Sensitivity Analysis of Soil Site Response Modelling in Seismic ... - ITC

Figure 1-4 A representation of the crosshole tomography method. Left borehole consists of the transmission
signals and the right one has the geophones, which receives the signals transmitted from the other
borehole.
Material properties should contain shear wave velocity or shear modulus, damping ratio, unit weight
and thickness. Water table depth is also another parameter that is needed to implement.
Unit Weight
Unit Weight parameter is the weight of a unit volume of soil is referred to as its unit weight. The units
of unit weight will be force per unit volume, whereas the units of density are mass per unit volume.
Unit weights can be calculated as follows;
•
•
Dry Unit weight γ d =ρ d g kN/m 3
Bulk Unit weight γ =ρ g kN/m 3
• Saturated Unit Weight γ sat =ρ sat g kN/m 3
•
•
Unit weight of water γ w =ρ w g kN/m 3
Submerged unit weight γ =γ sat - γ w kN/m 3
The gravitational acceleration “g” is generally taken as; 9.81 m/s 2 . Above calculations are in scientific
international units but for SHAKE2000 for unit weight pounds cubic feet is used.
Shear Modulus
Modulus of rigidity or shear modulus can be explained using elastic properties of materials. The quantity
µ, sometimes also called the rigidity, that is experimentally observed to relate stress and strain according
to Hooke's law (Weisstein, 1999 ),
[Stress]= µ[Strain]
It can also be explained as, a measure of the resistance of the body to shearing strains.
Stress can be describes as, a force per unit area provided either by gravity or by the flow of viscous
fluid. And strain can be described as, the dimensionless parameter describing deformation. It can be
thought of as the movement of one corner of a cubic box from its initial position under a stress. In
simple words, it is the relative change in shape and/or volume of a body.The concept of the formulas
shown here are related with Elasticity in Mechanics, here the basics are given but the broader explanation
is out of this research therefore it will not be explained in detail. This parameter is used if shear
wave velocity of the material is not known in SHAKE2000 and should have a unit of kilo pounds per
feet.
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Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal