Study On Mechanism Of Pile Coating Anti Crystallization Blocking Of Tunnel Drainage Pipe

With the increase of tunnels and underground projects,the problem of crystalline blockage of tunnel drainage pipe is becoming more and more prominent,which seriously threatens the normal operation of drainage system and the safety and stability of the whole tunnel lining structure.Aiming at the problem of crystal blocking of tunnel drainage pipe,based on the theories of structural mechanics,hydrodynamics,molecular dynamics and basic physics,the anti crystal blocking mechanism and influencing factors of flocking on the inner wall of tunnel drainage pipe were systematically studied by means of literature review,field investigation,macro and micro test,indoor test,simulation and theoretical analysis,It provides theoretical and technical support for preventing crystallization blocking of tunnel drainage pipe.The research contents and main conclusions were as follows:（1）Through on-site investigation and indoor macro and micro test analysis,the groundwater quality characteristics,crystal composition and micro morphology,and the influencing factors of crystal plugging at the crystallization of tunnel drainage pipe under five geological conditions such as limestone were proved.Under the five geological conditions,the crystals are calcium carbonate mainly in granular and massive calcite crystal forms,and some contain a small amount of aragonite crystal forms.The main influencing factors of crystallization pipe plugging in sandy mudstone stratum were p H value of groundwater,the main influencing factors of crystallization pipe plugging in limestone stratum and argillaceous dolomite stratum were cation content dominated by Ca²⁺and Mg²⁺,and the main influencing factors of crystallization of drainage system in moderately weathered sandy slate stratum were chemical type,p H value and temperature of groundwater.（2）Based on the field investigation and literature,an indoor model test device for flocking and anti crystallization blocking of drainage pipe was developed,and the anti crystallization blocking law,crystal distribution law and crystal micro morphology of flocking and anti crystallization blocking of drainage pipe were studied.The results show that the indoor model test device can meet the needs of model test,and the average crystallization rate of non flocked drainage pipe was approximately inversely correlated with the experimental flow rate,which was reduced from 1.30g/d to 0.83g/d;The anti crystallization efficiency of M1 flocking drainage pipe with pile length of5mm and 10mm can reach more than 40%at each flow rate;There were few crystals in the transverse direction of fluff perpendicular to the water flow direction and more crystals in the longitudinal direction of fluff along the water flow direction.The flocking drainage pipe can not change the crystal form and micro morphology of crystals.（3）By means of indoor model test,simulation and theoretical analysis,the variation law of crystals attached to the fluff of flocking drainage pipe with time was studied,and the anti crystallization blocking mechanism of flocking drainage pipe was revealed.Anti crystallization blocking mechanism of flocking drainage pipe:the existence of fluff on the inner wall of flocking drainage pipe redistributes the cross-sectional velocity,and eddy currents appear on the downstream side of fluff,resulting in regional distribution of crystals on the downstream side of fluff,which can not form a whole.The crystals and fluff were not coordinated and deformed,resulting in periodic accumulation and falling off of crystals attached to fluff,Keep a certain cross-section in the drainage pipe for a long time without pipe blockage.（4）Through the combination of indoor model test and numerical simulation,the effects of fluff material,length,diameter and flocking spacing on flocking and anti crystallization blocking of drainage pipe were analyzed,and the key indexes of flocking and anti crystallization blocking of drainage pipe were put forward.The results show that the anti crystallization efficiency of M1 material was 30%～80%,that of M2 material was less than 50%,and that of M3 material was less than 10%.The binding energy between the material and calcium carbonate calcite crystal（1-10）and（104）surface was as follows:PVC>M1>0>M2>M3.The indoor test shows that M1 material with length of 5mm and 10mm can be preferentially selected for pipe wall flocking.The anti crystallization efficiency was 10%～80%at the longitudinal spacing of 25mm,less than 40%and 60%at 35mm and 45mm respectively,and only works at low flow rate;The anti crystallization efficiency increased first and then stabilized with the increase of flocking spacing along the water flow direction,while the flocking spacing perpendicular to the water flow direction had little effect.The increase of fluff diameter（0.6mm～1.4mm）helps to improve the local velocity below the water surface of flocking drainage pipe,but the low velocity area near the bottom of pipe wall gradually increases,and the worse the anti crystallization blocking effect was.The maximum flow rate of flocking parameters of 1.4-35-0.5-10 was nearly 30%higher than that of ordinary drainage pipe.The average value of the maximum flow rate of other flocking parameters was 3.71%higher than that of ordinary drainage pipe,and54.5%higher than the inlet flow rate of drainage pipe（2cm/s）.The increase of local flow rate of flocking drainage pipe was not the main role in preventing crystallization and pipe blockage.（5）The field in-situ test of flocking and anti crystallization blocking of drainage pipe was carried out.Combined with the indoor and field test results,the fluff material M1,the fluff length of 10mm,the longitudinal spacing of 25mm and 45mm,and the circumferential spacing of 7.82mm（arc length）can be selected as the fluff parameters for the first stage of engineering application.