Research on design method for thickness of freezing wall in thick alluvium over 600 m

The freeze sinking method is the main method when a shaft passes through thick alluvium over 600 m, and the design and calculation method of freezing wall thickness is one of the most difficult problems that must be overcome by freeze sinking method in deep alluvium. Moreover, the relevant parameters involved in the calculation of the thickness of the frozen wall of deep alluvium are difficult to determine and cannot be designed and applied in engineering. In the paper, combined with the drilling practice of west ventilation shaft of Zhaogu No.2 Coal Mine with 704.6 m thick alluvium by freeze sinking method, the classical Domke Elastic-plastic Formula and the Vialov-Zaletsky Finite Section High Plastic Formula were put forward to separately calculate the freezing wall thicknesses in sandy soil layer and cohesive soil layer of 600～1 000 m thick alluvium; and proposes key parameters such as the height of the heading section and the compressive strength of the frozen soil in the calculation formula. It was proposed that when blasting excavation method was adopted for deep drilling in deep alluvium with thickness of 600 m or more, the height of blasting excavation section should be taken as the calculation section height to substitute the high plasticity calculation formula of the Vialov-Zaletsky Finite Section, to calculate the correct viscosity thickness of frozen wall of soil layer. According to the great discrete characteristics of test values of compressive strength of frozen soils from deep different horizons, it was proposed that the design of freezing wall should be comprehensively considered from the perspectives of safety, advancement, and economic rationality; and the test characteristics in compressive strength of frozen soil and non-frozen soil and the tunneling technology characteristics of frozen section of deep thick alluvium were analyzed systematically; In the selection of calculation strengthvalues of frozen soils, the mean value and the low value should be distinguished, the mean value should be used to calculate the thickness of the frozen wall in the general state of each layer, the low value should be used to calculate the thickness of the frozen wall in the most unfavorable layer of the horizon; It is proposed to give reasonable play to the influence of the height regulation of the excavation section on the stability of the frozen wall, and to determine the calculated strength of the frozen soil and the design thickness of the frozen wall in the thick alluvium cohesive soil layer. The design method has been verified in engineering practice, and it has achieved excellent results in safety, high quality and economy with rapid construction, and scientifically guided the construction.