Driving effect of engineering construction on geological environment change

Engineering construction, especially large-scale engineering construction, plays a great role in promoting China's social and economic development. Since the founding of New China, especially since the reform and opening up, China has built a large number of water conservancy projects, traffic projects and energy projects, which have produced remarkable economic and social benefits. The mileage of railways and highways in China has increased year by year. From 1949 to 2008, the railway mileage increased from 2 1800 km to 79,700 km, with an average annual increase of 2.2%. Highway mileage increased from 80,700 km to 3,730,200 km, and from 1949 to 1999, with an average annual growth rate of 5.8%. After 1999, highway construction accelerated, and the average annual growth rate increased to 1 1.5%. China started to build expressways from 1988. By 2008, the total mileage reached 60,300 kilometers, with an average annual increase of 3,000 kilometers. By the end of 2008, there were 86,353 reservoirs in China, including 529 large reservoirs 1 10,000 m3, 365,438 medium reservoirs 1 10,000 m3, and medium reservoirs 1 seat 1 10,000 m3. From Figure 3- 17 and Figure 3- 18, it can be concluded that China's railway construction has maintained a steady development trend, and highway construction and water conservancy construction have accelerated after 1999. On the whole, the impact of engineering construction on geological environment has intensified.

Figure 3-Schematic diagram of railway and highway mileage growth in China in 2008.

From a regional perspective, there are great differences in engineering infrastructure in different regions, and the impact intensity of engineering construction on geological environment is obviously different. Taking highway construction as an example, the average highway density in China is 0.39Km/Km2, and the average highway density in eastern coastal areas is much higher than that in western areas (Figure 3- 19). The provinces with average highway density greater than 1.40Km/Km2 are Shanghai, Jiangsu, Henan and Shandong in turn, which shows that the highway construction in these four provinces has developed rapidly and the transportation infrastructure is relatively perfect. The density of highways in Chongqing, Beijing, Anhui, Tianjin, Guangdong, Hubei and Zhejiang provinces exceeds 1.00Km/Km2, which is close to the level of developed countries. However, the highway density in Shaanxi, Hainan, Yunnan, Jilin, Guangxi, Heilongjiang, Ningxia and other provinces is less than 0.60Km/Km2, which shows that the highway construction in these provinces still has great potential.

Figure 3- 18 to 0985 ~ 2008: Changes of the number of large and medium-sized reservoirs and small reservoirs in China.

Figure 3-19 Schematic Diagram of Regional Highway Density Distribution in China in 2008

Engineering construction activities have disturbed the crust surface to varying degrees, especially large-scale engineering activities often have a strong and far-reaching impact on the geological environment, resulting in various geological environmental problems and even geological disasters. Large-scale reservoir construction will generally flood a large area of cultivated land, greatly changing the original hydrological and ecological conditions, thus changing the geological environment elements, and easily inducing problems such as bank reconstruction and reservoir siltation. For example, after the completion of Sanmenxia Reservoir, the bank collapse is very serious, and the sedimentation rate of the reservoir is accelerated, so it is necessary to add a sediment discharge project at the bottom of the dam. Large-scale engineering construction has changed the stress balance of geological bodies and easily induced geological disasters. Many railways in China, such as baoji-chengdu railway, chengdu-kunming railway, yingtan to Xiamen, etc. Most of them pass through mountainous areas, with strong weathering of rocks, developed cracks and steep slopes, and a lot of slope cutting and tunnel excavation works have been carried out along the line. After the completion of the railway, it suffers from landslides and mudslides every year, causing subgrade damage, traffic disruption and serious economic losses. After the start of the western development, all kinds of engineering construction have caused secondary geological disasters, such as collapse and landslide, man-made debris flow, surface water and groundwater pollution. The geological environment capacity is facing severe challenges. According to statistics, in recent years, geological disasters induced by engineering construction activities account for more than 5 1% of the total number of geological disasters, and 50% or even 70% of geological disasters along the railway are related to improper excavation or support [12].