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Severe blockages of tunnel drainage systems greatly affect the lining structure of the tunnels, thus jeopardizing their stability and safety. In order to study the blockages of tunnel drainage pipes, the flow rate of a calcium carbonate crystal tunnel was measured in the mountainous area of Southwest China. According to the actual flow velocity results, numerical simulation was combined with finite element software (ANSYS Fluent). This analyzed the calcium carbonate crystallization near the interface of the tunnel drainage pipe. The results are as follows: (1) for both the Y-shaped three-way pipe and the T-shaped pipe, the values of maximum water velocity are similar but occur at different locations. At the interface of the transverse drainage pipes, flow velocity is the highest; (2) at the three-way joint segment, the water that flows in the longitudinal drainage blind tube is influenced by the water coming from the annular drainage blind tube. At the interface of the transverse drainage pipe, water flows at a lower speed in the Y-shaped three-way pipe than in the T-shaped pipe—the difference is about 3.75 times; (3) the smoothness of calcium carbonate deposition is correlated with water velocity and the content of calcium carbonate. The calcium carbonate crystal will occupy a larger space at locations with a higher calcium carbonate content and a lower flow velocity; (4) the drainage capacity of tunnel drainage pipes declines most when the volume fraction of calcium carbonate reaches 80%. Compared with the situation when calcium carbonate does not exist, the drainage capacity decreases by 84.78% for T-shaped pipe and by 77.64% for Y-shaped three-way pipe when the volume fraction of calcium carbonate is 80%. [ABSTRACT FROM AUTHOR]

In the alkaline geological environment, crystallization blockage of tunnel drainage systems is a common engineering problem and it is difficult to treat. The microscopic mechanism of crystallization and the environmental influence factors are still unclear. Based on the molecular dynamics (MD) technique, this study establishes nanoscale models of CaCO3 and the polyvinyl chloride (PVC) pipe, which is commonly used in drainage systems, under different alkaline environments. The goal is to study the interfacial interaction between CaCO3 and PVC and to reveal the effect of the alkaline environment on the adsorption of CaCO3 by PVC at the atomic scale. Analysis of the adsorption properties predicted by the CaCO3-PVC MD model reveals that CaCO3 molecules attract each other and form many atomic clusters at approximately 0.11 nm from the PVC interface. The peak difference between the strongly alkaline solution and the pure water solution at this distance reaches 31.6%. An in-depth exploration of the differences in adsorption between CaCO3 and PVC under different alkaline environments indicates that the mobility of CaCO3 rises gradually as the alkalinity of the solution increases. In particular, the mobility of CaCO3 in strongly alkaline solutions is approximately 60% higher than that in pure water. Moreover, as the alkalinity of the solution increases, the binding energy of the interface increases, the affinity of the interface increases, and the CaCO3 adsorption capacity gradually increases. The results of laboratory experiments were consistent with the MD simulation results, which indicates that MD simulation can play an important role in the design and evaluation of engineering practice. The innovation of this paper is to try to use the molecular dynamic (MD) technique in the field of materials to explain the practical problems in the field of traditional civil engineering, and the feasibility of molecular dynamic simulation is verified by indoor simulation experiments. The findings of this study can help for a better understanding of crystallization patterns in tunnel drainage pipes in alkaline geological environments and attempt to provide a theoretical basis and new ideas for solving this problem. [ABSTRACT FROM AUTHOR]

The blocking of tunnel drainage pipe caused by crystals from groundwater calcification is prone to bring about lining cracking and water leakage. In this paper, in order to prevent tunnel drainage pipes from the crystallization, this study proposed a method to prevent the binding of Yin and Yang ions based on the alternating electric field. For the purpose of concluding the crystallization rules of drainage pipes and verifying the feasibility of this method, an indoor orthogonal test was adopted to study the crystallization rules and anti-crystallization efficiency of three drainage pipes under three alternating electric fields at three voltages (6 V, 9 V, 12 V) and at three flows (34.7 ml/s, 76.9 ml/s and 192.0 ml/s). The results showed that: During the test, all the three voltages can reduce the crystallization of drainage pipes, and the anti-crystallization efficiency of all the three tested pipes was optimal at 6 V under each of three alternating electric fields, reaching 22%, 25%, 7%, respectively. Case 2 had the best anti-crystallization effect at 6 V. The reason is that, at 6 V, the crystals had the loosest and minimum grains and the largest interplanar spacing, so they were inclined to be discharged through the pipe under the water flow. At 34.7 ml/s, Case 2 had the best anti-crystallization effect at 12 V; At 76.9 ml/s and 192.0 ml/s, Case 2 had the best anti-crystallization effect at 6 V. The alternating electric field can prevent the tunnel drainage pipe from crystallization and blocking, and different drainage pipes in the alternating electric fields should be selected based on according to the groundwater in tunnel. [ABSTRACT FROM AUTHOR]

