竖向重复加卸载下倾斜桩复合地基变形规律试验
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摘要
施工不当或者侧向堆载、开挖常常导致桩身倾斜,扶正难度较大,且目前对倾斜桩复合地基的变形性状缺乏相关研究,其可能导致新的工程病害,基于此,设计模型箱和加载装置,对竖向重复加卸载下倾斜桩复合地基变形规律开展试验研究。结果表明:循环加载过程中,倾斜桩顶及其复合地基沉降和侧移均随荷载增大而增大,其增长率随荷载增大而增大、随加载次数增大而减小;卸载过程中,卸载初期的倾斜桩顶及其复合地基沉降和侧移变化不明显,最后1～2级低压力时才出现弹性变形;相同荷载作用下,桩顶沉降量随倾斜角增加而增大,倾斜桩存在"沉降临界倾斜角"(试验前3次加卸载循环其值为6°),随土体密实度提高而降低,倾斜角小于该临界值时,倾斜对桩的沉降影响不大,反之,桩顶沉降量随倾斜角增加而快速增大;倾斜桩存在"侧移临界倾斜角"(试验为9°),为侧移峰值对应倾斜角;倾斜角度小于该临界值时,桩顶侧移随倾斜角增大而增大,反之,桩顶侧移随倾斜角增大而减小,"侧移临界倾斜角"大于"沉降临界倾斜角";相同荷载作用下,倾斜桩复合地基的沉降大于倾斜桩沉降,而侧移比倾斜角6°桩大,比倾斜角12°桩小,桩身倾斜时,倾斜桩与复合地基的侧移量远比其沉降量小,但是侧移比沉降更为敏感。工程中,应尽量减少桩身倾斜,降低倾斜桩及其复合地基的沉降量和侧移量。
Improper construction, lateral surcharge, or excavation often leads to the tilting of pile bodies and causes problems of centralizability; however, the deformation characteristics of inclined pile composite foundation is not fully understood and may lead to new engineering diseases. A model box and loading device were designed to study the deformation law of inclined pile composite foundation under vertical repeated loading and unloading. The results are as follows: During the process of cyclic loading, the settlement and lateral displacement of the inclined pile top and its composite foundation increase as the load increases. Moreover, its growth rate increases as the load increases and decreases as the loading time increases. During the process of cyclic unloading, the settlement and lateral displacement of the inclined pile top and its composite foundation at the initial stage of unloading are not apparent, and elastic deformation occurs only during the last one or two stages of low pressure. Under the same load, the settlement of the pile top increases with the increase in the tilt angle. The inclined pile has a "critical inclination angle for settlement(6° during one to three loading and unloading cycles for the test)" that decreases with the increase in soil compactness. When the inclination is less than the critical value, the settlement of the pile has negligible effect and the settlement increases rapidly with the increase in the angle of inclination when it is greater than the critical value. The inclined pile has a "critical inclination angle for lateral displacement(9° for the test)" that corresponds to the peak value of lateral displacement. When the tilt angle is less than the critical value, the pile top lateral displacement increases with the increase in tilt angle. When the angle of tilt is larger than the critical value, the pile top lateral displacement decreases with the increase in tilt angle. The "critical inclination angle for lateral displacement" is greater than the "critical inclination angle for settlement". Under the same load, the lateral displacement of the composite foundation with an inclined pile is larger than that of the 6° pile and smaller than that of the 12° pile, and the settlement is larger than that of any inclined pile. When the pile is inclined, the lateral displacement of both the inclined pile and the composite foundation is considerably smaller than the settlement, but the lateral displacement is more sensitive than the settlement. In engineering, the inclination angle of the pile should be reduced as far as possible, and the settlement and lateral displacement of the inclined pile and its composite foundation should be reduced.
Improper construction, lateral surcharge, or excavation often leads to the tilting of pile bodies and causes problems of centralizability; however, the deformation characteristics of inclined pile composite foundation is not fully understood and may lead to new engineering diseases. A model box and loading device were designed to study the deformation law of inclined pile composite foundation under vertical repeated loading and unloading. The results are as follows: During the process of cyclic loading, the settlement and lateral displacement of the inclined pile top and its composite foundation increase as the load increases. Moreover, its growth rate increases as the load increases and decreases as the loading time increases. During the process of cyclic unloading, the settlement and lateral displacement of the inclined pile top and its composite foundation at the initial stage of unloading are not apparent, and elastic deformation occurs only during the last one or two stages of low pressure. Under the same load, the settlement of the pile top increases with the increase in the tilt angle. The inclined pile has a "critical inclination angle for settlement(6° during one to three loading and unloading cycles for the test)" that decreases with the increase in soil compactness. When the inclination is less than the critical value, the settlement of the pile has negligible effect and the settlement increases rapidly with the increase in the angle of inclination when it is greater than the critical value. The inclined pile has a "critical inclination angle for lateral displacement(9° for the test)" that corresponds to the peak value of lateral displacement. When the tilt angle is less than the critical value, the pile top lateral displacement increases with the increase in tilt angle. When the angle of tilt is larger than the critical value, the pile top lateral displacement decreases with the increase in tilt angle. The "critical inclination angle for lateral displacement" is greater than the "critical inclination angle for settlement". Under the same load, the lateral displacement of the composite foundation with an inclined pile is larger than that of the 6° pile and smaller than that of the 12° pile, and the settlement is larger than that of any inclined pile. When the pile is inclined, the lateral displacement of both the inclined pile and the composite foundation is considerably smaller than the settlement, but the lateral displacement is more sensitive than the settlement. In engineering, the inclination angle of the pile should be reduced as far as possible, and the settlement and lateral displacement of the inclined pile and its composite foundation should be reduced.
