(1. Shanghai Geological Survey and Research Institute, Shanghai 200072; 2. Shanghai Lingang New Town Management Committee, Shanghai 20 1306)

Based on the three-dimensional urban geological survey results of Lingang New Town, this paper analyzes the geological environment characteristics of Lingang New Town and its influence on urban construction, with a view to serve the urban construction of Lingang New Town.

Keywords: geological environment characteristics; Impact assessment; Lingang new city

1 preface

The three-dimensional geological survey of Lingang New Town is a demonstration project of the three-dimensional geological survey of Shanghai. The focus of the work is the engineering geological structure and hydrogeological investigation related to the engineering construction, and at the same time, the geological problems such as land subsidence effect of the fill in Lingang New Town are investigated, and its influence on the construction of the new town is analyzed.

Lingang New Town, located in the southeast of Shanghai, is an important part of Shanghai International Shipping Center, and will be built by Yangshan Deepwater Port in the future. The new town is bounded by Lianggang Avenue and Hulu Expressway, and is divided into four major areas: the main urban area, the main industrial area, the comprehensive area, the heavy equipment industrial area and the logistics park, and the harbor forest is set between the construction land of the four major areas (Figure 1). Upon completion, Shanghai Lingang New Town will integrate modern logistics, port processing, finance and trade, business services, residence and tourism, and create a new image of China port city in the 2 1 century.

Figure 1 Schematic Diagram of Overall Layout of Lingang New Town Planning

2 Lingang New Town Geological Environment Characteristics

2. 1 Geological structure characteristics of foundation

The survey area belongs to the Yangtze block of South China plate, and the whole area is covered by Quaternary and Tertiary. The buried depth of bedrock surface is 220 ~ 340 m, which is shallow in the east and south, and gradually becomes deeper in the northwest. The lithology of bedrock strata is mainly Bailonggang basalt, Jurassic Laocun Formation breccia, lithic tuff and dacite. The fault structure is not obvious and the basement is relatively stable, which has little influence on the engineering construction. The shallow Late Quaternary strata of 100m related to the engineering construction are well developed, and the upper Pleistocene hard soil layer with dark green and brownish yellow marks and the middle hard soil layer are reserved. The shallow muddy clay and soft clay layers are relatively thin, while the sand layer and silt layer are relatively thick, and the overall stratum structure conditions are good, but the disadvantage is that there is a sandy silt layer (engineering geology (2)3 layers) generally distributed near the surface.

2.2 Hydrogeological structural characteristics

The aquifer in the survey area is relatively developed, and the pore aquifer of Quaternary loose rocks in the area includes phreatic-micro confined aquifer and its next five confined aquifers. The groundwater level is generally between 3.23 ~ 4.08 m, and the water level of the first confined aquifer is generally between-1.75 ~- 1.25 m, which is relatively high, which will adversely affect the development of underground space in the planning area. Groundwater in the planning area is not corrosive to concrete foundation, but moderately corrosive to steel structure.

2.3 characteristics of engineering geological structure

According to the Quaternary sedimentary law, the buried distribution characteristics and physical and mechanical indexes of engineering geological strata in the area, and combined with the planning of Lingang New Town, the engineering geological strata with a depth of 100m are analyzed and evaluated.

Layer (1) 1 is loose soil, with a thickness of 0.3 ~ 3.0m, mainly clayey soil, partially containing gravel, bricks and plant roots. The uniformity is very poor, so it is generally not suitable as the bearing layer of the natural foundation of buildings;

The third layer (1) is alluvial soil, which is loose and plastic, with a thickness of 0.4~8.5m and a buried depth of 0 ~ 1.7m at the top. The coastal zone is mainly silty soil with saturated shell fragments, and the shaking response is quick. The western part of the planning area is dominated by cohesive soil, saturated with organic matter. The fill in this area belongs to underconsolidated soil, which has obvious inhomogeneity, and its distribution is characterized by stratification, high water content, weak water permeability, poor drainage consolidation, low strength, high compressibility (Figure 2) and high sensitivity. The standard value of foundation soil bearing capacity is low, the foundation settlement is large, and the settlement difference in different sections is large, which may produce negative friction, which is extremely unfavorable to the project. For projects with pile foundation, the phenomenon of pile caps and foundation soil may also occur, which should be paid attention to.

