1, meaning of geotechnical engineering
Geotechnical engineering has several different definitions:
The basic terminology standard of geotechnical engineering is defined as: "Science and technology involved in the utilization, treatment and improvement of rocks and soil in civil engineering." China Encyclopedia is defined as "a branch of civil engineering, which is based on engineering geology, rock mechanics, soil mechanics and basic engineering and involves the utilization, transformation and transformation of rocks and soils." Some experts define it as "a branch of civil engineering, which studies rock and soil (including water) as support, load, medium or material, and improves or manages it if necessary." Although the above statements are not completely consistent, the main aspects are similar or the same. First, geotechnical engineering is a branch of civil engineering; Secondly, the research object is rock and soil, including water in rock and soil; Third, it is a technical science or engineering technology.
2 extension of geotechnical engineering
Geotechnical engineering is very practical. From the perspective of engineering practice, it includes the following aspects:
(1) Rock and soil are used as supporting bodies.
Buildings, roads, bridges, courtyards, large equipment, etc. They are all built on rocks and soil as the foundation and support. The main problems studied are bearing capacity and deformation.
(2) Rock and soil as load or self-supporting body
Slope engineering, foundation pit engineering, open pit mining and other ground excavations, tunnels, underground caverns and other underground excavations are all facing another kind of stability and deformation problems. At this time, the role of rock and soil may be both load and self-bearing. At the same time, the control of groundwater often has a decisive impact.
(3) Geotechnical materials
Fill projects, especially large-scale high fill and land reclamation, need to use a lot of rock and soil as materials; Cofferdams, dams and dikes are also made of rocks and soil. Besides studying the stability and deformation of these projects, the selection of geotechnical materials and quality control are the main problems.
(4) prevention and control of geological disasters
Geological disasters such as karst, collapse, collapse, landslide, debris flow and land subsidence pose a serious threat to the project, and the prevention and control project must be designed and constructed according to the specific situation and the law of geological evolution. The seismic effect of site and foundation is also a part of geotechnical engineering.
(5) Environmental geotechnical engineering
Geological and hydrogeological environment assessment, sanitary landfill of garbage, protection of earth-rock cultural relics, etc. They all involve complex environmental geotechnical engineering problems. With people's attention to environmental protection, understanding of the harmony between man and land, and the implementation of sustainable development policy, environmental geotechnical engineering has been paid more and more attention.
You can also cite some, but mainly the above five categories.
The above-mentioned projects not only involve natural rock and soil, but also include various artificial soils, including the reinforcement and improvement of natural soil, and the use of drainage, compaction, reinforcement, modification, grouting, anchoring, setting steel bars and other methods to change the strength, deformation and permeability of rock and soil. Geotechnical reinforcement and improvement is an important part of geotechnical engineering.
From the Ninth Excellent Survey and Application Project, we can know the scope of geotechnical engineering, such as Qinling Tunnel, Ling 'ao Nuclear Power Station, Three Gorges Five-level Ship Lock, Longyangxia Hydropower Project, Xiaolangdi Hydropower Project, Baiyun Airport, Xiaoshan Airport, multi-storey high-rise building, Tangshan karst collapse control, landslide control, large open-pit mine slope, urban underground common ditch, offshore oil production well site, Three Gorges Reservoir bank immersion area control and so on. , and deep foundation pit support, roads, tailings and electricity. Although not comprehensive, it can be seen that geotechnical engineering involves a wide range.
2, the relationship between geotechnical engineering and adjacent professional.
Geotechnical engineering is closely related to many specialties, overlapping with each other, and the boundaries are blurred. Near the border, you have me and I have you. Such as: engineering geology, structural engineering, water conservancy and hydropower engineering, road, bridge and tunnel engineering, port and waterway engineering, mining engineering, earthquake engineering, ocean engineering, environmental engineering, etc. The following only explains the relationship between geotechnical engineering and engineering geology, and the relationship between geotechnical engineering and structural engineering:
(1) Relationship between Geotechnical Engineering and Engineering Geology
Firstly, the difference between engineering geology and geotechnical engineering is expounded.
Engineering geology is a branch of geology and a science that studies geological problems related to engineering construction. Engineering geology originates from the needs of civil engineering, and its essence is an applied science. Geotechnical engineering is a branch of civil engineering, and its essence is an engineering technology. Geological experts (geologists) are engaged in engineering geology, focusing on geological phenomena, geological causes and evolution, geological laws, and the interaction between geology and engineering; Engineers are engaged in geotechnical engineering, and they are concerned about how to build a project or part of a project that meets the use requirements and safety requirements according to the engineering objectives and geological conditions, and solve geotechnical technical problems in engineering construction. Therefore, there is a difference between the two, regardless of subject field, work content and focus.
