Failure mechanism and reinforcement measures of shallow slopes of expansive soils in Northern Xinjiang
-
摘要: 膨胀土渠道边坡稳定是北疆供水工程正常运行的前提。以北疆高寒区供水工程为例,渠道膨胀土边坡在干湿交替、冻融循环作用下破坏明显,主要表现为浅层膨胀土开裂造成坡面完整性的降低及其内部基土力学特性的劣化,严重影响渠道膨胀土边坡的整体稳定性。以膨胀土渠道现场失稳断面实测资料为基础,结合离心试验结果及复合材料中的界面理论,对渠道膨胀土边坡的浅层破坏机制及加固措施进行研究。结果表明,浅层膨胀土开裂是引起渠道浅层破坏的决定性因素,且其具体破坏有别于传统的牵引式滑坡,主要呈现出沿着渠坡浅层发生的膨胀土剥落破坏。此外,膨胀土的持续失水过程造成了土颗粒间强黏结接触向及弱黏结接触的转化,造成了膨胀土裂隙发育到一定深度后传播路径发生偏转,裂隙贯穿浅层土体,最终造成渠道膨胀土边坡发生浅层破坏。在此基础上,提出在现场修坡完成需采取防护手段来降低浅层土体的开裂,并建议在渠坡后缘出现张拉裂隙时及时采取抗滑支挡加固措施。Abstract: The stability of canal slopes of expansive soils is the premise of normal operation of water supply projects in Northern Xinjiang. Taking the water supply project in the high and cold region of Northern Xinjiang as an example, the canal slopes at expansive soils are destroyed obviously under the action of alternate wet and dry, freeze-thaw cycle, which is mainly manifested as the reduction of slope integrity caused by the cracking of shallow expansive soils and the deterioration of internal mechanical properties of the basic soils, which seriously affects the overall stability of the canal slopes of expansive soils. Based on the field measured data of the failure section of expansive soil canals, combined with centrifugal test results and interface theory in composite materials, the shallow failure mechanism and reinforcement measures of canal slopes of expansive soil are studied. The results show that the cracking of shallow expansive soils is the decisive factor causing the failure of shallow canals, and the specific failure is different from that of the traditional traction landslides, which mainly exhibits the failure of spalling of shallow expansive soils along the canal slopes. In addition, the continuous water loss process of expansive soils results in the conversion of strong bond contact between soil particles to weak bond contact, and causes the propagation path deflection of expansive soil cracks after they develop to a certain depth, and the cracks penetrate into the shallow soils, finally causing shallow damage to the expansive soil slopes. On this basis, it is suggested that the protective measures should be taken to reduce the cracking of shallow soils after the slope repair, and the anti-sliding retaining reinforcement measures should also be taken in time when the tensile crack appears at the back edge of the canal slopes.
-
Keywords:
- water supply canal /
- expansive soil slope /
- shallow crack /
- failure mechanism /
- retaining measure
-
0. 引言
