A Closer Look at Prevailing Civil Engineering Practice - European ...

A Closer Look at Prevailing Civil Engineering Practice, What, Why and How
Vincent T. H. CHU
(iii) Soil nail head and facing provides containment effect to limit the
deformation near slope surface.
Soil nail head serves to provide reaction in mobilizing tensile force in soil
nail. Moreover, it provides confinement to soils in active zone behind soil
nail head and avoids the occurrence of local failure between adjacent soil
nails.
4. What is the purpose of installation of erosion control mat in
slopes
Steep slopes are prone to intermittent high velocity flows during rainstorm
and this causes erosion at slope surface which prevents the growth of
vegetation.
Erosion control mat is installed to control soil erosion and provide soil
stability until vegetation can be established. The principal function of
erosion control mat is to prevent pre-vegetated soil loss by stabilizing and
protecting soils from rainfall and surface erosion. Moreover, it could provide
a long-term artificial erosion control system which would increase the shear
resistance of vegetation and provide long-term, tenacious reinforcement of
the root system.
5. For Peck’s pressure envelope for braced excavation, should total
weight or effective weight be used in rectangular and trapezoidal
envelope
The use of active and at-rest theory is not applicable in braced excavation.
In essence, upper struts tend to be more heavily loaded while lower struts
appear to be less loaded when compared with active pressure theory.
Peck then measured the bracing loads which were converted back to soil
pressures. For example, the pressure envelope for non-cohesive soils is
0.65rHK a (r=soil density, H=height of excavation and K a =active pressure
coefficient).
Some engineers consider r as total soil weight without applying any water
pressure. However, Peck has said “the earth pressures are essentially
effective active pressures multiplied by a factor and redistributed as a
rectangle or a trapezoid.” Hence, effective weight of soils should be used
for r with water pressures added separately.
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