What Are the Different Types of Geotechnical Services?

Rock and soil A collective term for any kind of rock and soil that makes up the earth's crust from the perspective of engineering and construction. Rock and soil can be subdivided into five categories: hard (hard rock), sub-hard (soft rock), weakly connected, loosely unconnected, and with special composition, structure, state, and properties. It is customary in China to refer to the first two categories as rocks and the latter three as soil, collectively referred to as "rock and soil".

Geotechnical

Geotechnical engineering is a new technical system established by European and American countries in the practice of civil engineering in the 1960s. Geotechnical engineering is to solve rock and soil engineering problems, including foundation and foundation,

From the perspective of rock and soil classification, there are different aspects and standards. The main classifications are the classification of causes, as well as the classification of hardness, the classification of integrity, the classification of rock and soil according to the degree of weathering,

1 Introduction

Looking forward to the development of geotechnical engineering, the author believes that it is necessary to comprehensively consider the characteristics of geotechnical engineering disciplines, the requirements of engineering construction for the development of geotechnical engineering, and the impact of related discipline development on geotechnical engineering.

The objects of geotechnical research are rock and soil. The rock mass has experienced a variety of complex geological processes throughout the history of its formation and existence, and therefore has a complex structure and geostress field environment. However, due to the different geological processes experienced by different types of rock masses in different regions, their engineering properties are often very different. After the rock emerges from the surface, soil is formed by weathering. They may remain in place, or they may be deposited in different places to form soil layers through the erosion and transportation of wind, water, and glaciers. There are differences in the weathering environment, the dynamic conditions of handling and sedimentation in various regions during the stratigraphic period, so the soil is not only complex in engineering properties but also has strong regional and individual characteristics.

The strength characteristics, deformation characteristics and permeability characteristics of rocks and soils are determined by experiments. In the indoor test, the representativeness of the original sample, the unavoidable disturbance in the sampling process, the release of the initial stress, the error caused by objective reasons such as the difference between the test boundary conditions and the actual situation in the ground, make the results of the indoor test and the ground Actual geotechnical properties differ. In the in-situ test, it is difficult to estimate the errors caused by the representativeness of the on-site measurement points, the disturbance of the rock and soil when the test elements are buried, and the reliability of the test method.

The above characteristics of geotechnical materials and their tests determine the particularity of the discipline of geotechnical engineering. Geotechnical engineering is an applied science. In the analysis of geotechnical engineering, not only comprehensive theoretical knowledge, indoor and outdoor measurement results, but also the experience of an engineer are required to obtain satisfactory results. When looking forward to the development of geotechnical engineering, we must pay attention to the particularity of geotechnical engineering disciplines and the characteristics of geotechnical engineering problem analysis methods.

Geotechnical problems in civil engineering construction have promoted the development of geotechnical engineering disciplines. For example, the first problem encountered in civil engineering construction was soil stability. The earliest contribution in soil mechanics theory was the establishment of Coulomb's law in 1773. Then developed Rankine (1857) theory and Fellenius (1926) arc slip analysis theory. In order to analyze the development of settlement of soft clay foundations under load over time, Terzaghi (1925) developed a one-dimensional consolidation theory. Looking back on the development of geotechnical engineering in China over the past 50 years, it has been developed closely around the geotechnical engineering problems that arise in China's civil engineering construction. Before the reform and opening up, geotechnical engineering workers paid more attention to geotechnical engineering issues in the construction of water conservancy, railway and mine engineering. Geotechnical engineers pay more attention to geotechnical problems in construction engineering, municipal engineering and transportation engineering. The functionalization of civil engineering, three-dimensional urbanization, high-speed transportation, and improvement of the integrated residential environment have become the characteristics of modern civil engineering construction. The growth of the population has accelerated urban development, and the process of urbanization has promoted the rapid development of large cities in number and scale. People will continue to expand new living space, develop underground space, widen the ocean, build cross-sea bridges, subsea tunnels and artificial islands, transform deserts, build highways and high-speed railways. Looking forward to the development of geotechnical engineering, we cannot leave the analysis of the development trend of modern civil engineering construction in China.

