He Junmei, Lu Yaodong, Chen Huichuan, Liang Jiahai, Liang Xiangyang
(Guangdong Geological Survey Institute, Guangzhou 518)
According to the geological survey results in recent years, it is considered that the 1: 25, ecological environmental geological survey in the Pearl River Delta Economic Zone is in the development trend of urbanization, the characteristics of human activities, the fragility of geological environment and environmental geological problems.
Keywords vulnerability of geological environment Environmental geological problems Sustainable urbanization Pan-urbanization Pearl River Delta Economic Zone
The Pearl River Delta Economic Zone is located in the south-central part of Guangdong Province, bordering the South China Sea and Hong Kong and Macao. It is one of the three most developed economic units in China's coastal areas and one of the most densely populated areas. There are only a handful of floating population in China, urban-rural integration is basically realized, and the rapid urbanization process is rapid. A series of environmental geological problems are increasingly becoming the social and economic sustainable development in this area.
In recent years, under the unified arrangement of China Geological Survey, Guangdong Geological Survey Institute organized and implemented the 1 ∶ 25, Eco-environmental Geological Survey of Pearl River Delta Economic Zone. Based on the results of this project, this paper summarizes the progress of environmental geological survey in recent years.
1 understanding of the development trend of urbanization and the characteristics of human activities
Urbanization trend is the most important physical feature of social and economic structure change and the objective manifestation of social form developing to the highest level, and urbanization level is a prominent symbol of the modernization degree of a country or region. Since the reform and opening-up, the Pearl River Delta Economic Zone has experienced a historic socio-economic leap, with rapid progress in industrialization, rapid rise of urban agglomerations with Guangzhou and Shenzhen as the core, interactive development of the overall level of urbanization, village "market town", market town "town town", county towns and small cities "metropolis" and large and medium-sized cities "internationalization". Since 1995, the vast rural areas in this area have reached the mature stage of urbanization, urban-rural integration has basically been realized, and the degree of urbanization and internationalization has been continuously improved. After more than 2 years of development, the Pearl River Delta Economic Zone has concentrated two megacities, Guangzhou and Shenzhen, nearly 1 large and medium-sized cities, more than 2 county-level central cities and more than 4 established towns, and the trend of pan-urbanization has gradually emerged (Figure 1). Although in terms of urban connotation, the mature rural urbanized areas in the region are not cities in a strict sense, and there is a huge difference between "permanent population" and "registered population", in terms of land landscape, the whole region has formed a very extensive metropolitan area, and after the core area of Pan-metropolitan area matures, there is a trend of continuous expansion to the surrounding areas, and the extended non-Pearl River Delta areas are gradually integrated with the Pearl River Delta. With the influence and drive of the Delta on the surrounding areas,
under the trend of pan-urbanization, human activities in this area have obvious regional characteristics.
(1) Human activities have increased. It has been expanded from farming activities, mining activities, land reclamation, embankment construction, etc. to the sketch map of the urbanization pattern of the Pearl River Delta Economic Zone extracted from the remote sensing image in Figure 1
Description: the map is within the built-up area, and the pan-urbanization of the Buddha, Guangzhou, Dongguan and Shenzhen areas is clearly visible.
Urban development and economic construction are closely related, and human activities now cover the utilization of various space resources on the surface of the earth.
(2) The effects of human activities are multiple. And different types of human activities may cause the same type of eco-environmental geological problems. For example, the area reclamation project may cause siltation in estuaries and ports, wetland changes, coastal mangrove ecosystem degradation and salt tide upwelling; Mine development causes surface water pollution, groundwater pollution and soil pollution as well as agricultural activities.
(3) The human activity space has both aggregation and diffusion. Human activities are mainly concentrated in the metropolitan area in the overall planning of social development in this area, which generally includes Guangzhou (excluding Zengcheng and Conghua), Dongguan, Shenzhen (including Baoan District), Foshan (Chancheng District, Nanhai District and Shunde District), Zhongshan, Jiangmen (urban area and Xinhui District) and Zhuhai (including Doumen District). Human activities in the plain area are mainly urban construction activities, linear projects such as railways and highways, point projects such as landfill sites, and agricultural activities; The development and utilization of environmental resources, such as building materials, minerals, slopes, etc., are given priority to in hilly-Taiwan areas and hilly-low mountainous areas; The coastal zone is dominated by area reclamation projects and the development and utilization of beach resources.
(4) The intensity of human activities tends to be stronger. After the reform and opening up, especially since 199, the intensity of human activities has been increasing day by day. The data of three phases listed in Table 1 and Table 2 reflect the trend of increasing human activities. Judging from the results of remote sensing interpretation in the eastern part of the economic zone, urbanization is expanding on a large scale, and the urban construction area has increased from 8.6% in 199 to 14.8% in 2, nearly doubling < P >. The cultivated land area has been decreasing from 19% in 199 to 13.6% in 2 (Table 3). With the signing of the "9+2" Pan-Pearl River Delta Cooperation Framework Agreement, the pace of urban development in this area will be further accelerated. According to the statistics of urban planning area, by 21, the urban area of the whole region will exceed 1.×14 km2, and the non-agricultural construction land will reach 1.5×14 km2 (accounting for more than 1/3 of the total land area of the whole region). At that time, more than 7% of the flat land in the whole region will become construction land. It can be predicted that human engineering activities will be unprecedented in the next few years or even decades.
