| Mountainous and hilly areas in China account for more than 70% of the land.There are various types of mountainous areas,complex landform,harsh environment lead to frequent geological disasters such as collapse,debris flow and landslide.Affected by natural or human factors,the slope is prone to local slope deformation,bulging and damage of protective wall and cracking of slope platform.This state is the critical state of slope deformation and damage.Once the slope is unstable,it will cause great potential safety hazards to roads,railways and residential buildings,and bring huge property losses and serious social impact.In the slope treatment engineering,many anti slide piles are still constructed in the form of manual hole digging.In order to improve the drilling efficiency,the reinforcement method of mechanical drilling anti slide pile is proposed.This method selects DTH hammer reverse circulation drilling in construction,which can complete the drilling of anti slide pile hole more efficiently and safely.DTH hammer reverse circulation drilling technology has the characteristics of high drilling efficiency,strong slag discharge capacity and good adaptability to complex terrain in mountainous areas.During the construction of loose and broken strata,combined with casing technology,while drilling and protecting the hole,it can meet the needs of rapid hole formation in complex strata and realize the emergency disposal of landslide.However,in the process of drilling,formation water often flows into the hole,which makes the situation in the well complex,and is prone to problems such as sticking and backflow of cuttings.It is a difficult point to keep the air influx to the minimum under the condition of different drilling technology.According to the formation water yield,analyze the transportation status of rock cuttings and gas-liquidsolid three-phase flow,and select the minimum gas injection,which is conducive to reducing the cost and improving the drilling efficiency.In order to explore the minimum gas injection required for the upward return of cuttings by air reverse circulation under the conditions of different formation water volume,ROP and cuttings particle size,and study its influencing factors,a set of reverse circulation multiphase flow test device is designed and processed.The minimum gas injection required for the upward return of cuttings under different conditions is measured with the variables of intrusion water volume,ROP and rock cuttings particle size,and the transport and velocity changes of cuttings are measured by high-speed camera.The results show that the flow is annular and multiphase;When the ROP is less than 0.9m/h,the gas injection rate increases with the increase of ROP and the increase rate is low.When the ROP is greater than 0.9m/h,the increase rate of gas injection rate increases significantly with the increase of ROP.When the particle size of cuttings is2 mm and the ROP is less than 1.2m/h,the gas injection rate increases-unchanged-increases with the increase of intrusion water volume;When the particle size of rock cuttings is 2mm and the ROP is 1.5m/h,the gas injection rate remains stable after increasing to a certain value with the intrusion water volume.When the particle size of rock cuttings is 3mm,the gas injection volume under different ROP conditions will remain stable after increasing to a certain value with the intrusion water volume.When the particle size of rock cuttings is 4mm,the gas injection rate increases and decreases with the growth rate of intrusion water volume,and when the intrusion water volume is greater than 0.012 m 3/ Min,the gas injection rate has a flat trend.When the intrusion water volume is 0.006 m 3/ Min,the particle size of rock cuttings has little effect on the gas injection.In other cases,the gas injection with rock cuttings increases with the increase of particle size of rock cuttings;most of cuttings in transport are distributed in the center of the pipeline and move spirally,and their axial velocity remains constant after the displacement increases to the maximum.In order to further analyze the flow law of multiphase flow and verify the test results,this paper analyzes the interaction of components in multiphase flow and establishes the mathematical model of multiphase flow process;The results show that the axial velocity of multiphase flow in the center of the flow field increases with the increase of multiphase flow displacement,and remains unchanged after reaching the maximum velocity in the middle of the flow field until leaving the flow field;The axial velocity of multiphase flow at the edge of the flow field decreases with the increase of multiphase flow displacement,and finally maintains a low velocity and rises.The maximum cuttings velocity and multiphase flow pressure drop increase with the increase of the ROP.When the ROP is less than 0.9m/h,the increase of the maximum cutting velocity and multiphase flow pressure drop with the ROP is low.When the ROP is greater than 0.9m/h,the maximum cuttings velocity and multiphase flow pressure drop increase significantly with the increase of the ROP.When the particle size of cuttings is 2mm and the ROP is less than 1.2m/h,the maximum velocity of cuttings and multiphase flow pressure drop show an increasing constant increasing trend with the increase of intrusion water volume;When the particle size of cuttings is 2mm and the ROP is 1.5m/h,the maximum velocity of cuttings and the pressure drop of multiphase flow remain stable with the increase of intrusion water to a certain value.When the particle size of cuttings is 3mm,the maximum cuttings velocity and multiphase flow pressure drop under different ROP conditions remain stable after increasing to a certain value with the intrusion water volume.The maximum velocity of cuttings and the pressure drop of multiphase flow increase with the increase of cuttings particle size,but the increment is low and the change is not obvious.Finally,the axial velocity of rock debris particles at 450 mm upward from the pipeline inlet is compared when the intrusion water volume is 0 in the test and simulation results.The variation laws of the two are roughly the same.The test results verify the accuracy of the numerical simulation results. |
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