Dear reader, throughout last few posts we were discussing about site classification for design of structure for earthquake. Of these site class A, class B, class C, class D and class E have some criteria upon which we can determine them say shear wave velocity, standard penetration resistance, undrained shear strength of soil at site.
The site class F requires site-specific tests; these are collapse behavior, organic content say peat or other highly organic clays, plasticity and thickness of clay layer of soft or medium stiff. When a site represent these classes, complying any of these; we can classify it as site class F. That is from boring data and in-situ tests, we can primarily suspect a site as class F and then more elaborate site-specific evaluations are conducted. Field identification of different types of soils have discussed in our previous posts.
Here we can ensure a site as class E. In determining this we have to know about plasticity index, water content, undrained shear strength of soil; the thickness of layers of soil layer is also important. Dear reader at first we will learn about determination of s̄u.
Sui = Undrained shear strength (psf), ≤5000 psf
In kpa this value is ≤240kpa; use ASTM D2166 or D2850 to determine this parameter.
dc= Total thickness of soil layers within top 100ft (cohesive soil is considered)
K = Number of the cohesive layers within top 100ft
di = Thickness of soil layer at any depth within upper 100ft