Geotechnical engineering is a subset of civil engineering that is related to natural materials and materials available near or on the ground, which are called soil or rock materials. In geotechnical engineering, branches such as engineering geology, soil mechanics, foundation engineering and rock mechanics are emphasized.
Soil mechanics is a branch of engineering that studies the physical characteristics and behavior of soil masses under loads. Foundation engineering is the application of the principles of soil mechanics to scientific issues.
In general, this science includes the application of the concepts of soil mechanics and rock mechanics in foundation design problems. Considering the introduced branches, geotechnical engineering to the physical and mechanical properties of rocks, prediction and performance of soil and bedrock reaction against loads from the structure, stability of natural and artificial slopes, soil and rock performance from chipping And excavation, stability of retaining walls, both temporary and permanent, examining the performance of problematic soils, problems of pressure control and water movement from under and the body of earthen dams, as well as maintenance and reconstruction of old buildings.

Objectives of geotechnical studies and its experiments
The goals pursued in geotechnics are:

• Identify underground layers
• Determining their physical and mechanical properties
• Determining the type of foundation and the depth of its establishment
• Determining the bearing capacity of Pi
• Determining the reaction coefficient of the soil under the foundation for designing the foundation structure
• Classification of land type according to Iranian 2800 regulations
• Determining the type of cement used in foundation concrete
• Check the groundwater status
• Provide technical recommendations for foundation construction
• Study of geology and general seismicity of the study area in terms of information and statistics
Before starting a project in the desired land, all these studies and experiments should be done and all studies in the field of general geology of the study area should be done and reviewed.

Geotechnical studies for a residential project
All the things that are done in a report of geotechnical and soil mechanics studies for a residential project before it is built are:

• Information about the bedrock of the region, existing formations
• Information about historical earthquakes and their location and time
• Study and study of device earthquakes in the desired area
• Using the focal mechanism of earthquakes to determine the kinetic mechanism of faults,

Structural features of the region as well as the direction of stresses on the earth’s crust, seismic properties and the direction of movement of lithosphere plates
• Determining the site land in terms of soil and rock type
• Determine the characteristics and distance of faults near the project
• Land type classification

The purpose of the studies and experiments performed to construct a residential project
All these studies and experiments are performed for the following purposes:

• Determine the type of foundation based on the soil identified below
• Determining the stability of the project site soil against overturning and slipping in the event of an earthquake and wind force
• Determine the bearing capacity of the foundation based on the specifications obtained from the tested soil
• Determining and calculating soil stresses and lateral pressures
• Finally, providing technical recommendations in terms of necessary proposals for the type of material (such as cement type, foundation type, frost depth,

Land improvement, depth of foundations, suggestions for excavation, determination of sewage and surface water disposal system,

Suggestions for excavation and compaction operations)

On-site loading tests

In order to evaluate the geotechnical improvement, in addition to on-site tests and quality controls, large-scale tests are performed in a limited number that obtain the operating conditions of the structure under actual loading conditions. Some of the experiments in the field of geotechnical science are as follows:
• Candle loading and micro-candle testing
Nile and anchor tensile test
• Vibrating loading of stone and sand columns
• Testing the load of jet grout columns and deep soil mixing

• Field studies and tests such as standard penetration test, in situ density test, plate loading test and direct in situ shear test
• Consider existing buildings and facilities around the project
• Determine the appropriate depth of boreholes according to the type of soil and the number of layers
• Classification of subsurface soils and determination of their mechanical, physical and chemical properties
• We take the soil sample from the project site and perform the relevant tests on it in the soil laboratory. (Experiments such as hydrometric testing, granulation testing, etherberg limits, density and percentage of natural moisture, as well as direct shear testing)
• Investigation of studies and experiments and determination of soil geotechnical characteristics to calculate soil bearing capacity (characteristics such as natural soil specific gravity, effective internal friction angle of soil, effective soil adhesion resistance, modulus of soil elasticity)
• Investigating the potential of problematic soils in the study area