The development of a discipline is also affected by the level of science and technology and the development of related disciplines. After World War II, especially since the 1960s, world science and technology have developed rapidly. The development of electronic technology and computer technology, and the improvement of calculation and analysis capabilities and testing capabilities, have improved and improved the computer analysis capabilities of geotechnical engineering and indoor and outdoor testing technologies. Scientific and technological progress has also prompted the emergence of new materials and technologies for geotechnical engineering. The rapid development of geosynthetics is called a revolution in geotechnical engineering. A characteristic of the development of modern science is the mutual penetration of disciplines, resulting in disciplinary intersections and the emergence of new disciplines. This development trend also affects the development of geotechnical engineering.

Geotechnical engineering is a new discipline that gradually combines soil mechanics and basic engineering, engineering geology, and rock mass mechanics into one and applies it to the practice of civil engineering from the late 1960s to the early 1970s. The development of geotechnical engineering will revolve around the geotechnical engineering problems that arise in the construction of modern civil engineering, and will be integrated into the new results obtained in other disciplines. Geotechnical engineering involves the use, remediation, or transformation of rocks and soil in civil engineering construction. Its basic problems are the stability, deformation, and seepage of rock or soil. The author believes that the following 12 areas are areas of research that should be given attention, from which we can look forward to the development of geotechnical engineering in the 21st century.

2 Regional soil distribution and characteristics

Classical soil mechanics is based on cohesive and non-cohesive soils with ideal structural strength. However, due to different formation conditions, formation age, composition, and stress history, the engineering properties of soil have obvious regional characteristics. Zhou Jing gave a detailed analysis of the engineering characteristics of flake sand widely distributed in the middle and lower reaches of the Yangtze River in China, and mainly composed of weathered fragments of mica and other dark heavy minerals. The differences in deformation characteristics, dynamic and static strength characteristics, and liquefaction resistance of sand indicate that flake sand has some special engineering properties. However, the previous understanding of the engineering properties of sand is mainly based on the results of a large number of indoor and outdoor tests on quartz sand. Academician Zhou Jing pointed out: "As we all know, the current in-situ test methods for evaluating the liquefaction potential of saturated sand in China, namely the standard penetration method and the static sounding method, are mainly based on the experience in the quartz sand formation, especially in the Tangshan earthquake Experience. Some regulations use the relative density of saturated sand to evaluate its liquefaction potential. Obviously, these criteria should not be used simply for flaky sand formations in the middle and lower reaches of the Yangtze River. " The flake sand strata that are widely distributed on both sides of the middle and lower reaches of the Yangtze River in China have certain special engineering properties. The difference from standard quartz sand indicates that the soil has obvious regionality, and this phenomenon is universal. Geotechnical engineers at home and abroad have found that the engineering properties of saturated clays in many areas have different characteristics, such as London clay, Boston blue clay, Bangkok clay, Oslo clay, Lela clay, Shanghai clay, Zhanjiang clay, etc. Although these clays have commonalities, their individuality is more important for project 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, organic soil, etc. have a wide range of distribution. For example, China's soft clay is widely distributed in Tianjin, Lianyungang, Shanghai, Hangzhou, Ningbo, Wenzhou, Fuzhou, Zhanjiang, Guangzhou, Shenzhen, Nanjing, Wuhan, Kunming and other places. Great differences have been found in the engineering properties of Shanghai clay, Zhanjiang clay and Kunming clay. In the past, people paid more attention to the commonalities of geotechnical materials, or the commonalities of certain types of soils, but there were few in-depth systematic studies on their personalities. It is the development direction of geotechnical engineering to conduct in-depth systematic research on the engineering properties of various types of regional soils. Much work needs to be done to find out the distribution of regional soils. Geotechnical engineers should be clear that only by understanding the engineering characteristics of the soil in their area can they better serve economic construction.

