地球科学进展  2018 , 33 (8): 842-851 https://doi.org/10.11867/j.issn.1001-8166.2018.08.0842

研究论文

急陡沟道物源起动模式及水土耦合破坏机制分析

龚凌枫, 唐川*, 李宁, 陈明, 杨成长, 蔡英桦

成都理工大学 地质灾害防治与地质环境保护国家重点实验室,四川 成都 610059

Source Inition Pattern and Coupling Mechanism of Granular Deposit and Seepage in Steep Longitudinal Gully,Wenchuan

Gong Lingfeng, Tang Chuan*, Li Ning, Chen Ming, Yang Chengzhang, Cai Yinghua

State Key Laboratory for Geo-Hazard Prevention and Geo-Environment Protection,Chengdu University of Technology,Chengdu 610059,China

中图分类号:  P315.2;P642.23

文献标识码:  A

文章编号:  1001-8166(2018)08-0842-10

通讯作者:  *通信作者:唐川(1961-),男,安徽合肥人,教授,主要从事地质灾害、工程地质、GIS与遥感应用研究.E-mail:tangc@cdut.edu.cn

收稿日期: 2018-04-24

修回日期:  2018-07-10

网络出版日期:  2018-08-10

版权声明:  2018 地球科学进展 编辑部 

基金资助:  国家自然科学基金项目“急陡沟道泥石流起动—侵蚀—冲出模型研究”(编号:41672299)国家重点研发计划项目“强震区地质灾害动态演化机制与长期效应”(编号:2017YFC1501004)资助.

作者简介:

First author:Gong Lingfeng(1989-), male, Guangshui County, Hubei Province, Ph.D student. Research areas include geological hazard assessment and prediction. E-mail:308488910@qq.com

作者简介:龚凌枫(1989-),男,湖北广水人,博士研究生,主要从事地质灾害评价与预测研究.E-mail:308488910@qq.com

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摘要

急陡沟道泥石流物源主要来源是崩塌、滑坡堆积体,堆积体的起动是急陡沟道泥石流冲出量巨大的主要原因。堆积体的物质组成、赋存特征及渗透、径流状态是造成其起动模式不同的本质原因,而较大的纵坡降为其起动提供了良好的地形条件。根据汇水条件及渗透特性设计了2组模型箱试验,模拟坡体内不产生稳定渗透及有稳定渗透条件下的破坏模式。实验表明急陡沟道泥石流起动有“消防管效应”和“坡体流态化”2种基本的模式,前者出现在不饱和或高渗透系数坡体,后者出现在具有一定细颗粒物质的土体中。其中消防管效应仅沿径流路径形成深而窄的侵蚀沟道,且搬运距离与水动力的持续性有关,固体物质搬运作用弱;坡体流态化主要特征为初期的缓慢渗透破坏及后期瞬时流动剪切破坏,侵蚀形成较宽的沟道,且侵蚀量相对较大。

关键词: 急陡沟道 ; 泥石流 ; 起动模式 ; 水土耦合机制

Abstract

Generally, collapse and landslide are the main sources of granular deposits while the initiation of deposits is triggered by the tremendous runoff from steep longitudinal gully. Substance composition, topographic condition and catchment characteristics directly affect the models of deposits initiation, and larger longitudinal grade provides better topographic condition for the initiation. Several sets of experiments on model casing were designed to simulate the failure mode of slopes under the states of stable and unstable seepages according to catchment and penetration characteristics. It was revealed from the experiments that the initiation of granular deposits had two fundamental modes, that is, fire hose effect and static liquefaction. The former one generally happens at the unsaturated slope or the slope of high permeability while the latter case occurs at the soils containing fine particles. It was concluded that the fire hose effect could generate the deep and narrow eroded channel along with the runoff, the movement distance was related to the continuous hydrodynamic force, and the transporting capacity of solid substances was weak. In addition, slope fluidization was featured with slow seepage failure at the early stage, instantaneous shear failure at the late stage, and wider channel came out due to serious erosion.

Keywords: Steep longitudinal gully ; Debris flows ; Initiation model ; Coupling mechanism.

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龚凌枫, 唐川, 李宁, 陈明, 杨成长, 蔡英桦. 急陡沟道物源起动模式及水土耦合破坏机制分析[J]. 地球科学进展, 2018, 33(8): 842-851 https://doi.org/10.11867/j.issn.1001-8166.2018.08.0842

Gong Lingfeng, Tang Chuan, Li Ning, Chen Ming, Yang Chengzhang, Cai Yinghua. Source Inition Pattern and Coupling Mechanism of Granular Deposit and Seepage in Steep Longitudinal Gully,Wenchuan[J]. Advances in Earth Science, 2018, 33(8): 842-851 https://doi.org/10.11867/j.issn.1001-8166.2018.08.0842

