1、1 中文 2258 字 Ground fissure hazards in China Introduction: Ground fissures are very popular earth surface phenomena, showing the discontinue or broken of the earth surface. Usually, they occur accompanying with other geological hazards. There are many kinds of ground fissures: tectonic fissures, incl
2、uding fault fissures, earthquake fissures, volcanic fissures； slip-collapse fissures, including landslide fissures, mining fissures. Ground fissures have long history in China. The earliest ground fissures were recorded about five thousand years ago, “Ground fissures occurred before Yellow Emperor p
3、assed” (Taiping Yulan, the 880th).Those ancient ground fissures were pure natural ground fissures .However, the modern ground fissures have been caused by both natural and man-made genesis since the beginning of 20th century and occurred only tens of years. History of modern ground fissures in China
4、 The first group fissure was observed on the walls of the buildings in Northwestern University in Xian city in 1958.At the beginning； people did not pay attention to it, and thought that it might be caused by the bad quality of the buildings. Along with the development of pumping ground water, the f
5、issures become longer and longer, and the scarps become higher and higher. However, people did not pay attention to them until the tragedy-Tang Shan earthquake (July 28, 1976, M=7.8) happened, when ground fissures became to severe that they were thought might be the precursor of a potential earthqua
6、ke in Xian region (LI,et al,1986).In many other provinces of North China region, such as Hebei, Shanxi, Shandong and Jiangsu, ground fissures also occurred in this period. Since the beginning of 1980s, ground fissures have become a very severe geological hazard in many places (XIE, 1988). The charac
7、teristics of ground fissures in China The ground fissures so called as earth fissure in USA are called tensile fissure in China. As their opposing sides move perpendicular to the plane of failure, they are also called horizontal tensile fissures. This kind of ground fissures occur since the beginnin
8、g of 2 subsidence process. Usually after Harvey rein they are visual clearly. They can occur either independently or accompany with shear displacements, in the district where groundwater has been over tapped, and also in some area of extraction of oil or gas. The fissures usually are not very deep,
9、only 5 30m,with the crack open at the width of 2 50cm on the surface of land, and the deeper the narrower. By erosion of water, the open cracks become as 2m, commonly wide enough to trap a vehicle. This kind of hazard happened for many times in Xian. The ground fissures so called as surface faults i
10、n USA are called shear fissures in China. There opposing sides move parallel to the plane of fracture, usually one side sinks while another rises relatively, in the same way of normal fault. Usually, preexisting faults are the foundation of this kind of ground fissures. As the fissures look like nor
11、mal faults, they are also called tectonic ground fissures. However, the creeping rate(12 mm/a average in Xian region) is ten times larger than the normal active faults in the same area. This characteristic of ground fissures is very typical in China. The scarps are 0.2 0.5m and the lengths are sever
12、al kilometers. The longest one (12.5km) is in Xian, with the average scarp of 0.4m.Along the ground fissures, the heights of scarps are changing, the nearer the subside centers, the higher the scarps are. Distribution of ground fissures in China There are mainly four ground fissure zones: Fen-Wei ba
13、sin ground fissure zone, and Dabieshan faults ground fissure zone, in North China area, including seven provinces: Hebei, Shanxi, Shaanxi, Jiangsu ,Shandong and Anhui. Some ground fissures are also discovered in following 8 more provinces: Liaoning, Jilin, Gansu, Guangdong and Yunnan, with little ha
14、zard (XIE, 1998). Fen-Wei basin ground fissure zone is the most typical and sever among the four ground fissure zones. Fen-Wei basin is composed by Fen River basin and Wei River basin, where many destructive earthquakes happened and the present earthquake activity is still in high level. In the basi
15、n there are typical normal earthquake faults, with the maximum offset 8km. Ground fissures hazards in this zone are most disastrous and typical with differential vertical creeping and opening horizontal movement. 3 Xian is the most severely suffered from the hazard among the 50 cities affected by gr
16、ound fissures. Datong, Hancheng, and Yuci are the other big cities (the population is over a million in each city) with severe ground fissures problems. Ten ground fissures distribute over the whole down town area of Xian city (Figure4) with an aggregate length of 72km, covering 155km2,creeping with
17、 an average rate of 12mm/a(vertical shear movement), and maximum 70mm/a nearby a new subsidence center (sink rate is over 200mm/a).These ten ground fissures have nearly the same predominant direction (about N700E,parallel to Lintong-Changan fault),creep in the same way, mainly dip to south with 75 8
18、5 high angle, separating nearly 1km each other, showing the same tectonic characteristics clearly(GENG, etal,1992).They have become ten destructive belts, destroyed all kinds of civil engineering located in the belts, made losses of millions US dollars in 1980s. It has been noticed that the volume o
19、f over extracted ground water, ground subsidence and ground fissure activity have close correlativity. The rate of decrease of ground water level increase to 4m/a in subside center areas. Ground fissure hazard management 1 Ground fissures hazard prediction According to the characteristics, geologica
20、l environment and mechanism of ground fissures the potential ground fissures can be predicted. The prediction is composed of three parts: (1) Geotechnical investigation. The present distribution of ground fissures, preexisting faults, potential faults and subsurface shape in concerned area should be
21、 investigated. Firstly, according to characteristics and geological environment of ground fissures, aerial photographic interpretation may help to find the locations where there is the maximum of surface elevation gradient to guide the field investigation. Secondly, the field investigation in the po
22、tential ground fissures hazard area will help to find some precursors of the evaluation of fissures. Usually, the bending stress becomes strong enough to make fine crack on the rigid engineering structures with special pattern before the hazard. Thirdly, geophysical and geotechnical investigation on subsurface conditions of the potential hazard area, including seismic survey, gravity survey, electric survey, radiation survey and soil gases survey, will