引文
[1] 吕凡任,陈云敏,陈仁朋,等.任意倾角斜桩承受任意平面荷载的弹性分析[J].浙江大学学报:工学版,2004,38(2):191-194. LU Fan-ren, CHEN Yun-min, CHEN Ren-peng, et al. Analysis of Batter Pile Under Arbitrary Inclined Loads in Semi-infinite Solid [J]. Journal of Zhejiang University: Engineering Science, 2004, 38 (2): 191-194.
[2] 苏子将,罗书学,康寅.软土地基中倾斜桩基承载力数值分析[J].岩土工程与地下工程,2008,28(5):75-76. SU Zi-jiang, LUO Shu-xue,KANG Yin. Numerical Analysis of Bearing Capacity of Inclined Piles in the Soft Soil [J]. Geotechnical Engineering and Underground Engineering, 2008, 28 (5): 75-76.
[3] 王云岗,章光,胡琦.斜桩基础受力特性研究[J].岩土力学,2011,32(7):2184-2190. WANG Yun-gang, ZHANG Guang, HU Qi. Study of Force Characteristics of Battered Pile Foundation [J]. Rock and Soil Mechanics, 2011, 32 (7): 2184-2190.
[4] ZHANG L M, MCVAY M C,HAN S J, et al. Effects of Dead Loads on the Lateral Response of Battered Pile Groups [J]. Canadian Geotechnical Journal, 2002, 39 (3): 561-575.
[5] MEYERHOF G G, YALCIN A S. Behaviour of Flexible Batter Piles Under Inclined Loads in Layered Soil [J].Canadian Geotechnical Journal, 2011, 30 (2): 247-256.
[6] 曹卫平,陆清元,樊文甫,等.竖向荷载作用下斜桩荷载传递性状试验研究[J].岩土力学,2016,37(11): 3048-3056. CAO Wei-ping, LU Qing-yuan, FAN Wen-fu, et al. Experimental Study of Load Transfer Behavior of Batter Piles Under Vertical Loads [J]. Rock and Soil Mechanics, 2016, 37 (11): 3048-3056.
[7] 王新泉,陈永辉,安永福,等.塑料套管现浇混凝土桩倾斜对承载性能影响的模型试验研究[J].岩石力学与工程学报,2011,30(4):834-841. WANG Xin-quan, CHEN Yong-hui, AN Yong-fu, et al. Model Test Study of Effect of Inclination on Bearing Behaviors of Plastic Tube Cast-in-place Concrete Pile [J]. Chinese Journal of Rock Mechanics and Engineering, 2011, 30 (4): 834-841.
[8] 李龙起,罗书学.非均匀地基中倾斜桩基竖向承载特性模拟试验研究[J].岩土力学,2012,33(5):1300-1305. LI Long-qi, LUO Shu-xue. A Simulation Test Study of Vertical Bearing Capacity of Inclined Pile Foundation in Inhomogeneous Strata [J].Rock and Soil Mechanics, 2012, 33 (5): 1300-1305.
[9] 徐江,龚维明,张琦,等.大口径钢管斜桩竖向承载特性数值模拟与现场试验研究[J].岩土力学,2017,38(8):2434-2440. XU Jiang, GONG Wei-min, ZHANG Qi, et al. Numerical Simulation and Field Test of Vertical Bearing Capacity of Large Diameter Steel Pipe Inclined Pile [J]. Rock and Soil Mechanics, 2017, 38 (8): 2434-2440.
[10] 胡文红,郑刚.浅层土体加固对倾斜桩竖向承载力影响研究[J].岩土工程学报,2013,35(4):697-706. HU Wen-hong, ZHENG Gang. Influence of Shallow Soil Improvement on Vertical Bearing Capacity of Inclined Piles [J]. Chinese Journal of Geotechnical Engineering, 2013, 35 (4): 697-706.