1 引 言

汶川大地震后,山间缓坡地带或坡面沟谷中出现了大量高位松散岩土体[1,2]。Tang等[3]通过对北川9·24群发性泥石流进行调查,总结了坡顶“悬挂物源”和“沟道堆积物源”2类物源。斜坡堆积物源由于所处位置较高,相对沟道位置高差较大,依附于高陡斜坡之上的物源稳定性与物源厚度、土体的饱水状态、植被覆盖率及类型、坡体坡度、岩土体类型密切相关。根据震后泥石流灾害调查统计资料分析,50%以上的泥石流固体物质来源于崩塌滑坡,部分泥石流中该比例甚至可达99%。耦合诱发的巨灾风险防范,如泥石流是灾害形成机理,灾害链、灾害群及其诱发的动力学、非动力学模型仍是各领域学者急需研究的前沿课题[4,5]。而急陡沟道泥石流因其成灾作用强,快速成为震区的关注对象,例如,福堂沟、烧房沟、高家沟、瓦窑沟、羊店村后山泥石流、小岗剑沟[6,7,8]、映秀磨子沟[9]等。研究成果较详细地介绍了急陡沟道的成灾背景及部分治理措施,但其起动及运动机理尚需深入。急陡沟道泥石流多发育在岩性条件良好的区域,为侵入类花岗岩(高家沟、瓦窑沟、羊店村后山、福堂沟)、动力变质和接触变质作用的花岗岩(烧房沟)、巨厚层状灰岩(小岗剑)。在很长的历史时期内,其剥蚀作用较弱、侵蚀作用较小,基本处于相对稳定的状态,所以即使沟道陡峻也无较大危害。据调查震前福堂沟、烧房沟、高家沟、彻底关沟、瓦窑沟、羊店村后山、小岗剑沟等沟道均发生过小规模的泥石流。而震后小岗剑泥石流沟在工程治理作用下又暴发了多次大规模的泥石流,之后更是在后缘崩塌碎屑流的作用下将治理工程完全掩埋[6,7],阻断交通和河流。高家沟泥石流对沟底近30 m深的高速公路隧道造成潜在威胁,表明急陡沟道泥石流的侵蚀性较强。2013年7月10日的泥石流将之前的治理工程基本摧毁,其侵蚀作用应加以重视。瓦窑沟泥石流导致都汶高速绵虒服务区停止运营、福堂沟泥石流堵塞公路和岷江。可见,急陡沟道泥石流的起动、运动或堆积,均造成较大的灾害。因此,对急陡沟道泥石流的形成机理研究较为重要。

近年来,崩塌堆积条件下的碎石土堆积特征及其起动条件研究已有深入的成果,对泥石流灾害研究起到极大的促进作用。以美国科罗拉多州的泥石流形成研究为背景,美国联邦地质调查局(United States Geological Survey, USGS)注意到,在急陡沟道条件下,泥石流的物源起动中“消防管效应”较为明显。Cannon等[10]和Godt等[11]认为这一过程主要是山谷汇流导致松散堆积物起动形成泥石流,唐川等[12]总结为陡峻石质流域上游暴雨产生沟道径流如同“消防水管”导致水流快速集中,并强烈冲刷和侵蚀堆积有丰富松散固体物质的沟道形成泥石流的过程。Yu等[13]以中国台湾地区陈有兰溪流域桃芝台风诱发的117条泥石流数据为基础,建立基于地形地貌、地质条件及水文条件的消防管效应统计模型。

崩坡积物颗粒粒径分布较广,但由于表层长期的淋滤作用,堆积物质主要为大粒径块石。堆积成分主要为花岗岩、灰岩,棱角分明,抗压能力强,不易风化,孔隙率大,降雨入渗速度快,颗粒之间联结弱。一般认为,在强降雨的作用下,部分地表水下渗进入碎石土体并进一步在地表形成径流。坡体流态化源于地表水侵入进一步改变碎石土体的自重,在细颗粒迁移过程中孔隙发生堵塞的条件下同时改变了孔隙水压力在碎石土中的空间分布,或者产生瞬态的孔隙水压力。或在表面径流的作用下同时作用于碎石土体内部造成坡体的破坏[11,14~19]

急陡沟道泥石流灾害危险性和风险分析及有效的工程控制有赖于对位于高陡斜坡及沟道的崩塌、滑坡堆积体起动特征准确的分析。本文以高家沟泥石流为典型实例,在分析暴发前后坡体形态、颗粒物质特征基础上,对急陡沟道泥石流沟道两侧高陡斜坡物源赋存特征进行分析,阐明急陡沟道泥石流发育背景及工程地质条件。并通过野外调查数据分析及室内物理实验,不同物源特征、地形条件、赋存状态对泥石流起动方式的影响,探讨不同条件下坡体破坏及物源起动过程和机制。

2 地质环境及发育背景

研究对象位于汶川震区岷江流域,区内地形总体上属深切割构造侵蚀中山和高山地形,地势陡峻,地形临空条件发育,为沟域内崩塌、不稳定斜坡等不良地质现象的发育,以及泥石流松散固体物源的汇集提供了有利条件;地形条件有利于降雨的汇聚,流域水动力条件强大,冲蚀能力较强。汶川地震之后,进一步发育有崩塌、滑坡、松动岩体,在震后多次强降雨的作用下,新增大量的泥石流物源,为泥石流暴发提供了物源基础,如高家沟物源分布(图1)。

图1   高家沟泥石流流域图

Fig.1   Watershed map of Gaojia gully

受制于陡峻的地形,震区陡峻山区崩塌或滑坡堆积体呈倒三角锥或是喇叭状,表现为中上部碎石土体较薄,底部土体较厚的形态。碎石土堆积体表现为宽级配、大颗粒、渗透性强、孔隙率大的特征。沟道中的部分堆积体陡于松散堆积物休止角,主要是由于粗颗粒间的结构力、级配组合及地形条件制约,也是其欠稳定状态的原因[20,21]。结合实验中观察到的现象,急陡沟道泥石流物源起动主要总结为固体颗粒物质与内部渗透[22]、地表径流相互作用下的坡体破坏。在经过物源崩塌运动堆积之后,坡体一般呈现反粒序分布[23,24,25]