3 Research on constitutive model

In classical soil mechanics, the settlement is regarded as an elastic body, and the Boussinesq formula is used to solve the additional stress, while the stability analysis regards the soil as a rigid plastic body and analyzed by the limit equilibrium method. A constitutive model that is more in line with the stress-strain-strength (and sometimes time) relationship of the actual soil can combine deformation calculation and stability analysis. Since Roscoe and his students (1958-1963) created the Cambridge model, scholars from various countries have developed hundreds of constitutive models, but few have been widely recognized in the engineering community, and strictly speaking, they have not yet. The stress-strain relationship of the rock mass is more complicated. It seems that it is difficult, or impossible, to attempt to establish an ideal constitutive model that can reflect various geotechnical and applicable to various geotechnical projects. Because the stress-strain relationship of the actual engineering soil is very complicated, it has non-linearity, elasticity, plasticity, viscosity, dilatancy, anisotropy, etc. At the same time, the stress path, strength exertion, and state and composition of rock , Structure, temperature, etc. all have an impact on it.

Research on constitutive models of rock and soil can be carried out in two directions: first, to build a practical model for solving practical engineering problems; first, to establish a theoretical model that can further reflect the stress-strain characteristics of certain rock and soil bodies. The theoretical models include various types of elastic models, elastoplastic models, viscoelastic models, viscoelastic plastic models, internal time models and damage models, and structural models. They should be able to better reflect one or more deformation characteristics of rock and soil, and are the basis for establishing practical engineering models. The engineering practical model should be a constitutive model for geotechnical and geotechnical problems in a certain area, and it should be able to reflect the main characteristics of the geotechnical body in this case. Using it for engineering calculation analysis, you can obtain satisfactory analysis results with the accuracy required for engineering construction. For example, Shanghai practical clay constitutive model suitable for foundation pit engineering analysis, Shanghai clay practical constitutive model suitable for settlement analysis, etc. The author believes that the research and establishment of multiple engineering practical models may be the research direction of constitutive models.

In the past research of constitutive models, many scholars only paid attention to the establishment of constitutive equations, but did not pay attention to the study of model parameter measurement and selection, nor did they pay attention to the verification of constitutive models. In the future research, special attention should be paid to the determination and selection of model parameters, the verification of constitutive models, and the popularization and application research. Only in this way can we better serve the engineering construction.

4 Interaction between different media and common analysis

Li Guangxin (1998) believes that the analysis and interaction of different media in geotechnical engineering can be divided into three levels: the micro-level interaction of geotechnical materials; the interaction between soil and composite soil or soil and reinforced materials Role; interaction between the foundation and the building (structure) [2].

The soil is composed of three phases: solid, liquid and gas. The solid phase exists in the form of particles in the form of particles. The interaction between solid, liquid and gas three phases has a great influence on the engineering properties of soil. The complexity of soil stress-strain relationship is fundamentally related to the interaction of soil particles. It is very meaningful to study the constitutive relationship of soil from the microscopic interaction between particles. The study of solid-liquid-gas phase interactions in soil will also promote the development of unsaturated soil mechanics theories and help to further understand the engineering properties of various types of unsaturated soils.

Compared with soil, the structure of rock mass has its particularity. The rock mass is a complex composed of structures bounded by structural planes of different sizes, different forms, different genesis, different directions, and different orders. The rock mass has discontinuities in engineering properties. Rock mass engineering properties also have anisotropy and heterogeneity. Based on the research progress of rock mass fracture mechanics and other new theories and methods, it is also very meaningful to carry out research on the geometric effects and mechanical effects of structural planes that affect the stability of engineering rock masses.

When the natural foundation cannot meet the requirements of the building (structure) for the foundation, the natural foundation needs to be processed to form an artificial foundation. Pile foundation, composite foundation and homogeneous artificial foundation are three types of artificial foundation commonly encountered. Studying the interactions between piles and soils, and reinforcements and soils in composite foundations is very meaningful for understanding the bearing capacity and deformation characteristics of pile foundations and composite foundations.

The interaction and co-analysis of foundations and structures have attracted people's attention and achieved some results. However, the application of co-action analysis to engineering design has a large gap. In most engineering designs, the foundation and buildings are calculated separately. Further carrying out the analysis of the interaction between the foundation and the building (structure) will help to gain a deeper understanding of the real engineering properties and improve the level of engineering design. The development of modern computing technology and computers has provided good conditions for the analysis of the interaction of foundations and structures. There is an urgent need to solve practical constitutive models of various engineering materials and interaction interfaces, especially the reasonable simulation of interface interactions.

