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To address the safety issues of bridge structures affected by local scouring from the Yellow River mudflows, this study employod bidirectional fluid-solid coupling theory and turbulence theory to establish a numerical analysis model for sand-laden mudflow impacting bridge piers, which was validated against experimental data from literature. Based on this, calculations were conducted for three different cross-sectional pillars to assess scouring effects. The results indicate that circular cross-section pillars exhibit better resistance to scouring, making them more suitable for the Yellow River bridge piers, while triangular cross-section pillars demonstrate superior diversion capabilities, rendering them more suitable for abutments. Building upon this, numerical simulations were conducted for circular cross-section bridge piers under four different sediment concentrations. Comparative analysis reveals that as sediment concentration increases, the likelihood of pier scouring by mudflows increases, corroborated by comparisons with impact forces. Moreover, within a certain range of sediment concentrations, the dynamic response of bridge piers increases with sediment concentration; however, beyond this range, the dynamic response sharply declines. [ABSTRACT FROM AUTHOR]

Aiming at the poor geological conditions of water conveyance tunnel in Lanzhou water source construction engineering by double shield TBM excavation, the comprehensive methods and treatments were put forward by data statistics, engineering analogies, and other methods. Before TBM tunneling, F, fault zone and F, fault zone were excavated by drilling and blasting method. After initial support which guaranteed the stability of surrounding rock, TBM slided through and installed segments. Based on geological analysis along tunnel, combination the observation of tunneling face, rock muck analysis and tunneling parameter analysis, the geological conditions of surrounding rock in front of tunneling face were comprehensively predicted by using three-dimension seismic method and three-dimensional resistivity method. The principle of " drainage first, drainage and plugging combined" was adopted, the variable slope drainage system was established, the operation mode of the drainage system was determined according to the amount of water gushing. According to the characteristics of the front shield blocked, the method of releasing surrounding rock pressure by manual excavation of the heading tunnel from the telescopic shield was adopted to make the TBM out of blocked. Based on identifying geological conditions, the use of chemical grouting and cement grouting consolidation broken surrounding rock, controlling TBM tunneling parameters, slow tunneling through the fracture zone. TBM tunnneling practice shows that the adopted technology is effective and the poor geological conditions have not caused serious consequences for TBM. [ABSTRACT FROM AUTHOR]

Aiming at the tunneling performance of double shield TBM under complex geological conditions, based on double shield TBM construction at water conveyance tunnel in Lanzhou water source construction engineering, this paper studied the equipment utilization ratio, disc cutter consumption and tunneling speed of TBM under different geological conditions by the method of statistical analysis of field measured data. The results show that. a) for class Ⅱ, Ⅲ and IV surrounding rocks, the TBM utilization rate increases with the decrease of surrounding rock types, but the TBM utilization rate of class Ⅴ surrounding rocks is generally lower than 10% because of water gash and TBM block accidents. b) The TBM disc cutter consumption of hard rock is significantly higher than that of soft rock. Hard rock with the decrease of surrounding rock classification, the disc cutter consumption is obviously reduced. c) For the surrounding rocks of Class Ⅱ, Ⅲ and Ⅳ and Ⅴ, with the decrease of the class of surrounding rocks, the penetrate rate increases obviously. The advance rate of TBM is affected by the penetrate rate and the utilization ratio of equipment. The average tunneling speed of Class Ⅱ, Ⅲ and Ⅳ surrounding rocks increases with the decrease of the surrounding rock class. However, the surrounding rock of class Ⅴ is affected by the low utilization rate of equipment, and its average tunneling speed is the lowest. [ABSTRACT FROM AUTHOR]