大厚度自重湿陷性黄土地基处理深度和湿陷性评价试验研究

 为解决大厚度自重湿陷性黄土地区地基处理深度和湿陷性评价等难题，在湿陷性黄土厚度大于36.5 m的场地进行以下浸水试验：不同深度的挤密桩处理地基深层浸水载荷试验，不同深度的孔内深层强夯处理地基载荷浸水试验，不打注水孔、埋设TDR水分计的原位浸水试验。研究结果表明：(1) 大厚度自重湿陷性黄土地基处理6～12 m、深层浸水时，发生显著地基下沉；15～20 m时，地基沉降较小；处理深度大于20 m时，地基沉降基本可忽略。(2) 浸水试坑22.5～25.0 m以上土体含水率增加较快，甚至达到饱和，以下土体含水率增加缓慢，基本没有发生湿陷。建议22.5～25.0 m作为大厚度自重湿陷性黄土地基处理和湿陷性评价的临界深度。(3) 大厚度自重湿陷性黄土地基在采取有效的综合处理措施之后，甲类建筑可以不全部消除湿陷量，乙、丙类建筑可以根据控制建议适当放宽对剩余湿陷量的要求。(4) 不同地区、不同微结构类型土的湿陷性应当采用不同的湿陷系数 来判定，即“湿陷系数 = 0.015”在自基础底面至基底下15 m的范围内可继续使用；15 m以下适当放宽，按不同深度对 进行修正，可使大厚度自重湿陷性黄土湿陷性评价趋于合理，有效节约大量地基处理费用。

EXPERIMENTAL STUDY ON COLLAPSIBILITY EVALUATION AND TREATMENT DEPTHS OF COLLAPSIBLE LOESS UPON SELF WEIGHT WITH THICK DEPTH

The in-situ soaking tests on loess collapsibility upon deadweight with the thickness greater than 36.6 m were carried out including a deep layer soaking test on a foundation treated with compaction piles of different lengths，a soaking test on a foundation treated with the deep dynamic compaction inside holes and a soaking test on a foundation buried with TDR moisture meters without water injection holes. The significant foundation subsidence occurred due to deep soaking when the thick deadweight collapsible loess foundation was treated 6 to 12 m in depths upon. When the depths of treatment were from 15 to 20 m，the ground settlement upon deep soaking was small. When the treatment depth was more than 20 m，the settlements of the foundation can be ignored. When the water pit of soaking test was 22.5 to 25.0 m in depth，the soil moisture content increased rapidly and even reached saturation，while if the water pit was deeper，the moisture content increased slowly with little collapse of loess. So 22.5 to 25 m can be viewed as the critical depth of foundation treatment and collapsibility evaluation for thick deadweight collapsible loess. The collapsibility in different regions and soil microstructures should be evaluated adopting different coefficients of collapsibility.