However, engineering geology is closely related to geotechnical engineering. Some people say that engineering geology is the foundation of geotechnical engineering, and geotechnical engineering is the extension of engineering geology. It's not necessarily exact, but it makes sense. The geotechnical materials faced by geotechnical engineers, regardless of performance or structure, are naturally formed and have experienced a long geological history, which is the product of various complex geological processes. The performance and structure of rock and soil can only be determined through investigation, but not completely. Some key problems need to be speculated or predicted according to geological laws. Especially in mountainous areas with complex geological structures, experienced engineering geologists can roughly judge the outline of geological structures through ground investigation, and build engineering geological models from coarse to fine and from shallow to deep by means of geophysical exploration, drilling and trench well. Without geological foundation, how to identify faults? How can we identify the spatial distribution of weak interlayer and structural plane? How can we explain the occurrence and movement of groundwater? If a tunnel is to be excavated, which sections will collapse? Which sections will be flooded? In areas with complicated geology, civil engineering is difficult to move without engineering geologists.
(2) the relationship between geotechnical engineering and structural engineering
Obviously, geotechnical engineering is closely related to structural engineering. Building structures and bridge structures are all built on foundations. Whether the foundation is stable directly affects the safety of the structure; Whether the foundation will produce excessive deformation will directly affect the function of the structure, and the secondary stress may make the structure exceed the design limit. There is something wrong with the foundation, which is difficult to remedy. Therefore, structural engineering pays great attention to the stability and deformation of foundation. At present, the general foundation design is completed by structural engineers considering the requirements of superstructure, and only complex foundation problems or foundations that need special treatment need the participation of geotechnical engineers. Similarly, geotechnical engineers must understand the type of structure, load and its distribution, especially the type and stiffness of foundation, and understand the restrictions on foundation deformation, so as to be targeted. Close cooperation between geotechnical engineers and structural engineers is very important.
Structure and foundation are a whole, interacting and influencing each other. The deformation of the foundation will change the stress of the structure, and the load distribution and different stiffness of the structure will produce different foundation deformation. People often adjust the stiffness of foundation and structure to adapt to the deformation of foundation, and the analysis of the synergistic effect of foundation, foundation and superstructure is a hot spot at present. On the contrary, the bearing capacity and stiffness of foundation can be improved by foundation treatment to meet the requirements of superstructure.
Geotechnical engineering and structural engineering, you have me and I have you, and there are countless examples of overlapping each other. For example, pile foundation, as an extension of the structure, is a part of the structure, but the bearing capacity and deformation of pile foundation mainly depend on the more closely related rock and soil. Another example is foundation pit engineering, earthwork excavation, groundwater treatment, earth pressure calculation, etc. They are all related to rock and soil, but slope protection piles, underground continuous walls, anchors and internal supports are all structures. Slope engineering and the treatment of geological disasters seem to belong to geotechnical engineering, but they are often inseparable from structural measures. Simple geotechnical engineering, such as land reclamation, dike engineering, large high fill and so on, is not much. Although structural engineers and geotechnical engineers have division of labor and emphasis, most of them cooperate with each other. Therefore, structural engineers should have the necessary geotechnical knowledge, and geotechnical engineers should also have the necessary structural knowledge. Due to the dominant position of structural specialty in general, the main tasks undertaken by geotechnical engineers are often complex or specialized geotechnical tasks that structural engineers are difficult to undertake.
4, the main characteristics of rock and soil
Cracks in rock and porosity of soil are the main characteristics that distinguish rock and soil from man-made materials such as concrete and steel.
(1), rock fracture
Rock is always thin or dense, wide or narrow, long or short, with various cracks, which is the main feature that distinguishes rock from concrete. Some of these cracks are rough and some are smooth; Some are straight, some are curved; Some filled in, some didn't; Some occur regularly, and some have poor regularity. The causes of cracks are various, including primary joints formed by magma solidification and contraction, bedding formed by sedimentary discontinuity, structural joints formed by tectonic stress, unloading cracks and weathering cracks formed by supergene, schistosity and cleavage formed by metamorphism, etc. They constitute an extremely diverse and complex fracture system in rocks. People regard rocks and cracks as a whole called "rock mass" and generalize cracks as "structural plane". Obviously, the structural plane is the weakest link in the rock mass. As far as mechanical properties are concerned, the mechanical parameters of rocks, structural planes and rock masses are quite different. Understanding the occurrence, parameters and distribution of structural planes is the key and difficult point in geotechnical engineering survey and design.