土的渗透特性是土重要的工程性质之一,影响着土木工程的施工。目前无黏性土渗透特性的试验研究,多是采用竖向圆柱体模型槽进行,试验中土体受到的水流的作用方向是由下至上的竖直方向,而对于土体承受水平向渗流时土体渗透特性的研究不多[1],渗流方向对土体渗流变形特性的研究还尚未给予足够重视。对土渗流的研究表明,实际施工中渗流的优势方向往往是水平方向,通常土体水平向的渗透性大于竖向,而抵抗水平向渗透破坏的能力低于抵抗竖向渗透破坏的能力[2-6]。
本文针对粉砂竖向和水平向渗透特性研究存有的不足,利用自主设计的实验装置,对粉砂开展竖向和水平向渗流试验,对比分析了两种不同方向渗流场下粉砂的渗透特性。基于室内模拟试验,建立三维离散元与计算流体力学耦合的细观力学模型,对粉砂在竖向和水平向的渗流情况进行分析和计算。通过数值计算结果,对竖向和水平向渗流作用下的粉砂内部接触力、渗流速度及流场的分布规律进行细观分析,将数值模拟与室内试验的结果进行分析、比较。
1. 不同渗流方向下粉砂渗透变形室内试验模拟
1.1 试验仪器和方法
（1）试验仪器
粉砂的竖向渗透变形试验借助实验室自主设计的圆柱形渗流试验仪进行,该装置示意图如图1所示。粉砂水平向渗流渗透变形特性的研究是在自主设计的水平渗流试验装置中进行的,见图2。模型由进水系统,装样区及排水系统3个主要部分组成。进水系统可以通过对进水水头高度的调节自由选择水头加载高度。
![]()
图 1 圆柱形渗流试验仪示意图Figure 1. Schematic diagram of instrument for cylindrical seepage tests（2）试验方法及步骤
粉砂烘干并分层装样。称样烘干24 g取出装样,每10 cm分为一层进行装样；排气饱和。装样完成,分次提升水箱供水高度对试验土样进行饱和,最后一次使水头抬升至与试样顶端齐平,静置24 h；逐级调整水头进行试验。逐级抬升水头高度,对测压管水头高度读数并记录,同时量测渗流量大小,记录试验进程中的渗流现象,直至该级渗流稳定,转入下一级水头；当试验过程中,流量忽然增大,并出现明显的渗流通道,可以认定为试样发生渗透破坏,不再继续加大水头高度,试验完成。
1.2 粉砂竖向和水平向渗流试验结果分析
对粉砂在竖向渗流下的渗透流速受水力梯度影响下的变化规律进行研究,得到渗流速度随水力梯度变化的关系曲线,如图3所示。对粉砂在水平向渗流作用下的临界水力梯度进行研究,结果如图4所示。
![]()
图 3 竖向渗流下渗流速度随水力梯度变化曲线Figure 3. Relationship between seepage velocity and vertical hydraulic gradient![]()
图 4 水平向渗流下渗流速度随水力梯度变化曲线Figure 4. Relationship between seepage velocity and critical hydraulic gradient由图3得到,在水力梯度
<0.787时,渗流速度随水力梯度呈近似线性的变化,此时土样处于渗流稳定阶段；当水力梯度为1.1时,渗流速度忽然增大,粉砂颗粒流失量也徒增,此时土体发生渗透变形。图4粉砂在水平向渗流下的变化规律显示：水力梯度小于0.45时,粉砂土渗透流速随着水力梯度的增大呈线性增长,水流清澈,粉砂流出较少。当水力梯度增至0.52时,试样整体的流速瞬间增大,粉砂流出量明显增多且呈持续流失状态,此时粉砂土样内部颗粒运移不再规律,试样开始发生渗透破坏。 表1给出粉砂在两种渗流方向下的渗透系数、临界坡降与破坏坡降。粉砂在竖向渗流时的临界水力梯度为0.787,破坏水力梯度为1.10；而水平向渗流中,所能承受的临界水力梯度为0.45。在影响因素诸如种类、级配、密度、孔隙大小等相同的前提下,粉砂竖向渗流的临界水力梯度比水平向高出近44%。由于土体在受到水平向渗流时,平均渗透系数取决于最透水土层的厚度和渗透性；而对于竖向渗流,其平均渗透系数取决于最不透水土层的渗透性。加之,竖向渗流中重力作用与渗流方向一致,会产生对土层的压密作用,使得该渗流方向下的渗透系数小于水平向,而土体能够承受的水头高于水平向的渗流。
表 1 不同渗流方向下粉砂渗透系数、临界坡降和破坏坡降Table 1. Datat of permeability coeffieient of silt, critical slope and failure slope under different seepage directions渗流方向 渗透系数/(10-4 cm·s-1) 临界水力梯度 破坏水力梯度 竖向 6.13 0.787 1.10 水平 6.25 0.450 0.52 2. 不同渗流方向下粉砂渗透变形颗粒流模拟
对于固相颗粒,通过求解运动和动量方程模拟颗粒运动,采用离散元的颗粒流理论进行模拟；对于液相介质,采用均一化流体计算技术模拟其在孔隙中的运动,也就是通过求解平均Navier-Stokes方程模拟孔隙中流体的运动[7-9]。
2.1 数值模型
对粉砂土不同向渗流形态的模拟中,边界条件的界定也略有不同。竖向渗流下,颗粒周边的边界为固壁边界条件,上下为压力边界条件。水平向渗流下,模型的前后和上下边界为固壁边界条件,左右设置为压力边界条件和自由边界条件。生成的土体模型如图5所示。
对于竖向的渗流,按照试验中模型,上覆为自由边界,没有压重。对于水平向的渗流,试样在重力和浮力作用下保持平衡,当作用渗流力后,土中小颗粒将从模型右侧流出,因此在试样右侧设置了相互交叉垂直的线墙,如图6所示。
2.2 数值计算流程
采用PFC3D对流固耦合问题进行计算流程如图7所示。
2.3 数值模拟结果
（1）粉砂土竖向和水平向渗流下渗透变形情况
a）粉砂竖向渗流下的渗透变形情况
图8给出了粉砂在竖向渗流作用下,土样随水力梯度的变化情况。
![]()
图 8 竖向渗流下粉砂土随水力梯度变化情况Figure 8. Variation of silty sand with gradient under vertical seepage水力梯度从0.1,0.2,0.3,...,逐级增加,水力梯度施加至0.7时,粉砂几乎无变化；当水力梯度增至0.8时,土样出现从底部被整体抬升的趋势,发生少量细小颗粒流失的现象；水力梯度继续增至1.0时,土体发生了整体的抬升,土体表面颗粒簇发生整体迁移的现象。模拟结果表明,试样的临界水力梯度在0.8左右。
