Main geological disasters in Shandong Peninsula urban agglomeration area

When discussing regional stability above, earthquake disasters have been involved. Earthquake is also an important geological disaster. In the discussion on water resources, the problems of drought and flood disasters in Shandong Peninsula are also analyzed. This section focuses on other major geological disasters in Shandong Peninsula.

Geological disasters are inevitable phenomena in nature. Improper development or failure to prevent it will stimulate, accelerate or aggravate the occurrence and development of geological disasters and increase their harmfulness. Geological disasters in nature include slowly changing geological disasters, such as seawater intrusion, land subsidence and collapse. And sudden geological disasters, such as landslides, mudslides, karst collapses, etc. , the following brief analysis.

1. Seawater invasion disaster

In coastal areas, seawater intrusion often occurs, which makes land groundwater polluted by seawater, increases salinity and loses its value as drinking water and industrial and agricultural water supply. Seawater intrusion will also destroy the mechanical properties of rock mass and increase the risk of disasters such as landslides. Seawater intrusion will also enhance karstification of carbonate rocks, and so on.

Seawater intrusion is a common phenomenon around Bohai Sea (Figure 18). In fact, except for a few areas where seawater completely invades (1 area in Figure 18), most of them are areas where seawater invades and groundwater mixes, forming a mixed zone of saline water and brackish water, and its influence width exceeds 1km to 15km.

Figure 18 Current Situation of Seawater Invasion in Bohai Rim Region (According to Sun Xiaoming, 2005)

Laizhou is an important seawater intrusion area. After the groundwater continuously meets and mixes with the invaded seawater through the seepage path of 32km, the groundwater salinity can be changed from 150g/L to 2g/L brackish water (Figure 19). See Figure 20 for the change of groundwater salinity in Dawang-Yangkou.

Figure 19 Profile of groundwater salinity change from Guti to Yangzi area in the south bank of Laizhou Bay (according to Xu Jianguo, 2005).

Fig. 20 Profile of groundwater salinity change in Dawang-Yangkou (according to Xu Jianguo, 2005).

Seawater intrusion in the south bank of Laizhou Bay began in the late 1970s, and seawater intrusion occurred in some areas. Later, in the early 1980s, Weifang, Long Island, Cook and other places strengthened the exploitation of groundwater resources. In addition, the construction of reservoirs in the middle and upper reaches of rivers reduced the supply of surface water, induced a large number of seawater intrusion, and made the interface between salty (seawater) and fresh water (groundwater) migrate to land, forming a broad mixed zone of seawater and fresh water, which mineralized the original fresh groundwater.

See Table 29 for the relationship between groundwater overexploitation and seawater intrusion in Laizhou Bay.

Table 29 Groundwater Overexploitation and Seawater Intrusion in Laizhou City

(Institute of Marine Geology, China Geological Survey)

Laizhou 1976 seawater intrusion area is15.8km2; By 1989, the seawater intrusion area has accounted for 1 1. 12% of the whole city area, and the intrusion speed has increased from 46m/a to 404.0 m/a; By 200 1, the seawater intrusion in Laizhou City has reached 260km2 (Ping Li, 2004); At present, the seawater intrusion area is 304km2. According to the preliminary statistics of 1976 ~ 1989, the cumulative groundwater exploitation in Laizhou Bay area is 38× 108m3, the average groundwater level drops by about 15m, the groundwater funnel area reaches 2000km2, and the negative area below sea level is 1600km2.

The seawater intrusion area in Longkou City is 78.4km2, and Yantai has been exploiting groundwater since 1970s. Due to seawater intrusion, the chloride ion content in groundwater has changed from 0. 13g/L to 198 1 year to 1.7g/L and 1989, and the seawater intrusion line has reached 850m.

The seawater intrusion area of Qingdao reached 95.6km2, which also started in 1970s. 198 1 ~ 1988, the peak of seawater intrusion in Dagu River Basin moved inward by 750m ... The exploitation of groundwater resources began at 198 1 year, and an area of about 100km2 was formed in Ligezhuang area. 1990 due to the water diversion project from Guizhou to Qingdao, the amount of groundwater exploitation decreased, and the funnel was leveled in the wet season of 1994.

Other areas in Qingdao, such as Chengyang River in the lower reaches of Baisha River and Xin 'an in Huangdao, also have seawater intrusion. Together with Jiaonan, jiaozhou city and pingdu city, the seawater intrusion area of these places has reached1.59km2.

