Geoscience Reference
In-Depth Information
Recent advances in the geotechnics
of organic soils and peat
7.1 INTRODUCTION
In recent years, in terms of economic development, concerns about peat and its dif-
ficulties from the geotechnical standpoint have led to the development of many new
techniques for improving it. Peat is soil with a high compressibility and low shear
strength. This implies that the engineers have to build structures, like roads and high-
ways, railways, ports and airports, land reclamations, storage tanks, chemical plants,
bridges, tunnels and residential buildings in less favourable areas (Mysliñska, 2003). A
variety of methods (which have been explained in Chapter 6) are widely used for sta-
bilizing soft soils. Various new ground improvement techniques have been suggested,
and recently there have been new advances in organic soils and peat stabilization,
such as electrokinetics, new deep mixing method, biocementing and reinforced stone
columns.
7.2 ELECTROKINETICS
Electrokinetics is defined as the physicochemical transport of charge, action of charged
particles and effects of applied electric potentials on the formation of and fluid
transport in porous media (Acar and Alshawabkeh, 1993; Acar
et al
., 1995).
Isomorphous substitution and broken continuity of a clay structure presents a net
negative charge at the surface of clay particles. The clay attracts positively charged
ions from the pore water to balance the negative charge. The charge distribution at
the colloid surface is shown in Figure 7.1. This distribution shows an increase in
anion concentration and a decrease in cation concentration with distance from the
clay surface. Dipolar water molecules can be electrically attracted toward the surface
of clay when the clay or colloid is placed in water. The negative surface charge of
the clay or colloid and the electrically attracted water are together termed the diffuse
double layer (Hunter, 1993). The nature and thickness of the double layer affects the
clay's characteristics. In general, the tendency (for particles) for flocculation decreases
with increasing thickness of the double layer.
The diffuse layer can be compressed in solutions of high concentration, mainly
because diffusion away from the surface is lower. The properties of the cations also
have an effect, the higher their charge, the more strongly they are attracted. Sodium