Fig. 2 Load-settlement curve of filled soil

(2) 1 layer is brownish yellow clayey soil, wet, soft and plastic, with a thickness of 0.5~2.5m, a buried depth of 0.3~2.0m at the top, iron-bearing manganese nodules and iron oxide spots, and a specific penetration resistance of 0.43 ~ 1.74mpa, with medium and high compressibility. As the bearing layer of natural foundation,

(2) The third layer is gray sandy silt, slightly dense and saturated, with a layer thickness of 2.80 ~ 16.30m and a buried depth of 0.6~8.5m at the top. It contains mica and organic spots, with occasional shell fragments. The vibration response is rapid, the specific penetration resistance of static sounding is 3.4 1MPa, and the standard penetration blow count is 65438. Vibration liquefaction of this layer: the non-liquefaction areas are mainly distributed in the east of Luchaogang Town in the southeast of the planning area, Peng Zhen Town in the west, Xingang Town in Vientiane Town and some areas of the planning comprehensive area. Mild liquefaction areas are mainly distributed in the central part of the planning area and the eastern part of the main city. The medium liquefaction area is distributed locally, mainly in the south of Donghai Farm, the east of the comprehensive area of the planning area and the south of Luchaogang Farm. Infiltration liquefaction: it exists in underground engineering construction in the planning area, such as foundation pit engineering, tunnel engineering and pipeline engineering. Attention should be paid to the influence of sand infiltration and liquefaction on engineering.

(4) This layer is gray muddy clay, saturated, with a thickness of 1.50 ~ 12.50m, a top buried depth of 5.8 ~ 19.5m, containing organic specks, mica and shell debris, with a compression modulus of 2.23Mpa and a specific penetration resistance of 0.63Mpa, belonging to coastal-shallow sea.

(5) This layer is mainly gray clayey soil, with a thickness of 2.70 ~ 2 1.50 m and a top burial depth of17.0 ~ 25.3m.. The missing area of layer (6) has a large thickness, and sandy silt lenses are distributed locally. This layer is divided into five sub-layers, (5) 1- 1 gray clay layer, (5) 1-2 gray silty clay layer, (5)2 gray sandy silty soil layer, (5)3 gray silty clay mixed with silty soil layer and (5)4 gray-green silty clay layer. Among them, (5) layer 1- 1 and (5) layer 1-2 are wet saturated, soft and plastic, with high compressibility and low strength, which are the compression layers of buildings with heavy loads. In addition, these two layers can be used as bearing layers of settlement control composite piles because of their moderate buried depth. (5) The second layer is a slightly confined aquifer in the planning area, but its distribution is discontinuous and its thickness is small. However, it may be exposed in large-scale foundation pit excavation and tunnel engineering, and attention should be paid to the phenomenon of sand flow caused by this layer. (5) Layer 3 and (5) Layer 4 are submerged valley strata, which are distributed in the missing area of layer (6). The thickness and buried depth change greatly, and the soil quality is uneven, which is easy to cause uneven settlement of buildings with heavy loads.

(6) Dark green-straw yellow cohesive soil layer, wet, layer thickness 1.50 ~ 7.35 m, buried depth 22.2 ~ 29.0 m, containing iron oxide spots. From top to bottom, the clay content decreases gradually, and the silt content increases gradually. The specific penetration resistance of static exploration is 1.99Mpa, and the layer and its lower part (7.

(7) The yellow-gray sandy silt and silty sand are saturated, and the buried depth of the top layer is 25.0 ~ 50.0 m, and the buried depth of the ancient river cutting area is relatively deep. This layer is distributed in the planning area, with good soil quality, and can be used as the bearing layer of pile foundation for large and heavy buildings.

(8) The second layer is silty clay mixed with silty soil, wet, with a thickness of 3.50 ~ 18.0m and a buried depth of 54.6~73.0m at the top, mixed with a thin layer of silty sand or silty sand blocks, with occasional iron oxide spots and shell debris. The distribution of the planning area is discontinuous, and the buried depth and thickness change greatly.