5 Geotechnical test technology

Geotechnical testing technology is not only very important in the practice of geotechnical engineering construction, but also plays a decisive role in the formation and development of geotechnical engineering theory. Theoretical analysis, indoor and outdoor testing, and engineering practice are three important aspects of geotechnical engineering analysis. Many theories in geotechnical engineering are based on tests. For example, Terzaghi's effective stress principle is based on the measurement of pore water pressure in compression tests. Darcy's law is based on permeability tests. The Cambridge model is It is based on compression tests and iso-triaxial compression tests of normal and slightly super-consolidated clays. Testing technology is also an important means to ensure the rationality of geotechnical engineering design and the quality of construction.

Geotechnical engineering test technology is generally divided into several aspects such as indoor test technology, in-situ test technology and on-site monitoring technology. In terms of in-situ testing, the displacement field and stress field test in the foundation, the earth pressure test on the surface of the underground structure, and the strength and deformation characteristics of the foundation soil will be the focus of research. With the progress of the overall test technology, These traditional difficulties will make breakthrough progress. Virtual test technology will be widely used in geotechnical engineering test technology. The timely and effective use of scientific and technological achievements in other disciplines will play an increasingly important role in promoting the development of testing technology in the field of geotechnical engineering, such as electronic computer technology, electronic measurement technology, optical test technology, aerial survey technology, electricity, and magnetic fields. New developments in testing technology, acoustic testing technology, and remote sensing testing technology are likely to find application integration points in geotechnical engineering testing. The reliability and repeatability of test results will be greatly improved. Due to the improvement of the overall scientific and technological level, the improvement of the test mode and the improvement of the accuracy of the test instruments will eventually lead to a great improvement in the reliability of the test results in geotechnical engineering.

6 Computer analysis of geotechnical engineering problems

Although computer analysis of geotechnical engineering can only give qualitative analysis results in most cases, computer analysis of geotechnical engineering is very meaningful for engineers to make decisions. Carrying out computer analysis and research on geotechnical engineering problems is an important research direction. The scope and field of computer analysis of geotechnical engineering problems is wide. With the development of computer technology, the field of computational analysis is still expanding. In addition to the constitutive model and the interaction and common analysis of different media mentioned earlier, it also includes various numerical calculation methods, soil slope stability analysis, limit numerical methods and probability numerical methods, expert systems, AutoCAD technology, and computer simulation technology. Applications in geotechnical engineering, and back analysis of geotechnical engineering. Geotechnical computer analysis also includes dynamic analysis, especially seismic analysis. In addition to the commonly used finite element methods and finite difference methods, computer numerical analysis methods for geotechnical engineering include discrete element method (DEM), Lagrangian yen method (FLAC), discontinuous deformation analysis method (DDA), and numerical manifold element method. (NMM) and semi-analytical element method (SAEM) are also used in geotechnical engineering analysis [3].

Based on in-situ testing and on-site monitoring, various information obtained during the construction of the geotechnical engineering was used for inverse analysis, and the design of the government was revised and the construction was guided based on the results of the inverse analysis. This information-based construction method is considered to be a reasonable construction method and is the development direction.

7 Reliability analysis of geotechnical engineering

In the design of building structures, China has adopted the limit state design method based on probability theory and expressed by partial coefficients. The foundation design and the superstructure design have not yet been unified at this point. The application of limit state design methods based on probability theory is the direction. Due to the particularity of geotechnical engineering, there are still many technical problems to be solved in the application of probability limit state design for geotechnical engineering. According to the characteristics of geotechnical engineering, it is necessary to actively carry out theoretical research on the reliability analysis of geotechnical engineering problems so that the design methods of the superstructure and the foundation can be unified as soon as possible.