Table 3 Comparison of NDVI index zoning values between 199 and 2
Percentage of NDVI value zoning types in total area in 199 (%) and percentage in total area in 2 (%)
-1~-.5 Water bodies (rivers, lakes and seas) 24.3 24.1
- Cultivated land and aquaculture 19.4 13.6
.5~.75 bamboo forest, shrub and grassland (vegetation) 25.4 24.9
.75~1 forest (vegetation) 22.3 22.6
(5) Human activities are becoming more and more orderly. The disorder of human activities will be alleviated. The so-called disorder refers to the situation that human activities are blind, do not consider the consequences, and lack guidance and supervision, which easily leads to eco-geological environment variation and leads to eco-environmental geological problems. With the improvement of education level, the strengthening of people's environmental awareness, the improvement of legal system and supervision system and the development of related technologies, human activities will be standardized, so that disorderly activities will be curbed to a certain extent. Nevertheless, large-scale planned human activities still need to fully consider the possible consequences.
2 vulnerability of geological environment: from the geological point of view, environmental geological problems
Human activities are the external cause of the formation and development of environmental geological problems, while vulnerability of geological environment is its internal cause. Understanding the vulnerability of geological environment is undoubtedly helpful to the study of environmental geological problems. The vulnerability of geological environment in the Pearl River Delta Economic Zone is mainly reflected in the following aspects.
2.1 The residual soil layer in the bedrock area is relatively developed
The bedrock area in this area accounts for about 6% of the total land area, among which the magmatic rock distribution area dominated by intrusive rocks (granitoids) accounts for about one third. Due to the strong weathering of rocks, residual soil layer is developed in bedrock area. Granite distribution area is mainly prone to soil erosion because of the high content of unstable minerals such as feldspar and mica (generally about 7%) and the thick residual soil layer (> ＞2 m). Except for the weathered residual soil in the middle and high mountains and coastal islands, the hilly-terrace area is generally more than 5 m; The residual soil in the distribution areas of metamorphic rocks and volcanic eruption rocks is mostly clayey soil mixed with breccia debris, and its thickness is generally less than ＜3 m, so the debris flow in the distribution areas is prone to occur.
2.2 The soft soil layer is generally developed in the Quaternary loose sediment area
The Quaternary loose sediment layer is widely distributed in the Pearl River Delta Economic Zone, accounting for about 2/5 of the land area in this area, and the genetic types include alluvial, diluvial, alluvial, marine and alluvial. Alluvial, diluvial and alluvial-diluvial deposits are mainly distributed in mountain valleys and river terraces at the edge of the delta, generally less than 1 m thick, and often have a dual structure. The upper part is medium-fine sand or silty sand clay, and the lower part is coarse gravel with carbonized wood blocks. The 14C age of peat soil formed by the first terrace alluvial is 758 17A. The alluvial deposits and marine deposits are widely distributed in the delta plain and coastal areas, and are mainly the products of the interaction between bay deposits and coastal river alluvial deposits in the middle and late Holocene transgression period, with an average thickness of 25.1 m and a maximum thickness of 63.6 m. The upper reaches are mainly grayish yellow or grayish brown silty clay and muddy clay, and the lower reaches are mostly dark gray silty silt and silt.
the distribution area of soft soil is nearly 8 km2, accounting for about one-fifth of the total land area of the whole region. Among them, the delta plain with the densest cities and towns is the most widely distributed area, and the distribution area of soft soil accounts for 82.25% of the total distribution area of soft soil in the economic zone. From the tip of the Pearl River Delta to the estuary, the thickness of soft soil increases, the layers increase, the degree of consolidation deteriorates, the cause of formation changes from floodplain to marine phase, and the lithology changes from muddy soil phase to silt. According to the drilling data, 14C dating and sporopollen analysis results, the soft soil in the delta can be roughly divided into three layers in the vertical direction, which respectively correspond to the three major transgressions that occurred in the delta during the late Pleistocene-Holocene. The younger the sedimentary age, the greater the thickness of the soft soil, the greater the water content, liquid limit, liquid index and porosity ratio, while the older the sedimentary age, the greater the mechanical strength, showing that the compressibility decreases, compressive modulus and cohesion increase (. Under the influence of natural power or human activities, soft soil layer is easy to produce ground subsidence and cause harm to the ground and engineering buildings.
in addition, the distribution area of easily liquefied sandy soil in the delta river network area and Huizhou section of Dongjiang River is 213 km2, the buried depth is generally 1.5~12.8 m, the thickness is 1.5~1.5 m, and the SPT count is 2.3~7.4. Loose and saturated silty sand, fine sand and silty soil are prone to liquefaction and damage to the ground and engineering buildings once subjected to dynamic loads (earthquake, piling, blasting and mechanical vibration).
