3D finite elements analysis of vertically loaded composite piled raft

In recent years,a new type of foundation named composite piled raft foundation (also called long short composite piled raft) has been developed.Where designing shallow foundations would mean unacceptable settlement,or other environmental risks exist which could impair the structure in the future,composite piled raft foundations could be used.Finite element method was applied to study the behavior of this type of foundation subjected to vertical loading.In order to determine an optimal pile arrangement pattern which yields the minimum settlement,various pile arrangements under different vertical stress levels were investigated.Results show that with increasing the vertical stress on the raft,the effectiveness of the arrangements of short and long piles become more visible.In addition,a new factor named "composite piled raft efficiency" (CPRE) has been defined which determines the efficiency of long short piles arrangement in a composite piled raft foundation.This factor will increase when short piles take more axial stresses and long piles take less axial stresses.In addition,it is found that the changes in settlements for different long short piles arrangement are in a well agreement with changes in values of CPRE ratio.Thus,CPRE ratio can be used as a factor to determine the efficiency of piles arrangements in composite piled raft foundation from the view point of reducing raft settlements.

Behavior of zeolite-cement grouted sand under triaxial compression test

Permeation grouting with cement agent is one of the most widely used methods in various geotechnical projects,such as increasing bearing capacity,controlling deformation,and reducing permeability of soils.Due to air pollution induced during cement production as well as its high energy consumption,the use of supplementary materials to replace in part cement can be attractive.Natural zeolite(NZ),as an environmentally friendly material,is an alternative to reduce cement consumption.In the present study,a series of consolidated undrained(CU)triaxial tests on loose sandy soil(with relative density Dr=30%)grouted with cementitious materials(zeolite and cement)having cement replacement with zeolite content(Z)of 0%,10%,30%,50%,70%and 90%,and water to cementitious material ratios(W/CM)of 3,5 and 7 has been conducted.The results indicated that the peak deviatoric stress(qmax)of the grouted specimens increased with Z up to 50%(Z50)and then decreased.The strength of the grouted specimens reduced with increasing W/CM of the grouts from 3 to 7.In addition,by increasing the stress applied on the grouted specimens from yield stress(qy)to the maximum stress(qmax),due to the bond breakage,the effect of cohesion(c’)on the shear strength reduced gradually,while the effect of friction angle(φ’)increased.Furthermore,in some grouted specimens,high confining pressure caused breakage of the cemented bonds and reduced their expected strength.

Effects of natural zeolite and sulfate ions on the mechanical properties and microstructure of plastic concrete

One of the strategic materials used in earth-fill embankment dams and in modifying and preventing groundwater flow is plastic concrete(PIC).PIC is comprised of aggregates,water,cement,and bentonite.Natural zeolite(NZ)is a relatively abundant mineral resource and in this research,the microstructure,unconfined strength,triaxial behavior,and permeability of PIC made with 0%,10%,15%,20%,and 25% replacement of cement by NZ were studied.Specimens of PIC-NZ were subjected to confined conditions and three different confining pressures of 200,350,and 500 kPa were used to investigate their mechanical behavior and permeability.To study the effect of sulfate ions on the properties of PIC-NZ specimens,the specimens were cured in one of two different environments:normal condition and in the presence of sulfate ions.Results showed that increasing the zeolite content decreases the unconfined strength,elastic modulus,and peak strength of PIC-NZ specimens at the early ages of curing.However,at the later ages,increasing the zeolite content increases unconfined strength as well as the peak strength and elastic modulus.Specimens cured in the presence of sulfate ions indicated lower permeability,higher unconfined strength,elastic modulus,and peak strength due to having lower porosity.