多因素影响下顶管施工引起土体变形计算研究

Study on soil deformation caused by pipe jacking construction with multi-factor

为解决圆形顶管施工穿越特殊地层(如下穿切割塑料排水板)时引起地层变形的影响分析等问题,考虑刀盘挤土效应产生的正面附加压力、顶管与土体之间非均匀分布的侧向摩擦力,因塑料排水管的切削而不能忽略的顶管机刀盘的正面摩擦力引起的地层变形,基于Mindlin解得到在顶管施工阶段地表竖向位移计算公式;最后结合顶管工程项目实例验证计算方法的合理性,并与实测结果对比。分析结果表明:考虑多因素共同影响的地表沉降曲线与现场实测值较为吻合,能够反映顶管顶进过程中纵向地表沉降规律,总体表现为先隆起后沉降。沉降最大值位于开挖面后方8 m左右处;隆起最大值位于开挖面前方5 m左右处。在本文所考虑的影响因素中,影响程度最大的是顶管刀盘的正面附加推力,在沉降变形最大值中占比约为80%,在隆起变形最大值中占比约为56%。选取不同断面分析对比不同深度处土体沉降情况,沉降突变及差异主要表现在顶管轴线两侧12 m范围内。沉降槽曲线近似服从正态分布,不同土层深度的土体沉降最大值均位于顶管轴线正下方。在土体深层沉降中,随着与顶管轴线距离的增加,曲线不再满足随着深度的增加沉降值增大,反而在距离轴线4~6 m远处出现反转,直至随着深度的增加沉降值反而减小。

It is important to solve the problems such as the analysis of the influence of the formation deformation caused by the circular pipe jacking construction when crossing the special formation(for example, the pipe jacking machine passes through and cuts the plastic drain pipe) in engineering. The frontal additional pressure generated by the cutter squeezing effect, non-uniformly distributed lateral friction between jacking and soil, and the frontal friction of the pipe jacking cutter that cannot be ignored due to the cutting of the plastic drain pipe are considered from the Mindlin solution. The resulting formation deformation was obtained by calculating the vertical displacement of the surface during the construction of the pipe jacking. Finally, the rationality of the calculation method was verified with an example of the pipe jacking project, and compared with the measured results. The results show that the surface settlement curve considered by multiple factors in this paper is in good agreement with the measured values in the field, which can reflect the law of vertical surface settlement during jacking of the pipe. It generally manifests as first uplift and then settlement. The maximum settlement is located about 8 m behind the excavation surface. The maximum value of uplift is located about 5 m in front of the excavation surface. Among the influencing factors, the most influential is the additional thrust on the front of the pipe jack, which accounts for about 80% of the maximum settlement deformation and about 56% of the maximum uplift deformation. Different sections were selected to analyze and compare the settlement of the soil at different depths. The sudden changes in settlement and the differences were mainly realized within 12 m on both sides of the pipe jacking axis. The settlement tank curve approximately obeys the normal distribution. The maximum soil settlements at different soil depths are directly below the pipe jacking axis. In deep soil settlement, as the distance from the pipe jacking axis increases, the curve no longer satisfies that the settlement value increases with increasing depth. Instead, a reversal occurs at a distance of 4~6 m from the axis, until the settlement value decreases with increasing depth.