Research on freeze sinking techniques for deep alluvium

摘要

The current research condition at home and abroad on the construction techniques of deep alluvium is described and the main techniques and suggestions of freeze sinking method of deep alluvium are introduced. The construction quality of freezing holes is the key factor affecting the freezing quality. The verticality of the freezing holes should be enhanced by means of controlling its maximum deflection distance, and the advanced method of rectifying deflection should be adopted. The key of the freezing wall design of deep alluvium is to enhance its strength and stability. Therefore the temperature of the shaft side cannot be higher than -12℃, the mean temperature of valid thickness of the freezing wall cannot be higher than -15℃, the deformation of shaft side cannot be more than 30 mm, and the brine temperature should be controlled at -32℃ or so. Mechanical excavating method and drilling and blasting method are used in freezing shaft section. When the mechanical excavating method is used, the hydraulic pressure excavator should be developed. When the drilling and blasting method is used, under the prerequisite for pledging the safety of freeze pipe, the charge calculation should be made based on the shock failure criterion for freeze pipe by blasting. Rational cut parameter and smooth surface blasting parameters are determined. The deflection condition of each freeze pipe in blast operating zone should be analyzed in detail and the minimum distance between freeze pipe and shaft side should be calculated so as to assure construction safety with efficient technical measures. The umbrella-shared boring machine is used in freezing weathered rock, sandy gravel or pebble bed. Management information system is used during the whole construction process.