再生混凝土骨料包裹桩承载特性试验研究

王志佳; 何旭; 李胜民; 黎洪磊; 张建经; 李良勇

doi:10.3969/j.issn.0258-2724.20210109

再生混凝土骨料包裹桩承载特性试验研究

doi: 10.3969/j.issn.0258-2724.20210109

1.
海南大学土木建筑工程学院，海南海口 570228
2.
西南交通大学土木工程学院，四川成都 610031

基金项目: 国家自然科学基金（51708163）；海南省科协青年科技英才学术创新计划项目（QCXM201807）

详细信息

作者简介:
王志佳（1987—），男，讲师，博士，研究方向为地基处理和岩土地震工程学，E-mail：993041@hainanu.edu.cn

通讯作者:
张建经（1960—），男，教授，博士，研究方向为地基处理和岩土工程抗震， E-mail：jianzhang1102@126.com

中图分类号: TU43
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- 被引次数: 0
出版历程
- 收稿日期: 2021-02-02
- 修回日期: 2021-05-21
- 网络出版日期: 2022-10-14
- 刊出日期: 2021-06-11

Experimental Study on Bearing Capacity of Geosynthetic-Encased Recycled Concrete Aggregate Column

1.
College of Civil Engineering and Architecture, Hainan University, Haikou 570228, China
2.
College of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China

摘要

摘要:
采用再生混凝土骨料替换包裹碎石桩碎石芯料，形成一种新型地基处理方式——再生混凝土骨料包裹桩，以改善采用包裹碎石桩处理液化及软弱土地基时碎石强度未能充分发挥的问题. 开展了模型试验，研究包裹长度、刚度及长径比对再生混凝土骨料包裹桩单桩承载特性和骨料破碎度的影响. 研究结果表明：包裹长度为1倍～6倍桩径时，延长包裹长度可显著提高桩体承载力，包裹长度小于1倍或大于6倍桩径时，包裹长度对承载力改善不明显；包裹材料的临界刚度约为100 kN/m，当小于临界刚度时，增加包裹刚度能显著提高桩体承载力，大于临界刚度时，增加包裹刚度不再明显改善桩体承载力；再生混凝土骨料包裹桩桩长不变时，长径比大于10的桩体承载力较低，桩体主要在10～30 cm深度内产生不同程度的局部弯曲，长径比小于7的桩体承载力较高，桩体主要发生轻微鼓胀变形，无局部弯曲；混凝土骨料的破碎度与桩体能承受的极限荷载呈正相关，增加包裹长度、刚度及桩径均会增加芯料的破碎度. 因此，进行再生混凝土骨料包裹桩单桩设计时应充分考虑包裹长度、刚度和长径比与芯料破碎度之间的关系，以获取最优设计方案.
- 再生混凝土骨料 /
- 包裹桩 /
- 承载特性 /
- 土工合成材料 /
- 模型试验
Abstract:
Recycled concrete aggregates are used to replace the gravel core material of encased stone columns, forming a new foundation treatment method—recycled concrete aggregate encased column, to improve the problem that the gravel strength cannot be fully exerted when the encased stone column is used to treat liquefied and soft soil foundations. Laboratory model tests were performed to study the effect of encasement length, stiffness, and the ratio of column length to diameter on the bearing characteristics and aggregate fragmentation degree of the encased recycled concrete aggregate column. The results show that when the length of encasement is 1 to 6 times the column diameter, the bearing capacity of the column can be significantly increased by increasing the encasement length. When the length of encasement is less than 1 or more than 6 times the column diameter, the length change of encasement does not significantly influence the bearing capacity of the column. The critical stiffness of encasement is about 100 kN/m. When the stiffness of the encasement is less than the critical stiffness, increasing the encasement stiffness can prominently improve the bearing capacity of the column. However, when the stiffness of the encasement is greater than the critical stiffness value, increasing the encasement stiffness cannot significantly improve the bearing capacity of the column. When the length of the geosynthetic-encased recycled concrete aggregate column is fixed, columns with a length-to-diameter ratio greater than 10 have a lower bearing capacity, and mainly produce local bending to varying degrees within the depth range from 10 cm to 30 cm, while columns with a length-to-diameter ratio less than 7 have a relatively higher bearing capacity and mainly experience slight bulging deformation without local bending. Besides, there is a positive correlation between the fragmentation degree of the recycled concrete aggregate and the ultimate load that the column can withstand. Increasing the encasement length, stiffness and column diameter will increase the fragmentation degree of the core material. Therefore, when designing a single geosynthetic-encased recycled concrete aggregate column, full consideration should be given to the relationship between the encasement length, stiffness, the ratio of column length to diameter, and the fragmentation degree of the concrete aggregate, to obtain the optimal design scheme.
- recycled concrete aggregate /
- encased column /
- bearing capacity /
- geosynthetics /
- model tests

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图 1 土体和混凝土骨料级配曲线

Figure 1. Grading curves of sand and concrete aggregate

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图 2 土工包裹材料拉伸试验结果

Figure 2. Tensile behavior of geosynthetics samples

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图 3 试验装置示意（单位：cm）

Figure 3. Schematic of test device (unit： cm)

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图 4 拉线位移计的布置

Figure 4. Arrangement of stay wire displacement meter

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图 5 包裹长度的荷载沉降曲线

Figure 5. Load-settlement (F-S) curves of column top for different encased lengths

