Sustainable Ground Improvement Technique for Geo-Disaster Mitigation - Sustainable Practices in Geoenvironmental Engineering - page 443

Although metamorphism is sometimes considered to be a part of diagenesis, these two
processes should be separated because the mechanisms involved between diagenesis and
metamorphism are basically different. Metamorphism is the recrystallization of rocks
under changes in physical and chemical conditions, primarily heat and pressure.
Natural catastrophic events such as hurricanes, typhoons, earthquakes, tornadoes, tsu-
namis, volcanic eruptions, rainstorms, and blizzards can trigger or cause soil movements
such as landslides, rock falls due to dislodgement of rocks at higher elevations, debris low,
liquefaction, etc. Such events of soil movements can be classiied as geo-disasters—the
level of impact of such disasters being magniied when damage to the built environment
and loss of human lives and other life forms are involved.
12.2.1 Soft Soils and Stability
Unconsolidated compressible soils of medium to low densities—often called soft soils - are
susceptible to excessive distortion and deformation when subjected to overpowering exter-
nal forces, i.e., external forces larger than internal resisting forces. The problem becomes
acute when such soils are located on slopes or constitute part of a load support system. The
behavior of soft soil under loads is well-recognized and understood in geotechnical engi-
neering practice, and normal procedures for avoiding distortion-deformation and exces-
sive soil movement have been (and still are) to increase the density of the soil by applying
soil stabilization procedures such as mechanical compaction, consolidation procedures,
binder additives (lime, cement, ly ash, pozzolans, etc.). Soil density is a direct relection of
soil particle packing—meaning that the higher the density of a soil, the tighter is the pack-
ing of particles. The combination of particle packing and physicochemical forces acting
between particles results in interparticle action or particle interaction. The closer the soil
particles are to each other, the greater is the bonding established as a result of interparticle
action—with the obvious end-point of a tight-packing soil mass being that of a rock. The
lesson that one learns is that the physical stability of a soil is increased in proportion to its
compactness, and that the bonding achieved through interparticle action, especially when
tight particle packing exists, provides for the optimum scenario for a stable soil mass. As
long as soil particles are held tightly together, the soil mass should be stable, and the likeli-
hood of occurrence of geo-disaster such as landslides, ground settlement under load will
be minimized.
12.2.2 Soft Soil Engineering and Ground Improvement
Conventional techniques in soft soil engineering for stabilizing soft soil—i.e., increasing
the bearing strength or capability of the ground to support heavier loads and to withstand
greater displacement forces—include such procedures as cement mixing, use of lime, ly
ash, and other types of binding agents, pile foundations, drainage work, etc. These tech-
niques are designed to improve ground functionality—otherwise called ground improve-
ment. Evaluation and adoption of a suitable ground improvement procedure should be
based on at least four key considerations: (a) capability of improved ground or site to meet
site functionality requirements, (b) ability to meet objectives or requirements for sus-
tainable management of the geoenvironment, (c) total life cycle cost, and (d) durability
of improved ground. The selection of materials and procedure to be used should take
into account the durability of the materials involved to avoid failure of the improved site
because of failure of the material used in the ground improvement procedure.