(9) The sandy soil layer is saturated, distributed continuously, with large thickness, fine particles in the upper part and more clay particles, which are generally sandy silt, and the particles in the lower part gradually become coarse, which is silt or fine sand, with gravel at the bottom. This layer can be used as the bearing layer of the pile foundation of super-large building, but the cost is high because of its deep burial.

See Figure 3 for the schematic diagram of typical engineering geological profile in the survey area.

2.4 Geological disasters

2.4. 1 land subsidence

2.4. 1. 1 current situation

The overall settlement of the planning area of Lingang New Town is smaller than that of the central city. From 1980 to 1995, the cumulative settlement in most areas of the planning area is between 50 and 100 mm, and the average annual settlement is between 3 and 7 mm/a. During the period of 1996 ~ 200 1 year, the land subsidence in the planning area has increased (Figure 4), and the cumulative subsidence is between 50 and100 mm. The annual average subsidence in the northern area is related to a large number of groundwater exploitation. At present, the amount of groundwater exploitation in Nanhui area is controlled and the exploitation is not concentrated, so the land subsidence caused by groundwater exploitation has declined, and the current subsidence rate is basically below 5 mm/a.

2.4. 1.2 trend analysis

Fig. 3 Schematic diagram of typical engineering geological profile of Lingang New Town

Land subsidence in the planning area is mainly caused by groundwater exploitation and engineering construction. Due to the exploitation of groundwater, the construction and transformation of tap water pipe network in this area will continue to develop in a short time; There is a large area of loose fill in this area, and its self-weight consolidation settlement is quite large. According to the preliminary test calculation, for the fill with a thickness of 6m, the complete consolidation settlement can reach 8 ~ 8~ 12.5cm, and the western part of 94 pond in the planning area has been consolidated for a period of time, and the subsequent self-weight consolidation settlement is small; However, the eastern part of 94 pond is newly filled, and the subsequent consolidation settlement will be relatively large.

2.4.2 Scouring and siltation of beaches

The shape of the beach in Lingang New Town remains basically unchanged, and the beach area over 5m has little change in the natural state. The evolution of the beach mainly moves to the southeast, which is consistent with the general trend of the evolution of the Yangtze River estuary.

Generally speaking, the east bank slope of Lu Chao Port is relatively stable, and the erosion and siltation range is small. The south bank slope of Lu Chao Port is characterized by large nearshore slope and flat offshore bed. The water depth between them is about 6 ~ 7m, and their evolution is different. The steep coastal slope eroded from 1958 to 1977, silted from 1977 to 1997, and eroded from 1997 to 2003; The flat seabed outside it rose in 1958 ~ 1989 and eroded in 1989 ~ 2003. The scouring and silting range of the steep coastal slope is about 1.5km horizontally and about 4m vertically. The vertical erosion and deposition of the flat seabed changes about 3m, and the average deposition rate is 1958 ~ 1977, 1977 ~ 1989, 4.3cm/a, 1989 ~ 65438. Since 1997, the steep coastal slope has also changed from siltation to scouring. It can be seen that in recent years, the coastal erosion of Lu Chao Port has been continuously strengthened. In recent 10 years, the seabed of Luchao Port, which is located on the north bank of Hangzhou Bay, is mainly scoured, while the east of Nanhuizui is mainly silted.

3. Analysis of the influence of geological environment on the planning and construction of Lingang New Town

3. 1 Give full play to the advantages of engineering geological structure features and appropriately adjust the urban structure layout.

3. 1. 1 building suitability evaluation

According to the distribution loss of main foundation soil layers that affect engineering geological conditions, Lingang New Town is divided into engineering geological areas, namely (2) 1 layer that affects natural foundation conditions, (1) 3 layers that affect natural foundation conditions, and (6) layers that affect pile foundation conditions (see Figure 5).

I 1 engineering geological section, (2) 1 layer and (6) layer are distributed, and (1) layer is missing. The natural foundation and pile foundation conditions are good, which is suitable for all kinds of buildings and can be arranged according to the needs of urban functions.