8 Environmental Geotechnical Research

Environmental geotechnical engineering is a new discipline that closely combines geotechnical engineering and environmental science. It mainly uses the perspectives, technologies and methods of geotechnical engineering to serve the governance and protection of the environment. Human production activities and engineering activities cause many environmental hazards, such as the collapse of goafs caused by mining, the regional ground subsidence caused by excessive extraction of groundwater, industrial waste, municipal solid waste and other wastes, especially toxic and hazardous wastes pollute the environment, and construction disturbance The impact of the surrounding environment and so on. In addition, disasters such as earthquakes, floods, wind and sand, mudslides, landslides, ground fissures, and hidden karst caused ground collapse to cause damage to the environment. The management and prevention of the above environmental problems have raised many new research topics for geotechnical engineers. With the acceleration of urbanization and industrialization, research on environmental geotechnical engineering will become more important. From the perspective of maintaining a good ecological environment and sustainable development, we should understand and value environmental geotechnical engineering research.

9 Design theory by settlement control

The foundation of a building (structure) generally needs to meet both the requirements of the bearing capacity and the requirements of less than a certain deformation settlement (including less than a certain settlement difference). Sometimes after the bearing capacity meets the requirements, whether its deformation and settlement meet the requirements can basically be checked. There are two cases: one is that the settlement must be small after the bearing capacity is satisfied, such as end-bearing pile foundation, and the other is that there is no strict requirement for deformation, such as loose embankment foundation and sand and gravel. Raw material pile site foundation and so on. There are also settlements that meet the requirements, and the bearing capacity must meet the requirements without checking. In this case, the design can only be controlled according to the settlement amount.

The control of settlement and differential settlement is the key to building buildings on deep soft clay foundation. Most of the construction foundation engineering accidents in soft ground areas are caused by excessive settlement or poor settlement, in particular, uneven settlement is the most harmful to buildings. The settlement of deep soft clay foundation buildings is closely related to project investment. Reducing the amount of settlement requires increased investment, so it is very important to properly control the amount of settlement. The design according to the settlement control can ensure the safety of the building and save the engineering investment.

According to the settlement control design, it is not necessary to meet the requirements of the foundation bearing capacity regardless of whether it meets the requirements. The design theory based on settlement control also includes checking and verifying whether the bearing capacity meets the requirements.

10 Stability and deformation of the retaining system of foundation pit engineering

With the development of high-rise buildings and the development of urban underground space, deep foundation pit projects are increasing. The stability and deformation of the retaining system of foundation pit engineering is an important research area.

The research on the stability and deformation of the foundation pit engineering envelope system includes the following aspects: calculation of earth pressure, reasonable type and scope of the envelope system, design and optimization of the envelope structure, "temporal and spatial effects" of the foundation pit project, Deformation, and the impact of excavation on the surrounding environment. Foundation pit engineering involves three basic issues of soil stability, deformation, and seepage, and it is necessary to consider the interaction of soil and structure. It is a comprehensive subject and a systematic project.

The foundation pit project is regional and strong. Some foundation pit engineering is the main contradiction of the stability of the retaining structure caused by earth pressure, some seepage caused by the seepage in the soil is the main contradiction, and some control the ground deformation around the foundation pit is the main contradiction. The earth pressure theory is still not perfect. Static earth pressure is determined empirically or calculated according to semi-empirical formula. Active earth pressure and passive earth pressure are calculated according to Coulomb (1776) earth pressure theory or Rankine (1857) earth pressure theory. These all appear Before Terzaghi's principle of effective stress. When considering the effect of groundwater on earth pressure, whether to use water and earth pressure sub-calculation or water and earth pressure is more realistic, and the understanding in the academic and engineering circles is not consistent.

The earth pressure acting on the retaining structure is related to the displacement of the retaining structure. The earth pressure on the foundation pit retaining structure is generally between active earth pressure and stationary earth pressure or between passive earth pressure and stationary earth pressure. In addition, soil has creep properties, and the earth pressure acting on the retaining structure is also related to the action time.