b）粉砂水平向渗流下的渗透变形情况
粉砂土的水平向渗流中水力梯度也是由0.1,0.2,0.3依次逐级抬升,图9给出了粉砂土在水平向渗流下试样随水力梯度变化的情况。
![]()
图 9 水平向渗流下粉砂土随水力梯度变化情况Figure 9. Variation of silt with gradient under horizontal seepage从图9中可以看出,当水力梯度增至0.3时,试样底部细小颗粒也开始发生迁移,水力梯度继续增大至0.4,此时试样发生颗粒成团的流失,土体发生了渗透变形。水力梯度加载至0.5时,土体颗粒发生了更加显著的整体性渗流破坏。根据模拟结果,得到粉砂土水平向渗流的临界水力梯度在0.4左右。
（2）粉砂土竖向和水平向渗流下配位数变化情况分析
土体的配位数表示了颗粒间的接触数,是表达土颗粒间接触情况的参数之一,总配位数是颗粒与颗粒之间以及颗粒与墙之间的平均接触数,反映出试样的压密程度；力学配位数为颗粒与颗粒之间接触数大于2时的颗粒接触数,反映额土骨架的压密程度。图10,11给出了粉砂土在竖向和水平向渗流作用下,配位数随水力梯度的变化情况。
![]()
图 10 竖向渗流下粉砂配位数随水力梯度变化Figure 10. Variation of coordination number with gradient under vertical seepage![]()
图 11 水平向渗流粉砂配位数随水力梯度变化Figure 11. Variation of coordination number with gradient under horizontal seepage图10,11可以看出,当竖向渗流的水力梯度为0.8,水平向渗流水力梯度为0.4时,土体的两个配位数都发生迅速的下降,说明此时的土体状态发生了较大的变化,即渗透变形发生。图中,总配位数和力学配位数都在随着水力梯度的增大而不断降低,总的配位数较力学配位数下降更快速,幅度也更大。这是由于水力梯度增大,颗粒发生了移动,颗粒的接触数减小,但在水力梯度增加至土体渗透变形前的整个过程中,总配位数下降幅度明显大于力学配位数,说明发生移动的多为小颗粒,小颗粒的运移使土体中接触数减少,随之小颗粒填充至骨架颗粒孔隙间,与大颗粒发生接触,保持了力学配位数的大小。
3. 结论
（1）粉砂在水平向能承受的渗流破坏作用一般低于竖向渗流。
（2）数值模拟结果与模拟试验过程中粉砂的渗流变化过程相符,数值方法所测得的临界水力梯度与试验测得的结果亦较为吻合。
（3）竖向和水平向渗流下,粉砂的总配位数和力学配位数均随着水力梯度的抬升而衰减,当土体发生渗透破坏,土体配位数出现迅速降低。
-
![]()
图 1 北疆渠道现场典型断面失稳破坏图
Figure 1. Typical section of instability failure of canal in Northern Xinjiang
![]()
图 2 北疆渠道失稳破坏断面实测剖面图
Figure 2. Typical section of instability failure of canal in Northern Xinjiang
![]()
图 4 膨胀土渠道边坡离心试验破坏特征
Figure 4. Failure characteristics of centrifugal tests on canal slope expansive soils
![]()
图 6 裂隙的3种断裂模式及二级裂隙的形成过程
Figure 6. Three fracture modes of fracture and formation process of secondary fracture
-
[1] 邓铭江. 新疆水资源及可持续利用[M]. 北京: 中国水利水电出版社, 2005. DENG Ming-jiang. Water Resource of Xinjiang and Sustainable Use[M]. Beijing: China Water Resources and Hydropower Press, 2005. (in Chinese)
[2] 邓铭江. 中国西北“水三线”空间格局与水资源配置方略[J]. 地理学报, 2018, 73(7): 1189-1203. https://www.cnki.com.cn/Article/CJFDTOTAL-DLXB201807002.htm DENG Ming-jiang. “Three Water Lines” strategy: its spatial patterns and effects on water resources allocation in northwest China[J]. Acta Geographica Sinica, 2018, 73(7): 1189-1203. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-DLXB201807002.htm
[3] 蔡正银, 黄英豪. 咸寒区渠道冻害评估与处治技术[M]. 北京: 科学出版社, 2015. CAI Zheng-yin, HUANG Ying-hao. Evaluation and Treatment Technology of Frost Damage in Canalsin Saline and Cold Regions[M]. Beijing: Science Press, 2015 (in Chinese)