高家沟泥石流流域面积3.79 km2,常年流水,丰水期流量一般为2~4 m3/s,具有典型的陡涨陡落的特征,上游支流发育。2011年7月1~3日,汶川县银杏片区普降暴雨,至3日凌晨5时,累计降雨量达163.1 mm,受暴雨影响高家沟再次暴发了大规模泥石流灾害,约42.58×104 m3的泥石流物质启动,在岷江形成堰塞体,堵塞岷江主河道。据野外调查,此次出现2次阵性泥石流,主要原因是沟道内的2处堵塞体(图1图2)溃决。

图2   高家沟7·3泥石流后堵塞点液化破坏
(a)典型堵塞点(A-A’)剖面图;(b)南天门支沟出口处堵塞体(B-B’)起动后深切沟槽

Fig.2   Liquefaction destruction in Gaojia gully(July 3,2011)
(a)Profile of typical accumulation, A-A’;(b)Barrier failure of profile B-B’

其中堵塞点1处崩塌堆积体位于南天门沟、龙窝槽沟与主沟的交汇点之间。崩塌体所在区域岸坡坡度为30°~40°,沟段纵比降约800‰(39°),基岩为晋宁期第四期侵入岩花岗岩陡壁。A-A'处堆积体顺坡向长约300 m,横向宽50~100 m,堆积体坡度40°~50°,堆积体厚度为5~15 m;B-B'处堆积体顺坡向长约160 m,横向宽度为80~130 m,堆积体坡度40°~50°,堆积体厚度7~12 m。2处堆积体以碎块石为主,结构松散,颗粒粒径为0.1~1.0 m,占比为50%~60%,其中粒径小于40 mm的粒径分布曲线如图3a所示。此处具有泥石流发育的物源、水力及地形条件,故本文选取此次泥石流的堵塞点1处2个典型点为原型探讨急陡沟道泥石流的起动模式及其水土耦合破坏机制。因2处堆积体粒径分布(图3a)、沟道坡度、岸坡坡度(表1)相似,仅表现为水源条件的巨大差异(表1)。

图3   实验系统示意图

Fig.3   Experimental system diagram

表1   支沟及主沟上游沟段特征参数

Table 1   Channel characteristic parameters of main gully and tributary gullies

名称沟长
/km
平均纵坡
/‰
流域面积
/km2
沟谷形态
主沟上游段1.887991.77V型谷
1#支沟0.691 0110.13V型谷
2#支沟0.561 0510.03V型谷

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3 模型实验实验方案及过程

水源特征的差异在于供给平衡状态,结合室内供水的局限及堆积体的渗透性好的特征,本文选取了与原位材料级配、沟道纵坡、岸坡坡度、堆积体密度、初始含水率、渗透系数等相近的模型材料,但因室内试验局限,模型材料较原型密实度微小。而将堆积体不同的破坏特征归结为汇水面积差异,反映在室内试验即为能否形成有效的饱水土体。其中模型一模拟南天门支沟处堆积物源起动,模型二模拟1#支沟处堆积体物源起动。模型一与模型二实验设计相同,包括模型尺寸、颗粒物质级配组成、含水率、密度、渗透系数等(表2)。唯一不同的设计是模型一底部强渗透,而模型二底部为不渗透。意在探讨同样物理性质的坡体在不同饱水特性条件下的坡体起动形式。

表2   堆积体原型及模型参数对照表

Table 2   Physical and mechanics parameters of barrier dam prototype and experimental models

性质
编号
密度/(kg/m3)含水率(ω0)/%渗透系数(K) /(m/s)
原型模型原型模型原型模型
模型一1.69×1031.55×1036.366.361.2×10-31.8×10-3
模型二1.69×1031.55×1036.366.361.2×10-31.8×10-3

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实验选用自制的框架式模型箱,长、宽、高尺寸分别定为180,50和100 cm,模型箱由3面可拆卸的透明塑料板拼装而成,四周用角钢固定(图3b)。实验材料采集于高家沟沟口堆积体,母岩成分与上游基岩均为侵入岩花岗岩。在室内进行颗粒筛分、配样,控制40 mm以下颗粒物质级配特征满足堵塞体1处的原位实验参数,其颗粒级配曲线如图3a所示。利用水管供水,流量计记录流量,最大供水量为28 L/min。实验数据监测与采集系统主要包括:变形破坏监测、应力监测、水文监测、其他监测及数据采集系统。坡表变形采用德国莱卡(Leica)CH-9435型三维激光扫描仪进行监测。另外,通过录像记录坡体侵蚀实景。应力监测包括孔隙水压力和土压力的监测和数据采集,其中孔隙水压力采用CYSBG-20微型孔隙水压力传感器,传感器量程0~20 kPa,精度等级0.25级。模型实景及孔压计布置图如图3c所示。

实验中后缘花岗岩采用砖块砌筑,形成60°左右的后缘基岩。基岩采用交错状态堆砌,模型框底部设置出水孔,使其具有良好的稳定性同时又具有较好的渗透性。在铺设崩塌堆积体前,按照野外原样的颗粒级配铺设,并在坡体表层土层中添加20~40 mm的粗砾石,尽量模拟堆积体的反粒序分布特征,同时模拟堆积物中的保护层以防在极小的流深条件下固体物质起动,并夯实以尽量保证自然状态下的密实度。与此同时,分层设定土压力计、含水率计及孔隙水压力计。待完全铺设完毕后静置36 h后进行水力侵蚀实验。

