(A) the main results

Based on the detailed investigation of geological disasters, the advanced risk management theory in the world is introduced, and the evaluation of geological disasters is extended from susceptibility and danger to risk evaluation. Combined with the domestic reality, the relevant technical method system is formed. Mainly includes:

1) Based on the actual situation in the loess area, the evaluation unit is divided by hydrological method (Figure 1), and the parameters of loess slope such as slope, slope height, slope type and slope direction are accurately obtained, and the probability of landslides with different slopes, heights, types and directions is analyzed.

Figure 1 Division of Risk Assessment Units by Hydrological Method

2) The risk and hazard classification standards are established, and the risk classification system of loess landslide disaster is designed based on the results of risk and hazard evaluation.

3) A landslide risk analysis and control method based on water level control is proposed. Establish a synergistic coupling model of groundwater seepage field and slope stress field, determine the landslide instability probability under different reservoir water levels (Figure 2), evaluate the personal life risk and property risk under different reservoir water levels, consider the allowable risk and water supply demand as a whole, determine a safe and reasonable reservoir water level, and put forward comprehensive risk control measures such as relocation and avoidance, drainage and water level control.

4) Typical geological disasters are selected as the analysis objects, and the risk analysis and superposition under different failure modes, the determination of allowable risks, the evaluation of social risks, the risk determination of disaster-bearing bodies located on the upper slope and the value estimation of disaster-bearing bodies as scenic spots are studied respectively, and the landslide risk analysis process and calculation method for multi-risk source identification are established (Figure 3).

Fig. 2 Failure probability of landslide under different reservoir water levels

Figure 3 Flow chart of group life insurance risk assessment based on multiple risk sources

5) Put forward the working idea and technical route of loess landslide survey and risk mapping based on GIS, DEM, RS and ground investigation (Figure 4).

Technical roadmap of risk mapping based on GIS, DEM, RS and ground investigation.

6) The scale type and precision type of geological disaster risk assessment for different application objects are systematically studied. The contents, methods and technical points of geological disaster investigation and risk assessment with different scales and accuracies are put forward (Figure 5 ~ Figure 8), and a set of technical methods and systems of geological disaster investigation and risk assessment with different scales and accuracies are established.

(2) Technical characteristics and indicators

1. Accuracy of risk assessment

Geological hazard investigation is the basis of geological hazard risk management. Different applicants have different management subjects, and the corresponding survey and evaluation accuracy requirements are also different. Geological hazard investigation and risk assessment can be divided into four types according to scale: small scale, medium scale, large scale and detailed scale (table 1). The four scale types of geological disaster investigation and risk assessment can adopt three precision requirements: high precision, medium precision and low precision respectively (Table 2).

Fig. 5 Risk zoning results of1∶ 50,000 landslide in Yan 'an City.

Fig. 6 Risk zoning results of Dabiegou area 1 ∶ 25000 in Yan 'an City.

Fig. 7 Risk zoning results of1:1million based on the scoring system.

Fig. 8 Landslide risk zoning results of Baota shan1:1000 in Yan 'an City.

Table 1 Investigation and Evaluation of Geological Hazard Types

Table 2 Summary of classification principles of geological disaster risk assessment results

2. Technical points of risk assessment

(1) small loess landslide risk assessment (1∶ 50,000)

Small-scale (1∶ 50,000) landslide evaluation is suitable for large areas, and vulnerability evaluation indexes include disaster point density, slope, slope height, slope type, geotechnical type, vegetation, rainfall, engineering activities, etc. The evaluation factors that need to be increased from prone to danger are the possibility (time probability), sliding distance and sliding speed of landslide in a certain period of time; The evaluation factors that need to be increased from danger to risk are the type, value and vulnerability of the insured object.

(2) Risk assessment of medium-sized loess landslide (1 ∶ 25000)

For the landslide risk assessment in the range of tens to hundreds of square kilometers, it is suitable for the medium scale of 1 ∶ 25000. In advance, through information sources such as high-precision DEM and fast bird remote sensing data, the potential landslide-prone slopes are identified, the boundaries of landslide danger areas are preliminarily defined, and the information of insured objects is interpreted. Then, the above information is verified, corrected or cancelled one by one through field verification, and finally a risk assessment map meeting the requirements of scale accuracy is formed.

Table 3 Index System of Loess Landslide Disaster Risk Assessment

(3) Risk assessment of large-scale loess landslide (1:1000)

For large-scale landslide risk assessment (1 ∶ 10000), slope risk classification system can be used for evaluation. Based on the theory of landslide risk management, the overall index system of loess landslide risk assessment is determined. Based on the statistical law of field investigation, the main sources of loess landslide disasters and the main factors affecting disasters are analyzed, and the scoring evaluation system is determined from four aspects: instability possibility evaluation index, landslide strength evaluation index, insurance object evaluation index and vulnerability evaluation index (Table 3).