11 composite foundation

With the development of ground treatment technology, composite ground technology has been used more and more. Composite foundation refers to the part of the soil that is reinforced or replaced during the foundation treatment, or reinforced material is set in the natural foundation. The reinforcement area is an artificial foundation consisting of the base (natural soil) and the reinforcement. . The reinforcement and the matrix in the composite foundation directly bear the load together. According to the direction of the reinforcement, it can be divided into two categories: vertical reinforcement composite foundation and horizontal reinforcement composite foundation. According to different load transfer mechanisms, vertical reinforced composite foundations can be divided into three types: granular composite foundations, flexible composite foundations and rigid composite foundations.

Composite foundation, shallow foundation and pile foundation are three common types of foundation foundation. There are no very strict boundaries between shallow foundations, composite foundations, and pile foundations. The soil pile composite foundation with a pile-soil stress ratio close to 1.0 can be considered as a shallow foundation, and the friction pile foundation considering the interaction of pile and soil can also be considered as a rigid pile composite foundation. The author believes that treating it as a rigid pile composite foundation is more conducive to understanding its load transfer system. The bearing capacity and settlement calculation of shallow foundations and pile foundations have accumulated more mature theories and engineering practices, and the theory of bearing capacity and settlement calculation of composite foundations needs to be further developed. The theory of composite foundation calculation is far behind the practice of composite foundation. The research on composite foundation theory should be strengthened, such as bearing capacity and settlement calculation of various types of composite foundation, especially settlement calculation theory; optimal design of composite foundation; seismic behavior of composite foundation; reliability analysis of composite foundation. In addition, the properties of various composite soils need further understanding.

While strengthening the theoretical research of composite foundation, it is also necessary to strengthen the development of new composite foundation technology and the application research of composite foundation technology.

12 Properties of foundation under cyclic and dynamic loads

The strength and deformation characteristics of geotechnical materials under cyclic or dynamic loads have many special characteristics compared with those under static loads. Different types of dynamic loads have different strength and deformation characteristics of the soil. Under different types of dynamic loads, their common feature is that they must consider the effects of loading rate and number of times. In the past two or three decades, researches on shear deformation characteristics of soil under dynamic load and soil dynamic properties (including deformation characteristics and dynamic strength) have been extensively carried out. With the development of highways, high-speed railways, and marine engineering, it is necessary to understand the behavior of the foundation soil and its impact on the surrounding environment under cyclic and dynamic loads. Different from the dynamic load of general power machine foundations, the external dynamic load of highways, high-speed railways, and marine engineering is moving, and at the same time it generates vibrations. The force of the foundation soil will be more complicated, and the strength of the soil will be more complicated. , Deformation characteristics and creep characteristics of soil need further research to meet the needs of engineering construction. The period of the traffic load is long, and the vibration frequency of the traffic load itself is also low. The vibration wave generated by the load has a longer wavelength, a longer wave propagation, and a larger influence range. The calculation of the dynamic response of the foundation in expressways, high-speed railways, and marine engineering is more complicated. Studying the calculation method of the dynamic response of the foundation under the action of traffic loads can further study the self-vibration of the load caused by the traffic load and the vibration of the surrounding environment. Application prospects.

13 Research on special geotechnical problems

Looking forward to the development of geotechnical engineering, we must also pay attention to the study of special geotechnical engineering problems, such as: the stability of surrounding mountain slopes caused by rising water levels in the reservoir area; geotechnical engineering problems in underground tunnels crossing rivers and seas; ultra-deep foundations of super high-rise buildings Engineering problems; ultra-deep foundation engineering problems of super bridges and sea-crossing bridges; unloading deformation and failure of rock and soil caused by large-scale surface and underground engineering excavations; etc.

Geotechnical engineering is an applied science and serves engineering construction. The problems raised in engineering construction are the topics that geotechnical engineering should study. The development direction of geotechnical engineering disciplines is closely related to the development of civil engineering construction. The hotspots of world civil engineering construction have moved to East Asia and China. China has a vast territory and complex engineering geology. The scale of civil engineering construction in China, the duration of continuous development, and the technical problems of geotechnical engineering encountered in engineering construction cannot be compared with other countries. This has created good conditions for China's geotechnical research to become world-class and gradually lead. Looking forward to the development of geotechnical engineering in the 21st century, challenges and opportunities coexist, let us work together to push China's geotechnical engineering to a new level. ^[1]