为了模拟自然状态下的坡体充分入渗,实验过程先进行短时的降雨入渗。由于坡体受雨面积约为0.9 m2,无法形成自然状态下的有效径流。待坡体中孔隙水压力及含水率数值稳定后进行径流冲刷实验,保证汇水条件下的产流特征。

其中,模型堆载完毕静置36 h后进行第一次坡体三维激光扫描,获得原始状态下的坡体形态,此后每进行一次流量调整时扫描一次。在实验过程中若坡体出现明显侵蚀即进行快速扫描。在中间层数据采集仪器暴露即停止实验,其中模型一实验耗时90 min,模型二耗时90 min。

4 实验结果分析

4.1 坡体变形破坏与侵蚀特征

图4图5分别为模型一和模型二三维激光扫描采集的数据生成的坡体表面变形图,主要反映了固体物质的侵蚀与堆积特征。其中图4a和图5a为坡体原始堆积形态,图4b和图5b为实验结束时坡体的破坏特征,图4c和图5c是由结束时的破坏参数与实验初始值之差,反映坡体表层变形特征。

图4   模型一坡表变形图

Fig.4   Slope deformation of experimental modelⅠ

图5   模型二坡表变形图

Fig.5   Slope deformation of experimental modelⅡ

总体上看,模型一在开始形成坡表细沟侵蚀,随着时间的增加不断拓宽加深,后保持不变。但在流量增加为8 L/min时,沟道继续加深并缓慢拓宽。其变化特征主要表现为坡体中部的深沟侵蚀及坡脚的扇形堆积,中部红色区域最大侵蚀深度达25 cm,且侵蚀沟道深而窄。前缘堆积深度为5~10 cm,前缘堆积特征明显,说明其运动距离较短,极强地依赖于水动力条件;模型二变化特征主要表现为坡体的整体破坏及前缘的短程淤积,其侵蚀深度一般小于20 cm,堆积主要发生在模型箱出口处外部。相较于模型一,模型二的侵蚀与淤积主要为整体起动与快速淤积。

4.2 孔隙水压力分布

图6图7分别为模型一和模型二的降雨及径流冲刷实验的时间序列和对应时刻的孔隙水压力(分别用PP1~PP4表示)曲线图。

图6   模型一降雨时间序列及孔隙水压力曲线

Fig.6   Curve of rainfall time versus pore water pressure in experimental model Ⅰ

图7   模型二降雨时间序列及孔隙水压力曲线

Fig.7   Curve of rainfall time versus pore water pressure in experimental model Ⅱ

4.2.1 模型一孔隙水压力分布特征

图6可知,模型一具有良好的渗透特性,在阶段I约210 mm/h的雨强和径流量为6 L/min时,PP2孔隙水压力均显示为0 kPa,这是由于汇水面积仅为0.9 m2,降雨无法形成有效的内部渗透作用;阶段II中在径流流量为6 L/min时PP1相对于PP3先达到饱和,形成约0.3 kPa的孔隙水压力,此时PP3约为PP2的一半,表明此时由于底部良好的渗透作用,垂直入渗较明显,且潜水面仅存在于距离碎石土底部较近的位置;阶段III时由于径流流量加大为8 L/min,PP1处孔隙水压力快速增加与PP3几乎一致。

4.2.2 模型二孔隙水压力分布特征

图7可知,在前期径流量为4 L/min时,阶段I时坡体孔隙水压力总体上为稳定状态,PP1和PP2位于坡体上部,相对于下部的PP3和PP4,其显示的孔隙水压力要小;同时由于PP2大于PP1、PP3大于PP4,表明距离坡表越近孔隙水压力越小。PP1和PP4始终保持变化趋势一致且孔隙水压力值大小近似,坡体浅层孔隙水压力等值线近似平行于坡面。

阶段II时位于坡脚下部的PP3略微较坡脚上部的PP4先出现孔隙水压力下降,由视频采集仪可知坡脚出现了局部的坡体流态化破坏,并进一步自下而上出现浅层的坡体破坏,起动固体物质冲出模型箱呈喇叭状堆积于模型箱外部出口处(图7)。该阶段PP3孔隙水压力接近0 kPa,PP4甚至先一步PP3出现负孔隙水压力,表明此处碎石土出现短暂的基质吸力。说明在较小的流量下,前期细颗粒的运移及坡脚液化破坏导致细颗粒流失,坡体内部的渗流通道变得更为通畅,导致来水沿最下部的渗流即可充分排水,坡表基本无法形成有效的渗流。表明小流量条件下渗流主要沿大颗粒固体物质内部运动,无法形成有效的侵蚀。

出现渗透破坏后,坡体的渗透特性变好,长时间的4 L/min流量对坡体作用较小。此时,将径流流量调整为8 L/min,PP1出现第一次较大的波动:先出现约0.1 kPa的小幅上升,而后显著下降,甚至短暂地接近0 kPa后直线回升。主要是由于阶段II中坡体流态化造成坡体上部形成陡坡,此时的坡体破坏出现在上部,下部主要为固体物质堆积(图7)。由上述起动过程可知,坡体的破坏主要源于下部的坡体流态化、拉槽及后续进一步的局部坡体流态化。而后续的坡体流态化主要对应于相应的水动力条件的变好,因此水动力条件与坡体的渗透特性具有较大的相关性。通过对孔隙水压力计的位置及数据采集值分析,孔隙水压力等值面与坡面近平行分布,该特性与坡体沿一定深度形成拉槽起动有关联。

