Determine attenuation coefficients of saturated sand from standard penetration test, applied to Nhon Hoi economic zone

Tóm tắt

Vietnam is located in a strong earthquake zone with many areas having
a ground acceleration (ag) of greater than 0.08 g (TCVN 9386:2012).
According to Vietnamese standard TCVN 9386:2012, the calculation and
design of construction grade III or higher in areas where have ground
acceleration ag ≥ 0.08 g must include seismic design. In calculations of
earthquake-resistant pile foundation, the bearing capacity of the pile
including the tip resistance strength (qb) and endurance strength (fi) need
to be multiplied by attenuation coefficients (eq1 and eq2). They are the
most important parameters and depend on the soil types, saturation
conditions, and earthquake intensity. The article introduces a method to
determine the attenuation coefficients according to the standard TCVN
10304:2014. In addition, analyzing the theoretical basis to give the
expression to determine attenuation coefficients based on the durability
factor (Ired) and pore water pressure ratio (Ru) of saturated sand under
the earthquakes. Furthermore, the paper presents a method to determine
Ru from the results of standard penetration test (SPT) by combining the
method of Seed and Alba (1986) with the method of Marcuson and Hynes
(1990). In which, Seed and Alba's method was used to determine factor of
safety against liquefaction (FSL), and then Marcuson and Hynes' method
was used to determine Ru from FSL. The application in Nhon Hoi Economic
Zone shows that: The silty fine grained sand, which is medium dense and
saturated, has a attenuation coefficient of tip resistance eq1 = 0.74÷0.76
and attenuation coefficient of friction eq2 = 0.90; The fine grained sand,
which is dense and saturated, has eq1 = 0.79÷0.82 and eq2 = 0.94