The total salinity of the Bohai Sea is 34.4g/L, and that of the Yellow Sea is 33.33 g/L. After the seawater in Dalian is mixed with fresh water with a total salinity of 0.62g/L, the total salinity of underground salt water is 8. 14g/L, which is composed of 76.78% karst fresh water and 23.22% seawater (Lv Yaoru,

Study on Geological Ecological Environment and Sustainable Development in Shandong Peninsula Urban Agglomeration Area

Where: Vf, Vb, Vs—— When brine with the volume of Vb is formed, the corresponding volumes of groundwater and brine are Vf and VS (L); CClf, CClb and CCLS-chloride ion content in fresh water, mixed brine and seawater respectively.

In Laizhou Bay area of Shandong Peninsula, the salinity of brine reaches 50 ~ 150 g/L, which is not the total salinity of seawater itself, but actually the brine after evaporation and concentration. That is to say, after seawater infiltration, the groundwater is concentrated by natural and artificial evaporation, and the salinity reaches 50 ~ 220 g/L, including the brine accumulated by underground evaporation after the invasion of ancient seawater. From this numerical point of view, the seawater intrusion in Laizhou Bay is superimposed on the influence of ancient seawater intrusion.

The seawater intrusion area along the southeast coast of Laizhou Bay increased sharply from 1979 to 1993, and the area expansion rate decreased slightly in recent years (Figure 2 1).

Figure 2 1 Variation of seawater intrusion area along the southeast coast of Laizhou Bay (according to Xu Jianguo et al., 2005)

Seawater intrusion also occurs in coastal cities around the world. The content of Cl- ions in groundwater can be used as an index of seawater intrusion intensity. The intensity of seawater intrusion in Dalian area on the north shore of Bohai Sea has been discussed earlier. The following lists the increase of Cl- ions caused by seawater intrusion in some foreign areas.

Table 30 Cl- content in seawater of some coastal countries (regions) in the world

The seawater intrusion in Laizhou Bay area is serious, including the groundwater formed by the infiltration of high concentration brine.

2. Land subsidence disaster

Land subsidence was found at 1985 due to the exploitation of oil and gas resources and groundwater resources in Dongying City, Laizhou Bay. The seismological department has used large-scale precise leveling to retest the crustal deformation law. The results show that the hilly area of Lubei Plain, the southern bank of Laizhou Bay and the eastern part of Chengning Uplift have been in a uplift state for decades. The largest uplift area is in the uplift area of Jiaobei fault block, with a rising rate of 4 ~ 8 mm/a, and the largest land subsidence of Dongying-Kenli is 80mm, with a subsidence rate of 4 ~ 8mm/a north of Lijin County. In 2000-2003, the land was re-surveyed, and it was found that the land subsidence was 248-397 mm. In 2002-2003, there were 43 observation points of land subsidence in Dongying City, and the subsidence exceeded/10 ~30mm-30 mm.

Land subsidence is bound to induce or aggravate seawater intrusion, and large groundwater drop funnels in other areas of Laizhou Bay also have the problem of aggravating seawater intrusion.

3. Ground subsidence in mining area

Land subsidence is a relatively slow deformation process, and land subsidence is mainly caused by mining, with a slow development process and a sudden phenomenon. The coal, gold, iron and other mineral resources in Shandong Peninsula have caused many land subsidence phenomena, especially the large-scale caving mining method in coal fields, which has caused more serious land subsidence and subsidence. See table 3 1 for the general situation of land subsidence in the mining area of Shandong Peninsula urban agglomeration.

Table 3 1 Overview of Land Subsidence in Mining Area of Shandong Peninsula Urban Agglomeration

(Shandong Provincial Department of Land and Resources)

At present, some closed mines have been reclaimed. In the process of mining, tailings and dumping sites have a great impact on the environment and need to be treated. Generally speaking, the relative impact of mine environmental problems of coal mines, gold mines and iron mines in Shandong Peninsula urban agglomeration area is less than that in the northern wing of Bohai Sea, but it is also a geological disaster that needs attention in the future.

The geological disasters caused by groundwater exploitation in Shandong Peninsula are comprehensively evaluated, as shown in Figure 22.

4. Landslide and debris flow geological disasters

Landslide, collapse and debris flow are common geological disasters, which often occur in Shandong Peninsula. Landslides, mudslides and other disasters are mostly sudden, which is easy to cause sudden disasters. However, there are many corresponding signs of early deformation, such as cracking of rock and soil along the trailing edge, extrusion uplift of landslide leading edge, or a small number of landslides, caving and other precursor phenomena.