The risk of landslide is generally determined by hazard × hazard consequence. If the hazard evaluation results and hazard evaluation results are obtained respectively, the risk can be determined by comparing the matrices in pairs. Therefore, the overall design of the scoring system is divided into three parts: risk scoring table, hazard scoring table and risk assessment grading table (Table 4).

Table 4 Determination of Risk Classification Matrix

Note: VL level is very low; L level is low; M level is intermediate; Class h advanced.

(4) single loess landslide risk assessment (> 1 ∶ 5000)

The landslide risk assessment of a single entity should reach a quantitative level, which is generally carried out in the engineering geological exploration stage of the site. The stability and instability mode of slope are analyzed by using various exploration data, and on this basis, the risk of property loss, personal life risk and group life risk caused by slope instability are analyzed. Therefore, the risk assessment at this stage requires high accuracy, and the scale should be 1: 5000 or higher.

3. Parameters and methods required for risk assessment.

The parameters to be obtained in the assessment should be designed to meet the needs of risk assessment with different accuracy. In addition to the general investigation on the formation conditions, basic characteristics, influencing factors and stability of landslides, we should also investigate the annual frequency of landslides with a certain volume scale, the sliding distance and speed of potential landslides, the insured object and its economic value, and the temporal and spatial probability and vulnerability of the insured object. Due to different investigation areas, different uses of evaluation results, or limited by investigation stage and investigation funds, the methods and results of obtaining the above parameters are different in accuracy. Generally speaking, low-precision surveys are suitable for small areas, and the methods used are also general data collection, remote sensing interpretation and ground investigation. Medium-precision survey is suitable for medium and large scale, and the main methods used are engineering geological mapping, empirical methods, interviews with people in the industry, simple models and statistical techniques. High-precision survey is suitable for a single landslide, and the main methods used are super-large-scale engineering geological mapping, drilling, geophysical exploration, mountain engineering, testing experiments, and asset evaluation of the insured object.

Second, the scope of application and application examples

The risk assessment and management of geological disasters in Baota District of Yan 'an City is of great practical significance to the prevention and control of local geological disasters, and the main achievements have been widely used in land use planning, early warning and forecasting of geological disasters and scientific research activities.

1) In terms of land use planning, landslide survey and risk zoning were carried out based on the government's public service demand, a set of geological disaster investigation and zoning methods based on county scale were formed, and a demonstration base for geological disaster risk management in Baota District of Yan 'an City was established, which provided technical methods and demonstrations for government land use planning, disaster reduction and prevention, and scientific management of geological disasters; Reasonably guide land developers, investors and residents. Knowing risks, avoiding risks and making rational decisions on economic activities have achieved good economic and social benefits.

2) In the aspect of early warning and prediction of geological disasters, based on the results of risk zoning, the county-level geological disaster early warning is divided into four different early warning precisions: small-scale, medium-scale, large-scale and single hidden danger point early warning, which partially solves the problem of too large early warning area and plays a due role in promoting and demonstrating the existing geological disaster monitoring and early warning work.

3) In terms of scientific research influence, many papers have been published based on geological disaster risk assessment and management, and the results have been cited many times, among which "Geological Disaster Risk Investigation Method and Practice" has been cited 30 times. At the same time, many graduate students have been trained in China Geo University, Chang 'an University and other universities, which has effectively promoted the development of geological disaster risk assessment and management in China.

The risk assessment and management of geological disasters in China is still in its infancy, and the risk assessment and management of geological disasters in Baota District of Yan 'an City has played a demonstration role and has broad application prospects.

Third, promote the transformation mode.

1. Publicity and reporting

Posters and handbooks on popular science of geological disasters were compiled to publicize the knowledge of prevention and control of geological disasters and the methods of avoiding risks to the local people (Figure 9); The risk of Baota shan landslide in Yan 'an City, the holy land of revolution, was interviewed by Xinhua News Agency (Figure 10), and reasonable measures for risk avoidance and engineering control were put forward.

Figure 9 Popularization of popular science

Photo 10 Interview with Xinhua News Agency

Figure 1 1 conference exchange

2. Meeting exchange

At academic conferences such as "Academic Forum on Urban Construction and Geological Disaster Prevention", the technical methods of geological disaster risk assessment and management and their application in Baota District of Yan 'an City were exchanged with the participants (Figure 1 1).

3. Personnel training

The lecture notes of landslide risk analysis and risk management training course were compiled, and the landslide risk analysis and risk management training course was held in 2008. 1 13 representatives from universities, research institutes and production units all over the country participated in the training (Figure12); On 20 1 1 year, the "International Advanced Seminar on Geological Disasters" was held, and 2 15 representatives from all over the country participated in the training (Figure 13).

Figure 12 Landslide Risk Analysis and Risk Management Training Course

Figure 13 International Symposium on Geological Disasters

Technical support unit: Xi Geological Survey Center of China Geological Survey.

Contact: Zhang Mao Province

Mailing address: No.438 Youyi East Road, Xi, Shaanxi Province

Postal code: 7 10054

Tel: 029-8782 1980

E-mail: xazms @126.com.