20 1 1 The Enqian Expressway, which started construction, runs through Xuanen County, Enshi Prefecture, Hubei Province from north to south, with complex topographical and geological conditions and frequent geological disasters. Doing a good job in monitoring and preventing geological disasters along the line is of great significance for protecting the lives and property of residents along the line and ensuring the safety of expressway construction. On June 6, 20 13, a landslide occurred in the trunk ditch of Group 5 of Huangjiahe Village, Gaoluo Township, Xuanen County (on the right side of K54+340 m of Jian 'anlai Expressway), and the land department immediately organized emergency evacuation. On June 7th, 2065438 16: 40, the landslide damaged two precast T-beams of the viaduct under construction, resulting in a direct economic loss of 300,000 yuan, successfully avoiding 87 people and avoiding property losses of nearly 5 million yuan.
2 Geological hazard characteristics
2. 1 Geological environment conditions
The original topography of Gangou landslide is a ridge intersecting with the expressway line at a small angle, and there is a natural gully on the left side of the landslide. Yellow-green, blue-gray, purple-red sandy shale is exposed around the landslide, and the rock stratum intersects the slope at a large angle. Groundwater mainly includes surface pore water and fissure water.
2.2 the basic characteristics of landslides
Gangou landslide is about 130m in length, 70m in width, 6m in average thickness and 54,600m3 in volume, which is a small landslide. The landslide body is mainly composed of residual slope gravel soil, partially filled with clay, and its structure is loose. The contact surface of the landslide slides along the rock stratum in a ladder shape, impacting the T-beams piled up on the pavement of the expressway under construction and accumulating, forming a steep bank with a height of about 5 ~ 7m at the rear edge of the landslide.
2.3 Landslide Cause Analysis
Sandy shale in landslide area has poor weathering resistance, loose slope and easy creep. The En-Lai Expressway under construction cuts at the front of the landslide, and the rock stratum is exposed, resulting in the free height of the front edge exceeding 20m, which provides favorable conditions for slope instability. On June 6, 20 13, local sudden rainstorm, rainstorm and engineering activities * * * all induced landslides.
Figure 1 Landslide Panorama
Figure 2 Trees dumped on the surface
3. Geological hazard inspection and monitoring
3. 1 Daily inspection and monitoring
On August 20 12, Enlai Expressway began to level the site and prepare for construction. Xuanen County Land and Resources Bureau quickly contacted the expressway construction unit and the construction unit, and * * * carried out geological disaster inspection on this section once every seven days. On June 6th, 20 13, when Hu Jiamao, director of Gaoluo Township Land Institute, led Yao Benkuan, a worker of Gaoluo Land Institute, he found two cracks on the right side slope of K54+340 m of Jian 'an-Enlai Expressway, about 20m long and 5-20cm wide, and the maximum height of the cracks with his mother after displacement was 0.5m. The inspection team made a detailed investigation on the deformation and increased the monitoring frequency to 1 time within 3 hours. Five households in Huangjiahe Village and Hubei Luqiao Construction Group were also issued with "two certificates", and emergency signals and evacuation routes were clarified.
Fig. 3 Deformation detection of the right side slope of Enlai Expressway
Fig. 4 Tension cracks at the rear edge of landslide
Figure 5 Issuing "Two Cards"
3.2 Danger warning
On the morning of June 6, 20 13, a sudden rainstorm occurred in the local area with a rainfall of 229 mm. The County Meteorological Bureau and the Land and Resources Bureau jointly issued a three-level warning of geological disasters. The inspection team found that five cracks were added at the trailing edge of the landslide, and the maximum opening reached1.0m. After receiving the dangerous situation report, the county land and resources bureau quickly arranged 10 people to be on duty for shift monitoring, and set up a emergency headquarters with the township government and the construction unit to be responsible for deformation monitoring and emergency treatment. On the afternoon of the 6th, the deformation was further aggravated. From time to time, loose soil rolled down the inner slope of the expressway under construction, and many water outlets were found in the cracks in the rock stratum, which made the water quality turbid and the rear edge showed obvious signs of increased deformation. The sliding surface is likely to be integral and unstable. After consulting with the headquarters and reporting to the county people's government, the four-level early warning of geological disasters was launched on June 6 15.
4. Safe haven resettlement for geological disasters
4. 1 Pretreatment
Danger is critical, in order to nip in the bud, the headquarters has a clear division of responsibilities, and the emergency rescue team and equipment are ready, ready at any time, and ready for rescue and various logistical support.
4.2 Out of danger
On June 6, 20 13, emergency headquarters rang the gong and quickly organized threatened residents and construction workers to evacuate the dangerous area according to the scheduled route, which took only 28 minutes to complete.
4.3 Temporary resettlement
According to the predetermined plan, the headquarters will place the evacuated personnel in the safe area of T-beam No.2 yard, the emergency rescue team will quickly set up tents, and the logistics department of Hubei Road and Bridge Company will be responsible for accommodation and other matters.
4.4 Emergency management
In order to eliminate the hidden danger of disasters, the expressway construction unit organized 1 excavator to clean up the accumulation layer in the middle and rear part of the landslide on June 4, and built a retaining wall along the inner side of the expressway to dredge the gully on the left side of the landslide. After emergency treatment, the hidden dangers of geological disasters were basically eliminated, and the headquarters arranged three people to continue deformation monitoring. On June 18, the monitoring showed that the deformation tended to be stable, the evacuated residents returned to live, and the expressway resumed construction at the same time.
5 Experience and Enlightenment
5. 1 Reasons for successful hedging
Through emergency measures, the landslide did not cause casualties, and 78 people were successfully avoided, and the economic losses were effectively controlled. The main reasons for this successful emergency avoidance are: first, to intervene in the prevention and management of geological disasters as soon as possible for important projects and strengthen supervision; Second, the daily inspection work is carried out in a solid manner, and the key areas that are easy to highlight are fully grasped; Third, the monitoring and early warning response is rapid, and the geological disaster emergency plan is implemented; Fourth, the evacuation and transfer of threatened personnel are timely and effective.
5.2 Problems needing improvement in the future
Key projects have a great impetus to the economic development in mountainous areas, but the construction of mountain projects has obviously changed the geological environment, destroyed the stratigraphic structure and easily caused geological disasters. The geological conditions in Xuanen County are complex and prone to geological disasters. How to prevent and avoid geological disasters in the field of engineering construction, reduce the potential threat of geological disasters, and reduce the possible losses caused by geological disasters, put forward better requirements for the management and technical capabilities of land departments. In the future work, we should take various ways to strengthen the knowledge training of geological disaster prevention, constantly improve the management level of geological disaster prevention in grass-roots land and resources departments, and effectively improve the ability of disaster prevention and avoidance. Further handle the relationship between engineering construction and geological environment, conduct overall management and professional guidance on the construction that may lead to hidden dangers of geological disasters, and prevent the occurrence of geological disasters from the source.