复杂接触条件下超长距离混凝土顶管–围岩摩擦特性及现场卡管处置验证研究

为揭示超长距离岩石顶管法施工中卡管的形成原因,采用大型岩石直剪试验研究7类复杂接触条件下砂岩与混凝土管间的剪切摩擦特性。研究结果表明:仅考虑膨润土泥浆的接触条件的平均摩擦因数(AFC)获得全部试验结果的最优值,后期接触面的AFC可高出初始值50%~70%,其中以管外原位岩屑,膨润土泥浆与含砂废弃泥浆三者组合的AFC达到最大值。然后由试验成果及改进的经验公式对现场卡管的顶力进行预测,经与现场监测对比取得了较吻合的结果,最后依据顶力传递损耗规律提出一种临时中继间法成功将卡管问题解决,因此现场中降低管–岩接触摩阻力应首先控制管外的沉渣,避免在管外形成导致管壁摩阻力增大且减小膨润土浆液有效注射量的高黏度混合物,其次还需保证管外需有充足的注浆量。

Experimental study on the complex contact frictional property of an ultra-long distance large section concrete pipe jacking with the verification of on-site solution of pipe stuck

To reveal the generation mechanism and variation law of friction resistance between the outer wall of a large section of concrete pipe string and the surrounding rock during construction via ultra-long-distance rock pipe jacking,the shear friction behaviors and mechanical mechanism between sandstone and concrete pipe string wall under seven complex contact conditions were investigated through large-scale direct rock shear tests. The results show that the optimal values of the average friction coefficient for all test results are obtained by only considering bentonite slurry contact condition. In the later stage,the average friction coefficients at the contact surface can be higher than the initial values by 50%–70%. Among them,the average friction coefficient for a combination of extra-pipe in-situ debris,bentonite slurry and sand-laden waste slurry reaches a maximum value. The jacking force needed for stuck pipes was predicted based on the test results and the modified empirical formula, which is identical to the field-monitored value. Finally, a temporary intermediate jacking station(TIJS) method for solving the pipe stuck problem was proposed based on the law of jacking force transmission loss. It is pointed out that the focus of reducing in-situ pipe-rock friction resistance should be placed firstly on controlling the extra-pipe sediment to prevent the formation of high-viscosity mixture that leads to an increase in the friction resistance of the pipe wall and a decrease in the effective injection volume of bentonite slurry. Besides,it is also necessary to ensure a sufficient grouting volume outside the pipes.