Fig. 4 Schematic diagram of cumulative land subsidence in the planning area of Lingang New Town 1996 to 200 1.

Compilation of geological survey results in East China: 1999~2005

There are (1)3 layers and (6) layers in the geological profile, (2) 1 layer is missing, and the formation age of (1)3 layers is greater than 10 year. The condition of pile foundation is good, and the natural foundation condition is general, which is suitable for the bearing requirements of high-rise buildings, heavy equipment buildings and general foundations. Compilation of geological survey results in East China: 1999~2005

There are (1) layers 3 and (6) in the engineering geological section, (2) layer 1 is missing, and the formation age of (1) layer 3 is less than 10 years, so the pile foundation conditions are good. (1) The third layer can't be used as the bearing layer of natural foundation without treatment, so it is suitable for high-rise layout. Ii1engineering geological section, (2) 1 layer distribution, (1)3 layers and (6) layers are missing, the pile foundation condition is poor, and the natural foundation condition is good, so it is suitable to arrange multi-storey buildings (structures);

Compilation of geological survey results in East China: 1999~2005

The engineering geological section is distributed with (1) three layers, and (2) 1 and (6) layers are missing. The formation age of (1) three layers is more than 10 years, and the pile foundation conditions are poor and the natural foundation conditions are general, so it is suitable to arrange multi-storey buildings (structures) with general foundation bearing requirements and landscape greening. Compilation of geological survey results in East China: 1999~2005

The engineering geological section is distributed with (1)3 layers, (2) 1 layer, and (6) layer is missing. The formation age of (1)3 layers is less than 10 year, and the pile foundation conditions are poor. (1) layer 3 can't be used as the bearing layer of natural foundation without treatment, so some should be arranged. 3. 1.2 suitability evaluation of underground space development

There is a sand layer in the shallow part of the planning area, which is thick and stable, and the middle sand layer (5) is scattered, so quicksand may appear in underground engineering construction. It is unfavorable for underground engineering construction. The soft soil layer in the planning area is distributed continuously, with little change in buried depth and thickness, which is easy to deform and has great influence on the slope of foundation pit. For tunnel shield, it is recommended to cross in paragraphs (4) and (5).

Fig. 5 Schematic diagram of engineering geological zoning

3.2 The possible impact of ground subsidence (especially uneven subsidence) on the safety of the new town.

3.2. 1 seawall settlement-flood control safety

According to the analysis of 2.4. 1, the land subsidence caused by groundwater exploitation in the planning area will continue to develop, and the land subsidence caused by self-weight consolidation of fill will also exist, which will make the flood control capacity of seawall decline continuously. Therefore, the elevation lost due to land subsidence should be reserved in the design, and the monitoring should be strengthened to increase it in time.

3.2.2 Uneven settlement-Safe operation of infrastructure (rail transit, underground pipelines)

The "settlement funnel" formed by groundwater exploitation in the planning area and the inhomogeneity of fill in the area will cause uneven ground settlement. Many linear projects in the planning area, such as Pudong Railway and Rail Transit Line 3, pass through the planning area, and a large number of linear projects in the new urban area will be affected by uneven ground settlement in different degrees during construction and operation, which will cause rail transit to be inoperable and pipelines to crack in serious cases.