5 起动模式及水土耦合机制

5.1 消防管起动模式

由于模型一在相同的岩土体条件下,不管是降雨或者地表形成一定径流时,地下水都能较好地渗透,基本上是随着径流的运动,地表水快速下渗。此时坡体的破坏主要为地表的水力侵蚀破坏,其模式为水流拖曳固体物质的起动方式:地表径流边下渗边径流形式沿坡表向下运动,不断地携带固体物质,固体物质不停地起落,随着沿程裹挟物质及径流下渗,水动力消耗速度极快。若无持续的水力补充,此类物源起动通常仅限于形成较小规模的稀性流,且表面颗粒较大,固体物质的起动受集中冲蚀的水动力条件控制。

若水动力条件较好,泥石流浆体对固相的牵引力在急陡沟道条件下获得持续的动力补充,此时由于浆体黏滞力较小,难以引起泥石流整体起动,固体颗粒的运动主要受水流的直接冲击作用影响,后续泥石流浆体及起动的固相则在重力作用下保持运动,因而陡坡条件下动力较强。该模式即表现为“消防水管效应”,与已有成果描述一致[3,26~29]

图2a中高家沟堵溃点1处7·3泥石流后的残留固体物质。沟道左侧1#支沟上游汇水面积0.13 km2,消防管效应明显,沟道下部残留少部分固体物质,右侧崩塌堆积物源由于上游汇水面积仅为0.03 km2,水动力条件较小,固体物质保留较完整。因此,急陡沟道条件下的消防管效应起动外动力条件与流域汇水能力有关,坡体内部不能形成有效的饱和渗透是其与坡体流态化起动形式差异的主要原因。

5.2 坡体流态化起动模式

坡体流态化模式在室内试验的观测资料中完整表现为细颗粒运移—坡脚局部破坏—自下而上流态化(图8)。具体表现为模型二中坡表初期较小的径流量时,细颗粒随着渗流路径缓慢迁移,大颗粒不发生明显移动,部分细颗粒残留于坡体内部,另外一部分随内部渗流路径流失,此时坡脚渗水浑浊(图8a)。随着径流量加大,坡体内部细颗粒积累于坡脚出水口处,由于渗透性变弱而形成更高的孔隙水压力出现局部流态化(图8b)。随着水源的持续补充,水位抬升、孔隙水压力升高、前缘临空面扩大出现自下而上的坡体流态化破坏,并形成拉槽(图8c,d)。

图8   坡体流态化破坏过程
(a) 局部液化;(b) 底部流态化;(c) 流态化扩大;(d) 自下而上流态化破坏

Fig.8   Failure process of slope liquefied experimental model Ⅱ
(a)Partial liquefaction; (b)Fluidization at the bottom; (c)Fluidization expansion; (d)Fluidization failure from bottom to top

试验过程中坡体的破坏表现出一定的突然性、瞬时性,阶段性物源的起动量大。累进性破坏主要依赖于具有较好坡度条件的坡体或者径流量的加大。该模式即“坡体流态化”。

图2b为堵溃作用后堵溃点B-B'上游沟道残留固体物质,左侧沟道处为一支沟冲积物质,与右侧崩坡积物及沟道堆积物共同形成堵塞点。南天门支沟与主沟流向夹角约150°,较利于固体物质堆积,形成堵溃点厚度7~12 m(图1图2b),发育有丰富的物源。上游支沟及主沟汇水面积约为0.8 km2,平均沟道纵比降为800%,汇水面积大径流速度快。产生的径流部分溢流,部分形成孔隙水,或在相对隔水层处形成潜流。

堆积体物源入渗分为降雨入渗和地表径流入渗,其中降雨入渗主要是由于降雨初期较小的雨强时产生垂直入渗,但由于降雨补给较弱,堆积体纵坡较大,难以形成饱和带。堵溃点B-B'径流入渗主要沿较强渗透性土层底部进入沟道,或下部不透水层出露,此为细颗粒运移阶段。在连续降雨条件下,由于持续的缓慢入渗,浸润面有向下延伸的趋势,此时由于表层碎石土体的较强渗透性,坡表尚不能形成径流,降雨主要以内部径流产生不规则渗流通道。通道主要由坡体中的大颗粒物质作为骨架,较小颗粒作为孔隙填充物,在较小的渗透压力的作用下保持稳定。此时,虽然不能产生明显的渗透破坏,但内部的细颗粒运移正在往坡脚运移、集聚,坡体内部的出水主要为浊水或前缘局部破坏。

当相对隔水层以上土体饱和或雨强加大时产生坡表径流。此时由于孔隙水水压力增加,地下水位升高,较陡峻的坡度提供了良好的重力变形空间,使饱和坡体有剪切破坏的趋势。甚至由于渗透特性的差异及相对隔水层的存在,局部的超孔隙水压力会导致局部土体抗剪强度的丧失,失去下部土体支撑及泥石流浆体的裹挟作用导致上游堆积体发生更大规模的破坏,坡体自下而上流态化起动。

6 结 论

通过急陡沟道泥石流物源赋存特征及地形条件进行的针对性物源起动模式实验主要有以下结论:

(1)急陡沟道泥石流物源主要为来源于崩塌、滑坡破坏堆积于沟道中的固体物质,占冲出固体物质的50%以上。

(2)在急陡沟道物源赋存特征及降雨特征影响下,物源起动模式主要为“消防管效应”及“坡体流态化”:前者主要发生在不饱和或高渗透系数坡体在快速集中径流冲蚀条件下;后者出现在可饱和土体中。