[4] 刘静德, 李青云, 龚壁卫. 南水北调中线膨胀岩膨胀特性研究[J]. 岩土工程学报, 2011, 33(5): 826-830. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201105030.htm LIU Jing-de, LI Qing-yun, GONG Bi-wei. Swelling properties of expansive rock in middle route project of South-to-North Water Diversion[J]. Chinese Journal of Geotechnical Engineering, 2011, 33(5): 826-830. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201105030.htm
[5] 张晨, 蔡正银, 黄英豪, 等. 输水渠道冻胀离心模拟试验[J]. 岩土工程学报, 2016, 38(1): 109-117. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201601013.htm ZHANG Chen, CAI Zheng-yin, HUANG Ying-hao, et al. Centrifuge modelling of frost-heave of canals[J]. Chinese Journal of Geotechnical Engineering, 2016, 38(1): 109-116. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC201601013.htm
[6] 陈生水, 郑澄锋, 王国利. 膨胀土边坡长期强度变形特性和稳定性研究[J]. 岩土工程学报, 2007, 29(6): 795-799. CHEN Sheng-shui, ZHENG Cheng-feng, WANG Guo-li. Researches on long-term strength deformation characteristics and stability of expansive soil slopes[J]. Chinese Journal of Geotechnical Engineering, 2007, 29(6): 795-799. (in Chinese)
[7] MORGENSTERN N R, PRICE V E. The analysis of the stability of general slip surfaces[J]. Géotechnique, 1965, 15(1): 79-93. doi: 10.1680/geot.1965.15.1.79
[8] 程展林, 龚壁卫. 膨胀土边坡[M]. 北京: 科学出版社, 2015. CHENG Zhan-lin, GONG Bi-wei. Expansive Soil Slope[M]. Beijing: Science Press, 2015. (in Chinese)
[9] 包承纲. 非饱和土的性状及膨胀土边坡稳定问题[J]. 岩土工程学报, 2004, 26(1): 1-15. doi: 10.3321/j.issn:1000-4548.2004.01.001 BAO Cheng-gang. Behavior of unsaturated soil and stability of expansive soil slope[J]. Chinese Journal of Geotechnical Engineering, 2004, 26(1): 1-15. (in Chinese) doi: 10.3321/j.issn:1000-4548.2004.01.001
[10] 朱洵, 蔡正银, 黄英豪, 等. 湿干冻融耦合循环及干密度对膨胀土力学特性影响的试验研究[J]. 水利学报, 2020, 51(3): 286-294. ZHU Xun, CAI Zheng-yin, HUANG Ying-hao, et al. Research on mechanical properties of expansive soils under cyclic action of coupling wetting-drying and freeze-thaw and density[J]. Journal of Hydraulic Engineering, 2020, 51(3): 286-294. (in Chinese)
[11] 朱洵, 蔡正银, 黄英豪, 等. 湿干冻融耦合循环作用下膨胀土力学特性及损伤演化规律研究[J]. 岩石力学与工程学报, 2019, 38(6): 1233-1241. https://www.cnki.com.cn/Article/CJFDTOTAL-YSLX201906014.htm ZHU Xun, CAI Zheng-yin, HUANG Ying-hao, et al. Research on mechanical properties and damage evolution law of expensive soils under the cyclic action of coupling wetting-drying and freeze-thaw[J]. Chinese Journal of Rock Mechanics and Engineering, 2019, 38(6): 1233-1241. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-YSLX201906014.htm
[12] 蔡正银, 陈皓, 黄英豪, 等. 考虑干湿循环作用的膨胀土渠道边坡破坏机理研究[J]. 岩土工程学报, 2019, 41(11): 1977-1982. CAI Zheng-yin, CHEN Hao, HUANG Ying-hao, et al. Failure mechanism of canal slopes of expansive soils considering action of wetting-drying cycles[J]. Chinese Journal of Geotechnical Engineering, 2019, 41(11): 1977-1982. (in Chinese)
