1. School of Civil Engineering,Lanzhou University of Technology,Lanzhou 730050,China; 2. School of Civil Engineering,Chongqing Jiaotong University,Chongqing 400074,China; 3. Department of Military Installations Engineering,Army Logistical University of PLA,Chongqing 401311,China; 4. Northwest Electric Power Design Institute Co., Ltd. of China Power Engineering Consulting Group,Xi′an 710075,China
Abstract：In order to clarify the load transfer model for root piles and the action law of pile-soil, the uplift bearing capacities of equal section pile, belled pile and root pile are tested. Meantime, the change rules of the bearing capacity under different densities of root are explored through numerical stimulation. The result shows that: (1) The root pile is more suitable under the conditions of complex load and strict requirements for displacement. Moreover, the multi-layer variable cross-section setting of the root pile makes the bearing capacity of material, play a further role and achieves the goal of economic saving. (2) In the test condition, the relationship between the crack rate of soil around piles and the load is exponential distribution. Under the same load, the higher the fissure rate, the lower the bearing capacity. Under the ultimate load, the higher the fissure rate, the more fully the bearing capacity of soil will be exerted. (3) Increasing the density of roots (cross-section area) is beneficial to reducing the earth pressure around the roots and preventing the plastic failure from happening in the original period of the foundation. In generally, the ratio of the roots to the branch cross-section area with the same diameter should be set from 0.1 to 0.3.
 刘建平. 等截面抗拔单桩承载性状研究[D]. 北京:中国地质大学(北京), 2006. (LIU Jian-ping. Study on Capacity Behavior of Single Uplift Piles[D]. Beijing: China University of Geosciences(Beijing), 2006.(in Chinese))  殷永高. 根式基础及根式锚碇方案构思[J]. 公路, 2007,52(2): 46-49. (YIN Yong-gao. Scheme conception of root foundation and anchor block[J]. High Way, 2007,52(2): 46-49. (in Chinese))  龚维明, 有智慧, 殷永高, 等. 根式沉井基础群井效率系数现场水平试验研究[J]. 土木工程学报, 2010, 43(5): 89-95. (GONG Wei-ming, YOU Zhi-hui, YIN Yong-gao, et al. Field test of lateral group efficiency of root caisson foundations[J]. China Civil Engineering Journal, 2010, 43(5): 89-95. (in Chinese))  钱德玲. 支盘桩抗压和抗拔特性的研究[J]. 岩土力学, 2003,24(S2): 517-520.(QIAN De-ling. A study of compression and extraction resistance behavior of squeezed supporting disk piles[J]. Rock and Soil Mechanics, 2003,24(S2): 517-520. (in Chinese))  龚维明, 王 磊, 殷永高. 厚覆盖土层地区根式基础应用与试验研究[J]. 土木工程学报, 2015, 48(S2): 69-74. (GONG Wei-ming, WANG Lei, YIN Yong-gao. Applied and experimental study on the root foundation in the thick covering stratum region[J]. China Civil Engineering Journal, 2015, 48(S2): 69-74. (in Chinese))  龚维明, 胡 丰, 童小东, 等. 根式基础竖向承载性能的试验研究[J]. 岩土工程学报,2008,30(12):1789-1795. (GONG Wei-ming, HU Feng, TONG Xiao-dong, et al. Experimental study on vertical bearing capacity of root foundation[J]. Chinese Journal of Geotechnical Engineering, 2008, 30(12): 1789-1795. (in Chinese))  张立奎, 章 征, 殷永高. 根式沉井基础水平向荷载试验研究[J]. 桥梁建设, 2009,39(3): 33-36. (ZHANG Li-kui, ZHANG Zheng, YIN Yong-gao. Horizontal load test study of root type caisson foundation[J]. Bridge Construction, 2009,39(3): 33-36. (in Chinese))  葛 楠, 孙 砚, 侯超群, 等. 砂土中根式抗拔桩模型试验研究[J]. 长江科学院院报, 2019,36(8): 146-152. (GE Nan, SUN Yan, HOU Chao-qun, et al. Model experimental research on root uplift pile in sand[J]. Journal of Yangtze River Scientific Research Institute. 2019,36(8): 146-152. (in Chinese))  唐孟雄, 陈 达. 基岩内抗拔桩极限承载力的计算方法[J]. 岩土力学, 2015, 36(S2): 633-638. (TANG Meng-xiong, CHEN Da. A computational method of ultimate capacity of uplift piles in basement rock[J]. Rock and Soil Mechanics, 2015, 36(S2): 633-638. (in Chinese))  建筑桩基检测技术规范:DB37/T 5044—2015[S]. (Technical Code for Testing of Building Foundation Piles:DB37/T 5044-2015[S]. (in Chinese))  LEE C J, BOLTON M D, AL-TABBAA A. Numerical modelling of group effects on the distribution of dragloads in pile foundations[J]. Géotechnique, 2002, 52(5): 325-335.