梯田坎墙土压力及墙后膨胀土降雨增湿膨胀效应评价
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摘要
非饱和膨胀土地区的梯田埂坎稳定性差以及垮坎是农业坡改梯工程建设中最棘手的问题。本文基于BISHOP的非饱和土抗剪强度理论,首先,计算了天然非饱和状态下PP织物袋坎墙土压力;然后,分析在雨水逐层入渗条件下墙后膨胀土自由完全膨胀时坎墙的稳定性;最后,基于温度场的热胀作用等效模拟膨胀土的吸水膨胀作用的方式,对降雨作用下PP织物袋坎墙及墙后填土膨胀特性进行了数值模拟与评价,并对比分析了数值结果及理论解析结果的异同。研究结果表明:在天然非饱和状态下,墙后膨胀土拉张区深度大于坎墙高度,坎墙未受到土压力作用。雨水逐层入渗、墙后膨胀土水平自由完全膨胀条件下,当雨水入渗至临界饱和深度时,膨胀变形释放导致坎墙因发生过大的位移而破坏。理论解析中未考虑墙后膨胀土的竖向膨胀效应,而数值模拟中充分考虑了墙后膨胀土的多向膨胀效应,数值模拟分析得出坎墙破坏时的临界饱和深度明显大于理论解析的结果,因此数值模拟结果比理论解析结果更接近实际情况。
Poor stability of the ridge of terraced field and collapse of the ridge are the most intractable problems in the construction of the project of terracing slope cropland within the region of unsaturated expansive soil. Based on BISHOP's unsaturated shear strength theory,the earth pressure of the ridged-wall built with PP bag(polypropylene geotextile bag) under the natural unsaturated state is calculated herein at first,and then the stability of the ridged-wall during the complete free expansion of the expansive soil behand the wall under the condition of the layer-by-layer rainwater infiltration is analyzed. At last,the numerical simulation and evaluation on the expansion characteristics of both the ridged-wall of PP bag and the backfill soil behand the wall under the effect of rainfall are carried out in accordance with the mode of equivalently simulating the wet-expansion effect of the expansive soil on the basis of the thermal expansion effect of temperature field,while the similarity and difference between the numerical result and the theoretical analysis result are comparatively analyzed as well. The study result shows that under the natural unsaturated state,the ridge-wall is not affected by earth pressure if the depth of the tensional area of the expansive soil behand the wall is larger than the height of the ridge-wall. When rainwater infiltrates to the critical saturation depth,the ridge-wall is to be failed due to the overlarge displacement caused by the release of the relevant expansive deformation under the condition of the complete horizontal free expansion of the expansive soil behand the wall. The vertical expansion effect of the expansive soil behand the wall is not considered in the theoretical analysis,while the multi-directional expansion effect of the expansive soil behand the wall is fully considered in the numerical simulation,from which the result of the critical saturation depth during the failure of the ridge-wall obtained from the numerical simulation is obviously lager than that from the theoretical analysis,thus the result from the numerical simulation is closer to the actual situation than that from the theoretical analysis.
Poor stability of the ridge of terraced field and collapse of the ridge are the most intractable problems in the construction of the project of terracing slope cropland within the region of unsaturated expansive soil. Based on BISHOP's unsaturated shear strength theory,the earth pressure of the ridged-wall built with PP bag(polypropylene geotextile bag) under the natural unsaturated state is calculated herein at first,and then the stability of the ridged-wall during the complete free expansion of the expansive soil behand the wall under the condition of the layer-by-layer rainwater infiltration is analyzed. At last,the numerical simulation and evaluation on the expansion characteristics of both the ridged-wall of PP bag and the backfill soil behand the wall under the effect of rainfall are carried out in accordance with the mode of equivalently simulating the wet-expansion effect of the expansive soil on the basis of the thermal expansion effect of temperature field,while the similarity and difference between the numerical result and the theoretical analysis result are comparatively analyzed as well. The study result shows that under the natural unsaturated state,the ridge-wall is not affected by earth pressure if the depth of the tensional area of the expansive soil behand the wall is larger than the height of the ridge-wall. When rainwater infiltrates to the critical saturation depth,the ridge-wall is to be failed due to the overlarge displacement caused by the release of the relevant expansive deformation under the condition of the complete horizontal free expansion of the expansive soil behand the wall. The vertical expansion effect of the expansive soil behand the wall is not considered in the theoretical analysis,while the multi-directional expansion effect of the expansive soil behand the wall is fully considered in the numerical simulation,from which the result of the critical saturation depth during the failure of the ridge-wall obtained from the numerical simulation is obviously lager than that from the theoretical analysis,thus the result from the numerical simulation is closer to the actual situation than that from the theoretical analysis.
