What are the most important tests that can be made for soil and rocks for construction purposes?

There are more than one test to evaluate the bearing capacity and settlement  of the foundation level like plate load test, consolidation test, shear strength parameters and compaction test that it will be depend also on type of soil then all those tests will be done with geotechnical investigation.

The primary considerations for foundation support are bearing capacity, settlement, and ground movement beneath the foundations.

cone penetration or cone penetrometer test (CPT)

standard penetration test

Today, the CPT is one of the most used and accepted soil methods for soil investigation worldwide.

Common tests to measure the strength and stiffness include the triaxial shear and unconfined compression test.

Surface exploration can include geologic mapping, geophysical methods, and photogrammetry

Geophysical exploration is also sometimes used. Geophysical techniques used for subsurface exploration include measurement of seismic waves (pressure, shear, and Rayleigh waves), surface-wave methods and/or downhole methods, and electromagnetic surveys (magnetometer, resistivity, and ground-penetrating radar).

 In general, geotechnical engineers:

1. Estimate the magnitude and location of the loads to be supported.
2. Develop an investigation plan to explore the subsurface.
3. Determine necessary soil parameters through field and lab testing (e.g., consolidation test, triaxial shear test, vane shear test, standard penetration test).
4. Design the foundation in the safest and most economical manner.

First of all, geology of the soil