The in situ spraying method is widely used because of its advantages as a trenchless pipeline repair technology, including a fast construction speed and close bonding between the repair lining layer and the reinforced concrete pipe. However, current research on high-performance spray repair materials, the bearing capacity of pipelines before and after repair, and the failure modes between the two interfaces after repair is insufficient. Through laboratory tests designed with multiple sets of control tests, this paper outlines the bearing capacity of reinforced concrete pipelines with corrosion thinning defects repaired with ultra-high-performance concrete. The variation law of the residual bearing capacity of reinforced concrete pipes and the influence of different corrosion degrees, repair thicknesses, and interface forms on the bearing capacity of reinforced concrete pipes were studied following UHP-ECC for pipe repair. The results showed that the bearing capacity of the structure decreased with an increase in the corrosion thickness of the pipeline. After repair with ultra-high-performance concrete, the bearing capacity of corroded pipelines greatly improved. When the corrosion and repair thicknesses were the same, the bearing capacity of the repaired pipeline with different interface forms was very different. After the interface was implanted with nails, spray repair was carried out and the bearing capacity of the pipeline improved the most, followed by the naturally bonded interface. When plastic film was pasted on the repair interface, the bearing capacity of the pipeline improved the least.
After long-term operation, tunnel lining segments encounter various problems. Aiming at these problems, in this paper, we present a method of strengthening tunnel lining segments by in situ spraying mortar. An experimental study of the in situ spraying mortar was carried out to determine the compressive strength, flexural strength and interface properties (splitting tensile strength and shear strength) between concrete and H-70 mortar. The experimental results show that the mechanical properties of H-70 mortar are less dependent on the curing humidity than ordinary concrete under standard curing conditions, the 7-day compressive strength of H-70 is 55 MPa, which is 61% of the 28-day compressive strength. This shows that H-70 has high early strength and is very suitable for rapid reinforcement. The interface roughness has a significant effect on the splitting tensile strength, and it can be increased by chiseling to improve the bearing capacity of the strengthened structure. A full-scale loading experiment was carried out on the segment strengthened by in situ spraying mortar. The loading process, failure mode and ultimate bearing capacity of the strengthened structure were analyzed by full-scale loading experiment. The research shows that the ultimate bearing capacity of the tunnel segment strengthened by in situ spraying mortar increased significantly. The ultimate bearing capacity of the strengthened structure is 10% higher than that of the unstrengthened structure. The advantages and disadvantages of in the situ spraying-mortar strengthening method are analyzed in comparison with the internal-tension steel-ring strengthening method.
For buried municipal tunnels—such as cable tunnels and utility tunnels with structural defects—due to the sheltering of the internal pipelines, shelves, and other auxiliary facilities, traditional trenchless rehabilitating methods are not applicable since an intact ring is needed for spraying and lining. In these tunnels, only the exposed area at the crown of the ring can be partly rehabilitated. In this paper, three-edge bearing tests (TEBTs) for partially rehabilitated reinforced concrete (RC) pipe sections are carried out to simulate the case of a municipal tunnel and the effects of different repair materials (cement mortar and epoxy resin) and different dimensional parameters of the liner (lining thickness, lining range) on the partial rehabilitation effect of defective RC pipes are studied. The deforming compatibility of the liner–pipe interface is discussed, and the flexural rigidity of the partially rehabilitated section is calculated. The results show that the load-carrying capacities of partial rehabilitated RC pipes are effectively improved.
A large number of drainage pipes and canals in China have been in disrepair for a long time and there have been problems such as leakage and corrosion. In response to these problems, this paper studies a non-excavation technology for repairing the arched canal structure—the in-situ spraying method. To study the influence of the original canal structure on the mechanical characteristics of the lining structure by in-situ spraying and the restraint effect on the lining structure, a field model test with a similar ratio of 1:2 was conducted in the field test pit. By conducting four stages of three-point concentrated load loading tests, the mechanical characteristics of the lining structure were investigated to reveal the influence of the canal structure on the force of the lining structure. The test results show that: the maximum crack width of the newly added lining structure is 0.27 mm and the normal service ultimate bearing capacity of the arched structure repaired by H-70 reaches 150 kN; comparing the loading test and the numerical simulation results, the difference between the two vault displacement results is 4.65% and the results are relatively consistent. The displacement of the bottom of the lining structure is small and the participation of the bottom plate is small, while the displacement of the upper arch structure of the lining is significantly larger than the lateral displacement, indicating that the canal structure can effectively limit the lateral displacement of the newly added lining and that the canal structure is greatly reduced. The bending moment of the lining structure is improved and the restraint effect on the arch foot is more obvious. This paper proposes the use of H-70 to repair arched canal structures by the in-situ spraying method and seeks to prove the feasibility of this method and fill the gap of research in this area. This paper provides the structural design basis and experimental knowledge for the construction of the repair method, which has important practical significance for the pipeline repair project in the future.
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