Groundwater in rock mass flows along cracks and caves in rock mass. With the different shapes and distributions of cracks and caves, there are different types of groundwater, such as vein fissure water, reticular fissure water, layered fissure water and cave water.
(2) Porosity of soil
Soil is a porous granular material. For saturated soil, there are solid and liquid; For unsaturated soil, there are solid, liquid and gas. So as to generate effective pressure and pore pressure; Pore pressure includes pore water pressure and pore gas pressure. The principle of effective stress has become the main sign that soil mechanics is different from general material mechanics, and there are two principles and methods in geotechnical calculation: total stress method and effective stress method. In saturated soil, due to the increase and dissipation of pore water pressure, the bearing capacity of foundation is different under different loading rates; Whether timely support has different performances on the stability of soft soil foundation pit; Different permeability coefficient and stratum combination lead to different settlement rate of foundation and so on. Hydrostatic pressure in saturated soil will produce soil squeezing effect, which will lead to pile breaking, bending and floating. The hydrostatic pressure during the earthquake caused the liquefaction of sand and silt. The pore gas pressure of unsaturated soil forms matrix suction, which decreases with the increase of water content in soil, so it is unstable. With the increase of humidity, the strength of expansive soil and loess decreases significantly. Unsaturated soil foundation pits are prone to accidents in rainy season, and granite residual soil slopes are prone to shallow landslides in heavy rain, all of which are related to the reduction of matrix suction. In a word, mastering pore pressure is an important key in geotechnical engineering.
5. Dependence on natural conditions and uncertainty of conditions.
Geotechnical engineering, as a branch of civil engineering, is developed on the basis of traditional mechanics. But it was soon discovered that simple mechanical calculation could not solve practical problems. The main reasons are the dependence on natural conditions and the uncertainty of calculation conditions. Compared with structural design, structural engineers are faced with artificial materials such as concrete and steel, which are relatively uniform. Both materials and structures are selected by engineers during design, and the calculation conditions are very clear, so the calculation based on mechanics is credible. However, both materials and structures of rock and soil are naturally formed, which is beyond the choice and control of engineers. They can only find out through investigation, not completely. Therefore, there are uncertainties of conditions and parameters, fuzziness of calculation conditions and incompleteness of information to varying degrees. Therefore, although the geotechnical engineering calculation method has made great progress and played an important role, there are many differences between the calculation assumptions, calculation modes and calculation parameters and the actual situation, and there are always more or less differences between the calculation results and the actual situation, which requires the comprehensive judgment of geotechnical engineers. "Not accurate calculation, but correct judgment", emphasizing conceptual design, has always been the knowledge of geotechnical engineering.
6. Uncertainty of parameters and diversity of test methods
There are two reasons for the discreteness of test data of the same rock and soil mass. First of all, due to the interference of sampling, transportation, sample preparation and test operation, as well as the errors caused by test and calculation, the test data are randomly distributed. The uncertainty in this aspect is basically the same as the test data of concrete and steel, but it is more variable. Secondly, the geotechnical test data is also related to the position of the sample, which is a characteristic that other engineering materials do not have. The properties of rock and soil are different even in the same layer. There are not only regular horizontal and vertical phase transitions, but also irregular refractive index dispersion. Therefore, the indicators of a single sample test are generally not representative, and there must be a certain number of test indicators. After statistical analysis, representative values can be obtained. Structural design pays attention to section calculation, while geotechnical engineering analysis pays attention to system analysis, without section calculation. Compared with the size of the sample, the size of the analyzed rock and soil mass is many times larger, so the comprehensive level of the rock and soil mass parameter value should be considered, so the calculation method of the standard value is different from that of concrete and steel. The reliability analysis of structural section has been basically mature and has been incorporated into the code; However, the reliability analysis of geotechnical engineering is still in the research stage, and it is difficult to be widely used in engineering because of its complex problems and insufficient accumulation. Geotechnical engineering testing can be divided into three categories: indoor testing, in-situ testing and prototype monitoring, as well as various model tests, all of which have their own characteristics and uses. Different test methods will get different results for the same parameter. Choosing a reasonable test method has become an important link for geotechnical engineering calculation to achieve the expected results. For example, the modulus of soil includes compression modulus, deformation modulus, lateral modulus and inversion modulus. Laboratory tests of soil shear strength include direct shear and triaxial shear. Direct shear includes quick shear, consolidated quick shear and slow shear; Triaxial shear includes unconsolidated undrained shear, consolidated undrained shear, consolidated undrained shear and consolidated undrained shear to measure pore water pressure; In-situ tests include large-scale shear tests in vane shear test and field. Due to different test conditions, the test results are also different. Which test method is reasonable is determined by the geotechnical engineer according to the specific situation. The diversity of this test method is also an important feature that distinguishes geotechnical engineering from other engineering technologies. In the analysis and calculation of geotechnical engineering, attention should be paid to the matching of calculation methods, calculation parameters and safety degree, and the correct selection of calculation parameters is the most important.
