堰塞金沙江上游的白格滑坡形成机制与过程分析
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摘要
2018年10月10日和11月3日,西藏自治区江达县白格村金沙江右岸先后2次发生滑坡堵江事件,堰塞湖与溃坝洪水给金沙江上游沿岸居民及其生产和生活设施带来巨大灾害。滑坡发生后,作者先后2次赶赴现场,参与灾害调查与救灾工作。基于现场调查,结合相关资料,对滑坡的形成机制与过程进行系统分析。结果表明:1)白格"10·10"滑坡是一个高位、高剪出口、高速非完全楔形体基岩滑坡,方量约107 m~3。2)滑坡地处金沙江缝合带,岩性为元古界熊松群片麻岩组,具有多期、多次变形与变质特点,糜棱岩化和蚀变很严重。3)滑坡按高程划分为3区,即前缘的阻滑区、中部的主滑区和后缘的牵引区,分割高程大致为3 500和3 000 m。主滑区为楔形体,系2组发育良好的结构面切割形成;阻滑区为四面体,由2组发育较差的结构面切割形成;牵引区为完全风化的岩土体夹团块状碎裂岩体。4)滑坡存在2个滑动方向,即主滑区的S80°E方向和阻滑区的N70°E方向,剪出口高程约2 950 m。5)主滑区楔形体重力是滑坡的主要动力来源,滑坡的孕育过程是相对完整的阻滑区岩体在主滑区重力驱动下的渐进破坏过程。6)滑坡过程如下:首先,主滑区和阻滑区启动;其次,失去支撑的牵引区再启动;随后,先启动的滑体高速撞击四川岸,逆坡爬高约95 m,并在两侧形成碎屑冲刷区;然后,先启动的滑体折返,并与后启动的滑体在河面上方相撞,冲击河水形成高速水砂射流,在两岸形成水砂射流冲刷区;而后,堰塞坝下游坡滑动,形成次级滑移区;最后,冲击产生的雨雾降落,完成滑坡坝表面冲刷。7)白格"11·3"滑坡是牵引区的部分岩土体在起阻滑作用的碎裂岩体渐进解体后下滑的结果,方量约3×106 m~3。8)牵引区目前严重变形的方量约5.50×106 m~3,存在再次滑坡与堵江的风险,需要采取合理的工程措施消除隐患。
In October 10 th and November 3 rd 2018, two landslides happened successively on the right bank of the upper reaches of Jinsha River,which dammed the river at Baige village, Jiangda county, Tibetan Autonomous Region. The dammed lakes and their breaching flood brought about severe disaster to local residents and their production and life facilities along the river. Based on the field investigation immediately after the slides and other related materials, a systematic analysis is made on the formation and process of the slides in the paper. Results show that: 1) the"10·10" slide is a high position, high shear crack, high speed and incomplete wedge slide and its volume is around 107 m~3; 2) geologically the slide is situated in the suture zone of Jinsha River and the bedrock is Xiongfeng gneiss group of Proterozoic, which is characterized by multiphase repeated deformation and metamorphism and is severely mylonitized and altered; 3) the sliding area can be vertically divided into 3 zones of antisliding zone, major sliding zone and hauling zone, which are separated roughly at elevation 3 500 m and 3 000 m, respectively. The major sliding zone is of wedge shape cut by two well-developed structural planes, the anti-sliding zone is of tetrahedron shape formed by two undeveloped structural planes, while the hauling zone is completely weathered earth mass mixed with clumped and heavily fractured rock; 4) the slide has two sliding directions of S80°E in the major sliding zone and N70°E in the anti-sliding zone and the elevation of shear crack is around 2 950 m above sea level; 5) the power driving the slide is mainly from the gravity of the wedge in the major sliding zone and the developing process of the slide is the progressive failure of the comparatively intact rock mass in the anti-sliding zone under the gravity of the major sliding zone; 6) the sliding process can be divided into 6 steps. Firstly the major sliding zone and the anti-sliding zone begins, secondly the support-losing hauling zone starts up, thirdly the first started mass collides with the left bank of the river(the bank in Sichuan Province) at high speed, then moves up the slope for around 95 m and laterally to form the debris-scouring zone, fourthly the first started mass moves downward and collides with the mass from the hauling zone above the river and the merged mass punches the river water to form high-speed sandy water jet, resulting in jet-scouring zones on the both banks, fifthly the downslope of the landslide dam fails, resulting in the secondary landslide and finally the punch-induced misty rain leads to the flush of the dam surface; 7) the "11·3" landslide is the local failure of the earth mass in the hauling zone due to the progressive disintegration of the fractured rock mass acting as retaining wall and its volume is around 3×106 m~3; 8) there still exist badly deformed mass in the hauling zone and the estimated volume is 5.5×106 m~3, so further sliding and damming risk is big and feasible control measures should be taken.