[11] 郑刚,王丽.竖向荷载作用下倾斜桩的荷载传递性状及承载力研究[J].岩土工程学报,2008,30(3):323-330. ZHENG Gang, WANG Li. Load Transfer and Bearing Capacity of Inclined Pile Under Vertical Load [J]. Chinese Journal of Geotechnical Engineering, 2008, 30 (3): 323-330.
[12] 郑刚,李帅,杜一鸣,等.竖向荷载作用下倾斜桩的承载力特性[J].天津大学学报:自然科学版,2012,45(7):567-576. ZHENG Gang, LI Shuai, DU Yi-ming, et al. Bearing Capacity Behaviors of Inclined Pile Under Vertical Load [J]. Journal of Tianjin University: Nature Science Edition, 2012, 45 (7): 567-576.
[13] 周德泉,罗坤,冯晨曦,等.一种室内土工模型实验装置:中国,ZL 201520323607.3[P].2015-08-26. ZHOU De-quan, LUO Kun, FENG Chen-xi, et al. A Test Apparatus of Laboratory Geotechnical Model: China, ZL 201520323607.3 [P]. 2015-08-26.
[14] JGJ 79—2012,建筑地基处理技术规范[S]. JGJ 79—2012, Technical Specification for Building Foundation Treatment [S].
[15] 周德泉,李传习,杨帆,等.空隙岩体与溶洞充填混凝土竖向变形特性对比试验研究[J].岩土力学,2011,32(5):1309-1314. ZHOU De-quan, LI Chuan-xi, YANG Fan, et al.Experimental Comparison Study of Vertical Deformation Behavior of Rock Mass with Voids and Concrete Filled Solution Cave [J]. Rock and Soil Mechanics, 2011, 32 (5): 1309-1314.
[16] 周德泉,谭焕杰,徐一鸣,等.循环荷载作用下花岗岩残积土累积变形与湿化特性试验研究[J].中南大学学报:自然科学版,2013,44(4):1657-1665. ZHOU De-quan, TAN Huan-jie, XU Yi-ming, et al.Indoor Experimental Study for Accumulative and Wetting Deformation of Granite Residual Soil Under Cyclic Loading [J].Journal of Central South University: Science and Technology, 2013, 44 (4): 1657-1665.
[17] 周德泉,颜超,罗卫华.复合桩基重复加卸载过程中侧向约束桩变位规律试验研究[J].岩土力学,2015,36(10):2780-2786. ZHOU De-quan, YAN Chao, LUO Wei-hua. Experimental Study on Lateral Constrained Pile Variation in the Process of Repeated Loading and Unloading of Composite Pile Foundation [J]. Geotechnical Mechanics, 2015, 36 (10): 2780-2786.
[18] 邱伟,易善昌,龚维亮,等.基于EPS的海相深厚软基区路基不均匀沉降处治研究[J].中外公路,2018,38(4):19-23. QIU Wei, YI Shan-chang, GONG Wei-liang, et al.Study on Differential Settlement in Thick Marine Soft Clay Foundation Based on Expanded polystyrene [J].Journal of Chinese and Foreign Highway, 2018, 38 (4): 19-23.
[2] 苏子将,罗书学,康寅.软土地基中倾斜桩基承载力数值分析[J].岩土工程与地下工程,2008,28(5):75-76. SU Zi-jiang, LUO Shu-xue,KANG Yin. Numerical Analysis of Bearing Capacity of Inclined Piles in the Soft Soil [J]. Geotechnical Engineering and Underground Engineering, 2008, 28 (5): 75-76.
[3] 王云岗,章光,胡琦.斜桩基础受力特性研究[J].岩土力学,2011,32(7):2184-2190. WANG Yun-gang, ZHANG Guang, HU Qi. Study of Force Characteristics of Battered Pile Foundation [J]. Rock and Soil Mechanics, 2011, 32 (7): 2184-2190.
[4] ZHANG L M, MCVAY M C,HAN S J, et al. Effects of Dead Loads on the Lateral Response of Battered Pile Groups [J]. Canadian Geotechnical Journal, 2002, 39 (3): 561-575.
[5] MEYERHOF G G, YALCIN A S. Behaviour of Flexible Batter Piles Under Inclined Loads in Layered Soil [J].Canadian Geotechnical Journal, 2011, 30 (2): 247-256.
[6] 曹卫平,陆清元,樊文甫,等.竖向荷载作用下斜桩荷载传递性状试验研究[J].岩土力学,2016,37(11): 3048-3056. CAO Wei-ping, LU Qing-yuan, FAN Wen-fu, et al. Experimental Study of Load Transfer Behavior of Batter Piles Under Vertical Loads [J]. Rock and Soil Mechanics, 2016, 37 (11): 3048-3056.
