement,minimum principal stress and vertical stress of the soil on the top of open cut tunnel are obtained by the numerical simulation with the elasticity modulus of the EPS board as 0.5 MPa.Results show that the deformation of EPS board leads to the direction of minimum principal stress rotate to outer soil column.An obvious ＂stress arch＂appears at 0.83 times the height of open cut tunnel.Both the vertical and lateral earth pressure decrease under the＂stress arch＂.The greater is the settlement difference between the inner and outer soil columns,the greater is the lateral stress of＂stress arch＂,the higher is the upper load bearing and the more obvious is the soil arch effect.