## 4 Results and Discussion
### TBM Muck as a Road Fill or Subgrade Material  
Table 5 shows the average test results on three TBM muck samples when considered to be used as a road fill or subgrade material.  
Table 5 indicates that the liquid limit and plasticity index results for TBM muck do not meet the requirements of QCS 2014 standards. However, gradation, organic matter content, acid-soluble chloride and sulphate, CBR and swelling values were satisfactory. As suggested earlier, the raw TBM muck could be modified by stabilization or blending with other high-quality soils or aggregates to meet the specifications requirements. Future research works could be directed toward this end.  
It is worth noting that TBM muck could be also utilized in road sub-bases and bases according to QCS 2014, Section 6, Part 9. In order to consider this application, the sand equivalent value should be determined and compared to the QCS 2014 requirement of a  
\begin{table}
\begin{tabular}{l l c c} \hline \hline
**Test** & **Test Method** & **Average Test Result** & **QCS 2014 Limits** \\ \hline Rock particles exceeding 75 mm & ASTM D6913 & None & None \\ Material passing 0.075 sieve (\%) & ASTM D1140 & 13.00 & Max. 20 \\ Liquid limit (\%) & BS/EN 1377-2 & 51.00 & Max. 35 \\ Plasticity index (\%) & BS/EN 1377-2 & 15.00 & Max. 10 \\ Organic matter content (\%) & BS/EN 1377-3 & 0.10 & Max. 2.0 \\ Water-soluble chloride (\%) & BS/EN 1377-3 & 0.01 & Max. 1.0 \\ Water-soluble sulphate (\%) & BS/EN 1377-3 & 0.11 & Max. 1.5 \\ Acid-soluble chloride (\%) & BS/EN 1377-3 & 0.02 & Max. 2.0 \\ Acid-soluble sulphate (\%) & BS/EN 1377-3 & 0.75 & Max. 3.0 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison between the properties of TBM muck and QCS 2014 (specifications of suitable filling material related to buildings).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test** & **Test Method** & **Average Test Result** & **QCS 2014 Limits** \\ \hline Material passing the 75 mm sieve (\%) & ASTM D6913 & 100.00 & 100 \\ Material passing 0.075 sieve (\%) & ASTM D1140 & 13.00 & Max. 30 \\ Liquid limit (\%) & ASTM D4318, (Method A) & 50.00 & Max. 30 \\ Plasticity index (\%) & ASTM D4318 & 14.50 & Max. 10 \\ Organic matter content (\%) & BS/EN 1377-3 & 0.11 & Max. 2.0 \\ Acid-soluble chloride (\%) & BS/EN 1377-3 & 0.02 & Max. 2.0 \\ Acid-soluble sulphate (\%) & BS/EN 1377-3 & 0.76 & Max. 3.0 \\ California Bearing Ratio, CBR (\%) & ASTM D1883 (Soaked) & 41.01 & Min. 15.0 at 95\% MDD * \\ swelling (\%) & ASTM D1883 (Soaked) & 0.29 & Max. 2.0 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison between the properties of TBM muck and QCS 2014 (specifications of suitable road filling and subgrade materials).  
minimum of 25%. In addition, the CBR value should meet a minimum requirement of 80% for unbound materials as specified in QCS 2014. Thus, it is important to emphasize that additional work should focus on the improvement of TBM much through stabilization with Portland cement and fly ash or via blending with other high-quality soils or aggregates. The most cost-feasible stabilizers are cement, lime, fly ash, and bitumen (usually in the form of asphalt). Lime is best suited for fine materials such as clays. Portland cement is commonly used to improve the performance of low-quality or marginal aggregates. The amount of cement needed to achieve stabilization varies from 3.5% to 7%, by weight for granular materials, and from 7% to 10%, by weight for silts and clays. Steel slag, which is commonly abundant in Qatar, could be also considered for blending with the TBM muck.