• SVC, RAMPURHAT

Geotechnical Investigation

Geotechnical investigations are performed by geotechnical engineers or engineering geologists to obtain information on the physical properties of soil earthworks and foundations for proposed structures and for repair of distress to earthworks and structures caused by subsurface conditions; this type of investigation is called a site investigation. Geotechnical investigations are also used to measure the thermal resistance of soils or backfill materials required for underground transmission lines, oil and gas pipelines, radioactive waste disposal, and solar thermal storage facilities. A geotechnical investigation will include surface exploration and subsurface exploration of a site. Sometimes, geophysical methods are used to obtain data about sites. Subsurface exploration usually involves soil sampling and laboratory tests of the soil samples retrieved.

Geophysical Methods

Geophysical methods are used in geotechnical investigations to evaluate a site's behavior in a seismic event. By measuring a soil's shear wave velocity, the dynamic response of that soil can be estimated. There are a number of methods used to determine a site's shear wave velocity:

  • Crosshole method
  • Downhole method (with a seismic CPT or a substitute device)
  • Surface wave reflection or refraction
  • Suspension logging (also known as P-S logging or Oyo logging)
  • Spectral analysis of surface waves (SASW)
  • Multichannel analysis of surface waves (MASW)

Laboratory Tests

The Atterberg limits define the boundaries of several states of consistency for plastic soils. The boundaries are defined by the amount of water a soil needs to be at one of those boundaries. The boundaries are called the plastic limit and the liquid limit, and the difference between them is called the plasticity index.

ASTM D 1883. A test to determine the aptitude of a soil or aggregate sample as a road subgrade. A plunger is pushed into a compacted sample, and its resistance is measured. This test was developed by Caltrans, but it is no longer used in the Caltrans pavement design method. It is still used as a cheap method to estimate the resilient modulus.

ASTM D3080. The direct shear test determines the consolidated, drained strength properties of a sample. A constant strain rate is applied to a single shear plane under a normal load, and the load response is measured. If this test is performed with different normal loads, the common shear strength parameters can be determined.