某隧道进口段仰拱填充结构在施工期出现大量裂缝,且左线裂缝明显比右线裂缝多.通过现场考察发现,隧道进口段地表的地形明显存在一定坡度,左高右低,这种情况在一定程度上导致隧道左、右线所处位置的地下水头高度存在一定差别.通过对围岩渗流场计算得出,左线隧道仰拱中心底部最大水压力值为0.235 MPa,右线隧道仰拱中心底部最大水压力值为0.207 MPa,作用在左线隧道仰拱中心底部的最大水压力比作用在右线隧道仰拱中心底部的最大水压力约大12％.从衬砌结构受力计算结果得到,隧道左线仰拱填充结构的最大主力极值大于隧道右线仰拱填充结构的最大主力极值,且两者均大于或稍大于仰拱填充材料C20混凝土的极限抗拉强度,导致仰拱填充结构开裂,并出现隧道左线仰拱填充结构拉张裂缝较多,而右线仰拱填充结构拉张裂缝较少的现象.%A large number of cracks once appeared on the filling structure of the invert at the entrance region of a tunnel in the construction period, and the crack number of the left line was obviously more than that of the right line. Through field investigation, it was found that there was a certain gradient slope of ground surface at the tunnel entrance region and the left side was higher than the right side, thus it generated a ground water head difference between the left line and the right line of the tunnel to a certain degree. Then the results of the calculation on the seepage field of the surrounding rock showed that; the maximum value of water pressure acting on the center of the invert of the left line tunnel was 0. 235 MPa, and in the right line tunnel it was 0.207 MPa, so the former was greater than the latter about 12%. Furthermore, the results of stress calculation on the lining structure showed that: the maximum principal stress value of the filling structure of the left line invert was greater than that of the right line invert, and both were greater than or slightly larger than the ultimate tensile strength of C20 concrete which was used as the filling material of the invert. So these reasons had caused a large number of cracks on the filling structure of the invert, with the phenomenon that the crack number of the left line was more than that of the right line.
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