| In recent years, geo-hazard risk assessment and management has been a hot and difficult topic in research field. Although there are still many different views on the research methods, content, procedures home and abroad nowadays, the geo-hazard risk assessment techniques and management methods became the mainstream because of its improving in practice and gradual promoting in use. Baoji City in Shaanxi Province is one of the serious geological hazards regions in the northwest loess plateau, especially the potential geo-hazards are very serious around Baoji City and along railway, and it is a good testing field for studying the geohazard risk assessment. In order to explore different levels risk assessment technique method on geological hazard in the combination of examples, taking geological hazard risk assessment in Weibin district of Baoji City in Shaanxi Province as example in this paper, relying on the national science and technology support project" Geo-hazards risk assessment technology research" and on the China Geological Survey Project" Geo-hazard detailed investigation in the region of Baoji City in Shaanxi Province ", based on detailed catalog and database construction of geological hazard investigation in Weibin district, the status and progress of research on geo-hazard risk assessment at home and abroad was analyzed briefly and geological hazard development conditions, geo-environmental background, distribution regularity and the main impact factors in Weibin Disrict of Baoji City were systematically studied. Geo-hazard susceptibility, hazard and risk assessment zone in Weibin district were finished by three levels such as region (1:5 million survey data), the key area (1:1 million survey data) and monomer (1:2000 reconnaissance data) by using statistical analysis of the surface in combination of anatomy research of typical landslides, field survey and reconnaissance in combination of simulated calculation, qualitative analysis and in combination of quantitative model. Through these studies, the major progress and conclusions are obtained in this thesis as follows:1) The main types and distribution characteristics of geological hazard in Weibin district were preliminarily revealed as below:①Distribution of geological hazard was generally east to west - northwest to the zonal distribution controlled by Qingling Mountains and the Weihe River valley in Weibin district. The majority of geo-hazards are concentrated between the hilly - loess hilly beam hillside in the northern slope of Qingling Mountain.②Sub-band of geo-hazards was significantly affected by controlling of the tributary of the Weihe River and was a distribution of the North-South bands. The majority of geo-hazards in Weibin district are concentrated along the north-south gullies in Qingling Mountain. That is, geo-hazards are mainly developed along banks of Weihe River branches and not developed along banks of Weihe River.③The most dense area of geo-hazards in Weibin district is the branch of Qingshuihe River in Bayu town—both banks of Tanjiawa gully. There are nine loess landslides lying in less than 2km length of the gully and the largest surface density is up to 20% in the small gully basin. This area was easy to form landslides mainly due to Tanjiawa gully is close to Qingling southern bedrock piedmont fault, covered by thick loess, narrow valley, short process, longitudinal big drop, which lead to a strong role in water erosion , result in the natural slope angle and slope height of both gully sides tall.④The main type of geo-hazard is landslide (small and medium-sized loess landslides) and the second is landfalls and debris flows. The potential hazards that are more harmful are small and medium-sized landslides and loess collapse around the resident houses. The slope that is prone to landslide hazards is loess slope (including pure loess slopes, loess and red bed slope, loess and bedrock slope, etc.).2) The main factors which control the distribution of geo-hazards in Weibin area are structure terrain geomorphic and characteristics of rock and soil composition. About 90% of the landslides, landfalls occurred in the mid-lower slope zone between Qingling Mountains and the Weihe River valley. The terrain features of Qingling Mountains northern slope is controlled by the northern margin fault zone of the Qingling Mountains. Thin layer loess covered bedrock surface in the mid-lower part of the northern slope of Qingling because of the differential uplift between two side of the fault. The north-south gullies of the Qingling northern slope is incised by water which resulted in the steep slopes on both sides of the tributary valley of Weihe River high-terrace and the side of the loess plateau and gully development. These formations of the terrain conditions are a favorable environment for landslides, landfalls development3) The formation and evolution of the process of multi-levels overlay landslide and opposed loess landslides are initial revealed by the large-scale surveys, engineering investigations, indoor testing analysis, and stability simulation of typical landslide:①Xiayahe landslide and Gaojiahe landslide are large-scale loess - clay -sand mixed-layer landslide which have 4-level and 3-level potential sliding surfaces respectively and they are multi-period formation. By yet, they are still deforming and sliding somewhere. They belong to typical landslides with extended stratification. By reliability analysis for the landslide by using Monte-Carlo simulation method, the preliminary view is as follows:Landslide safety can be quantitative expressed by reliability analysis and the landslide reliability and its instability probability can be obtained by reliability analysis, which can provide basis parameters for quantitative risk assessment of monomer landslide and is conducive to comparative analysis of landslides hazard, revealing risk probability of landslide slide. At the same working conditions, the stability of landslide (Safety) and its reliability value (or failure probability) does not have one-to-one relationship.②Through numerical simulation analysis for Xiayahe landslide and Gaojiahe landslides, the research shows that: in natural conditions, 4 levels landslide of Xiayahe landslide are all in steady state, in the rain conditions , instability possibility of the 1, 2 level landslide may occur. 