引文
[1] 徐彬,殷宗泽,刘述丽.膨胀土强度影响因素与规律的试验研究[J].岩土力学,2011,32(1):44- 50.
[2] 唐朝生,施斌.干湿循环过程中膨胀土的胀缩变形特征[J].岩土工程学报,2011,33(9):1376- 1384.
[3] 吕海波,曾召田,赵艳林,等.膨胀土强度干湿循环试验研究[J].岩土力学,2009,30(12):3797- 3802.
[4] 唐朝生,崔玉军,ANH-MINH T,等.膨胀土收缩开裂过程及其温度效应[J].岩土工程学报,2014,34(12):2181- 2187.
[5] 申权,杨果林,胡敏,等.高速铁路新型路堑基床结构动力响应分析[J].地震工程学报,2017,39(6):1118- 1125.
[6] 白振锋,李光录,李想,等.PP织物袋梯田筑坎稳定性试验与研究[J].西北农林科技大学学报(自然科学版),2014,42(4):157- 164.
[7] 李光录,柳诗众,邓民兴.PP织物袋梯田筑坎技术在陕南秦巴山区的应用[J].中国水土保持,2011(11):29- 31.
[8] 李光录,柳诗众,邓民兴.陕南秦巴山区PP织物袋梯田筑坎结构和坎型研究[J].中国水土保持,2012(9):44- 45.
[9] BISHOP A W,ALPAN I,BLIGHT G E,et al.Factors controlling the shear strength of partly saturated cohesive soils[C]// Research Conference on the Shear Strength of Cohesive Soils,1960:503- 532.
[10] FREDLUND D G,MORGENSRERN N R,WIDGER R A.The shear strength of unsaturated soils[J].Canadian Geotechnical Journal,1978,15:313- 321.
[11] 卢肇钧,吴肖茗,孙玉珍.膨胀力在非饱和土强度理论中的作用[J].岩土工程学报,1997,19(5):20- 27.
[12] 李荣建,彭光辉,刘军定,等.一种分隔式PP织物袋:201420040107.4[P].2014- 08- 06.
[13] 李振.非饱和膨胀土增湿变形与增湿强度的试验研究[D].杨陵:西北农林科技大学,2006.
[2] 唐朝生,施斌.干湿循环过程中膨胀土的胀缩变形特征[J].岩土工程学报,2011,33(9):1376- 1384.
[3] 吕海波,曾召田,赵艳林,等.膨胀土强度干湿循环试验研究[J].岩土力学,2009,30(12):3797- 3802.
[4] 唐朝生,崔玉军,ANH-MINH T,等.膨胀土收缩开裂过程及其温度效应[J].岩土工程学报,2014,34(12):2181- 2187.
[5] 申权,杨果林,胡敏,等.高速铁路新型路堑基床结构动力响应分析[J].地震工程学报,2017,39(6):1118- 1125.
[6] 白振锋,李光录,李想,等.PP织物袋梯田筑坎稳定性试验与研究[J].西北农林科技大学学报(自然科学版),2014,42(4):157- 164.
[7] 李光录,柳诗众,邓民兴.PP织物袋梯田筑坎技术在陕南秦巴山区的应用[J].中国水土保持,2011(11):29- 31.
[8] 李光录,柳诗众,邓民兴.陕南秦巴山区PP织物袋梯田筑坎结构和坎型研究[J].中国水土保持,2012(9):44- 45.
[9] BISHOP A W,ALPAN I,BLIGHT G E,et al.Factors controlling the shear strength of partly saturated cohesive soils[C]// Research Conference on the Shear Strength of Cohesive Soils,1960:503- 532.
[10] FREDLUND D G,MORGENSRERN N R,WIDGER R A.The shear strength of unsaturated soils[J].Canadian Geotechnical Journal,1978,15:313- 321.
[11] 卢肇钧,吴肖茗,孙玉珍.膨胀力在非饱和土强度理论中的作用[J].岩土工程学报,1997,19(5):20- 27.
[12] 李荣建,彭光辉,刘军定,等.一种分隔式PP织物袋:201420040107.4[P].2014- 08- 06.
[13] 李振.非饱和膨胀土增湿变形与增湿强度的试验研究[D].杨陵:西北农林科技大学,2006.
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