Engineering and Construction

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, perme-
ability, expansion or collapse potential, and frost susceptibility.

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

In terms of the general procedures and requirements for subsurface exploration, Hvorslev (1949) states:

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.

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 subsurface exploration. Table 2.4 (from Sowers and Royster, 1978, based on the work by ASTM; Lambe, 1951; Sanglerat, 1972; Sowers and Sowers, 1970) summarizes the boring, core drilling, sampling and other exploratory techniques that can be used by the geotechnical engineer.

As mentioned earlier, the borings, test pits, or trenches are used to determine the thickness of soil and rock strata, estimate the depth to groundwater, obtain soil or rock specimens, and perform field tests such as Standard Penetration Tests (SPT) or Cone Penetration Tests (CPT). The Unified Soil Classification System (USCS) can be used to classify the soil exposed in the borings or test pits (Casagrande, 1948).

The subsurface exploration and field sampling should be performed in accordance with standard procedures, such as those specified by the American Society for Testing and Materials (ASTM, 1970, 1971, and D 420-03, 2004) or other recognized sources (e.g., Hvorslev, 1949; ASCE, 1972, 1976, 1978).

App. A (Glossary 1) presents a list of terms and definitions for subsurface exploration.