Crystal blockages of tunnel drainage systems severely undermine the tunnel lining structure and operation safety. In order to reduce the risk of crystal blockages of tunnel drainage systems, the distribution of highway tunnel defects was identified through a field survey, indoor test, and literature analysis, and an optimization method of tunnel drainage structures was proposed. The research suggested the following: (1) Lining water leakage and construction joint water leakage were the most common defects in the tunnel drainage system of Renhua–Xinfeng Expressway and Yingde–Huaiji Expressway in Guangdong Province, accounting for 60% and 32% of total defects, respectively. The number of defects that occurred in the drainage system of the tunnel was larger in the granite formation, with the number of road seepage and inspection chamber crystallization incidents reaching 2.5/km and 2.8/km, respectively. (2) The groundwater was mainly alkaline with a pH value of 8~12, Ca2+ (107 mg/L) was the cation with the largest ion concentration, and HCO3− (165 mg/L) was the anion with the largest ion concentration. The crystals in the tunnel drainage system were predominantly square, spindle, and rhombic calcite and aragonite composed of CaCO3, mixed with a small amount of sediment. (3) To reduce the risk of crystal blockages of the tunnel drainage system and ensure tunnel lining structure safety, a threefold optimization measure was proposed, namely, setting one-directional drainage pipes between the cable trench and the roadside blind drainage ditch, applying "π" type anti-crystallization drainage water-stop belts at the circular construction joints in the secondary lining, and both increasing the slope of the transverse drainage pipe and using an anti-crystallization drainage pipe. The research results will play an important role in guiding the design, construction, and maintenance of highway tunnel drainage systems in China. [ABSTRACT FROM AUTHOR]

With the increasing of the tunnel operation life, various diseases of the tunnel are gradually highlighted, especially the lining cracking and leakage caused by the crystal blocking pipe of the drainage system, which brings serious hidden trouble to the safe operation of the tunnel. In order to solve the problem of crystal plugging of horizontal drainage pipe in tunnel, the transverse drainage pipe of the tunnel was taken as the research object, combined with the field survey data, and the indoor test was used to analyze the anti‐crystallization law of flocking drainage pipe at different velocities. The results showed that the flocking drainage pipes had an anti‐crystallization effect, and the anti‐crystallization efficiency could be increased by more than 50% compared with the ordinary drainage pipes, and the flow rate at 6.82 cm/s could reach more than 60%. At the flow rate of 5.46 cm/s, the crystallization on flocking drainage pipes at the later stage of the test remained basically unchanged and was less than that on ordinary drainage pipes. The change in the weight of crystals on the flocking drainage pipes was approximately sinusoidal, and the change period was different at different flow rates; among which, the change period of crystallization on the flocking drainpipe was shorter when the villi length was shorter at low flow rates. [ABSTRACT FROM AUTHOR]

If the tunnel drainage pipes are blocked, the supporting structures will be in danger because they would receive more force than before. In order to investigate the blocking problem, some laboratory tests and in situ experiments were carried out. Microtests showed that the main component of crystal is calcium carbonate. Calcium ions, carbonate ions, and bicarbonate ions of groundwater should be related to the crystal. The polyvinyl chloride pipe, hydrophobic antistatic self-cleaning coated pipe, silicone rubber coated pipe, pipe under electromagnetic field, polytetrafluoroethylene coated pipe, and polyethylene coated pipe were used in laboratory and field experiments. The laboratory results showed that the electromagnetic field may be the best method to prevent crystallization because the crystallizing weight was less than 0.1 g in 30 days. The field tests showed that there was less crystals on the inner surface of hydrophobic antistatic self-cleaning coated pipe than that of the polyvinyl chloride pipe and the polytetrafluoroethylene coated pipe. The crystallization prevention effects of the other experimental pipes need more studies to examine. [ABSTRACT FROM AUTHOR]

A lot of crystallizations exist on the inner wall of tunnel drainage pipes in Chongqing. Tunnel support structure often bears larger load than usual because the tunnel drainage pipes are blocked easily by the crystals and the groundwater level would rise. In order to investigate what the crystals are, site investigations and laboratory tests of crystals and groundwater were completed. Some valuable results have been obtained. Firstly, the crystallizations are usually discovered in drainage pipe exits of tunnels which are under construction in Chongqing. Furthermore, the results of XRD have confirmed that the crystals are calcite. And calcite morphology could be found in most SEM images. But there are other morphologies in these images other than calcite because calcite is often influenced by some factors, such as important ions in groundwater, pH of groundwater, kinetics effect, and so on. Finally, some steps and solutions to solve blocking of tunnel drainage pipes caused by crystallization are suggested. One of the best solutions is that some special materials which could prevent crystals from being attached to pipes are coated on the inner surface of drainage pipes. The results could contribute to understand the crystallization phenomenon profoundly and help solve the similar situations of tunnel drainage pipe blocking. [ABSTRACT FROM AUTHOR]

