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A) Site Investigation

Site investigation is investigating the strata condition and evaluating the geotechnical parameters of the ground which is the basic and initial need of every project. The Ista Sazeh company provided services in the following fields related to site investigation:

• Desk study and geotechnical investigation
• Site survey including gathering existing data, study the topographic maps, aerial photos, and satellite images.
• planning for geotechnical researches.
• subsurface investigation including drilling, sampling, and in-situ tests.
• Laboratory tests.
• Evaluation and interpretation of the results and proposing designs.

Based on the limits and conditions of the project the priority of the steps could change. 

PLANNING THE GEOTECHNICAL INVESTIGATION

Generally, in geotechnical researches as the progress of the investigation goes on the initial plan of the site investigation might change. Since the underlying condition is completely anonymous the basic design of the site investigation could be temporary and gaining knowledge could help the designer to improve the initial layout. Cooperation between the designer and the investigator is necessary for designing the investigation plan. The order of the investigation steps is the designer’s responsibility. The Ista Sazeh company proposes the planning layout for the investigation based on the regulations and references, site conditions, and engineering judgment. 

The initial layout of the geotechnical investigation is affected by the following items:

• Needed parameters and the accuracy of their estimation.
• Pattern, distance, and the depth of the boreholes.
• Number, depth, and type of sampling (disturbed and undisturbed samples).
• Type and number of in situ and laboratory tests.
• The cost of geotechnical investigations.

Generally, the geotechnical investigation’s cost varies between 0.25 to 1 percent of the project cost. The cost of the geotechnical investigation might decrease as the total cost of the projected increase. In some cases, the site investigation cost can fall to 0.1 percent. The researches show that by improving and increasing the accuracy of the site investigation the cost of the project could decrease. However, the cost of the site investigation increased. 

SERVICES AND THE GOALS OF THE GEOTECHNICAL INVESTIGATION

• The desk study was based on the existing data from projects that had been done in the past. 
• Estimating the geotechnical parameters from back analysis of the adjacent structures. 
• Drilling test pits and horizontal galleries.
• Drilling boreholes and sampling from soil and rock.
• In-situ tests.
• Laboratory tests on the samples from the site.

One of the fields in which the experience and knowledge of a team can make a difference is in the site investigation area. If the location of the boreholes is critical the cost-effective research can develop valuable data. In geotechnical engineering, the complete understanding of the subsurface condition is never achieved. Therefore, an optimum estimation can be valuable to understand the underlying condition and estimate the phenomena that affect the design. 

TESTS RELATED TO GEOTECHNICAL INVESTIGATION

The geotechnical investigation is useful in in-situ and laboratory areas. First, the experts from the Ista Sazeh company gather the data to investigate the site. Then, the chemical, physical, and mechanical tests will be done at the laboratory. Finally, the results will present to the employer. 

The site investigation has different branches each of which needs specific devices. 

DRILLING IN THE GEOTECHNICAL INVESTIGATION

In geotechnical tests, the drilling step has an important effect on the results. The standard penetration test (SPT), cone penetration test (CPT), Lefranc, and Lugeon are the tests that perform during the drilling. 

The Lefranc and Lugeon tests are permeability tests. One of the main parameters that impact the geotechnical condition is the permeability of the soil. Hence, a great estimation of the soil permeability can lead to better design. The existence of water in the soil is a critical issue and the most of excavation collapses and instabilities are because of the water and its flow. With a falling head test and constant head test, valuable data can be achieved. Since the permeability of the clay is low the falling head test is useful for clays. As the speed of the water flow is low the time of the falling water is utilized to estimate its permeability. As the permeability of the sand is high falling head test is useless and the constant head test is appropriate for sand and gravel. 

IN-SITU DIRECT SHEAR TEST

The in-situ direct shear test is a useful test for evaluating the internal friction angle and the cohesion of the soil. The estimation of the factor of safety and bearing capacity of the foundations are the results of the in-situ direct shear tests.

PLATE LOAD TEST

The purpose of the plate load test is analysis the compactibility of the soil and the rock. In this test, an incremental load is induced to the soil or rock through a circular or square plate. Estimating the compactibility and the elastic modulus of the soil are the results of the test. 

B) SEISMICITY RESEARCH

Seismology is one of the geophysics branches which investigate the propagation of the wave in the ground. To estimate the seismicity of a region in which lack of data is the problem, probabilistic evaluation is needed. 

To design earthquake resistance structures a true understanding of the energy produced by the earthquake during the lifecycle is needed. The best way to understand the energy is by using an accelerogram. To access this purpose the risk analysis and seismology is needed in the following categories:

• Investigating the geology and seismology of the ground.
• Identification of the faults
• Estimation of the horizontal and vertical acceleration for structural design.
• Estimation of the side risks of the site (for example faulting).
• Evaluation of the response spectrum.
• Seismology inside the borehole.

In a geotechnical investigation for understanding the soil layers’ condition and its strength, inside borehole tests are needed. In these types of tests, the shear and pressure waves are used. 

C) GEOPHYSICS INVESTIGATION

GEOPHYSICS TESTS EXECUTION

• Study and determination of the groundwater surface. 
• Determination of the type and depth of the soil and the bedrock.
• Proposing the basics, criteria, and parameters needed for the geotechnical projects according to the sensitivity of the project.
• Gaining the parameters needed for the design.
• Investigation of the execution of the project in the adjacent environment. 
• Control of the safety and the assumptions used for the design. 
• Site survey in case of facing unpredicted geotechnical conditions.

GEOPHYSICS TESTS IN GEOTECHNICAL INVESTIGATION

Sometimes because of the size limitations and cost of the drilling other ways are proposed to understand the underlying conditions of the soil and the rock. The geophysics tests are the test to investigate the soil layers and their properties without any disturbance. The base of the geophysics method is the usage of physic in the area of geotechnics. 

GPR TEST

One of the geophysics tests is the GPR test. The GPR test is used to gather data from magnetic signals. The GPR test helps engineers to determine the location of the underground utilities, depth of the concrete, the concrete condition, and its density. 

GEOELECTRIC TEST

In the geoelectric test, accurate data from soil and rock condition is prepared with the transformation of the electricity.

ENGINEERING GEOLOGY AND GEOENVIRONMENTAL

The topics of the area are:

• The engineering geology
• preparation of the geology and geoenvironmental plans
•  soil pollution plans
• determination of the underground water surface
• determination of the energy transformation pipes location
• determination of the underground voids
• environmental investigation
• evaluation of the earthquake risk
• the investigation of the site condition.