Dear Ali Nabizade Please do recommend my answer if helpful

As a geotechnical engineer, the most important piece of equipment you use is typically the drilling rig. Drilling rigs are essential tools in geotechnical investigations, allowing engineers to collect soil and rock samples from below the ground surface for analysis. These samples provide critical information about the subsurface conditions, helping in the design and construction of structures such as buildings, bridges, dams, and other infrastructure projects.

Key aspects and capabilities of drilling rigs in geotechnical engineering include:

1. **Core Sampling:** Drilling rigs can extract core samples, which are cylindrical sections of soil or rock, preserving the layers and structure. Core samples provide valuable insights into the geology, soil composition, and rock properties.

2. **Borehole Logging:** Drilling rigs can be equipped with tools for logging information about the subsurface conditions. This includes measuring parameters such as soil strength, groundwater levels, and other geotechnical properties.

3. **In Situ Testing:** Some drilling rigs are designed to perform in situ tests directly in the borehole. This can include tests for soil density, permeability, and other geotechnical characteristics.

4. **Depth Penetration:** Drilling rigs can reach considerable depths, allowing engineers to explore and understand the subsurface conditions at various depths below the ground surface.

5. **Soil and Rock Classification:** By extracting samples, geotechnical engineers can classify soils and rocks according to engineering standards, providing crucial information for foundation design and construction methods.

6. **Instrumentation Installation:** Drilling rigs are often used to install instruments in boreholes for long-term monitoring of factors such as groundwater levels, settlement, and slope stability.

While other equipment such as laboratory testing apparatus, geophysical instruments, and surveying tools are also essential in geotechnical engineering, the drilling rig stands out as a fundamental tool for gathering direct information from beneath the ground surface. The accuracy and reliability of the data obtained from drilling operations significantly impact the success and safety of engineering projects.

I would rely on is a Cone Penetration Test (CPT) rig. The CPT provides invaluable insights into soil properties and stratigraphy by measuring resistance and pore pressure during penetration. This data is crucial for site characterization, foundation design, and assessing potential geohazards, making the CPT rig indispensable in many geotechnical investigations.