浸水饱和条件下黄土微型桩抗压和抗拔承载力试验

盛明强; 乾增珍; 杨文智; 鲁先龙

doi:10.11779/CJGE202112012

浸水饱和条件下黄土微型桩抗压和抗拔承载力试验 English Version

盛明强^1,,
乾增珍²,
杨文智^{2, 3},
鲁先龙^3, ,

1.
南昌大学,江西　南昌　330031
2.
中国地质大学（北京）,北京　100083
3.
中国电力科学研究院有限公司,北京　100192

基金项目:

国家自然科学基金项目 52069013

国家电网公司科技项目 GC17201100065

详细信息

作者简介:
盛明强(1975— ),男,江西安义人,博士,讲师,主要从事地基基础及防灾减灾方面研究。mqsheng@ncu.edu.cn

通讯作者:
鲁先龙, E-mail：luxianlong@163.com

中图分类号: TU43
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- 文章访问数: 252
- HTML全文浏览量: 32
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出版历程
- 收稿日期: 2021-05-09
- 网络出版日期: 2022-11-30
- 刊出日期: 2021-11-30

Field compression and uplift tests on micropiles in collapsible loess under completely-soaked and saturated conditions

1.
Nanchang University, Nanchang 330031, China
2.
China University of Geosciences, Beijing100083, China
3.
China Electric Power Research Institute, Beijing100192, China

摘要

摘要: 为开展浸水饱和条件下黄土微型桩基础抗压和抗拔承载性能试验,设计了一种桩周土体浸水饱和方案,并在甘肃地区2个湿陷性黄土场地分别完成了浸水饱和与天然含水率状态下微型桩单桩抗压抗拔和群桩抗压对比试验。结果表明：浸水饱和条件下黄土地基微型桩单桩抗压抗拔与群桩抗压荷载-位移曲线均呈“陡变型”变化规律,而天然状态下相应微型桩桩荷载-位移曲线则呈初始弹性段、弹塑性曲线过渡段和破坏直线段的三阶段“缓变型”变化规律。浸水饱和条件与天然状态下黄土抗压微型桩桩端阻力分担桩顶下压荷载的10%～15%,而相应黄土抗拔微型桩呈摩擦桩性状。天然状态下黄土微型桩单桩抗拔极限承载力为抗压极限承载力的66%～87%。当黄土浸水饱和后,相同微型桩单桩下压极限承载力平均下降70%,抗拔极限承载力平均下降50%,相同群桩基础下压极限承载力降低约75%。浸水饱和后黄土微型桩单桩和群桩基础下压极限承载力损失远高于相应基础的上拔极限承载力损失,相关试验研究成果可为今后黄土地区工程建设参考。
- 完全浸水 /
- 湿陷性黄土 /
- 微型桩 /
- 抗压 /
- 抗拔 /
- 现场试验
Abstract: In order to investigate the compression and uplift bearing capacity of micropiles in collapsible loess, a method for loess prewetting under completely soaked and saturated conditions is firstly designed. Consequently, the comparative field compression and uplift load tests on single micropile and group micropiles are respectively carried out in the two collapsible loess sites in Gansu Province. Both the site conditions and the load tests are documented comprehensively. The compression and uplift load-displacement curves of the single micropile and group micropiles in completely soaked and saturated loess generally follow a typical two-phase steep change pattern, which is quite different from those in-situ moisture content loess because they can be simplified into three distinct regions: initially linear, curvilinear transition and finally linear regions. Both in the in-situ moisture content loess and the completely soaked and saturated loess, the compression or uplift loaded single micropiles should be considered as the frictional pile foundations, and the tip resistances are only about 10% to 15% of the applied compression loads. For the micropiles in loess under in-situ moisture content, the ultimate uplift load capacities are 66% to 87% of those under compression. However, the loess under completely soaked and saturated condition will lead to a reduction of 70% in compressive bearing capacity and 50% in uplift bearing capacity for single micropile, and that for group micropiles is about 75% in compressive bearing capacity. These experimental results may provide a reference for the designers in loess in the future.
- complete immersion /
- collapsible loess /
- micropile /
- compression /
- uplift /
- field test