table 4 geological characteristics and physical and mechanical properties of soft soil in the pearl river delta
main characteristics of silt layer deposition period, main physical and mechanical properties of roof depth and thickness (average value)
the average maximum wWL ILEA1-2ESC
m%%-MPa-1mpa kPa
The shell debris in the first layer at the end of Holocene was . ~ 5.1.5 ~ 21.99.542.76.245.71.89 1.66 1.44 2.45 6.9
The second layer. In modern times, it contained oyster shells, often mixed with silty fine sand 2.6 ~ 2.81.5 ~ 11.6.37.5 5.64.11.64 1.34 .97 3.76 11.77 < P > The third layer contained shell fragments in the late Late Pleistocene. Floodplain saprophytic wood 5.3 ~ 24. .6 ` 7.9 3.7 2.4 42.3 38.6 1.26 1.18 .75 5.1 13.79 < P > 2.3 Neotectonic movement is active < P > Neotectonic movement has been active since Late Cretaceous-Tertiary, mainly inherited activities. According to the geological records of Guangdong Province, there are NE-NNE trending Lianhuashan deep fault zone, Zijin-Boluo fault zone, Dongjiang fault zone, Enping-Xinfeng deep fault zone, Wuchuan-Sihui deep fault zone, EW trending Gaoyao-Huilai deep fault zone, NW trending Xijiang big fault zone and Zhuhai-Xindu big fault zone in this area [4]. Gaoyao fault, Enping-Cangcheng fault, Jinji-he cheng fault, Guangzhou-Gulao fault, Guangcong fault, Guangsan fault, Shenzhen fault, Pinghai fault, Tanghu fault, Chishi-Shatian fault, Xijiang fault, Shajiao fault and Yamen fault are still active. For example, according to the monitoring data of Seismological Bureau, the activity of Guangcong fault was 26.5 mm from 1973 to 1979, with an average annual activity rate of 4.4 mm；; In March 1998, the maximum variation of the height difference between the two plates of the Guangsan fault in Guangzhou City was 3.34 mm, and that of the Hengkengli section of the Xijiang fault was 2.38 mm in November 1997, with an average activity rate of .56 mm/a from 1991 to 1995. The monitoring results of Shenzhen Geological Bureau in recent five years show that ① the Shenzhen fault is in a state of slow stress creep, with a tendency creep rate of .17 ~ .35 mm/a..
2.4 karst development of concealed carbonate rocks
The distribution area of carbonate rocks around Zhaoqing City, Guanghuapudi, Enping-Kaiping, Longgang District of Shenzhen City, Danshui Town of Huiyang City, Aipi Town and Paitan Town of Zengcheng City is 1 474 km2, but most of them are covered by Quaternary loose sediments. Carbonate rocks are mainly produced in Ordovician Luohong-Luodong Formation, Devonian Tianziling Formation, Chunwan Formation-Tianziling Formation, Carboniferous Lianxian Formation, Shiqiezi Formation (Cs), Tanshui-Zimenqiao Formation, Zimenqiao-Dabu Formation, Dapu Formation, Hutian Group (CH) and Permian Qixia Formation, with Hutian Group and Shiqizi Group as the main components. Take Guanghuapen Land as an example, the thickness of Quaternary loose sediment is generally 1~25 m, the surface is mainly cohesive soil (locally silt), and the bottom is often in contact with limestone, and the karst strong development zone is located at the elevation of -2~-8 m underground. The hydrogeological conditions and geotechnical structure in the concealed karst area are very conducive to the formation of ground collapse.
2.5 engineering fragility of soft rock
mudstone, sandy mudstone, shale, carbonaceous shale, coal, shale are often sandwiched in Cretaceous-Tertiary red beds distributed in Gaoyao-Sanshui-Guangzhou-Dongguan, Enping-Kaiping, Huizhou, Boluoyang Village, Huiyang, Huidong-Baipenzhu and Jurassic-Carboniferous coal measures distributed in the delta margin. The exposed surface of this kind of rock is easy to be weathered, and it often swells and is easy to soften when soaked in water. The softening coefficient is .26~.5, and the saturated compressive strength is .14~1.2 MPa. Among them, gypsum and salt rock are easy to produce dissolved holes or ditches under the long-term groundwater dissolution. If these rocks are selected as the bearing stratum of the foundation, the buildings are prone to slip and uneven deformation of the engineering foundation, and the mountain and the slope of the engineering construction site will produce geological disasters such as landslides along the weak surface, so this kind of rock stratum is unfavorable to the engineering construction.
3 environmental geological problems: genetic classification and socio-economic impact
the process of urbanization is a process of population agglomeration, industrial agglomeration, economic growth and social production and lifestyle change, as well as a process of large-scale resource consumption, spatial agglomeration, destruction of natural landscape pattern and formation of urban landscape pattern. On the one hand, socio-economic development and urbanization are constrained by the fragile factors of geological environment, on the other hand, they are inevitably triggered by human economic-engineering activities.