(3)消防管效应的产生条件是较强的集中水动力,其坡体破坏特征是出现深而窄的侵蚀沟道。冲出物质大颗粒物质较多,一般表现为稀性泥石流的特征,冲出距离较短,冲击作用及强渗透性造成的能量损耗也相对较大,在形成具有一定流深的泥石流浆体前其破坏能力较小,而陡峭地形和冲击作用下大颗粒物质运动能力较强。主要受水动力补充的影响。

(4)坡体流态化的发生依赖于土体的充分饱和,相对于较好的径流条件其具有相对不良的渗透特性。破坏特征是坡体的整体运移与大规模的堆积,表现为强侵蚀、强淤积。初期泥石流液化破坏主要为剪切破坏,后续坡体的起动受泥石流浆体的黏滞力和大坡降的影响,起动规模也较大。相对消防管效应,液化破坏水土混合充分,具有较多的细颗粒物质,较易形成黏性泥石流。

前述2种起动模式在急陡沟道泥石流中表现明显,但并不一定完全受制于地形条件:例如深厚堆积体中渗透特性变差也有可能形成浅层饱和带并液化破坏。水动力条件与坡体的渗透特性的对应特征,及坡体沿一定深度形成拉槽起动的影响因素尚需进一步深入研究。

The authors have declared that no competing interests exist.


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在汶川震区沟道型泥石流中,普遍存在一种窄陡沟道类型,窄陡沟道型泥石流具有沟道纵坡陡、平均宽度窄、流域面积小的地形特点,在震区容易瞬间汇流形成大规模突发性泥石流灾害。结合四川省都汶高速沿线2013年“7·10”特大群发性泥石流,重点以窄陡沟道型的磨子沟泥石流为实例,针对该泥石流对都汶高速、岷江等造成的冲击淤埋及堵塞问题,通过现场调查泥石流形成条件和发育特征,采用大型流体动力学计算软件CFX模拟再现50年一遇暴雨频率下此类窄陡型泥石流的动力学过程,分析其危险范围、评价其冲击都汶高速桥梁,堵塞岷江,淹没岷江两岸居民安置点的破坏性影响,为提出针对性的泥石流防治工程措施提供依据。
[10] Cannon S H, Kirkham R M, Parise M.

Wildfire-related debris-flow initiation processes, Storm King Mountain, Colorado

[J]. Geomorphology, 2001, 39(3/4):171-188.

DOI      URL      [本文引用: 1]      摘要

A torrential rainstorm on September 1, 1994 at the recently burned hillslopes of Storm King Mountain, CO, resulted in the generation of debris flows from every burned drainage basin. Maps (1:5000 scale) of bedrock and surficial materials and of the debris-flow paths, coupled with a 10-m Digital Elevation Model (DEM) of topography, are used to evaluate the processes that generated fire-related debris flows in this setting. These evaluations form the basis for a descriptive model for fire-related debris-flow initiation. The prominent paths left by the debris flows originated in 0- and 1st-order hollows or channels. Discrete soil-slip scars do not occur at the heads of these paths. Although 58 soil-slip scars were mapped on hillslopes in the burned basins, material derived from these soil slips accounted for only about 7% of the total volume of material deposited at canyon mouths. This fact, combined with observations of significant erosion of hillslope materials, suggests that a runoff-dominated process of progressive sediment entrainment by surface runoff, rather than infiltration-triggered failure of discrete soil slips, was the primary mechanism of debris-flow initiation. A paucity of channel incision, along with observations of extensive hillslope erosion, indicates that a significant proportion of material in the debris flows was derived from the hillslopes, with a smaller contribution from the channels. Because of the importance of runoff-dominated rather than infiltration-dominated processes in the generation of these fire-related debris flows, the runoff-contributing area that extends upslope from the point of debris-flow initiation to the drainage divide, and its gradient, becomes a critical constraint in debris-flow initiation. Slope-area thresholds for fire-related debris-flow initiation from Storm King Mountain are defined by functions of the form A cr(tan ) 3= S, where A cr is the critical area extending upslope from the initiation location to the drainage divide, and tan is its gradient. The thresholds vary with different materials.
[11] Godt J W, Coe J A.

Alpine debris flows triggered by a 28 July 1999 thunderstorm in the central Front Range, Colorado

[J]. Geomorphology, 2007, 84(1):80-97.

DOI      URL      [本文引用: 2]     

[12] Tang Chuan, Zhang Shucheng.

Study progress and expectation for initiation mechanism and prediction of hydraulic-driven debris flows

[J]. Advances in Earth Science, 2008, 23(8):787-793.

Magsci      [本文引用: 1]     

[唐川,章书成.

水力类泥石流起动机理与预报研究进展与方向

[J].地球科学进展,2008,23(8):787-793.]

DOI      URL      Magsci      [本文引用: 1]      摘要

<p>水力类泥石流是泥石流的一大类型,一旦暴发可造成巨大的人员伤亡和财产损失,因而其起动机理和预报是泥石流学科的前沿课题。尽管国内外研究在该领域取得了显著进展,但是由于该类泥石流起动机理的复杂性,已有的预报模型和其实用性仍然有相当的差距。概述了水力类泥石流起动与预报的国内外研究进展,提出未来该研究方向的主要研究内容。未来研究内容应该包括从环境地质学、地貌学和水文学角度认识水力类泥石流的起动成因和过程及相应的临界条件;研究以水文学为主线的水力类泥石流的起动机理和模型,并提出水力类泥石流的起动水文参数临界条件;建立以临界流量法和分布式水文模型为理论依据的水力类泥石流的预报途径和方法。该研究对加强水力类泥石流起动机理及预测预报的创新性研究和促进学科发展具有重要的科学价值和实践意义。</p>
[13] Yu Bin, Li Li, Wu Yufu, et al.