Fig. 22 Evaluation of the impact of groundwater-induced disasters on environmental quality in Shandong Peninsula urban agglomeration (Photo courtesy of Shandong Provincial Department of Land and Resources)

1648, the Tancheng-Juxian earthquake induced a landslide with a volume of 480× 104m3. Recently, a landslide occurred in Mashan, Changqing, Jinan, with a length of 600m, a width of 500m, an average thickness of 15m and a volume of nearly 300× 104 m3, all of which are large-scale landslides. In Shiya Village, Xiying Town, Licheng District, Jinan City, after the rainstorm in August, 2000, there were 35 landslide spots on the hillside, which formed debris flow, washed away farmland for 4hm2, killed 50 livestock, washed away 7 bridges and more than 3,000 trees. During the period of 1998, mudslides also occurred in mountainous areas of Zibo, which washed away more than 20 hectares of cultivated land, 270 hectares of crops, optical cables and power supply lines.

See Table 32 for geological disasters such as landslides in Shandong Peninsula urban agglomeration. The scale of collapse, landslide and debris flow in Shandong Peninsula is much smaller than that in western China. The most important thing is to reduce and avoid such disasters, which need to be monitored and discovered as soon as possible, so as to provide basis in time and take corresponding measures to prevent them. The most important point is that in the process of engineering construction, special attention should be paid not to excavate at will to avoid geological disasters such as landslides and mudslides caused by the destruction of the stable slope angle of rock mass in natural state.

Table 32 Overview of Collapse, Landslide and Debris Flow in Shandong Peninsula Urban Agglomeration

(Shandong Provincial Department of Land and Resources)

5. Karst collapse disaster

In carbonate rock distribution area, long-term over-exploitation of karst groundwater will make the karst groundwater level drop continuously, and lead to the change of hydrodynamic conditions of karst water and overlying Quaternary pore water, which will affect the stability of rock and soil, thus inducing karst collapse. At present, karst collapse in central and southern Shandong mainly occurs in Tai 'an, Zaozhuang, Laiwu and other places, which is very harmful.

Karst ground collapse in Tai 'an City (1)

It mainly occurs in the old county town of Tai 'an, the railway triangle and Jianguanzhuang in the eastern suburb. From 1970 to 1994, there were 52 collapses125km2. The collapse diameter is generally 1~6m, and the maximum is 1 ~ 6m. The buried depth of the railway triangle is 4 ~ 8m, and the buried depth of Jianguanzhuang area is 2 ~ 5m. The ground collapse in the old county led to the cracking and collapse of houses in nine villages. In the early 1990s, the speed of trains passing through this section in beijing-shanghai railway was limited to 5 km/h. Later, after investigation and treatment, such as using jet grouting piles, grouting, interlocking railway tracks and controlling groundwater exploitation, the karst collapse disaster in this area was controlled.

(2) Karst ground collapse in Zaozhuang City.

It mainly occurred in Shiquan water source, Dingzhuang-Dongwangzhuang water source and Dalu Lane in Xuecheng District, and accumulated 200 collapses from 1980 to 1996. At present, the distribution area of collapse is 25km2. Most collapses are point ellipses with a diameter of 3 ~ 10m. The largest collapse pit near the west bridge of Dongwangzhuang is 80m long, 60m wide and 1.5m deep.

The occurrence of collapse cracked the floors and walls of some villagers' houses, which brought certain threats to people's lives and property. At the same time, the groundwater level drops sharply, which leads to the sewage discharged along the river infiltrating into the ground and polluting the karst water.

(3) Karst collapse in Laiwu City

Karst collapse mainly occurs in the iron ore area around Zhengongqing-Xiquanhe, which is caused by long-term exploitation and discharge of karst groundwater in iron ore production and local industrial and agricultural production. During the period from1973 to1997, karst collapse occurred 139 times, with a maximum diameter of 35m and a maximum depth of 13m, with a cumulative collapse area of 6435.0m2.

In this karst subsidence area, houses in 13 villages were damaged to varying degrees. Among them, 199 households 100 1 houses were seriously damaged, and the crack width exceeded 4cm, so they were forced to move.

In addition, there are some large-scale karst collapses in Linyi City, Yiyuan County, Pingyin County, Mengxian County and Mengyin County, which have caused great economic losses.