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图 6 极限荷载随包裹长度的变化

Figure 6. Variation of ultimate load with encased length

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图 7 再生混凝土骨料包裹桩与包裹碎石桩的桩顶荷载沉降曲线对比

Figure 7. Comparison of column top load-settlement curves between recycled concrete aggregate encased column and encased stone column

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图 8 不同包裹刚度下的荷载沉降曲线

Figure 8. Load-settlement (F-S) curves of column top for different encasement stiffnesses

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图 9 极限荷载随包裹刚度的变化

Figure 9. Variation of ultimate load with encasement stiffness

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图 10 不同长径比下的荷载沉降曲线

Figure 10. Load-settlement (F-S) curves of column top for columns with different diameters

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图 11 不同长径比的桩体变形示意

Figure 11. Schematic of column deformation with different length-to-diameter ratios

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图 12 试验后混凝土骨料的粒径级配曲线

Figure 12. Grading curves of concrete aggregate after test

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表 1 试验模型相似比

Table 1. Similarity ratio for model test

无量纲因子	参数	原型	模型	相似比
${\pi _1} = \dfrac{l}{L}$	l/cm	700	70	10
${\pi _2} = \dfrac{d}{L}$	d/cm	100	10	10
${\pi _3} = \dfrac{F}{{\rho g L A}}$	F/kN	5 000	5	1 000
$ {\pi _3} = \dfrac{{{T_{\rm{g}}}}}{{\rho g L {t_{\rm{g}}}}} $	T_g/ （kN·m⁻¹）	130	13	10
${\pi _4} = \dfrac{{{J_{\rm{g}}}}}{{\rho g L {t_{\rm{g}}}}}$	J_g/ （kN·m⁻¹）	1 400	140	10

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表 2 砂土及混凝土骨料参数

Table 2. Properties of soil layers and concrete aggregate

材料	密度/（kg•m⁻³）	相对密度/%	含水率/%	颗粒密度/（g•cm⁻³）	内摩擦角/（º）
土体（GP）	1 664.1	55	3	2.65	39.12
再生混凝土骨料（SP）	1 528.0	70	0	2.83	42.00

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表 3 包裹材料拉伸强度指标

Table 3. Tensile strength indices of geosynthetics

名称	极限强度/ （kN•m⁻¹）	最大延伸率/%	延伸率 5% 的拉应力/ （kN•m⁻¹）	包裹材料刚度/ （kN•m⁻¹）
材料Ⅰ	2.58	15.42	1.24	24.80
材料Ⅱ	5.21	14.40	2.45	49.00
材料Ⅲ	7.51	16.70	3.69	73.80
材料Ⅳ	10.04	15.33	5.11	102.20

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表 4 试验分组

Table 4. Details of group tests

组号	试验工况	d/mm	L/mm	包裹长度L₁/mm
1	土体
2	无包裹	100	700	0
3	3d- Ⅰ	100	700	300
4	4d- Ⅰ	100	700	400
5	5d- Ⅰ	100	700	500
6	7d- Ⅰ	100	700	700
7	7d- Ⅱ	100	700	700
8	7d- Ⅲ	100	700	700
9	7d- Ⅳ	100	700	700
10	长径比 12.5- Ⅰ	56	700	700
11	长径比 10.0- Ⅰ	70	700	700
12	长径比 6.0- Ⅰ	117	700	700

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表 5 包裹桩极限承载力取值

Table 5. Values of ultimate bearing capacity of encased columns

来源	取值方法	取值标准
文献[6]	第 1 种	P-S 曲线转折点
文献[19]	第 2 种	S=30 mm → F_u
文献[18]	第 2 种	S=40 mm → F_u
文献[20]	第 3 种	S=20%d_c → F_u
文献[9]	第 4 种	S=10%d_c → F_u

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表 6 不同包裹长度下桩的极限荷载

Table 6. Ultimate load of columns with different encased lengths

编号	试验工况	J_g/（kN▪m⁻¹）	F_u/kN
1	土体		1.37
2	再生骨料桩	0	2.58
3	3d- Ⅰ	24.8	3.13
4	4d- Ⅰ	24.8	3.24
5	5d- Ⅰ	24.8	3.69
6	7d- Ⅰ	24.8	3.76

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表 7 不同包裹刚度下桩体承载力

Table 7. Bearing capacity of columns with different stiffnesses

编号	试验工况	J_g/（kN·m⁻¹）	F_u/kN
1	土体		1.37
2	再生骨料桩	0	2.58
3	7d- Ⅰ	24.8	3.76
4	7d- Ⅱ	49.0	4.09
5	7d- Ⅲ	73.8	4.48
6	7d-Ⅳ	102.2	4.82

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表 8 混凝土骨料破碎度

Table 8. Degree of fragmentation of concrete aggregate

试验工况	F_u/ kN	B_r/%
土体	1.36
无包裹桩	2.63	2.48
3d- Ⅰ	3.13	2.37
4d- Ⅰ	3.24	4.14
5d- Ⅰ	3.73	4.87
7d- Ⅰ	3.76	6.27
7d- Ⅱ	4.18	10.33
7d- Ⅲ	4.53	15.41
7d- Ⅳ	4.80	18.22
长径比 12.5- Ⅰ	2.57	0.36
长径比 10.0- Ⅰ	2.60	0
长径比 7.0- Ⅰ	3.76	6.27
长径比 6.0- Ⅰ	4.52	10.38

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