In October 10 th and November 3 rd 2018, two landslides happened successively on the right bank of the upper reaches of Jinsha River,which dammed the river at Baige village, Jiangda county, Tibetan Autonomous Region. The dammed lakes and their breaching flood brought about severe disaster to local residents and their production and life facilities along the river. Based on the field investigation immediately after the slides and other related materials, a systematic analysis is made on the formation and process of the slides in the paper. Results show that: 1) the"10·10" slide is a high position, high shear crack, high speed and incomplete wedge slide and its volume is around 107 m~3; 2) geologically the slide is situated in the suture zone of Jinsha River and the bedrock is Xiongfeng gneiss group of Proterozoic, which is characterized by multiphase repeated deformation and metamorphism and is severely mylonitized and altered; 3) the sliding area can be vertically divided into 3 zones of antisliding zone, major sliding zone and hauling zone, which are separated roughly at elevation 3 500 m and 3 000 m, respectively. The major sliding zone is of wedge shape cut by two well-developed structural planes, the anti-sliding zone is of tetrahedron shape formed by two undeveloped structural planes, while the hauling zone is completely weathered earth mass mixed with clumped and heavily fractured rock; 4) the slide has two sliding directions of S80°E in the major sliding zone and N70°E in the anti-sliding zone and the elevation of shear crack is around 2 950 m above sea level; 5) the power driving the slide is mainly from the gravity of the wedge in the major sliding zone and the developing process of the slide is the progressive failure of the comparatively intact rock mass in the anti-sliding zone under the gravity of the major sliding zone; 6) the sliding process can be divided into 6 steps. Firstly the major sliding zone and the anti-sliding zone begins, secondly the support-losing hauling zone starts up, thirdly the first started mass collides with the left bank of the river(the bank in Sichuan Province) at high speed, then moves up the slope for around 95 m and laterally to form the debris-scouring zone, fourthly the first started mass moves downward and collides with the mass from the hauling zone above the river and the merged mass punches the river water to form high-speed sandy water jet, resulting in jet-scouring zones on the both banks, fifthly the downslope of the landslide dam fails, resulting in the secondary landslide and finally the punch-induced misty rain leads to the flush of the dam surface; 7) the "11·3" landslide is the local failure of the earth mass in the hauling zone due to the progressive disintegration of the fractured rock mass acting as retaining wall and its volume is around 3×106 m~3; 8) there still exist badly deformed mass in the hauling zone and the estimated volume is 5.5×106 m~3, so further sliding and damming risk is big and feasible control measures should be taken.
引文
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[3]金沙江白格堰塞湖泄流致云南损失70余亿元[EB/OL].(2018-11-19)[2018-12-19].http://www.scjz.gov.cn/zqkx_3475/gnzq/201811/t20181119_49091.htm.
[4]西藏自治区地质矿产局.中华人民共和国区域地质调查报告(白玉县幅,熊松区幅1:200000)[R].拉萨:西藏自治区地质矿产局,1992.
[5]中国地震动参数区划图:GB18306-2015[S].北京:中国标准出版社,2016.
[6]Min H,Deng J H,Wei J B,et al.Slope safety control during mining below a landslide[J].Science in China,Series E:Engineering&Materials Science,2005,48(Supp 1):47-52.
[2]应急管理部与国家减灾办:11月全国自然灾害直接经济损失75.4亿元[EB/OL].(2018-12-12)[2018-12-22].https://baijiahao.baidu.com/s?id=1619615238182618387&wfr=spider&for=pc.
[3]金沙江白格堰塞湖泄流致云南损失70余亿元[EB/OL].(2018-11-19)[2018-12-19].http://www.scjz.gov.cn/zqkx_3475/gnzq/201811/t20181119_49091.htm.
[4]西藏自治区地质矿产局.中华人民共和国区域地质调查报告(白玉县幅,熊松区幅1:200000)[R].拉萨:西藏自治区地质矿产局,1992.
[5]中国地震动参数区划图:GB18306-2015[S].北京:中国标准出版社,2016.
[6]Min H,Deng J H,Wei J B,et al.Slope safety control during mining below a landslide[J].Science in China,Series E:Engineering&Materials Science,2005,48(Supp 1):47-52.