Long-Distance Pipe Jacking in Complex Urban Geological Environment

A steel underground pipeline with a diameter of 2.4 m and a total length of 3,617 m (plate thickness of 26 mm) has been constructed in a city in central Hubei, and the engineering, procurement, and construction (EPC) project has been lifted from the upstream channel to supplement water to the downstream lake inside the city. Through preliminary geological survey data, site topographic and geomorphic survey, urban construction, as well as the requirements of the construction party, the preliminary arrangement of working wells and receiving wells as well as the selection and customization of pipe jacking machines have been proposed. Frequency conversion motor and remote monitoring technology are adopted for geotechnical change and long-distance pipe jacking. Through detailed survey, the rock and soil change section as well as gradual change conditions have been determined, the accuracy of construction mechanics calculation and construction operation control have improved, the basis and analysis basis are provided, and some experiences in construction operation are summarized.

Microbial-Induced Carbonate Precipitation: A Review on Influencing Factors and Applications

Based on recent literary sources, this survey discusses the effects of main factors influencing the microbial-induced calcium carbonate precipitation (MICP), including the bacterial species, bacterial concentration, temperature, and pH value. While the MICP technology has been widely adopted to improve rock and soil characteristics, it has excellent development prospects in many other fields. The breakthrough solutions in the MICP technology are improving geotechnical and foundation sand properties, repairing cement-based materials, using mineralized film mulching to protect cultural relics, enhancing properties of tailings, desert control, and heavy metal environmental restoration, etc., are discussed. The experimental findings prove that MICP can improve the strength, stiffness, liquefaction resistance, erosion resistance, and permeability of geotechnical materials and maintain the good permeability and permeability of the soil and improve the growth environment of plants. It is an environment-friendly bioengineering technology. Because microbial mineralization involves a series of biochemical and ionic chemical reactions, there are many reaction steps in the solidification process and the solidification effect of MICP is restricted and affected by many factors. The comprehensive analysis and optimization strategy on MICP industrial implementation should account for micro- and macro-scale effects: the type of bacteria, the concentration of bacteria and cementation solutions, ambient temperature, pH value, and other factors directly affect the crystallization type, morphology, and size of calcium carbonate from the microscopic standpoint, while the macro-scale factors control the rock and soil mineralization. The limitations and prospects of the MICP technology are outlined.

Relationship Between Induced Polarization Relaxation Time and Hydraulic Characteristics of Water-Bearing Sand

Induced polarization method has become a popular method for evaluating formation permeability characteristics in recent years because of its sensitivity to water body and water-bearing pore structure. Especially, the induced polarization relaxation time can reflect the macroscopic characteristics of the pore structure of rock and soil. Therefore, in order to study the relationship between relaxation time and permeability, eight different sizes of quartz sand were used to simulate water-bearing sand layers under different working conditions, and the induced polarization experiment and Darcy seepage experiment were carried out on the same sand sample in this paper, respectively. The experimental results show that the relation time and the evolution of the permeability are closely correlated with the sizes of quartz sand. According to the experimental data, with the particle size of the quartz sand as the link, the power function equation is fitted to better describe the relationship between the permeability and the relation time. It is worth noting that the equations obtained are only empirical equations for quartz sand and are not suitable for general applications.