Classical soil mechanics is based on cohesive soil and cohesionless soil without ideal structural strength. However, due to the different formation conditions, formation age, composition and stress history, the engineering properties of soil have obvious regional characteristics. In Huang Wenxi's lecture, Zhou Jing analyzed in detail the engineering characteristics of flaky sand widely distributed in the middle and lower reaches of the Yangtze River in China. Its mineral composition is mainly composed of weathered debris of dark heavy minerals such as mica, and compared with Fujian timely sand in deformation characteristics, dynamic and static strength characteristics and liquefaction resistance, and pointed out that flaky sand has some special engineering properties. However, in the past, people's understanding of engineering properties of sand was mainly based on a large number of indoor and outdoor test results of timely sand. Academician Zhou Jing pointed out: "As we all know, at present, the in-situ testing method for evaluating the liquefaction potential of saturated sand in China, that is, the standard penetration method and the static sounding method, is mainly based on the experience in the timely sandy stratum, especially in the Tangshan earthquake. Some codes use the relative density of saturated sand to evaluate its liquefaction potential. Obviously, these standards cannot be simply applied to the flaky sand layers in the middle and lower reaches of the Yangtze River. The flaky sand layer widely distributed in the middle and lower reaches of the Yangtze River in China has some special engineering properties. The difference from the standard quartz sand shows that the soil is obviously regional and has certain universality. Geotechnical engineers at home and abroad have found that the engineering properties of saturated clay in many areas have different characteristics, such as London clay, Boston blue clay, Bangkok clay, Oslo clay, Lela clay, Shanghai clay and Zhanjiang clay. Although these clays have the characteristics of * * *, their individuality is more important for engineering construction.

China has a vast territory, many types of rock and soil, and is widely distributed. Taking soil as an example, soft clay, loess, expansive soil, saline soil, red clay and organic soil are widely distributed. For example, China's soft clay is widely distributed in Tianjin, Lianyungang, Shanghai, Hangzhou, Ningbo, Wenzhou, Fuzhou, Zhanjiang, Guangzhou, Shenzhen, Nanjing, Wuhan and Kunming. It is found that the engineering properties of Shanghai clay, Zhanjiang clay and Kunming clay are quite different. In the past, people paid more attention to the * * * of geotechnical materials or the * * * of a certain type of soil, but less in-depth and systematic research on its personality. It is the development direction of geotechnical engineering to deeply and systematically study the engineering properties of various regional soils. There is still a lot of work to be done to find out the distribution of soil in the region. Geotechnical engineers should know that only by mastering the engineering characteristics of the soil in their area can they better serve the economic construction.

2 model research

Study on constitutive model

In classical soil mechanics, the soil is regarded as an elastic body in settlement calculation, and the additional stress is solved by Businesk formula, while in stability analysis, the soil is regarded as a rigid-plastic body and analyzed by limit equilibrium method. By adopting a constitutive model which is more in line with the stress-strain-strength relationship (sometimes including time) of actual soil, deformation calculation and stability analysis can be combined. Since Roscoe and his students (1958 ~ 1963) founded the Cambridge model, scholars all over the world have developed hundreds of constitutive models, but few of them have been generally recognized by the engineering community, strictly speaking, not yet. The stress-strain relationship of rock mass is more complicated. It seems difficult or impossible to establish an ideal constitutive model that can reflect all kinds of geotechnical engineering. Because the stress-strain relationship of practical engineering soil is very complex, it has the characteristics of nonlinearity, elasticity, plasticity, viscosity, dilatancy and anisotropy. At the same time, the stress path, strength exertion, and the state, composition, structure and temperature of rock and soil all have influences on it.

There are two ways to study the constitutive model of rock and soil: one is to establish a practical model to solve practical engineering problems; The first is to establish a theoretical model that can further reflect the stress-strain characteristics of some rock and soil bodies. Theoretical models include various elastic models, elastic-plastic models, viscoelastic models, viscoelastic-plastic models, endochronic models, damage models and structural models. They should be able to better reflect some or several deformation characteristics of rock and soil, and are the basis for establishing practical engineering models. The actual engineering model should be a constitutive model for a certain area and a certain kind of geotechnical engineering problems, and should be able to reflect the main characteristics of geotechnical bodies in this case. It can be used in engineering calculation and analysis, and can get the analysis results that meet the accuracy requirements. For example, Shanghai clay practical constitutive model suitable for foundation pit engineering analysis, Shanghai clay practical constitutive model suitable for settlement analysis and so on. The author thinks that the establishment of various practical engineering models may be the direction of constitutive model research.

In the previous study of constitutive model, many scholars only paid attention to the establishment of constitutive equation, but did not pay attention to the determination and selection of model parameters and the verification of constitutive model. In the future research, especially