Because it has many advantages such as wide range of applicable geology, can effectively keep the excavation surface stable, less disturbance to the land around the pipe, and less surface settlement. However, this construction method relies on the mud pressure to balance the soil and water pressure on the excavation surface and the mud as the medium for transporting the sludge, which will inevitably use a large amount of mud and produce a large amount of waste mud. At present, the disposal method of this waste mud is generally transported to a dumping place by transportation. This method will cause great harm to the soil structure and plant and animal growth in the dumping site, and will also produce secondary pollution in the transportation process, and the transportation efficiency is low and the cost is high if the mud tanker is used to transport the emission. Mud and water pipe jacking waste mud composition is complex, is a suspension system composed of water, bentonite particles, clay particles and admixtures. The waste mud also has the characteristics of fine particles, viscous flow state, and not easy to dewater, so the natural drying and dewatering process is extremely slow. If not treated in an environmentally friendly way, the harmful substances in the waste mud will pollute the soil and water bodies of the dumping site, thus threatening the health and safety of people, animals and plants, so it is urgent to study the green and harmless treatment technology of waste mud for mud and water balance pipe jacking construction.
1. Treatment method selection At present, there are many ways to treat waste mud, and more research on waste mud treatment technology and methods have been conducted in recent years, and all of them have their own advantages and disadvantages. The flocculant and curing agent treatment method is to add flocculant and curing agent to the waste mud to make physical-chemical reaction and transform it into a solid similar to the soil structure, and then landfill or use it as construction material, the amount of curing agent is large, the treatment cost is high and the cost performance is low. The mechanical dewatering treatment method uses physical methods such as pressurization and dewatering machines for solid-liquid separation of waste mud to achieve the purpose of waste mud reduction and treatment, but the pure mechanical dewatering treatment has high energy consumption, low efficiency and high cost. Chemical flocculation separates the solid-liquid slurry, but the water content of the precipitated separated solids is still high, and the solid phase cannot be stacked and transported directly. Based on this, we propose a combined chemical-physical treatment method, i.e. chemical flocculation and mechanical dewatering of waste slurry, with the goal of resourceization, reduction and harmlessness.