3.3 Coastal change trend and its impact on urban safety

3.3. 1 Impact on the growth of land resources in the planning area

The planning area is located at Nanhui Beach and the north bank of Hangzhou Bay. Nanhuitan is the main body of the sand mouth on the south bank of the Yangtze River estuary. The confluence of the ebb and flow of the Yangtze River estuary and Hangzhou Bay is the dynamic condition for shaping this sand mouth, and the sediment from the rich basin of the Yangtze River is the material basis for forming this grand sand mouth. In the past 30 years, the Dongtan has been continuously silted, and the annual expansion rate is 40 ~ 90m. However, with the decrease of incoming sediment, the scouring and silting trend of Nanhui Beach will change to some extent. For example, when the Yangtze River is rich in sand, the south bank presents a sand mouth shape; When the amount of incoming sand decreases, it turns into an arc. The former is deposited on the beach and the latter is washed away. According to the forecast results, Nanhui Dongtan will still be silted, but the siltation rate will decrease and the scouring trend on the south bank will increase, which will seriously affect the land reserve resources. However, the phenomenon of high beach erosion began to appear at the eastern end of the northern shore of Hangzhou Bay in the middle and late 1970s, and it was promoted from east to west year by year. By the middle of1980s, the beaches in Fengxian had changed from siltation to erosion. In the future, with the decrease of sediment sources in the south bank of the Yangtze River estuary, the sediment transport capacity of tidal current will be enhanced, the beach erosion will obviously retreat, and the beach resources will gradually decrease. Moreover, the first-stage silt-promoting dam of artificial peninsula in Lu Chao Port prevented some sediment from moving to the north shore of Hangzhou Bay, reduced the sediment entering the west of Luchao Port, and enhanced the scouring effect on the north shore of Hangzhou Bay, thus affecting the growth of beach resources on the north shore.

3.3.2 Impact of beach scouring and silting on coastal engineering construction

The impact of beach scouring and silting on revetment structure is mainly the impact of scouring on its safety. According to the existing results, the safety factors of various seawalls will be reduced before and after 1m, and the reduction range is between 1 1%- 15%, thus affecting the safety of seawall structures. The influence of beach scouring and silting on bridge structure mainly lies in the decrease of mud level line, which leads to the decrease of bearing capacity of pile foundation and the increase of foundation deformation, further affecting the internal force of structure and foundation. According to the forecast, the coast of Hangzhou Bay in the planning area will be in a state of erosion, and attention should be paid to the influence on the pile foundation engineering of Donghai Bridge.

4 countermeasures

(1) In Area I of engineering geological division, the buried depth of the 6th and 7th floors is moderate, which is a good area for bearing stratum of pile foundation; The second area lacks 6 floors and 7 floors are buried deeply, and the pile foundation with 7 floors as the bearing layer is expensive. According to the geological conditions of the planning area, the location of buildings and structures or the type of foundation can be adjusted appropriately, and the bearing layer of pile foundation can be selected as five layers. Under the condition of satisfying the use and safety, the construction cost is saved. There is a large area of loose fill in the planning area. According to the characteristics of the proposed project and the soil quality of the fill, appropriate methods are adopted for treatment. Soft soil layer (4) in the planning area can be seen everywhere, which is easy to deform. In the process of foundation pit excavation and underground engineering construction, monitoring should be strengthened so as to take timely measures.

(2) The land subsidence in the planning area is developed, and the land subsidence (especially uneven subsidence) has a serious impact on the infrastructure (rail transit, underground pipelines, seawalls, etc.). ). It is suggested that a land subsidence monitoring network should be established in Lingang New Town to monitor the land subsidence dynamics and take preventive measures in time.

5 concluding remarks

The three-dimensional urban geological survey of Lingang New Town is a demonstration project and an exploration of Shanghai's three-dimensional geological survey, but there are still many shortcomings. This survey is mainly based on engineering geological survey, and has achieved certain results, which can better serve the engineering planning and construction of Lingang New Town. In the process of investigation, the Geodetic Center gave great support, and I would like to thank you!

refer to

[1] China Geological Survey. Compilation of geological survey standards: hydrological, engineering and environmental geological survey and exploration.

Zhang et al. Beijing: Geological Publishing House, 1986.

[3] Code for Geotechnical Engineering Investigation (DG J08-37-2002). Shanghai code for engineering construction.

Geological environment characteristics of Lingang New Town and its influence on construction

Yan Xuexin 1, Shao Jingfang 2, Chen Hongsheng 1, Shi Yujin 1

(1. Shanghai Geological Survey, Shanghai 200072; 2. Shanghai Lingang New Town Management Committee 20 1306)

Abstract: Based on the three-dimensional geological survey results of Lingang New Town, this paper analyzes the geological environment characteristics of Lingang New Town and its influence on urban construction. The purpose is to provide reference for the construction of Lingang New Town.

Keywords: geological environment characteristics; Impact analysis; Lingang new city