| The section from Tianshui City to Longnan City's Huixian of Shitian Expressway(Shiyan to Tianshui Expressway)has diverse climate conditions,complex topography and diverse geomorphology,where is characterized as the frequent occurrence and recurrence of geological disasters,which seriously threatens the normal operation of the expressway and maintenance.In this paper,the physical geography and socio-economic conditions and historical disaster data in the study area was taken into account to describe the natural environment conditions such as the geological and geomorphic environment,climatic and meteorological conditions in the study area by using remote sensing technology and field surveys;According to the actual situation of the disaster characteristics in the study area,this paper comprehensively analyzed the conditions of the regional climate,hydrogeological environment,topography,geological structure,stratum lithology and regional stability,and human activity interference.According to the three main aspects of risk theory including the leading factors(hazard factors),basic factors(hazard-pregnant environment)and development factors(hazard-bearing bodies),14 main influencing factors including slope,slope change rate,slope type,cutting depth,gully density,rock and soil type,geological structure,NDVI,precipitation,earthquake and human engineering activities,etc.were selected to build the index system for the risk assessment of geological hazards in Huixian section in Shi-Tian expressway from Tianshui City to Longnan,the analytic hierarchy(AHP)was employed to calculate the weight values ??of the influencing factors selected by this paper,and the GIS weighted superposition method was used to evaluate the geological hazard risk in the Shi-Tian expressway from Tianshui City to Huixian,Longnan City.The main results in this paper are as follows:(1)The study area is located in the transition zone of China's stepped terrain that is an earthquake-prone area.The geological and landform environment is complex and diverse.The topography of the study area has obvious topographical changes,abundant precipitation and concentrated short-term high-intensity precipitation,and river cutting density is relatively large;There are obvious differences in vegetation areas;the topography and topography are obviously undulating,and there are many types of landforms.There are three geomorphic units: denuded Zhongshan,mountain basin,and alluvial valley;the study area has complex and diverse geological structure conditions.The rock mass in the area is mostly soft rock,which is easy to be washed by heavy rain.It is the primary condition for frequent recurrence of geological disasters in this area.Geological crustal activities such as faults and folds are densely developed.In particular,human engineering activities have a strong disruptive effect on the geological environment of the area,especially the construction of highways and other activities that easily break the balance of the geological environment,which in turn causes geological disasters such as collapses,mudslides and landslides.(2)We found that there are mainly three types of geological hazards: landslide,collapse and debris flow in the study area.The developed landslide disasters in the study area showed a significant agglomeration and distribution characteristics,which are mainly distributed in the lower valley areas of Xihe County,Longnan City and Xihan River Basin in Li County.The main contributing factors of such disasters are rainfall,topography and geomorphology and rock and soil properties.The developed avalanche disasters are mostly scattered in the fan foot of the river alluvial fan.The rock and soil are broken and loosened into a loose or fragmented shape,which are concentrated and distributed in the areas on both sides of the Luohe and Shixia Rivers or on the road section.It is mainly controlled by geological structure,topography and precipitation and other meteorological conditions.This section is located in the Qinling fold belt and is a small seismic zone,and the meteorological factors such as precipitation in this area vary greatly.Debris flow disaster events have a wide range of distribution,high development frequency and poor stability.It has been found that the debris flow disasters in the study area are mainly concentrated in the upper and middle reaches of the Xihan River Basin,and the Yangshui River Basin in the Loess Mountains in the northern part of Xihe County.Debris flow disasters mainly develop along river channels,so they are controlled by short-term flow of water,topography and land cover(loose surface rock and soil).(3)The GIS weighted superposition method was employed to obtain the geological hazard risk assessment map from Tianshui to Huixian,Longnan City on the Shi-Tian Expressway in his paper.Results showed that: the high-risk areas of geological disasters are mainly distributed around the county seat of Xihe County and Lijia River in Hui County with an area of276.40 km2.The medium-risk zone is mainly distributed from Zaojiao Town in Qinzhou District to Yanguan and Xihe County Changdao in Li County,covering an area of 121.95 km2.The low-risk areas are mainly distributed from Xihe County Changdao to Chengxian County with an area of about183.90 km2.The non-hazardous zone is located in the study area from Chengxian County to Huixiandian Village with an area of about 79.01 km2. |
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