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（1 中國路橋工程有限責(zé)任公司，  北京  100011； 2 清華大學(xué)土木工程安全與耐久教育部重點(diǎn)實(shí)驗(yàn)室，  北京  100084）

［摘要］黑棉土是一種特殊的強(qiáng)膨脹土，為避免其脹縮導(dǎo)致的基礎(chǔ)和結(jié)構(gòu)損壞，需研究其力學(xué)特性及樁基承載特性。首先通過室內(nèi)試驗(yàn)測(cè)定黑棉土的有荷膨脹特性、側(cè)限壓縮特性和剪切特性。試驗(yàn)結(jié)果表明，當(dāng)上覆壓力由0kPa增加到300kPa時(shí)，土體的有荷膨脹率從36-6%減小至3-3%；含水率增大時(shí)，土體平均側(cè)限壓縮模量和抗剪強(qiáng)度均減小；含水率為52-0%的黑棉土在較大剪切位移（6mm）時(shí)的黏聚力較峰值強(qiáng)度下的黏聚力下降70%。之后通過離心機(jī)試驗(yàn)比較不同含水率的黑棉土地基中單樁的承載特性發(fā)現(xiàn)，相比含水率為23-0%的黑棉土地基，含水率為52-0%的黑棉土地基中單樁的剛度和承載力均明顯降低，樁端阻力的下降尤為明顯。建議在工程樁基設(shè)計(jì)中，濕化下黑棉土的摩阻力宜采用大剪切位移下土體抗剪強(qiáng)度。

［關(guān)鍵詞］膨脹土； 黑棉土； 單樁； 離心機(jī)試驗(yàn)； 承載特性

中圖分類號(hào)：TU443文獻(xiàn)標(biāo)識(shí)碼：A文章編號(hào)：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

*國家重點(diǎn)基礎(chǔ)研究發(fā)展計(jì)劃（2014CB047003）。

通訊作者：楊軍，博士，副研究員，博士生導(dǎo)師，Email：junyang@tsinghua.edu.cn。