Geotechnics

LABORATORY

Proper laboratory testing of soils to determine their physical properties is an integral part of the design and construction of structural foundations, the placement and improvement of soil properties, and the specification and quality control of soil compaction works. It needs to be kept in mind that natural soil deposits often exhibit a high degree of nonhomogeneity. The physical properties of a soil deposit can change to a great extent even within a few hundred meters. The fundamental theoretical and empirical equations that are developed in soil mechanics can be properly used in practice if, and only if, the physical parameters used in those equations are properly evaluated in the laboratory. So, learning to perform laboratory tests of soils plays an important role in the geotechnical engineering profession.

1. Soil sampling

• depth and number of drills
• disturbed/undisturbed samples

2. Grain size distribution

• gradation curve
• clay, silt, sand, gravel
• uniformity coefficient (c_u)
• coefficient of curvature (c_c)
• soil ternary diagram

3. Water content and bulk density

• water content (w)
• bulk density (ρ)
• particle density (ρ_s)
• wet unit weight (γ)
• particle unit weight (γ_s)
• sry unit weight (γ_d)
• saturated unit weight (γ_sat)
• submerged unit weight (γ’)
• porosity (n)
• void ratio (e)
• saturation ratio (S_r)

4. Atterberg’s limits.

• plastic limit (w_P)
• liquid limit (w_L)
• plasticity index (I_P)
• consistency index (I_C)

5. Relative density

• relative density (I_D)
• tamping capacity (C_i)

6. Soil permeability.

• Darcy’s Law
• coefficient of permeability (k)

7. Compaction properties of soils

• Proctor test
• compaction curve
• maximum dry density (ρ_{d, max})
• optimum water content (w_opt)

8. Compressibility of soils

• Oedometer test
• Oedometer modulus (E_oed)
• volumetric compresibility coefficient (m_v)
• compresibility coefficient (a_v)
• compresibility index (C_c)

9. Shear strength parameters of soils

• shear strength
• direct shear test
• triaxial compression test
• unconfined compressive test
• internal friction angle (φ)
• cohesion (c)

10. Drill logs