Abstract. According to the characteristics of the subway tunnel method construction and the special operation requirements of the highway, many risks of undercrossing engineering should be required urgent attention. So, based on one subway tunnel undercrossing the existing highway, the possible sources of risk are defined and analyzed. Furthermore, according to the evaluation method of fuzzy mathematics, for soft and hard strata complicated geological environment, the assessment and grading of risk sources are investigated during the subway tunnel undercrossing the existing highway. Those results are supporting the important suggests for constructors and designers.
During urban subway tunnel construction, the blasting inevitably has an impact on the ground structure. If it's energy is not controlled, the surface of existing structures would be easily causing damage. So, according to one subway tunnel undercrossing the existing highway, based on the numerical simulation, three different levels of surface orientation at distances of surface vibration velocity are obtained. And, the propagation and characteristics of vibration are investigated under the effect of blasting vibration velocity control measures.
The compressed and dehydrated mud was made into filter cake, and then fly ash, silica fume and cement were added to it to prepare foamed concrete with sodium α-olefin sulfonate as foaming agent. By analysing the changing characteristics of the compressive strength, apparent density, water absorption and microstructure of the foam concrete, the key mechanism of making the foam concrete was analysed in depth. The results show that mud filter cake can improve the comprehensive performance of foamed concrete. The best mix ratio is 20% of mud filter cake, 50% of cement addition, 20% of fly ash, 10% of silica fume, 0.55 of water cement ratio and 55% of foam volume. The compressive strength of foam concrete is 1.6MPa and the apparent density is 660.26kg/m3. The water absorption rate is 23.73%, which accords with China Construction Industry Standard JG / T266-2011. Proper addition of mud filter cake can improve the pore structure and cementing material matrix of foamed concrete, and enhance the strength of foamed concrete. However, too much addition will produce connected pores and cracks, and reduce compressive strength. The results can provide theoretical basis and technical reference for mud resource utilization.
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