7. Imperfection, imperfection and immaturity of geotechnical engineering.
Geology and mechanics are two theoretical pillars of geotechnical engineering, which complement each other, penetrate each other and graft each other. Mechanics is based on the basic theory, combined with specific conditions, to establish a model to solve. Its characteristics are from general to special, rigorous, and it is a deductive thinking method. Geology is an inductive reasoning method based on analyzing, synthesizing and comparing a large number of data obtained from investigation and study, finding out scientific laws, from special to general, emphasizing the analysis of causes and evolution, macro grasp and comprehensive judgment.
Because of the uncertainty of conditions and parameters and incomplete information, simple calculation is not only inaccurate but also not necessarily reliable. Therefore, it emphasizes the combination of qualitative analysis and quantitative analysis and comprehensive judgment. Comprehensive judgment depends on the theoretical basis and rich engineering experience of engineers. Just like a good doctor, he should have a profound understanding of medical theory and rich clinical experience. Ignoring experience is of course wrong, and inexperienced people can't solve complex engineering problems. It is also wrong to ignore theory, and it is easy to mistake local experience for universal truth and make conceptual mistakes. "Only when the fruits of experience are rooted in the tree of theory can they have vitality."
As can be seen from the above, geotechnical engineering is still an imprecise, imperfect and immature science and technology, and it is in a "developing" science and technology, so there are considerable risks. Academician Shen Zhujiang said: the development of soil mechanics is "from toddler to self-reliance", and rock mechanics develops late and has a low maturity.
8. Conceptual design of geotechnical engineering
The lofty conceptual design of geotechnical engineering can be understood as frame design in a narrow sense, and the design frame is summarized for further refinement. Conceptual design in a broad sense can be understood as a design idea.
Conceptual design can generally be summarized as follows: on the basis of fully understanding the functional requirements and mastering the necessary information, through generalizing the design conditions, first qualitative analysis, and then quantitative analysis, a framework is proposed, and the feasibility and effectiveness of technical methods, the operability of construction, the controllability of quality, environmental restrictions and possible negative impacts, and the economy are demonstrated, and one or several schemes are conceptually selected, and the necessary calculations and checks are carried out, and the construction inspection and inspection are carried out. Conceptual design in a broad sense is necessary not only in the initial stage of design, but also in the whole project.
To do conceptual design, we must have a profound understanding of the principle, rich experience, flexible operation ability, take the overall situation into account, master the key factors affecting the success or failure of the project, and have a basically correct estimate of the implementation effect of the design.
When doing conceptual design, we must pay attention to conform to scientific principles and not make conceptual mistakes. The concept is unclear, often only looking at the phenomenon, not seeing the essence, and dealing with problems by local experience. If the concept is wrong, you may make mistakes in principle. People with clear concepts can see the essence through phenomena, draw inferences from others, and consciously apply theory and experience. The basic characteristics of rock and soil, the law of groundwater infiltration and movement, and the synergy between structure and rock and soil are all important concepts.
There are three reasons for inaccurate geotechnical engineering calculation: geological conditions, calculation methods and calculation parameters, especially the calculation parameters are the most difficult to grasp. Therefore, first of all, we should do a good job in investigation and grasp the geological situation; Secondly, correctly select formulas and software, and fully understand their applicable conditions and possible deviations; We should also emphasize information construction and dynamic design. The quantitative calculation in advance is generally only an estimate, and only the prototype measurement is the most credible. Monitoring is not only an important measure to ensure safety, but also the most reliable scientific experiment.
9. Practice as a registered geotechnical engineer
Registered civil engineer (geotechnical) has passed three exams and is expected to start practicing soon. The rights, obligations and scope of practice of geotechnical registrars are issues of great concern to everyone. These problems will be implemented after the release of relevant government departments. I only talk about some personal opinions about the characteristics of geotechnical engineering:
(1) Obtaining the qualification of registered engineer means that the professional ability has reached the threshold of practice of related majors, and the legal ability in this respect is of course beneficial to both individuals and their units. But on the other hand, it is also responsible, and bears legal responsibility and lifelong responsibility for the technical documents signed by itself. As mentioned above, geotechnical engineering is still an imprecise, imperfect and immature science and technology with certain risks. Registered personnel should not only abide by laws and regulations, be familiar with standards and norms, but also have a profound theoretical foundation, rich engineering experience and the ability to make correct judgments when things happen. China has a vast territory, different conditions and a wide variety of geotechnical engineering. One can't have rich experience in all fields. Therefore, we must be cautious in the practice process, and we must not undertake all the business within the scope of geotechnical engineers. Article 26 of the Regulations on the Administration of Survey and Design Registered Engineers stipulates the obligations of registered engineers, of which the second paragraph is "engaging in practice activities within the prescribed scope"; Paragraph (3) reads "I am still capable of engaging in the corresponding practice activities". In other words, we must do our best. You can consult relevant experts for unfamiliar questions, but you will be responsible if you sign them.
