Soil Exploration

Soil Exploration

Subsurface exploration is conducted to identify the soil and rock layers, determine their engineering properties, and locate the groundwater table.

Boring Methods

Common Methods

Auger Boring: Good for shallow depths in soft soils.
Wash Boring: Uses water jet to displace soil.
Rotary Drilling: Used for deep borings and rock coring.

Field Tests

Standard Penetration Test (SPT)

A split-spoon sampler is driven into the soil.
Hammer: 63.5 kg (140 lb).
Drop: 760 mm (30 in).
N-value: The number of blows required to penetrate the last 300 mm (12 in) of a 450 mm drive.
Corrections applied for overburden pressure ( $C_N$ ) and energy efficiency ( $C_E$ ). $N_{60} = \frac{N \cdot \eta_H \cdot \eta_B \cdot \eta_S \cdot \eta_R}{60}$

Cone Penetration Test (CPT)

A cone with a friction sleeve is pushed into the soil at a constant rate.

Measures Tip Resistance ( $q_c$ ) and Sleeve Friction ( $f_s$ ).
Provides continuous profile.
Excellent for soft soils and delineating stratigraphy.

Sampling

Disturbed Samples: Obtained from SPT split-spoon. Used for classification (grain size, Atterberg limits).
Undisturbed Samples: Obtained using Shelby tubes (thin-walled). Essential for consolidation and shear strength tests on clays.

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