Abstract
Since complex barriers need to be passed through during the process of drilling long-distance horizontal freezing boreholes, the stability of the borehole wall at the soft and hard stratum interface is the key in controlling the deflection of the horizontal boreholes. The author puts forward to establishing the stability mechanical model of horizontal freezing borehole walls with fluid loss as the control index, starting from the stability mechanism of horizontal freezing boreholes and combined with the working conditions of horizontal freezing boreholes; selects two optimal fluid loss additives from the perspective of the molecular structure of bentonite materials, and determines the optimal formula by formulation optimization by virtue of orthogonal tests; applies the optimal formula into the long-distance pile and borehole penetration test, and validates the reliability of wall protection slurry formula materials for horizontal boreholes via comparing the water loss and soil erosion at the pile interface and analyzing the deflection rules, which is of certain value in engineering promotion and application.
Highlights
By taking the opportunity of subway construction, the underground space is faced with a great booming opportunity
After analyzing the two working conditions of horizontal freezing boreholes, the author established the mechanical model of the stability of borehole walls during the drilling and after the formation of boreholes, based on the principle of water loss and permeability of slurry in formation during drilling
The author puts forward to establishing the mechanical model of horizontal freezing borehole wall stability with fluid loss as the control index, starting from the working conditions of horizontal freezing boreholes; selects two optimal additives that can reduce the fluid loss of slurry from the perspective of the molecular structure of bentonite
Summary
By taking the opportunity of subway construction, the underground space is faced with a great booming opportunity. The artificial freezing method, featured with excellent strength in reinforcing soil, wonderful water sealing performance, flexible design, minor impact to surroundings and other advantages, plays an irreplaceable role in the development of underground space[2]. Due to the existence of the envelop enclosure and structures of the operating stations, it’s impossible for shield tunneling machines to push forward as normal, and soil reinforcement and barrier clearance by applying the freezing method in the soft ground in advance is one of the safest and most effective methods to ensure the normal move-forward of shield tunneling machines. Considering the long distance of drilling freezing boreholes in the freezing crossing projects and a plurality of barriers (underground diaphragm walls, piles, latticed columns, etc.) frequently to be crossed during the crossing procedure, how to ensure the stability of soft soil at the soft and hard formation interface is the key of successful drilling. There are few researches on the formula of slurry materials and the stability of borehole walls for horizontal freezing pile and borehole penetration
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