基于颗粒流计算的砾石层HDD导向孔水平段孔壁变形研究

Particle flow calculation-based investigation into the deformation of hole wall in the horizontal section of HDD pilot hole

水平定向钻进技术在城市管线铺设中应用越来越广,砾石作为松散颗粒的集合体,在进行导向孔钻进时,往往由于颗粒结构扰动而易发生变形甚至塌孔,但颗粒在钻进过程中的力学行为规律仍不明晰。本文利用颗粒流程序建立三维砾石模型,并分段进行有和无泥浆护壁导向孔水平段钻进模拟。通过在导向孔周围布设测量球,对导向孔周围颗粒变形特征进行研究。结果表明:孔壁失稳表现为上部颗粒相互嵌固形成“压力拱”,压力拱下部松散颗粒率先掉落,伴随着压力向两侧和底部传递,下部和侧向颗粒协调变形直至收敛。压力拱在后续钻孔扰动下,由于侧向约束的消除,压力拱向顶部扩展,产生更多的松散颗粒进入钻孔范围,最终导致塌孔。泥浆可以较好的约束松散颗粒的顶部掉落,维护压力拱的侧向约束。实际工程中应量化泥浆指标,选择合理的泥浆而避免塌孔事故发生。

Horizontal directional drilling(HDD)technology has been widely used in urban pipeline installatio.Gravel,as a collection of loose particles,is prone to deformation or even hole collapse due to particle structure disturbance during guide hole drilling,but the mechanical behavior of particles in the drilling process is still unclear.In this paper,a three-dimensional gravel model was established by using the particle flow program,and the horizontal drilling simulation was carried out in sections with and without mud protection pilot holes.The deformation characteristics of particles around the pilot hole were studied by placing measuring balls.The results show that the instability of hole wall is manifested as the“pressure arch”formed by upper particles embedded with each other,the loose particles in the lower part of pressure arch fall first,the lower and lateral particles coordinate deformation until convergence with the pressure transfer to both sides and bottom.Under the disturbance of the subsequent borehole,the pressure arch expands to the top due to the elimination of lateral constraints,resulting in more loose particles entering the borehole range,which eventually leads to hole collapse.The mud can restrain the top drop of loose particles and maintain the lateral constraint of pressure arch.In practical engineering,mud index should be quantified,and reasonable mud should be selected to avoid hole collapse.