| Under seepage force influence of the groundwater, soil will lose its bearing capacity, and flow with groundwater. This phenomenon is called quicksand. Quicksand usually happens in soil with fine particle, uniform particle, loose and saturated non-adhesive soils. Quicksand happens with lots of kinds, and it has great influence on the safety and normal use of the building. There are many negative influence of quicksand. On the one hand, construction will not proceed normally and foundation excavation cannot continue due to quicksand. On the other hand, foundation excavation itself is a destroy action for the initial geological environment, and quicksand will worsen destroy instability, which makes it possible for slope collapse, lateral large displacement and settlement, adjacent building deformation and failure. Therefore, it is crucial to control and govern quicksand during foundation pit construction and so on. As for grouting theory, in practical grouting engineering, the grout viscosity is always assumed to be a constant, by which way diffusion distance will be further compared with actual situation. This might lead poor government effect for the engineering.This research object of this paper is urea-formaldehyde resin. The government effect of the grout for quicksand is analyzed by studying the diffusion mechanism and reinforcement characteristics of urea-formaldehyde resin in water-bearing sand layer. Firstly, the basic physical and chemical property of the grout and mechanical property of the grout gel with different ratio are tested. Then, according to the test results, the proper ratio is chosen to perform indoor grout simulation experiment to study diffusion law of the grout in water-bearing sand layer. The relationship among grouting pressure, grouting time and grouting amount is obtained through the indoor grouting simulation experiment. This provides basic data for COMSOL numerical simulation calculation of grout diffusion mechanism in water-bearing sand layer considered time-dependent property of grout viscosity. At last, the diffusion law of urea-formaldehyde resin under different conditions, such as different particle size and different water-bearing conditions, are studied by applying finite element method software COMSOL, together with government performance of the grout for quicksand.The conclusions are:(1) With the ratio of UF and hardener increasing, the grout density changes little, while grout gelling time increases obviously. During gelling process, grout contractibility rate is very low, and grout solidified effect can reach above 99%. The uniaxial compressive strength of grout gel increases with increasing ratio. Grout gel has good anti-deformability during compression process. Viscosity test result shows that the relationship between grout viscosity and time fits the feature of exponential function. Grout viscosity will increase with increasing time.(2) For the indoor grouting simulation test, when the axial pressure keeps constant, if the smaller of particle size of the land layer, the larger of grout amount, grout pressure and grout time will be. When the axial pressure and the particle size of the sand layer keep constant, grout amount, grout pressure and grout time of water-free sand layer is bigger than those of water-bearing sand layer. COMSOL numerical result shows that in a certain period of time, the longer of the grout time, the higher of the grout pressure, and the lower of the initial grout viscosity, the further of the diffusion distance will be.(3) The government performance of the grout for quicksand can be evaluated by whether there will form fully-enclosed grouting reinforced curtain around the wellbore outline. In actual engineering, grouting pressure and grout hole arrangement are the main factors taken into consideration. COMSOL numerical calculation shows that it is conducive for forming reinforced curtain with higher grout pressure and smaller grout hole distance. |
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