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黑棉土力学特性和单桩承载特性试验研究*
沈兆普1,张大峰2,李连友1,吴志轩2,杨军2
摘 要

(1 中国路桥工程有限责任公司,  北京  100011; 2 清华大学土木工程安全与耐久教育部重点实验室,  北京  100084)

[摘要]黑棉土是一种特殊的强膨胀土,为避免其胀缩导致的基础和结构损坏,需研究其力学特性及桩基承载特性。首先通过室内试验测定黑棉土的有荷膨胀特性、侧限压缩特性和剪切特性。试验结果表明,当上覆压力由0kPa增加到300kPa时,土体的有荷膨胀率从36-6%减小至3-3%;含水率增大时,土体平均侧限压缩模量和抗剪强度均减小;含水率为52-0%的黑棉土在较大剪切位移(6mm)时的黏聚力较峰值强度下的黏聚力下降70%。之后通过离心机试验比较不同含水率的黑棉土地基中单桩的承载特性发现,相比含水率为23-0%的黑棉土地基,含水率为52-0%的黑棉土地基中单桩的刚度和承载力均明显降低,桩端阻力的下降尤为明显。建议在工程桩基设计中,湿化下黑棉土的摩阻力宜采用大剪切位移下土体抗剪强度。

[关键词]膨胀土; 黑棉土; 单桩; 离心机试验; 承载特性

中图分类号:TU443文献标识码:A文章编号:1002-848X(2017)15-0097-05

 

Experimental research on mechanics properties of black cotton soil and bearing features of single pile

Shen Zhaopu1, Zhang Dafeng2, Li Lianyou1, Wu Zhixuan2, Yang Jun2

(1 China Road and Bridge Corporation, Beijing 100011, China; 2 Key Laboratory of Civil Engineering Safety and Durability of China Education Ministry, Tsinghua University, Beijing 100084, China)

Abstract:Black cotton soil is one special type of strong expansive clay. The mechanics properties of black cotton soil and bearing features of single pile in this soil were studied to avoid the damage of foundations and structures due to the swell-shrink characteristic of this expansive clay. Firstly, loaded swelling ratio, confining compression feature and shear strength of black cotton soil were measured by indoor laboratory tests. Experimental results indicate that loaded swelling ratio reduces from 36-6% to 3-3% when overburden pressure increases from 0kPa to 300kPa. Confining compression modulus and shear strength of soil decrease with increase of soil water content(ω). Besides, the cohesion force of black cotton soil with ω=52-0% reduces  70% of that under peak shear stress when shear displacement increases up to 6mm. Then bearing features of single piles in black cotton soil foundation with different water content were analyzed by centrifuge tests. Compared with black cotton soil foundation with ω=23-0%, stiffness and bearing capacity of single pile with ω=52-0% significantly decrease and there is obvious decrease in pile end resistance. In pile engineering design, it is recommended to use the soil shear strength under the large shear displacement for determination of friction resistance of wet black cotton soil.

Keywords:expansive soil; black cotton soil; single pile; centrifuge test; bearing capacity feature

 

*国家重点基础研究发展计划(2014CB047003)。

 

通讯作者:杨军,博士,副研究员,博士生导师,Email:junyang@tsinghua.edu.cn。

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