Influencing Factors Of Crystalline Blockage In Highway Tunnel Drainage Pipes And Prevention Countermeasures

The problem of crystalline blockage of drainage pipes in road tunnels was born with the birth of tunnel drainage prevention engineering,and has been plagued by this problem during the construction of tunnels at home and abroad.Blockage of drainage pipes can lead to the accumulation of karst fissure water in the tunnel lining,increasing the water-bearing pressure of the lining,resulting in a series of problems such as cracking and leakage of the lining and floating of the elevated arch,which bring safety hazards to traffic.This paper combines the construction process of Hejiazhai Tunnel and Dabashan Tunnel of Anlan Expressway in Shaanxi Province to carry out field research and theoretical analysis on the problem of crystalline blockage of highway tunnel drainage pipes,and on the basis of which a tunnel model device was designed for field pilot tests to systematically investigate the influencing factors of crystalline blockage of tunnel drainage pipes and put forward corresponding countermeasures.The main research findings are as follows:（1）The pH and calcium ion concentration of the initial branch seepage water is generally higher than that of the palm face seepage water,which is related to the contact and reaction between the groundwater and the initial concrete.factors influencing the crystalline blockage of tunnel drains include water quality,geological conditions of the tunnel site area and drainage design.（2）The tests used two different compositions of test water to investigate the effects of pipe slope,material and drainage flow rate on pipe crystallisation and blockage respectively.It was found that the greater the slope of the pipe,the less crystallisation there was in the pipe;HDPE double-wall corrugated pipe was more crystallised than HDPE,PVC and PPR pipe;and the higher the drainage flow rate,the more crystallisation there was in the pipe under the premise of non-full pipe flow.The test water containing high HCO₃^-was more likely to cause crystallisation in the pipe in the early stages of the test than the test water containing high Ca²⁺.In addition,the p H,calcium ion concentration and total alkalinity in the pipe drainage had different trends over time under the two different water quality conditions,but the overall trend was to increase first and then decrease.（3）The static scale inhibition method was used to study the scale inhibition performance of polyepoxysuccinic acid（PESA）,polyaspartic acid（PASP）,polymaleic anhydride（HPMA）and butane 2-phosphate-1,2,4-tricarboxylate（PBTCA）individually and the synergistic scale inhibition effect under the condition of two-two compounding,the results showed that:PESA and PBTCA,HPMA and PESA,HPMA and PBTCA The results show that there is a certain synergistic effect between PESA and PBTCA,HPMA and PESA,HPMA and PBTCA,especially when the ratio of PESA to PBTCA is 4:1（total concentration of 25 mg/L）,the scale inhibition rate can reach 84%.Compared with the case without scale inhibitor,the p H and calcium ion concentration in the water after adding scale inhibitor decreased slowly with time,and the amount of crystallization produced in the pipeline was significantly reduced in the same time.（4）Citric acid and oxalic acid were chosen as the base compound organic acid,and new scale inhibitor was synthesized by introducing penetrating agent and dispersant.It was found that citric acid and oxalic acid in a 4:1 compound could achieve the optimal descaling effect.Compared with other compounding ratios,the calcium ion concentration and p H in the water of the descaling agent with this compounding ratio grew faster,and the descaling rate could reach 70.7%at 72 h of reaction.On this basis,the descaling rate increases slightly with the addition of penetrant,dispersant and stabilizer,reaching a maximum of 74.6%.