In pipe jacking, the continued growth of friction resistance around the pipe may cause problems, such as an insufficient jacking force, soil collapse, and even land subsidence, which seriously endangers the structural safety of the pipe and surrounding structures. Bentonite slurry is often used as a lubrication material, but the friction resistance increases due to the inappropriate slurry concentration, and this may cause construction safety problems. In addition, the slurry standing time increases the difficulty of re-jacking construction. To further study the above problems, the friction characteristics of a steel pipe-soil interface under different slurry concentrations and slurry standing times were studied using direct shear tests. The test results show that the peak shear stress and friction coefficient of the interface first decrease and then increase with the increase in the concentration, which is less than or equal to 20%. The peak shear stress and friction coefficient increase with the increase in the concentration, which is greater than 20%, and the position of shear failure changes from between the slurry soil mixture and pipe wall to between the slurry and pipe wall, and finally to the slurry interior. The influence of the slurry standing time on the friction characteristics of the interface is as follows: For the same slurry concentration, the peak shear stress and friction coefficient of the interface increase with the standing time, approximately increasing first and then stabilizing; for different slurry concentrations, the amplification of the peak shear stress and friction coefficient increase with the increase in the concentration.

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.

Polymer slurry is widely used in underground engineering treatment, but due to the concealed nature of underground projects, the diffusion pattern of slurry in the sand has been little studied. In this study, the basic physical properties of water-based polyurethane, oil-based polyurethane, and acrylate and epoxy resin were compared, and the performance of chemical grouted sands with different polymer slurry/sand mass ratios (PS/S) was tested. The higher the PS/S, the better the mechanical and impermeability properties of the chemical grouted sands. In this paper, water-based polyurethane was selected to carry out orthogonal tests on the diffusivity of slurry in sands. This experiment investigated the degree of influence of sand quality, grouting pressure and sand compactness on the diffusion of slurry in sands. The test results show that, in terms of factors affecting the final pressure of grouting, the sand density has the greatest influence, followed by the sand quality, and the grouting pressure is the smallest. In terms of slurry diffusibility, grouting pressure has the greatest influence, followed by sand compactness, and the sand quality is the smallest. The diffusion mechanism of slurry in the sand was deduced from the morphology of chemical grouted sands. Water-based polyurethane showed splitting-compression-penetration diffusion in sands of different grades, and the diffusion pattern of the slurry was not the same in low-pressure (1–1.5 MPa) grouting and high-pressure (2 MPa) grouting, and lateral splitting occurred in the case of high-pressure grouting diffusion.

PVC pipe jacking is prone to cause yielding or buckling under the jacking force and may lead to engineering failure. The relationship between the buckling modes, ultimate bearing capacity, different diameter–thickness ratios, and length–diameter ratios of PVC pipe jacking under different load forms was analyzed. The calculation methods for allowable jacking force and the single allowable jacking distance are obtained through theoretical analysis and three-dimensional finite elements. The buckling mode of the pipe under uniform load changes from symmetric buckling to asymmetric buckling and then to the overall Euler buckling form as the length–diameter ratio increases. The ultimate bearing capacity of the pipe approaches the theoretical value of yield failure when L/D $\le$ 6. For L/D $>$ 6, the pipe undergoes buckling, and the ultimate bearing capacity determined by the axial buckling value and the buckling load can be calculated according to the long pipe theory formula when L/D $>$ 8.5. Under eccentric loads, the failure mode transitions from local failure to Euler buckling with increasing pipe length. The ultimate bearing capacity of pipe is obviously lower than that of uniform load, but as the length–diameter ratio increases, this difference decreases until it becomes consistent.

The preparation and recycling of slurry is a very complicated and crucial task in large Horizontal Directional Drilling (HDD) river-crossing project. This paper introduced the successful and advanced experiences of the utilization and management of slurry in large HDD projects in China. Different property requirements of slurry in different periods of the project are discussed. Research is focused on the recycling system of slurry, including the filtration of slurry which returned from the drill hole, and how to add bentonite and additives in this filtrated slurry. The recycling of slurry can save a large amount of bentonite and additives. The disposal methods of waste mud in the job site were discussed, and two methods were recommended to be adopted to dispose waste mud. One is mechanical methods, using centrifugal machine; the other is chemical method, using chemical material to solidify waste mud.