Research On Engineering Geological Conditions In Nantong Area According To The Properties Of Soft Soil

The soft soil in the coastal area has the characteristics of high water content, high compressibility, low permeability, low bearing capacity and so on. As the use of the engineering site, its weak strength, poor stability, foundation deformation, ground settlement and other engineering hazards are common and outstanding. Therefore, the engineering properties of soft soil is an important research topic in the field of geotechnical engineering.The soft soil in Jiangsu coastal area is mainly distributed in the coastal areas and the coastal areas of the Yangtze River, which has the trend of thickening from the west to the East, from the south to the north; Based on a large number of borehole data and geotechnical test data, this paper analyzes the engineering characteristics of soft soil in Nantong area.The results show that the water content, porosity, density, compressibility and so on of soft soil in Nantong area are related to the buried depth: Overall water content, void ratio and compression coefficient decrease with the increase of depth, the mass density and compression modulus increased with the increase of depth. This correlation is more obvious with the increase of depth. According to the test results of the physical and mechanical properties of the soft soil in the area, water content and void ratio, void ratio and density, liquid limit and plastic limit, compression coefficient and water content have significant linear relationship, in which the results of regression analysis between water content and void ratio are very close to the theoretical conversion between the two. On the other hand, the spatial distribution of the physical and mechanical properties of the soft soil in the area has the following characteristics: The water content, void ratio, compression coefficient and cohesive force of the soft soil(upper soft soil) with a depth of less than 10 m are gradually increasing from inland to coast, however, the compression modulus and dry density are gradually reduced from inland to the coast. The spatial distribution of the physical and mechanical indexes of the soft soil layer(lower soft soil), which is larger than 10 m, is more complicated. The lower soft soil has a certain distribution law in a small range, but the overall law is not obvious.In this paper, the microstructure of undisturbed soil samples of different buried deep soft soil layers was analyzed. The relationship between the characteristics of the micro structure of the soft soil and macroscopic physical mechanics characteristics was established from qualitative and quantitative analysis. The minerals of soft soil in Nantong is mainly composed of illite and montmorillonite, in the form of honeycomb-shaped. The pore structure, shape factor, apparent porosity and pore distribution fractal dimension decrease with the increase of buried depth. With the increase of depth, ultralarge and large pores decrease, medium and small pores increase and tend to be uniform. There is a linear negative correlation between apparent porosity and dry density, compression modulus and cohesion as well as a positive correlation between the ratio of the macroscopic and the compression coefficient with the correlation coefficient between 0.81-0.94. The correlation between the pore fractal dimension and the macroscopic void ratio is a linear positive correlation, and there is a satisfied binomial relationship between pore fractal dimension and compression coefficient with the correlation coefficient 0.87-0.95. The pore space occupation ratio and the compression coefficient were obviously linear and a significant binomial relationship with cohesion. Their correlation coefficients are 0.901 and 0.967, respectively.Five major engineering geological strata groups, nine layers were established in Nantong area based on geological age, lithology, stratum structure, genetic type and physical and mechanical properties of rock mass. On the basis of these, the three-dimensional geological model was established to analyze the ground settlement and other engineering geological problems.