Research On The Construction Technology Of The Deep Pile Foundation In The Strong Karst Development Area

A part of project in the Shanghai-Kunming passenger expertise Changsha-Kunming Hunan Section CKTJ-2lot is located in the limestone karst development regions, the bridge foundation of which are used deep pile structures, karst development regions bring the construction of a greater degree technical difficulty:the deepest piles up126m, the maximum span of the cave is60m, the largest string holes through the layers is10Layers, this paper combines the need of project construction with the need of the author’s work, analysis and research deep pile foundation construction technology in developed karst areas from technology, quality, economy, efficiency and other aspects, construction experience and considerations summarized, the main work and innovation are as follows:1. For the karst deep pile strata is generally complex, if relying on hole soil into mud, mud suspension function is poor, slag difficult, drilling efficiency is restricted, cannot even play a protection role. Proposed the use of bentonite, polyacrylamide, cellulose several materials, obtained a reasonable ratio of mud by experiments.2. Aiming at the normal circumstances when the cave mud level decreased by adding clay plus rubble backfill way, by filling the cave, to ensure the effect of mud head. In the case of experiencing fractures particularly the continuity of another major cave, simply by the use of stone tablets plus clay or cement, even concrete measures are ineffective, this paper proposes the use of (clay+hemp)/(cement+hemp) and then throw-and-fill plugging method3. Aiming at the geological condition in karst developed area is complex and changeable, proposed respectively use of grouting reinforcement method (double size), sand replacement method, grouting method, advanced bored concrete pretreatment method. By pretreatment significantly reduces the frequency of fluid loss during drilling, hole collapse and other quality issues.4. Through dedicated research and development of steel cage mold machining and steel cage decentralization spreader, to reduce disturbance of the decentralization process of steel cage and ensure verticality of steel cage.5. Through the research on cave location of the steel cage by installing a100mesh iron gauze, to prevent the karst deep concrete piles from squeezing cave wall collapse during the pouring of concrete.Techniques and methods presented in this paper can be a reference for similar projects.