Research and application progress of grouting materials for advance pretreatment of headrace tunnel
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Abstract:
Most headrace tunnels are in high mountains and valleys with complex hydrological and special geological conditions. During the construction of the headrace tunnel, water inrush often occurs when suffering from unfavorable geological bodies. Pre-grouting is a significant technical means to prevent such occurrence of geological disasters. However, under the condition of high pressure and large flow dynamic water, the pre-treatment grouting materials can not meet the needs of the site, therefore it's of absolute importance to improve its dynamic water performance. Various inorganic grouting materials have been developed to realize high-performance pre-grouting, such as cement, microfine cement, and water glass, or organic grouting materials, such as polyurethane and epoxy. However, among the aforementioned grouting materials, cement hardening requires a long time, and epoxy and polyurethane are expensive. Besides, due to the high pressure, large flow rate, and rapid velocity water inrush environment, grouting materials face the issues of being washed out, diluted, and dispersed, resulting in difficulty of slurry condensation, low mechanical strength, and poor long-term water plugging effect of consolidated body. Therefore, improving the performance of pre-grouting materials under dynamic water conditions is urgent. Cement, polyurethane, and epoxy grouting materials have been commonly used for advanced pretreatment. Researchers have recently tried to improve the anti-scouring ability, mechanical properties, and durability of cement grouts by adding anti-washout admixtures, nanomaterials, and mineral admixtures to grout mix constituents. In addition, phosphate cement grouting materials have been developed to plug water quickly. Therefore, to promote the application of polyurethane grouting materials in ultra-high velocity dynamic water environments, hydroxypropyl methylcellulose has been added to water-soluble polyurethane slurry to improve its retention rate in flowing water. The relationship between density, mechanical behavior, and microstructure evolution of polyurethane has been researched. The time-varying effect of the permeability of epoxy slurry has become a focus when facing high-pressure and low-permeability geological bodies. In addition to commonly used pre-grouting materials, a superabsorbent polymer grouting material based on self-volume expansion by physical water adsorption has been developed. The latest research on cement, polyurethane, epoxy resin, and superabsorbent polymer grouting materials was reviewed. Based on this, the main problems requiring deep exploration in the future are recommended from three aspects: the development of special cement grouting materials, the development of polyurethane, which is low cost, foaming body with high strength, strong resistance to water inrush, and polyurethane-modified by inorganic materials.
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