针对传统流态土应用于岩溶区钻孔灌注桩工程时存在扩散范围过大、浪费材料的问题,拟采用添加外加剂以缩短初凝时间的方法解决。考虑不同的早强剂、速凝剂和减水剂,首先通过试验研究各外加剂对流态土初凝时间的改善效果,然后初步确定合适的外加剂,进而研究其对流态土流动度和强度的影响,最后提出适合岩溶区钻孔灌注桩处理的流态土配比建议。结果表明:掺入硫酸钠和减水剂都可以显著缩短流态土的初凝时间,其中减水剂的效果更好,而其他早强剂和速凝剂的促凝效果明显不如硫酸钠和减水剂;硫酸钠虽能起到促凝作用,但当龄期达到14 d和28 d时,掺入硫酸钠的流态土强度会比未掺硫酸钠的流态土强度稍低一些;对于流态土的流动性和强度而言,减水剂的掺入都是有利的,而硫酸钠的掺入都有一定的负面作用,但影响较小;综合考虑性能与成本因素,建议应用于岩溶区钻孔灌注桩工程的流态土采用10%水泥、6%减水剂和3%硫酸钠的配比。
There are problems such as excessive diffusion range and waste of materials when traditional fluidized soil is used in bored cast-in-place pile projects in karst areas. It is proposed to solve this problem by adding admixtures to shorten the initial setting time. Considering different admixtures, such as early strength agents, rapid setting agents and water reducing agents, the improvement effect of various admixtures on the initial setting time of fluidized soil is studied through laboratory tests first. Then, the appropriate admixture is preliminarily determined, and its influence on the fluidity and strength of fluidized soil is studied. Finally, the fluidized soil mix ratio suitable for bored cast-in-place pile treatment in karst areas is proposed. The results show that: The addition of sodium sulfate and water reducing agents can significantly shorten the initial setting time of fluidized soil, with water reducing agents having a better effect, while other early strength and rapid setting agents have significantly lower coagulation-promoting effects than sodium sulfate and water reducing agents. Although sodium sulfate can promote coagulation, the strength of the fluidized soil mixed with sodium sulfate will be slightly lower than that of the fluidized soil without sodium sulfate when the age reaches 14 and 28 days. For the fluidity and strength of fluidized soil, the addition of a water reducer is beneficial, while the addition of sodium sulfate has certain negative effects, but the impact is relatively small. Taking into account both performance and cost factors, it is recommended that the fluidized soil used in bored pile projects in karst areas should be a mixture of 10% cement, 6% water reducer, and 3% sodium sulfate.
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