考虑塔形滑移面的浅埋隧道松动土压力研究

Calculation of loose earth pressure in shallow tunnel considering soil arching effect

以不完全拱效应为基础,对浅埋隧道松动土压力展开研究。与Terzaghi土拱效应理论的垂直滑移面不同,本文综合考虑国内外对滑移面形式的研究,采用塔形滑移面计算模型,同时考虑主应力旋转角的分布特征,给出松动区内大主应力与水平面夹角分布公式,改进了浅埋隧道松动土压力的计算方法;将塔形滑移面间松动土体侧向土压力系数定义为滑移面上法向应力与平均竖向应力之比,并给出计算表达式;建立出主应力转角与隧道顶部位移的数量关系,进而得到不同拱顶沉降允许值下的平均竖向应力计算方法。将本文松动土压力计算公式同国内外学者提出的计算方法对比,结果相吻合,验证了本文公式的合理性。对公式中主要影响参数(侧向土压力系数、隧道宽高比、相对变形量、滑移面倾角)进行了分析,结果表明:竖向应力?v随着深度z的增加而增加,土拱效应的发挥程度也随着深度z的增加而增大,但其增速逐渐放缓,当达到某一深度(土拱效应完全发挥)后,随着深度z的增加?v趋向于定值;侧向土压力系数K随着土体内摩擦角φ及滑移面倾角α的增大而减小;在一定范围内,随着隧道宽高比B0/h的增大以及相对变形量λ的减小,其表面的竖向应力随之增大。因此,适当的增大浅埋隧道顶部相对变形量、减小隧道宽高比,其所承受的竖向应力随之减小。

This paper studies the loose earth pressure of shallow buried tunnel based on the incomplete arch effect. Differently from the vertical slip plane of the Terzaghi’s soil arch effect theory, this paper comprehensively considers the domestic and foreign studies on the form of slip plane, and adopts the tower slip plane calculation. At the same time, considering the distribution characteristics of the rotation angle of principal stress, the formula of the angle distribution between the major principal stress and the horizontal plane is given, and the calculation method of the loose earth pressure in the shallow buried tunnel is improved. The lateral earth pressure coefficient of loose soil mass on the slip plane is defined as the ratio of normal stress to average vertical stress on the slip plane. The main influence parameters in the formula(coefficient of lateral earth pressure, tunnel aspect ratio, relative deformation and slip plane Angle) are analyzed, and the results show that the vertical stress sigma increases withthe increase of depth z degree of the soil arch effect(play), but its growth is slowing, when reaching a certain depth of the soil arch effect(full), with the increase of depth z sigma tend to fixed value;The lateral soil pressure coefficient k decreases with the increase of the soil internal friction angle and the dip angle of the slip surface alpha. To a certain extent, the vertical stress on the surface of the tunnel increases as the ratio of width to height to B0/h increases and the relative deformation lambda decreases. Therefore, if the relative deformation at the top of the shallow buried tunnel increases appropriately and the ratio of width to height of the tunnel is reduced, the vertical stress it bears will decrease accordingly.