# Investigation of Cement and Fly Ash on the Improvement of Fine Sand Soil
## 2 Materials and Methods
### Method  
In this study, the effect of fixed 3% cement and varying percentages of fly ash (5%, 10%, 15%, 20%, and 25%) on the geotechnical properties of fine sand soil was experimentally evaluated. First of all, standard compaction tests were performed on fly ash and cement added samples and a pure sand sample to obtain the optimum water content and maximum dry unit weight. Proctor compaction tests were performed according to Method A, since the maximum diameter size of the sample was 0.6 mm and less than 20% of the soil sample was retained on a 4.75 mm sieve (ASTM D698 [22]). Soil samples were prepared at six different water contents at standard proctor compaction models which had a 101.6 mm diameter. For each experiment, a new soil sample was prepared, since the crushed sand particles after an experiment may change the fine-grained sand particles percentage. \begin{table}
\begin{tabular}{l c} \hline \hline
**Soil Classification (USCS)** & **SP** \\ \hline Specific Gravity, G\({}_{\text{s}}\) & 2.78 \\ Max. void ratio, \(\mathbf{e_{\text{max}}}\) & 1.190 \\ Min. void ratio, \(\mathbf{e_{\text{min}}}\) & 0.626 \\ Max. dry unit weight, \(\mathbf{\gamma_{\text{d,max}}}\) (kN/m\({}^{3}\)) & 16.76 \\ Min. dry unit weight, \(\mathbf{\gamma_{\text{d,min}}}\) (kN/m\({}^{3}\)) & 12.44 \\ Uniformity coefficient, C\({}_{\text{u}}\) & 2.50 \\ Coefficient of curvature, C\({}_{\text{c}}\) & 1.20 \\ Effective particle size, D\({}_{\text{10}}\) (mm) & 0.52 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Index parameters of fine sand soil. Figure 1: Grain size distribution of fine sand, cement and fly ash. Then, direct shear box tests were performed to determine the internal friction angle and cohesion values of the sand samples at their optimum water contents which were determined previously from standard compaction tests (ASTM D3080 [23]). Shear box tests were carried out at two relative densities (30% and 80%) in order to represent loose and dense conditions, respectively. A square direct shear box of a 60 \(\times\) 60 \(\times\) 25 mm size was used in the experiments. The soil sample amount was calculated according to minimum and maximum void ratios for each case. For the dense condition, the calculated soil amount was compacted in the mold in three layers, whereas for the loose condition, the free fall method was used. Normal stresses applied on top of the soil samples were 54.5 kPa, 109 kPa and 218 kPa, respectively. The horizontal load was applied with a speed of 0.5 mm/min [24; 25]. After that, California bearing ratio (CBR) tests were carried out (ASTM D1883 [26]). Curing ages were 7 and 28 days, respectively. The mixtures were cast in 3 layers and compacted into molds having a 152.4 mm diameter and 177.8 mm height under optimum water contents. After preparing the samples, molds were placed in sealed plastic bags and kept in desiccators during the aging period in order to maintain their moisture content. Eventually, their 7 and 28 day strengths were tested. The penetration speed of the experimenting rod was 1.3 mm/min. The stresses were recorded when the rod's penetration depth reached 2.5 mm and 5 mm, and the highest value was recorded as the CBR value of the specimen. The final experiment that was carried out through the soil samples was the falling head permeability test in order to evaluate the hydraulic conductivity of the mixtures (ASTM D5856 [27]). The falling head permeability test was preferred since sand has a maximum particle size of 0.60 mm and additives have a finer particle size than that. Mixtures were prepared according to their optimum water contents and maximum dry unit weights in a mold by compacting in three layers, and filter papers were placed on the top and bottom of the samples. The prepared samples for each experiment are listed in Table 3. For the proctor compaction tests, each mixture was prepared six times at different moisture contents. For direct shear tests, three samples were prepared for each mixture at two different relative densities: 30% and 80%, respectively.