基于拱效应的钻探塌孔机理分析及对策

针对钻探勘察中塌孔事故易发现象,通过地应力和地下水渗透力两个影响因素对塌孔的机理进行了探讨.钻孔开挖打破了初始应力平衡状态,经应力调整达到二次平衡状态后,在钻孔周围形成最大主应力环绕的拱效应现象.推导了拱效应区域与钻孔半径、土体侧压系数的理论公式,认为地应力是造成钻孔在黏性土等可塑、软塑土中“缩孔”的主因.通过5组工况对拱效应的理论进行了验证,在卵石层中,地下水向钻孔内渗透,冲蚀卵石间的填充砂是造成卵石向钻孔内坍塌的主因；提出采用黏性土护壁、套管护壁以及混凝土护壁3种预防、处理塌孔的对策,同时以宁天城际一期工程初步勘察钻探的实例对理论分析进行了验证.

Mechanics and Countermeasures of Drilling Slump Based on Arching Effect

Drilling slump is frequent in reconnaissance,it is analyzed through two factors of ground stress and ground water penetrability.Drilling breaks down the balance of ground stress,and the drilling hole is surrounded by the maximum principal stress vector when new equilibrium of ground stress is adjusted.The relationship among arching region,drilling hole radius and coefficient of horizontal press is deduced.It is considered that the ground stress is the main reason of drilling hole shrinkage.The arching effect theory is examined through numerical analysis by 5 group parameters.Ground water penetrability is the main reason of drilling slump in boulder bed.Three methods of drilling slump prevention and treatment are analyzed.Finally,a drilling engineering is taken as an example.