An Experimental Investigation On Soil Displacement And Deformation Of Drilling Process Using Transparent Soil Modeling

During the process of drilling, hazards like bore collapse and bore shrinkage are prone to occur. Meanwhile, underground soil deformation would exert negative influence on both engineering surroundings and natural environment.In order to reveal soil deformation mechanism during drilling process, transparent soil was introduced to carry out experiments. The transparent soil, in this paper is made of fused quartz sand and mineral oil to simulate sands body. Models simulating drilling was applied and geological conditions was simplified. Laser speckle image reflecting soil deformation under different conditions were spotted. With the introduction of digital image processing technique and PIV software, real-time analysis on soil deformation can be possible. Afterwards, soil particle transport mechanism, the form of soil displacement field and the evolving process of relative displacement field were further researched. Meanwhile, cross contrast was made to examine the effects of sand particle size, drilling pressure and drilling speed on soil deformation. The main research results are as follows.(1) On the basis of soil particle migration, soil deformation was divided into drill bit affecting zone, drill pipe affecting zone and periphery expansion zone. Specifically, In drill bit affecting zone, soil particles under drill bit migrated aslant downwards while other soil particles migrated aslant upwards. And in drill pipe affecting zone soil particles mainly migrated aslant upwards. While in periphery expansion zone, some soil particles moved radially orbiting drill bit and some others moved aslant upwards.(2) Experimental results showed that during drilling process there are 2 different types of displacement fields for soil, parabolic envelope one and the wbore column one. Soil particles’ movement due to drilling process tended to be in parabolic form within parabolic envelope displacement field. And the affecting area of displacement field is comparatively large, along with uneven distribution of velocity. To be more specific, being away from drill axis would lead to small velocity both horizontally and vertically and vertical velocity surpassed horizontal one. As for wbore column displacement field, which evolved vertically, its affecting area was comparatively small. And its most part was classified as drill pipeline affecting area. To be more specific, being away from drill axis would lead to small velocity horizontally while vertical velocity remained same of no matter being away or not from drill axis.(3) Experiments demonstrated that relative displacement field evolving process for soil vertically can be divided into 2 stages. In the first stage, as drilling processing relative displacement field expanded to its maximum. And then it gradually shrank and moved into next stage. Stage 1 is shorter than Stage 2, while their relative displacement fields evolving velocity are approximately same.(4) As illustrated by experiments,larger soil particle and drilling pressure would lead to smaller soil displacement field and contribute it to change from a parabolic envelope displacement field into a wbore column one. While as drilling speed ascended, soil displacement field in drill bit affecting zone expanded and soil migration velocity increased. And when the total affecting area of total soil displacement field stayed same, soil displacement field took part more place in drill bit affecting zone. Finally, the form of displacement field changed from wbore column one into parabolic envelope one.(5) Velocity contribution in parabolic envelope displacement field were described and analyzed with fitting. Consequently, expression explaining velocity contribution in this zone were conducted.