The analytical solutions of shrinkage after construction about the directional drilling engineering in sandy soil area

摘要

There is an annular space with mud surrounding the installed pipeline after the completion of the project using Horizontal Directional Drilling (HDD).The mud in the annular space is super saturated soil with rich water,moisture away with time decreases the mud pressure,the unloading changes the soil stress around the hole wall,causing stress redistribution and the shrinkage of hole wall,and what's even worse,a certain space will form around the pipeline and hole collapse and surface subsidence.The shrinkage after construction is the key factor for the project quality in the directional drilling engineering,the formula of the shrinkage of hole wall after construction is the main problem to be solved.Analyzing the rules of the secondary stress and the radius of plastic zone in soil layer through analyzing the soil stress surrounding the hole wall with the SMP failure criterion and elastic-brittle-plastic model about sandy soil,summing the rules of the secondary stress field and displacement distribution and deducing the calculation formula of the optimal mud pressure,radius of plastic zone and displacement.In addition,getting the value of the displacement through numerical simulation with the FLAC2D.It can be found that the displacement law curve and the hole wall displacement is proportional to the final hole radius and the cover depth of soil through contrasting the results of numerical calculation and numerical simulation.At the same time,through changing the value of internal friction angle and mud pressure with other conditions remain unchanged,getting that the more internal friction angle and mud pressure,the smaller displacement of hole wall,the greater the stability of the surrounding soils.Providing the reliable theory basis for analyzing the hole wall shrinkage of directional drilling in sandy soil areas.