Study On Slopes Risk Assessment And Countermeasures Of Highway In Maintenance Period

Slopes of highway in mountainous area are usually with high risks during project construction and maintenance periods due to inherent uncertain and disadvantageous factors. Such risk factors as geological, environmental, and technical as well as quality control, cost control and time control etc may cause the engineering hazards and result in enormous economic and life loss. On the other side, the traditional safety coefficient method, because of inevitable limitations in practical application is rather than a perfect evaluation method for slopes' evaluation.Risk assessment hereby is suggested to be used in the slope management. Firstly, the risk factors existed in slope project have been investigated and their associated parameters been studied. A slop risk assessment model based on the calculation of weight and risk value of each identified risk factor is introduced. Analytic hierarchy risk factors model is established to calculate the weights of factors while their counterpart assessment values are estimated by scoring the quality of associated parameters. Hence we get risk value of all factors, and then the total risk value of slope. At last, an assessment table of risk factors is made by emerging factors in different hierarchies.As we can see, the advantages of adopting risk management in slopes are obvious. First, the uncertain and potential danger of factors existed in slope project are been recognized and considered. Second, the transition process of slope condition from safe to dangerous can be taken into account. What's more, the important factors which need taking care can be identified, therefore controlled or improving by monitoring and treatment. Finally, the risk management system which is well organized can feedback the slope situation instantly, hereby helps engineers take efficient and effective countermeasures.Refer to research programme Study on Slopes Risk Assessment and Countermeasures for Transport Project of XiLuodu Hydropower Station Construction supported by China Three Gorges Project Corporation, in this thesis, three typical slopes with different geological environment are taken as examples, the applications of slope risk assessment model have been demonstrated. The main study results are as following:(1) Several approaches to identify risks factors and process of risk identification and classification are discussed. Risk assessment starts from risk factors identification and classification which are based on engineering experience, field survey and site investigation. Reasonable methods such like information record analysis, questionnaires, safety check list method, process (chart) analysis method, fault tree analysis method, Delphi method, Scenario analysis method etc are applied to recognize the potential risk factors existed in slope project. The procedure commences prejudging the risk characteristics and possible accidents caused by risk factors, and then analyzing the interrelationship between factors and accidents, hence estimating consequence lost which might be. Three preliminary indicators are employed to facilitate primary prejudgment, namely, sensitivity indicator, frequency indicator and controllability indicator.(2) The geological environment of three types of slopes (K20, K31 and K35) has been investigated. The factors of slope forming, characteristics, landform, physiognomy and rock and soil structure have been emphasized on. According to geologic investigation, K31 is regarded as typical calcareous rocks composed slope mixed with calcareous marl and marlite; K35 is an alluvial soils or fluvial soils formed slope with the sandy mudstone or rock underneath; the components of K20 are much complicated which might happen more slope failures. K20 shows a sand-soil stack structure whose overlying strata are composed of the quaternary Holocene landslide and residual clay, mixing with rubble or breccias occasionally, while underlying bedrock is commonly consisted of sandy rock, shale and mudstone, serious weathered.(3) The main risk factors, such as geological features (include bedrock, overlying strata), erosion, rainfall, groundwater, earthquake, external loading, human activities that provoke slope failures have been studied; Then, a set of associated parameters linked with factors have been proposed.(4) A slope risk assessment model is introduced. That is, firstly, establish Risk Factors AHP Model based on identification and classification of risk factors previously. Secondly, calculate the factor weight through judgment matrix; thirdly, determine assessment value of each factor according to site investigations and tests; therefore, their product is defined as risk value of each factor.(5) When we get factor weight, assessment value and risk value of all factors, assessment table of risk factors can be compiled which involves merging all risk factors. Based on this table, a set of factors will be chosen and analyzed accordance with different purposes, so engineers and policy maker can better understand the attributes of slope risk and the relationships between factors. What's more, table users can investigate the certain risk of slope disasters by analyzing and evaluating its influence to overall potential risks. And it also make it possible to explore the change of slope risk and predict its future trends, therefore previous risk protection and treatment will be made consequently.(6) Numerical calculation results and monitoring data analysis are also taken into account. The numerical calculation software FLAC has been employed to analyze slope risk. Meanwhile the monitoring data of displacement reflecting slope deformation are compared with numerical calculations results.(7) A new slope risk rating system by taking risk factors assessment, numerical calculation and monitoring into consideration is proposed. It is a rating system consisted of total 4 grades with 15 sub-degrees.(8) The risks of three types of slopes (K20, K31 and K35) are assessed. The study procedure goes as: First, establish the risk assessment models for three slopes; Second, rational analysis has been approached to evaluate risk characters of each slope; Third, FLAC as a means of numerical calculation has been employed and analyze of monitoring data. Finally, get the grades of three slopes. Meanwhile, some countermeasures and slope treatment are suggested.