Looking ahead to the future direction of geotechnical engineering, I believe it is necessary to comprehensively consider the characteristics of the geotechnical engineering discipline, the demands that engineering construction places on geotechnical engineering development, and the influence of related disciplines on geotechnical engineering. The objects of geotechnical engineering research are rock masses and soil masses. In the entire geological history of their formation and existence, rock masses have undergone various complex geological processes and therefore possess complex structures and in-situ stress field environments. Different types of rock masses in different regions, having experienced different geological processes, often differ greatly in engineering properties. After rock is exposed at the surface, it weathers to form soil; the soil either remains in place or, through the denudation and transport action of wind, water, and glaciers, is deposited elsewhere to form soil layers. The weathering environments and the dynamic conditions of transport and deposition in various regions during various geological periods all differ, so soil masses not only have complex engineering properties but also exhibit strong regionality and individuality in their properties. 

    The strength characteristics, deformation characteristics, and permeability characteristics of rock and soil are all determined through tests. In laboratory tests, objective causes of error—such as the representativeness of undisturbed specimens, the unavoidable disturbance during sampling and the release of initial stress, and the difference between test boundary conditions and actual conditions in the foundation—make laboratory test results differ from the actual behavior of rock and soil in the foundation. In in-situ tests, errors brought about by the representativeness of field measurement points, the disturbance to the rock and soil mass when embedding test elements, and the reliability of test methods are also difficult to estimate. 

    The above characteristics of geotechnical materials and their tests determine the particularity of the geotechnical engineering discipline. Geotechnical engineering is an applied science. In geotechnical engineering analysis, satisfactory results can be obtained only by applying comprehensive theoretical knowledge, indoor and outdoor measurement results, and engineers' experience. When looking ahead to the development of geotechnical engineering, one must attach importance to the particularity of the geotechnical engineering discipline and the characteristics of geotechnical engineering problem analysis methods. 

Geotechnical engineering problems arising in civil engineering construction have promoted the development of the geotechnical engineering discipline. For example, the earliest problem encountered in civil engineering construction was soil mass stability. The earliest theoretical contribution in soil mechanics was Coulomb's establishment of Coulomb's law in 1773. Subsequently, the Rankine (1857) theory and the Fellenius (1926) circular slip analysis theory were developed. To analyze the process by which the settlement of soft clay foundations under load develops over time, Terzaghi (1925) developed one-dimensional consolidation theory. Reviewing the development of geotechnical engineering in China over the past 50 years, it has developed closely around the geotechnical engineering problems arising in China's civil engineering construction. Before reform and opening up, geotechnical engineering workers focused more attention on geotechnical engineering problems in water conservancy, railway, and mine engineering construction. After reform and opening up, with the development of high-rise buildings, urban underground space utilization, and expressways, geotechnical engineering workers focused more attention on geotechnical engineering problems in building engineering, municipal engineering, and transportation engineering construction. The functionalization of civil engineering, three-dimensional urban development, high-speed transportation, and improvement of the comprehensive living environment have become characteristics of modern civil engineering construction. Population growth has accelerated urban development, and urbanization has promoted the rapid development of large cities in number and scale. People will continuously expand new living space, develop underground space, expand toward the sea, build cross-sea bridges, subsea tunnels, and artificial islands, transform deserts, and build expressways and high-speed railways. Looking ahead to the development of geotechnical engineering, one cannot depart from an analysis of the development trends of modern civil engineering construction in China. 

In recent years, with industrial development, the environment has been damaged to varying degrees, and environmental engineering has attracted increasing attention. Environmental geotechnical engineering is a new discipline closely combining geotechnical engineering with environmental science. It mainly applies the viewpoints, technologies, and methods of geotechnical engineering to serve environmental treatment and protection. Human production activities and engineering activities cause many environmental hazards, such as goaf collapse caused by mining, regional land subsidence caused by excessive groundwater extraction, industrial waste, municipal solid waste and other wastes—especially toxic and harmful waste—polluting the environment, and the impact of construction disturbance on the surrounding environment. In addition, disasters such as earthquakes, floods, wind-blown sand, debris flows, landslides, ground fissures, and ground collapse caused by hidden karst damage the environment. The treatment and prevention of the above environmental problems have presented many new research topics to geotechnical engineers. With the acceleration of urbanization and industrialization, environmental geotechnical engineering research will become even more important. Environmental geotechnical engineering research should be recognized and valued from the perspective of maintaining a good ecological environment and sustainable development!

From last year's Hangzhou subway accident, we can see that future space utilization will develop from space to joint utilization of space and underground space, so the maintenance and stability of foundation pit engineering have become primary issues. With the development of high-rise buildings and the development of urban underground space, deep foundation pit engineering is increasing day by day. The stability and deformation of the retaining system in foundation pit engineering are important research areas. 

Research on the stability and deformation of the retaining system in foundation pit engineering includes the following aspects: calculation of earth pressure, reasonable types and applicable scope of retaining systems, design and optimization of retaining structures, the "space-time effect" of foundation pit engineering, deformation of retaining structures, and the impact of foundation pit excavation on the surrounding environment, etc. Foundation pit engineering involves three basic problems—soil mass stability, deformation, and seepage—and must consider the interaction between soil and structure. It is a comprehensive topic and also a systems engineering project.

Foundation pit engineering is highly regional and individualized. In some foundation pit projects, the stability of the retaining structure caused by earth pressure is the main contradiction; in others, soil failure caused by seepage in the soil is the main contradiction; and in others, controlling the amount of ground deformation around the foundation pit is the main contradiction. At present, earth pressure theory is still far from perfect. At-rest earth pressure is determined empirically or calculated by semi-empirical formulas, and active and passive earth pressures are calculated according to Coulomb's (1776) earth pressure theory or Rankine's (1857) earth pressure theory; all of these appeared before Terzaghi's effective stress principle was introduced. When considering the influence of groundwater on earth pressure, whether to use separate calculation of water and earth pressures or combined calculation of water and earth pressures is more consistent with actual conditions remains a matter on which academic and engineering circles do not yet agree. 

The earth pressure acting on the retaining structure is related to the displacement of the retaining structure. The earth pressure borne by the retaining structure of a foundation pit is generally between active earth pressure and at-rest earth pressure, or between passive earth pressure and at-rest earth pressure. In addition, soil has creep behavior, and the earth pressure acting on the retaining structure is also related to the duration of action. 

Geotechnical engineering is an applied science that serves engineering construction. The problems raised in engineering construction are the topics that geotechnical engineering should study. The development direction of the geotechnical engineering discipline is closely related to the development trend of civil engineering construction. The hotspot of world civil engineering construction has shifted to East Asia and to China. China has a vast territory and complex engineering geology. The scale of China's civil engineering construction, the duration of sustained development, and the geotechnical engineering technical problems encountered in engineering construction are unmatched by other countries. This has created very good conditions for China's geotechnical engineering research to rank among the world's first class and gradually take a leading position. Looking ahead 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.