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图 1 试验场地黄土粒径级配累积曲线

Figure 1. Grain-size distribution curve of loess at two test sites

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图 2 试验场地黄土物理性质随深度变化曲线

Figure 2. Laboratory measured results for soil profile

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图 3 大坪村试验场地抗剪强度随深度变化规律

Figure 3. Laboratory measured results of direct shear test results for loess profile at Dapingcun site

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图 4 车道岭现场原位直剪试验原理及不同深度土体剪切应力-剪切位移曲线

Figure 4. Schematic layout and shear stress versus displacement curves for in-situ direct shear tests at Chedaoling

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图 5 试验场地黄土湿陷性系数随深度变化

Figure 5. Loess collapse index and corresponding classification of test results for soil profile

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图 6 试验基础周围黄土浸水饱和方案

Figure 6. Arrangement of loess prewetting until completely soaked and saturated condition by ponding

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图 7 灌水量随浸水时间变化曲线

Figure 7. Relationship between total poured water volume and prewetting time

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图 8 试验基础荷载-位移曲线

Figure 8. Measured load-displacement curves in field tests

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图 9 试验基础荷载-位移曲线特征及其极限承载力确定

Figure 9. Characteristics of measured load-displacement curves and definition of ultimate load capacity

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图 10 微型桩单桩轴力随深度分布规律

Figure 10. Distribution of axial load in micropiles

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表 1 试验场地黄土液塑限指标

Table 1 Atterberg limit test results

场地名称	液塑限指标
场地名称	液限/%	塑限/%	塑性指数
大坪村	32.6	18.1	14.5
车道岭	39.8	21.3	18.5

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表 2 微型桩单桩试验基础及其试验结果

Table 2 Basic information on single and group micropiles and load-displacement results at two test sites

基础型式	试验地点	荷载类型	基础编号	地基状态	l/m	d/m	Q _u/kN	s_u/mm	桩侧平均极限侧阻力/kPa
基础型式	试验地点	荷载类型	基础编号	地基状态	l/m	d/m	Q _u/kN	s_u/mm	计算值	平均值
单桩	大坪村	上拔	MP1^U	天然	6.0	0.30	220	4.91	38.94	44.82
			MP2^U	天然	8.0	0.30	300	7.12	39.79
			MP3^U	天然	10.0	0.30	525	15.66	55.73
			MP4^U	浸水饱和	8.0	0.30	150	8.43	19.89	19.23
			MP5^U	浸水饱和	8.0	0.30	150	8.55	18.57	19.23
		下压	MP1^C	天然	6.0	0.30	335	6.85	63.72	60.15
			MP2^C	天然	8.0	0.30	397	7.46	53.05
			MP3^C	天然	10.0	0.30	602	7.16	63.69
			MP4^C	浸水饱和	8.0	0.30	120	4.61	15.92	15.92
			MP5^C	浸水饱和	8.0	0.30	119	4.35	15.92	15.92
群桩	车道岭	下压	GMP1^C	天然	8.0	0.30	1400	23.56	－	－
群桩	车道岭	下压	GMP2^C	浸水饱和	8.0	0.30	360	3.84	－	－

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浸水饱和条件下黄土微型桩抗压和抗拔承载力试验 English Version

作者简介: 盛明强(1975— ),男,江西安义人,博士,讲师,主要从事地基基础及防灾减灾方面研究。mqsheng@ncu.edu.cn

通讯作者: 鲁先龙, E-mail：luxianlong@163.com

计量

出版历程

Field compression and uplift tests on micropiles in collapsible loess under completely-soaked and saturated conditions

计量

出版历程

目录

作者简介:
盛明强(1975— ),男,江西安义人,博士,讲师,主要从事地基基础及防灾减灾方面研究。mqsheng@ncu.edu.cn

通讯作者:
鲁先龙, E-mail：luxianlong@163.com