The crystalline blockage of tunnel drainage pipes in a karst area seriously affects the normal operation of drainage system and buries hidden dangers for the normal operation of the tunnel. In order to obtain the influencing factors and laws of tunnel drainage pipe crystallization in a karst area, based on the field investigation of crystallization pipe plugging, the effects of groundwater velocity, drainage pipe diameter, drainage pipe material, and structure on the crystallization law of tunnel drainage pipe in karst area are studied by indoor model test. The results show that: (1) With the increase of drainage pipe diameter (20–32 mm), the crystallinity of drainage pipes first increases and then decreases. (2) With the increase of water velocity in the drainage pipe (22.0–63.5 cm·s−1), the crystallinity of the drainage pipes gradually decreases from 1.20 g to 0.70 g. (3) The crystallinity of existing material drainage pipe is: M3 (poly tetra fluoroethylene) > M2 (pentatricopeptide repeats) > M4 (high density polyethylene) > M1 (polyvinyl chloride); M8 (polyvinyl chloride + coil magnetic field) is used to change the crystallinity of drain pipe wall material. (4) When the groundwater flow rate is 34.5 cm·s−1, M1 (polyvinyl chloride) and M8 (polyvinyl chloride + coil magnetic field) can be selected for the tunnel drainage pipe. The research on the influencing factors of tunnel drainage pipe crystallization plugging fills a gap in the research of tunnel drainage pipe crystallization plugging. The research results can provide a basis for the prevention and treatment technology of tunnel drainage pipe crystallization plugging. [ABSTRACT FROM AUTHOR]

Crystalline pipe plugging in tunnel drainage systems is one of the causes of tunnel lining cracking and water leakage. Therefore, effective prevention of crystalline pipe blockage in tunnel drainage systems is very important to ensure the safety and stability of the lining structure during tunnel operation. Combined with the theories of fluid mechanics, structural mechanics and basic physics, the flocking and anti-blocking mechanism of drainage pipe was comprehensively analyzed by using the method of mathematical modeling, including: (1) the calculation expression of average velocity of the flocked section of a flocked drainage pipe v = Q/(C1 − C2(r + r′)) and the calculation formula of flowing water pressure under the action of groundwater Fw =  KAγQ2/(2g(C1 − C2(r + r′))2); (2) the flow velocity v0 in the flocked drainage pipe shall meet v2 < 4gπrlτ1/γKA, crystals will be attached to the fluff and the crystals will maintain dynamic balance; (3) the flow velocity v0 in the flocked drainage pipe shall meet v2 ≥ 4gπrlτ1/γKA, crystals will not adhere to the fluff and the flocked drainage pipe will remain unobstructed. The research on the mechanism of preventing blockage of flocking drainage pipes fills the gap in research theory in this regard, contributes to the popularization and application of blocking prevention technology of flocking drainage pipes, reduces the maintenance cost during operation of tunnel drainage systems and ensures the safe and normal operation of tunnels. [ABSTRACT FROM AUTHOR]

Drainage pipe blockage resulting from crystals is one of the causes for cracking and leakage of tunnel lining. Therefore, effective prevention from drainage pipe blockage caused by crystals is crucial to ensure the safety and stability of lining structures during the operation of tunnel drainage system. Based on a large number of indoor model tests and numerical simulation analyses, binding energy between four materials and the calcium carbonate aqueous solution ("solid + liquid" system) and that between the four materials and the two typical growth crystals of calcium carbonate ("solid + solid" system) were studied. The research results indicated that: (1) The four materials all had an adsorption effect on the calcium carbonate aqueous solution system, and the PA6 had the greatest adsorption effect while the PP had the smallest adsorption effect; (2) There was spontaneous adsorption between the PVC or PA6 and the two typical growth crystals of calcium carbonate and no adsorption between the PP or SiC and the two typical growth crystals of calcium carbonate unless external energy was in place; (3) The PP and SiC can be used as the materials for drainage pipe flocking, but it shall be ensured that the fluffy material has a good geometrical property. The prevention technology for crystallization that causes drainage pipe blockage fills the gap in the research of drainage pipe blockage caused by crystals, which can reduce the maintenance cost for the operation of the tunnel drainage system and ensure safe and normal operation of the tunnel. [ABSTRACT FROM AUTHOR]