(2) The scope of geotechnical engineering specialty overlaps and overlaps with adjacent majors, so the practice of registered engineers will overlap and overlap with registered engineers of adjacent majors, which is objective. Therefore, it is inappropriate and impossible to draw a clear line. You have me, I have you, and it is normal to be near the adjacent professional boundaries. In the overlapping area, as long as it conforms to the corresponding laws and regulations, major A can do it, and major B can do it, and whoever does it is responsible. For example, professional geotechnical investigation can be carried out by registered geotechnical engineers or qualified geologists (if the country has this series). Pile foundation engineering design can be undertaken by registered structural engineers, registered geotechnical engineers, foundation pit engineering design, registered geotechnical engineers and registered structural engineers. In fact, concrete engineering analysis is really needed, such as slope protection with anchor retaining piles, which mainly involves geotechnical technical problems, and structural calculation is less, so general structural engineers may not be as familiar with it as geotechnical engineers. However, the structural design and calculation of large-area foundation pit with internal support system is quite complicated, so it may be more appropriate to be undertaken by structural engineers or to be coordinated by geotechnical and structural engineers.
10, geotechnical engineering technology control
Article 27 of the Regulations on the Administration of Survey and Design Registered Engineers stipulates the obligations of registered engineers, among which paragraph (2) is "implementing the standards and norms of engineering construction", which must undoubtedly be observed. Standards and norms are the basis for the government to implement technical control on engineering construction at present, and quality is the implementation of standards and norms. However, in the process of implementation, many specific problems are not easy to deal with. Geotechnical engineers are guided by standards and specifications, which may not be the best choice for a single project, thus obliterating the enthusiasm of geotechnical engineers to adapt to local conditions and adopt advanced technology. Then, can the standard specification be made more detailed and specific, so that geotechnical engineers can follow the rules? According to the characteristics of geotechnical engineering mentioned above, it is not easy to do. There are many kinds and combinations of geotechnical materials, and the geological background and hydrogeological conditions are diverse; In the interaction with the project, its status and role are different; There are also local characteristics and local experience in various places. It is very difficult to formulate a set of specific, unified and appropriate rules for such complicated and changeable situations and problems. It is difficult to guarantee that it will be universally applicable. Just like the medical field, there are medical principles, pharmacopoeia and various inspection standards, but there is no "prescription specification", which is the case in both Chinese and Western medicine. I think, according to the characteristics of geotechnical engineering, technical control can be divided into three levels:
The first level, involving public interests and national interests such as personal health, engineering safety and environmental protection, should be set as technical regulations, which should be formulated by the state, enforced and strictly supervised. Including the basic principles of survey and design, prevention and control of all kinds of disasters, limiting the spread of harmful substances and so on.
On the second level, it is necessary to formulate specific and unified standards for a large number of repetitive technical rules, such as terms, symbols, classification, common test methods and common analysis methods, for engineers to adopt.
On the third level, we should adjust measures to local conditions and combine specific engineering disposal problems, such as the layout of survey work and geotechnical engineering design scheme. The code only stipulates the basic criteria, and geotechnical engineers will make comprehensive judgments according to the specific conditions and bear the risk responsibility.
The practice of geotechnical registered engineers has created favorable conditions for achieving the above objectives. However, there are two conditions for real implementation. First, the system of combining technical regulations with technical standards has been basically completed, and the social awareness of the rule of law and the concept of integrity have made great progress; Second, the consulting industry, engineering insurance and other market economic systems have been basically matched. All these have a gradual process. The transition period after China's entry into WTO is coming to an end, and the problem of how to integrate with the international community is very urgent. The so-called international integration should be mainly understood as the integration of systems, including the integration of geotechnical engineering specialty system and supervision standard system. It is hoped that the relevant government departments and colleagues in geotechnical engineering will study these problems in depth, improve the macro-management level of geotechnical engineering in China as soon as possible and integrate into the global economy. References:
China Qualification Examination Network Geotechnical Engineer Channel