[7] 王新泉,陈永辉,安永福,等.塑料套管现浇混凝土桩倾斜对承载性能影响的模型试验研究[J].岩石力学与工程学报,2011,30(4):834-841. WANG Xin-quan, CHEN Yong-hui, AN Yong-fu, et al. Model Test Study of Effect of Inclination on Bearing Behaviors of Plastic Tube Cast-in-place Concrete Pile [J]. Chinese Journal of Rock Mechanics and Engineering, 2011, 30 (4): 834-841.
[8] 李龙起,罗书学.非均匀地基中倾斜桩基竖向承载特性模拟试验研究[J].岩土力学,2012,33(5):1300-1305. LI Long-qi, LUO Shu-xue. A Simulation Test Study of Vertical Bearing Capacity of Inclined Pile Foundation in Inhomogeneous Strata [J].Rock and Soil Mechanics, 2012, 33 (5): 1300-1305.
[9] 徐江,龚维明,张琦,等.大口径钢管斜桩竖向承载特性数值模拟与现场试验研究[J].岩土力学,2017,38(8):2434-2440. XU Jiang, GONG Wei-min, ZHANG Qi, et al. Numerical Simulation and Field Test of Vertical Bearing Capacity of Large Diameter Steel Pipe Inclined Pile [J]. Rock and Soil Mechanics, 2017, 38 (8): 2434-2440.
[10] 胡文红,郑刚.浅层土体加固对倾斜桩竖向承载力影响研究[J].岩土工程学报,2013,35(4):697-706. HU Wen-hong, ZHENG Gang. Influence of Shallow Soil Improvement on Vertical Bearing Capacity of Inclined Piles [J]. Chinese Journal of Geotechnical Engineering, 2013, 35 (4): 697-706.
[11] 郑刚,王丽.竖向荷载作用下倾斜桩的荷载传递性状及承载力研究[J].岩土工程学报,2008,30(3):323-330. ZHENG Gang, WANG Li. Load Transfer and Bearing Capacity of Inclined Pile Under Vertical Load [J]. Chinese Journal of Geotechnical Engineering, 2008, 30 (3): 323-330.
[12] 郑刚,李帅,杜一鸣,等.竖向荷载作用下倾斜桩的承载力特性[J].天津大学学报:自然科学版,2012,45(7):567-576. ZHENG Gang, LI Shuai, DU Yi-ming, et al. Bearing Capacity Behaviors of Inclined Pile Under Vertical Load [J]. Journal of Tianjin University: Nature Science Edition, 2012, 45 (7): 567-576.
[13] 周德泉,罗坤,冯晨曦,等.一种室内土工模型实验装置:中国,ZL 201520323607.3[P].2015-08-26. ZHOU De-quan, LUO Kun, FENG Chen-xi, et al. A Test Apparatus of Laboratory Geotechnical Model: China, ZL 201520323607.3 [P]. 2015-08-26.
[14] JGJ 79—2012,建筑地基处理技术规范[S]. JGJ 79—2012, Technical Specification for Building Foundation Treatment [S].
[15] 周德泉,李传习,杨帆,等.空隙岩体与溶洞充填混凝土竖向变形特性对比试验研究[J].岩土力学,2011,32(5):1309-1314. ZHOU De-quan, LI Chuan-xi, YANG Fan, et al.Experimental Comparison Study of Vertical Deformation Behavior of Rock Mass with Voids and Concrete Filled Solution Cave [J]. Rock and Soil Mechanics, 2011, 32 (5): 1309-1314.
[16] 周德泉,谭焕杰,徐一鸣,等.循环荷载作用下花岗岩残积土累积变形与湿化特性试验研究[J].中南大学学报:自然科学版,2013,44(4):1657-1665. ZHOU De-quan, TAN Huan-jie, XU Yi-ming, et al.Indoor Experimental Study for Accumulative and Wetting Deformation of Granite Residual Soil Under Cyclic Loading [J].Journal of Central South University: Science and Technology, 2013, 44 (4): 1657-1665.
[17] 周德泉,颜超,罗卫华.复合桩基重复加卸载过程中侧向约束桩变位规律试验研究[J].岩土力学,2015,36(10):2780-2786. ZHOU De-quan, YAN Chao, LUO Wei-hua. Experimental Study on Lateral Constrained Pile Variation in the Process of Repeated Loading and Unloading of Composite Pile Foundation [J]. Geotechnical Mechanics, 2015, 36 (10): 2780-2786.
[18] 邱伟,易善昌,龚维亮,等.基于EPS的海相深厚软基区路基不均匀沉降处治研究[J].中外公路,2018,38(4):19-23. QIU Wei, YI Shan-chang, GONG Wei-liang, et al.Study on Differential Settlement in Thick Marine Soft Clay Foundation Based on Expanded polystyrene [J].Journal of Chinese and Foreign Highway, 2018, 38 (4): 19-23.