The in-situ tests in the field have the advantage of testing the soils in their natural, undisturbed condition. Laboratory tests, on the other hand, make use of small size samples obtained from boreholes through samplers and therefore the reliability of these depends on the quality of the samples so called “undisturbed” samples. Further, obtaining undisturbed samples from non-cohesive (granular soils) is not easy, if not impossible and also sometime it is very difficult to obtain undisturbed samples from soft to firm cohesive soils.
Therefore, it is common practice to rely more on laboratory tests where such soils are encountered. Where the subsoil strata are essentially non-cohesive in character, the bias is most definitely towards field tests. These tests measure the physical properties of the subsurface soil directly, without removal. This provides the advantages of generating a more accurate reflection of conditions underground as well as avoiding the necessity of sending samples out for lab testing.
The field tests commonly used in subsurface investigation are:
|The Field Tests|
|Plate Load Test||Field CBR||In-situ Permeability Test||In-Situ Dry Density of Soil by Sand Replacement Method
|In-situ Van Shear Test||In-situ Direct Shear Test||Static cone penetration test (SCPT)||Dynamic Cone Penetration Test (DCPT)|
|Standard Penetration Test (SPT)||In-Situ Dry Density of Soil by Core Cutter Method|