نشریه پژوهش های تجربی در مهندسی عمران
سال دوم شماره 1 (پیاپی 3، بهار و تابستان 1394)

Plastic limit variations of clay soil depend upon different factors including lime type and percentage، curing moisture content، curing time، type and percentage of clay soil minerals and soil-lime mixture pH. Clay soil mineral type (i. e. soil mineralogy) is one of the most important factors. Clay soil consists of various minerals including kaolinite، montmorillonite، illite etc. Plastic limit variations routine would change duo to changes in mineral combination of clay soil under stabilization. The obtained results of present study indicate that plastic limit variations routine is ascending due to lime addition to clay soil for most of the minerals. Liquid limit variations، however، are different and it can be either ascending some minerals or descending for the others. Furthermore، the obtained results show that the higher the mixture curing moisture content، the higher the plasticity index.

Use of Reclaimed Asphalt Pavement in HMA is beneficial by reduction of initial costs. But the higher stiffness of aged binder may lead to workability issues in the field، therefore use of large percentages of RAP impacts the HMA properties. Utilizing Sasobit is a solution to use more RAP at a relatively lower temperature in HMA mixes. This study investigates the effects of 2 percent Sasobit on the reduction of compaction temperature by measuring low shear viscosity and workability of mixtures containing RAP binder. Low and intermediate temperature properties of RAP binder using mix designs were compared to properties of artificially aged binders. Virgin binder was aged in PAV to make artificial RAP binder. Comparison between physical parameters of RAP binder and binder aged in PAV was done and it was found that about 40 hours is sufficient for simulating the aging of RAP binder and making artificially aged binder. Results of this study on artificial RAP show that utilizing Sasobit is a feasible way to make HMA which contain 25% RAP. Utilizing RAP and Sasobit together in a HMA project would lead to select softer virgin asphalt binder with a lower performance grade.

Today، sanitary landfills are one the basic needs of human societies. Clay liners are used frequently in landfills in order to prevent leachate''s leaking into the outside environment. Existence of different chemicals in leachate can affect the geotechnical properties of clay liners and arise their need for a more conservative design. Therefore، investigating into the possible changes in geotechnical properties of clay liners because of the chemicals of leachate will be important. The main purpose of this research is to probe different effects of the variations in the pH between 3 to 11 on hydraulic conductivity، shear strength and one dimensional swell or settlement potential of cohesive soils. The coefficient of hydraulic conductivity and one dimensional swell or settlement potential have been measured by conducting falling head and one-dimensional consolidation tests، and parameters of shear strength of soil have been evaluates by conducting triaxial compression tests. The experiments have been performed on Kaolinite and the blend of Kaolinite and Bentonite with different percentages of Bentonite. Acetic acid has been used to produce pHs below 7 and sodium hydroxide has been used to produce pHs above 7. The type of chemicals and the amount of them، the type soil minerals، and time are some important parameters for understanding the effect of changes in pH on properties of clayey soil. In these considerations، an increase in hydraulic conductivity and settlement potential of cohesive soil with changes in pH has been detected، Moreover، it is been concluded that shear strength of cohesive soils will be decreased in pHs above or below 7.

The bearing capacity of piles shaft and stability of retaining walls and reinforced soil structures depend on the behavior of soil-structure interfaces. Using direct shear apparatus، behavior of a sand with fine angular grains was studied. Steel plates with two surface roughness values were separately embedded at the lower half of the shear box and consequently، the upper half was filled with dense or loose sand. Then، the behavior of interfaces forming between dense/loose sand and rough/medium rough steel plates was studied. Tests show that the shear strength and dilation in sand-structure interfaces are significantly less than the corresponding values for sand. In this regard، the peak friction angle of rough steel plate in contact with dense and loose samples is، respectively، about 40 and 25 percent less than those of dense and loose sand. In a similar fashion، the peak friction angle of medium rough steel plate in contact with dense and loose samples is about 60 and 45 percent less than those in dense and loose sand، respectively.

One of the main reason for bridge collapses may be flood flow scour. This interesting subject attracted many researchers، resulting in improvement of many theoretical and experimental works. In this study، local scour around complex pier was experimentally investigated. The experiments were carried out in a concrete rectangular flume. The flume was 0. 77 m wide، 0. 6 m deep and 21. 85 m long. The flume was filled by uniform sand with median size of d50=0. 71 mm and geometric standard deviation of σg= 1. 135. Complex pier consisted of a column، a pile cap that was rested on array of piles. The experiments were conducted using clear-water condition. To observe the geometric parameters effect (pile cap upstream extension، pile group arrangement، pile group upstream extension، and pile cap thickness) on scour depth، six models of complex pier were performed. A total of 82 experiments were carried out to study local scour. To evaluate the complex pier scour depth commonly procedures such as HEC-18، Coleman (2005)، Sheppard et al. (2004)، and Ataie-Ashtiani et al. (2010) were applied. The results show that، there is a good agreement between measured data and theoretical estimation and also there was no harmony between a measured and estimated data. The collected data were used to evaluate some leading existing theoretical and experimental methods for calculation the maximum scour depth around the complex piers.