2.3 Purpose of Subsurface Exploration

The general purpose of subsurface exploration is to determine the following (AASHTO, 1996):

1.Soil strata
   a.Depth, thickness, and variability
   b.Identification and classification
   c.Relevant engineering properties, such as shear strength, compressibility, stiffness, permeability,          expansion or collapse potential, and frost susceptibility.

Example of a soil boring log

2.Rock strata
   a.Depth to rock
   b.Identification and classification
   c.Quality, such as soundness, hardness, jointing and presence of joint filling, resistance to
      weathering (if exposed), and soluble nature of the rock.
3.Groundwater elevation
4.Local conditions requiring special consideration

Investigation of the distribution, type, and physical properties of subsurface materials are, in some
form or other, required for the final design of most civil engineering structures. These investigations are performed to obtain solutions to the following groups of problems:

Foundation problems or determination of the stability and deformations of undisturbed subsurface
materials under superimposed loads, in slope and cuts, or around foundation pits and tunnels; and determination of the pressure of subsurface materials against supporting structures when such are needed.

Construction problems or determination of the extent and character of materials to be excavated or
location and investigation of soil and rock deposits for use as construction materials in earth dams and fills, for road and airfield bases and surfacing, and for concrete aggregates.

Groundwater problems or determination of the depth, hydrostatic pressure, flow, and composition of
the ground water, and thereby the danger of seepage, underground erosion, and frost action; the influence of the water on the stability and settlement of structures; its action on various construction materials; and its suitability as a water supply.

TYPES OF SUBSURFACE EXPLORATION
There are many different types of subsurface exploration, such as borings, test pits, or trenches.

Table 2.3 presents general information on foundation investigations, samples and samplers, and sub-surface exploration.