黄土地区高层建筑采用素混凝土桩复合地基比较广泛,因变形验算的可信性较差,从多层向高层建筑的推广主要依据单桩复合地基载荷试验结果,以相对沉降比(变形控制标准)确定承载力特征值。复合地基载荷试验变形控制标准源于多层和小高层建筑,而高层甚至甲类建筑(30层以上)均沿用这一标准,不能反映建筑荷载增加时地基沉降增大的规律。黄土场地高层建筑素混凝土桩复合地基实测沉降量普遍较大,甚至发生沉降病害,从设计理论角度对变形控制标准进行讨论是必要的。首先,基于界面剪切试验确定剪应力—剪切位移关系,并推导接触面力学模型;然后,建立考虑桩—土相互作用的群桩复合地基与单桩复合地基载荷试验数值仿真模型,计算复合地基与载荷试验的沉降量比值。进一步对比已有实例的复合地基与载荷试验的沉降比,验证数值计算结果的准确性;最后,提出了针对黄土地区单桩复合地基载荷试验变形控制标准修正方法,并给出建议取值。结果表明:沉降量比值随建筑结构荷载的增加而显著增大;桩周土的土性对沉降比的影响不显著;沉降比主要与荷载相关,荷载越大,载荷试验的沉降量越较少反映实际群桩复合地基的沉降行为;提出了考虑结构荷载的黄土地区素混凝土桩复合地基载荷试验变形控制标准建议取值表。
The deformation control standard for composite foundation load tests was originally established for multi-story and low high-rise buildings. However, the standard continues to be applied to high-rise and Class A structures (above 30 stories) without accounting for the increase in foundation settlement under higher structural loads, raising concerns about its applicability. High-rise buildings with plain concrete pile composite foundations in loess regions often experience significant settlement, sometimes leading to settlement-related structural issues. It is necessary to discuss the deformation control standards from a design theoretical perspective.Firstly, the shear stress-shear displacement relationship is determined through interface shear tests and a mechanical model for the contact interface is derived. A numerical simulation model incorporating pile-soil interaction is then developed for both group-pile and single-pile composite foundations. The settlement ratio between composite foundations and load tests is calculated. The numerical results are validated by comparing the settlement ratios of the composite foundation in existing cases with those from the load tests. Finally, a revised deformation control standard for single-pile composite foundation load tests in loess regions is proposed, along with recommended values. The results show that: The settlement ratio increases significantly with structural load; Soil properties around the piles have minimal impact on settlement ratio; The settlement ratio is primarily governed by load, and as load increases, the settlement observed in load tests becomes less representative of the actual behavior of group-pile composite foundations; A recommended deformation control standard table for load tests on plain concrete pile composite foundations in loess regions is provided based on structural load considerations.
[1] 中华人民共和国住房和城乡建设部. 复合地基技术规范(GB/T 50783-2012)[S]. 北京:中国计划出版社, 2012. (Ministry of Housing and Urban-Rural Development of the People's Republic of China. Technical code for composite foundation[S]. China Planning Press.2012 (in Chinese))
[2] Shi B Z, Cheng X S, Gong L J, et al. Selection design and parameter optimization of composite foundations in collapsible loess areas[J]. Geotechnical and Geological Engineering, 2020, 38(3): 3175-3201.
[3] 赵治海,徐张建,燕建龙,等.湿陷性黄土场地孔内深层超强夯挤密桩试验研究[J].地下空间与工程学报,2020,16(4):1004-1011. (Zhao Zhihai, Xu Zhangjian, Yan Jianlong, et al. Study on the super down hole deep compaction in collapsible loess site[J]. Chinese Journal of Underground Space and Engineering, 2020, 16(4):1004-1011. (in Chinese))
[4] 丁小军, 王旭, 张延杰, 等. 大型油罐CFG桩复合地基变形与承载性能试验研究[J].岩石力学与工程学报,2013,32(9):1851-1857. (Ding Xiaojun, Wang Xu, Zhang Yanjie, et al. Experimental study of bearing and deformation features of CFG-pile composite ground for large oil storage tanks[J]. Chinese Journal of Rock Mechanics and Engineering, 2013, 32(9):1851-1857. (in Chinese))
[5] 邓友生,李龙,孙雅妮,等.水泥粉煤灰处理湿陷性黄土路基承载性能[J].交通运输工程学报,2023,23(4):92-103. (Deng Yousheng, Li Long, Sun Yani, et al. Bearing capability of collapsible loess subgrade through cement-fly ash treatment[J]. Journal of Traffic and Transportation Engineering, 2023,23(4):92-103. (in Chinese))
[6] Cheng X, Gong L, Liu G. Bearing capacity characteristics and differential settlement of composite foundation with column-Hammered and thrusted-expanded piles[J]. International Journal of Geomechanics, 2021, 21(9): 04021164.
[7] 吕擎峰,韩启亮,赵彦旭,等.黄土变刚度组合桩复合地基及其工作性能研究[J].地下空间与工程学报,2023,19(4):1289-1298. (Lv Qingfeng, Han Qiliang, Zhao Yanxu, et al. Study on composite foundation with variable stiffness combination pile in loess and its working performance[J]. Chinese Journal of Underground Space and Engineering, 2023,19(4):1289-1298. (in Chinese))
[8] Cheng X S, Wang H, Gong L J, et al. Study on bearing capacity characteristics of Cement-Flyash-Gravel piles and cement-soil compacted piles in composite foundations[J]. Engineering Research Express, 2024, 6:045103.
[9] Li L, Deng Y S. Strengthening mechanism of plum blossom pile composite foundation[J]. Acta Geotechnica, 2024,19:4791-4808
[10] 王旭, 张延杰, 蒋代军, 等. 饱和黄土区CFG桩与振动沉管碎石桩复合地基承载特性试验研究[J].岩土工程学报,2013,35(2):1062-1065. (Wang Xu, Zhang Yanjie, Jiang Daijun, et al. Experimental research on bearing features of CFG pile composite ground and vibrating sinktube detritus pile composite ground on saturated loess[J] Chinese Journal of Geotechnical Engineering, 2013,35(2):1062-1065. (in Chinese))
[11] Terzaghi K, Peck R P. Soil Mechanics in Engineering Practice[M]. New York: Wiley, 1948.
[12] 王永洪,王鑫,张明义,等.近海黏性土中桩土界面剪切特性与含水率效应[J].地下空间与工程学报,2024,20(4):1236-1246. (Wang Yonghong, Wang Xin, Zhang Mingyi, et al. Effects of water contentand shear properties on pile-soil interface of offshore cohesive soil[J]. Chinese Journal of Underground Space and Engineering, 2024,20(4):1236-1246. (in Chinese))
[13] 杨光华,李思平.关于复合地基的静载试验问题[A]// 中国岩石力学与工程学会第七次学术大会论文集[C].北京: 中国科学技术出版社, 2002:683-685. (Yang Guanghua, Li Siping. Problems in determining the bearing capacity of compound foundation with static loading test[A]// The 7th Academic Conference of the Chinese Society for Rock Mechanics and Engineering[C]. Beijing: China Science and Technology Press, 2002:683-685. (in Chinese))
[14] 中华人民共和国住房和城乡建设部. 建筑地基基础设计规范(GB50007-2011)[S]. 北京:中国建筑工业出版社, 2012. (Ministry of Housing and Urban-Rural Development of the People's Republic of China. Code for design of building foundation[S]. Beijing: China Architecture and Building Press, 2012. (in Chinese))