A formation model for debris flows in the Chenyulan River Watershed, Taiwan

[J]. Natural Hazards, 2013, 68(2):745-762.

DOI      URL      [本文引用: 1]      摘要

Many debris flows were triggered in the Chenyulan River Watershed in Taiwan in a rainstorm caused by the Typhoon Toraji. There are 117 gullies with a significant steep topography in the catchment. During this Typhoon, debris flows were initiated in 43 of these gullies, while in 34 gullies, it was not certain whether they have occurred. High-intensity short-duration rainfall was the main triggering factor for these gully type debris flows which are probably entrained by a "fire hose" mechanism. Previous research identified 47 factors related to topography, geology, and hydrology, which may play a role in the formation of gully type debris flows. For a better understanding of the probability of the formation of debris flows, it is proposed to represent the factors related to topography, geology, and hydrology by one single factor. In addition to the existing topographic and geological factor, a normalized critical rainfall factor is suggested with an effective cumulative precipitation and a maximum hourly rainfall intensity. In this paper, a formation model for debris flows is proposed, which combines these topographic, geological, and hydraulic factors. A relationship of these factors with a triggering threshold is proposed. The model produces a good assessment of the probability of occurrence of debris flows in the study area. The model may be used for the prediction of debris flows in other areas because it is mostly based on the initiation mechanisms and not only on the statistical analyses of a unique variety of local factors. The research provides a new and exciting way to study the occurrence of debris flows initiated by a "fire hose" mechanism.
[14] Au S W C.

Rainfall and slope failure in Hong Kong

[J]. Engineering Geology, 1993, 36(1/2):141-147.

DOI      URL      [本文引用: 1]      摘要

Abstract Slope failure as the result of heavy rainfall, is a major problem in Hong Kong. The results of a study on rainfall and subsequent slope failures occurring during 24 severe rainstorms from 1982–1989 are presented. It is suggested that intensity and areal extent of rainfall, as well as degree of urbanisation are important features determining the scale of a slope failure event.
[15] Chen H X, Zhang L M, Chang D S, et al.

Mechanisms and runout characteristics of the rainfall-triggered debris flow in Xiaojiagou in Sichuan Province, China

[J]. Natural Hazards, 2012, 62(3):1 037-1 057.

DOI      URL     

[16] Chen H X, Zhang L M, et al.

Simulation of interactions among multiple debris flows

[J]. Landslides, 2017, 14(2):595-615.

DOI      URL      摘要

Adjacent debris flows may interact in many ways: two or more concurrent debris flows may merge; one debris flow can run out over an existing debris flow fan. Such interactions may cause debris flow pr
[17] Crosta G B, Frattini P.

Rainfall-induced landslides and debris flows

[J]. Hydrological Processes, 2008, 22(4):473-477.

DOI      URL      摘要

In this preface we introduce the special issue on rainfall-induced landslides and debris flows. The topic is of high interest for many practical and scientific reasons. In fact, rainfall is the most relevant factor for the triggering of both shallow and deep-seated landslides, and rainfall analysis is the most frequently adopted approach for forecasting the occurrence of such phenomena. The six papers of the special issue cover most of the key issues relative to rainfall-induced landslides. Starting from the analysis of these contributions, we identify and discuss, in this paper, several main topics that deserve further research in the field of rainfall-induced landslide, such as the uncertainty of the data, the quality of geotechnical analysis, the validation of the models, and the applicability of results in the framework of natural hazards. Copyright 2007 John Wiley &amp; Sons, Ltd.
[18] Iverson R M, Reid M E,

LaHusen R G. Debris-flow mobilization from landslides

[J]. Annual Review of Earth & Planetary Sciences, 1997, 25(1):85-138.

[19] Chen Xiaoqing.

Experiment of Initiation Mechanism of Landslide Translation to Debris Flow[D]

. Chengdu: Southwest Jiaotong University, 2006.

[本文引用: 1]     

[陈晓清.

滑坡转化泥石流起动机理试验研究

[D].成都:西南交通大学,2006.]

[本文引用: 1]     

[20] Chen Xizhe.

Research on the strength of the coarse grained soil and the interlocking force

[J].Engineering Mechanics, 1994 ,11(4):56-63.

Magsci      [本文引用: 1]     

[陈希哲.

粗粒土的强度与咬合力的试验研究

[J].工程力学,1994,11(4):56-63.]

URL      Magsci      [本文引用: 1]      摘要

土的强度在土木工程中有重要意义,它是计算地基承载力、土坡稳定性和挡土墙上土压力的关键。现今国内外强度理论中,对无粘性土只计算内摩擦角ψ,粗粒土采用天然休止角α。作者进行了大量大型三轴压缩试验与现场陡坡试验并经工程实践,证明粗粒土中存在一种新的力。此力非通常的内摩擦力,称为咬合力。由于咬合力的存在,使粗粒土的强度大幅度提高。目前我国国家规范与一般高校教材中均无此内容。因此,这项研究具有相当的科学与经济价值。
[21] Li Zhenlin.

The Wenchuan Earthquake Landslide Accumulation Substance Pile Repose Angle of Simulation on Relations

[D]. Chengdu:Southwest University, 2013.

[本文引用: 1]     

[李振林.