3-dimension numerical simulation shows that the shear strain rate of the first sliding surface is the highest, followed by the second sliding surface, and there are little shear strain on the third, fourth sliding surface. The poor stability of 1, 2 level landslide and 3,4 level landslide in steady state are confirmed. 2-dimension simulation results of Gaojiahe landslide show that maximum value of compressive stress and tensile stress in the rain state was significantly increased and changes value of plastic strain was more than double level of plastic changes in natural conditions.1 level Landslide in the rain conditions would be failure of the overall trend and the back margin of 3 level landslide would be failure of the trend.③Tanjiawa landslide group with largest density in Weibin area is a combination of nine landslides, which belongs to a typical hedge loess landslide group. Landslides occurred in the adjacent and mutual influence, which constitute landslide-intensive group lying on both sides of the gully. 4, 5 and 7 landslides in the group are hedge landslide, and 7 landslide on the left bank first slid down to impact the slope foot of the other side, and then accumulated at the bottom of the gully to form accumulation dam. Water diffuse above the dam to wash the slope foot on the other side of the gully which leads to invading face up through the long-term cutting erosion and leads to slope foot loose of the previous accumulation body on the opposite banks.4,5 landslide slid down due to the role of triggering factors such as rainning.4,5 landslide slid down to hit the other side, for the same reason, causing portion of 7 landslides sliding again, which result in river bend to the other side in front of 7-1 landslide. Other hedge landslides have similar characteristics, too. At present, 4, 5 landslides have the possibility of local activities, belong to high-risk areas, should be paid attention to strengthening the monitoring and early warning.4) Geological hazard susceptibility zoning, hazard zoning and risk assessment zoning were respectively completed at 3 levels in Weibin areas by using evaluation methods in combination of qualitative analysis, synthesis information model and factor right overlap model. The results showed that: ①The geo-hazard high susceptibility zones in Weibin area accounted for 14.96 %, and the geo-hazards mainly distributed in the districts from the southern bedrock mountain zones to the loess plateau, and at the two sides of Qingjianghe River nearby Shengnong Town; The middle susceptibility zones accounted for 27.02%, which were mainly distributed at the two sides of Qingjianghe River in the south-west of Weibin district and its affluent, such as Shenshahe River, Lijiahe River, etc., and at the two banks of Weihe River in Chaoyu Town and the southern bedrock mountain zones, and in the middle of the loess plateau, the loess ridges and loess knolls at the southern bank of Weihe River; others were low susceptibility zones and non-susceptibility zones, accounting for 31.57% and 26.45%, respectively.②The geo-hazard extremely high and high dangerous zones in Weibin area accounted for 10.34 % and 16.99 %, respectively. And they mainly distributed in the zone of Gangu Village, Chaoyu Country -Puzishan, Gaojia Town, at the banks of Qingjianghe River from Dongyukou to Chenjia Village, Shennong Town, in the area of the loess ridges and loess knolls along the zones of Gaojiahe Village - Randengsi Temple - Zhangjialing Village in Shugu Town and Bayu Town; and others were middle dangerous zone, low dangerous zones and non-dangerous zones, accounting for 25.69 %, 30.79% and 16.18 %, respectively.③The extremely high risk zones and the high risk zones accounted for 3.65 % and 9.10 % respectively in Weibin district. And they mainly distributed in the zones of Kongkecao -Heishanwan -Sigouling in Chaoyu Country and Gaojia Town, at the two banks of Qingjianghe River from Dongyukou -Pianqiao -Shijiaying in Shengnong Town and nearby Beizui Village at the north bank of Weihe River in Chaoyu Country. The geo-hazard forecast along the road and railway should be strengthened in these extremely high and high risk areas and some slowing up measures should be taken. Others were the middle risk areas, low risk areas and extremely low risk areas, accounting for 21.61 %, 34.04% and 31.41%, respectively.④The geo-hazard risk assessment results of the key area in Weibin district showed that, the extremely high risk and high risk areas totally accounted for 5.92%, mainly distributed along the two banks of Qingjianghe River from Dawanbu -Zhujiagou -Yimenbu in Shengnong Town, These extremely high and high risk areas should be paid more attention, the forecast should be strengthened and some slowing up measures should be taken.In a word, the geo-hazard hazard and risk in Weibin district were not very high, but the areas around domestic architectures and the single geo-hazard risk at the two sides of important railways and highways should be paid attention.5) According to the discussion and analysis on the qualitative risk evaluation of the four layers landslide in Xiayahe monomer landslide, the followings could be indicated:①The total values of potential economy loss and personal casualty of each level potential sliding surface of Xiayahe landslide under different working conditions were preliminarily quantitatively calculated and different. The latent risk of different potential sliding surface of Xiayahe landslide was proposed, which could supply scientific gist of geo-hazard risk management for the local government.②The landslide with the second level potential sliding surface of Xiayahe landslide belongs to the high riskone, comparing with the international tentative society tolerable risk criterion. Its risk value lies in the non- acceptable range. Therefore, the slowing up measures should be taken or the prevention measures should be strengthened so as to decrease the landslide risk.6) According to some experiences and methods of geo-hazards risk management home and abroad, the geo-hazard risk management system and some slowing up measures for risk of Weibin district were preliminary studied. Meanwhile, the general method for decreasing and preventing the landslide, landfall and debris flow in Weibin district was put forward.
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