[13] 蔡正银, 朱洵, 黄英豪, 等. 湿干冻融耦合循环作用下膨胀土裂隙演化规律[J]. 岩土工程学报, 2019, 41(8): 1381-1389. CAI Zheng-yin, ZHU Xun, HUANG Ying-hao, et al. Evolution rules of fissures in expansive soils under cyclic action of coupling wetting-drying and freeze-thaw[J]. Chinese Journal of Geotechnical Engineering, 2019, 41(8): 1381-1389. (in Chinese)
[14] 蔡正银, 朱洵, 黄英豪, 等. 冻融过程对膨胀土裂隙演化特征的影响[J]. 岩土力学, 2019, 40(12): 4555-4563. CAI Zheng-yin, ZHU Xun, HUANG Ying-hao, et al. Influences of freeze-thaw process on evolution characteristics of fissures in expensive soil[J]. Rock and Soil Mechanics, 2019, 40(12): 1-9. (in Chinese)
[15] KHAN M S, HOSSAIN S, AHMED A, et al. Investigation of a shallow slope failure on expansive clay in Texas[J]. Engineering Geology, 2017, 219: 118-129.
[16] DONKOR P, OBONYO E. Compressed soil blocks: Influence of fibers on flexural properties and failure mechanism[J]. Construction and Building Materials, 2016, 121: 25-33.
[17] 唐朝生, 施斌, 崔玉军. 土体干缩裂隙的形成发育过程及机理[J]. 岩土工程学报, 2018, 40(8): 1415-1423. TANG Chao-sheng, SHI Bin, CUI Yu-jum. Behaviors and mechanisms of desiccation cracking of soils[J]. Chinese Journal of Geotechnical Engineering, 2018, 40(8): 1415-1423. (in Chinese)
[18] 柴波, 殷坤龙, 简文星, 等. 红层水岩作用特征及库岸失稳过程分析[J]. 中南大学学报(自然科学版), 2009, 40(4): 1092-1098. https://www.cnki.com.cn/Article/CJFDTOTAL-ZNGD200904043.htm CHAI Bo, YIN Kun-long, JIAN Wen-xing, et al. Analysis of water-rock interaction characteristics and bank slope failure process of red-bed[J]. Journal of Central South University (Science and Technology), 2009, 40(4): 1092-1098. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-ZNGD200904043.htm
[19] 李黎, 曹明莉. 混杂纤维增强水泥基复合材料弯曲韧性与纤维增强指数的定量关系[J]. 复合材料学报, 2018, 35(5): 1349-1353. https://www.cnki.com.cn/Article/CJFDTOTAL-FUHE201805037.htm LI Li, CAO Ming-li. Quantitative relationship between flexural toughness and fiber reinforcing index of hybrid fiber reinforced cementitious composites[J]. Acta Materiae Compositae Sinica, 2018, 35(5): 1349-1353. (in Chinese) https://www.cnki.com.cn/Article/CJFDTOTAL-FUHE201805037.htm
-
期刊类型引用(4)
1. 应宏伟，陈雨，王阳扬，刘冠. 含碎石芯软黏土复合试样大三轴试验研究. 湖南大学学报(自然科学版). 2024(11): 104-114 . 
百度学术
2. 邱俊峰，叶晨峰，陈峰，郑铖杰. 镍铁渣粉水泥固化砂土剪切强度与应力应变关系研究. 湖南文理学院学报(自然科学版). 2023(02): 78-82+95 . 百度学术
3. 殷天军，宁华宇，寇晓强. 深中通道沉管基础水下深层水泥搅拌桩应用全过程探讨. 中国港湾建设. 2022(07): 11-16 . 百度学术
4. 张振，郑文强，叶观宝，陈勇. 循环荷载下水泥土桩复合单元体变形特性及其地基长期沉降计算方法. 中国公路学报. 2022(11): 21-29 . 百度学术
其他类型引用(2)
下载:
计量
- 文章访问数: 261
- HTML全文浏览量: 36
- PDF下载量: 94
- 被引次数: 6