汶川震区滑坡堆积体物质组成与堆积体休止角关系模拟研究

[D]. 成都:西南大学,2013.]

[本文引用: 1]     

[22] Yang Shun, Ou Guoqiang, Wang Jun, et al.

Experimental analysis of scouring of debris flow initiation process under steady seepage condition

[J]. Rock and Soil Mechanics, 2014, 35(12):3 489-3 495.

[本文引用: 1]     

[杨顺, 欧国强, 王钧,.

恒定渗流作用下泥石流起动过程冲刷试验分析

[J]. 岩土力学, 2014, 35(12):3 489-3 495.]

URL      [本文引用: 1]      摘要

渗流是泥石流水动力条件主要来源之一,不同渗流流量具有不同的渗流力和冲刷力,从而可引起不同规模泥石流。通过开展室内水槽试验,利用测压管量测渗流过程中的孔隙水压力,并结合高清摄像技术从微观角度记录堆积土体内部细颗粒的运移、骨架颗粒的坍塌现象,以此分析研究土体渗透破坏、起动形成泥石流过程中的渗流和冲刷作用。在此基础上设定水槽坡度为7°,调节恒定渗流流量分别为120、170、265、320 ml/s,分析不同恒定渗流流量对固体堆积物失稳、泥石流起动过程中流态变化的影响。分析结果表明,在恒定渗流流量作用下,堆积土体内部细颗粒迁移、骨架颗粒坍塌造成土体颗粒重排列、孔隙水压力上升进而导致土体抗力降低是泥石流土体颗粒失稳、起动、冲刷的重要原因;随着渗流流量增加,流速迅速上升,土体内孔隙水压力逐步增大,骨架颗粒的失稳、移动主要受渗流及水流冲刷两方面共同作用,堆积土体颗粒的移动分别表现出缓慢小幅滑动后稳定、过渡型滑动和快速流滑现象。
[23] Shu Anping, Yang Kai, Li Fanghua, et al.

Characteristics of grain size processes for and grain order distribution in the deposition non-homogeneous debris flow

[J]. Journal of Hydraulic Engineering, 2012, 43(11):1 322-1 327.

[本文引用: 1]     

[舒安平, 杨凯, 李芳华, .

非均质泥石流堆积过程粒度与粒序分布特征

[J]. 水利学报, 2012,43(11):1 322-1 327.]

[本文引用: 1]     

[24] Wang Yufeng, Cheng Qiangong, Zhu Qi.

Inverse grading analysis of deposit from rock avalanches triggered by Wenchuan earthquake

[J]. Chinese Journal of Rock Mechanics and Engineering, 2012, 31(6):1 089-1 106.

[本文引用: 1]     

[王玉峰, 程谦恭, 朱圻.

汶川地震触发高速远程滑坡—碎屑流堆积反粒序特征及机制分析

[J]. 岩石力学与工程学报, 2012,31(6):1 089-1 106.]

[本文引用: 1]     

[25] Yang Hongjuan, Wei Fangqiang, Hu Kaiheng, et al.

Experimental study on vertical sorting of particles in debris flow with impact signals

[J]. Journal of Catastrophology, 2011, 26(4):29-34.

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[杨红娟, 韦方强, 胡凯衡, .

利用冲击力信号判断泥石流颗粒垂向分选的试验研究

[J]. 灾害学, 2011,26(4):29-34.]

DOI      URL      [本文引用: 1]      摘要

分别提出根据冲击力数据的波动强度和峰值情况进行泥石流颗粒垂向分选研究的系统方法,并配置了三组不同容重(2 095 kg/m3、2 008 kg/m3和1 960 kg/m3)的粘性泥石流样品开展泥石流冲击试验。两种方法的分析结果基本一致,即容重为2 095 kg/m3的泥石流分选不明显,其他两组泥石流呈现出正粒序分布且容重越小分选越显著。量纲分析表明,开展的试验粘滞力在运动中起主导作用,颗粒之间作用力较小,不容易发生反粒序分选,这与通过冲击力分析颗粒垂向分选的结果一致,因此提出的利用冲击力信号判断泥石流颗粒垂向分选的系统方法具有适用性。
[26] Coe J A, Glancy P A, Whitney J W.

Volumetric analysis and hydrologic characterization of a modern debris flow near Yucca Mountain, Nevada

[J]. Geomorphology, 1997, 20(1/2):11-28.

DOI      URL      [本文引用: 1]     

[27] Griffiths P G, Webb R H, Melis T S.

Initiation and Frequency of Debris Flows in Grand Canyon, Arizona[R]. U.S

. Geological Survey,1996.

[28] Melis T S, Webb R H, Griffiths P G, et al.

Magnitude and Frequency Data for Historic Debris Flows in Grand Canyon National Park and Vicinity, Arizona[R]. U.S

. Geological Survey, 1995.

[29] White S E.

Alpine mass movement forms (Noncatastrophic): Classification, description, and significance

[J]. Arctic & Alpine Research, 1981, 13(2):127-137.

DOI      URL      [本文引用: 1]      摘要

A variety of noncatastrophic and distinctly alpine mass movement forms may be classified under three basic terms: (1) talus, with rockfall talus, alluvial talus, avalanche talus, avalanche boulder tongue, and protalus rampart as subtypes; (2) rock glacier, subdivided into tongue-shaped and lobate; and (3) block slope, with the rare (in the alpine) block field, and block stream as subtypes. These mass movement forms reveal past and present local and microclimates, rates of erosion, postglacial valley wall, cliff, and ridge crest changes, and periglacial events during Neoglaciation.

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