Effects of gravel content and shape on the engineering properties of a soil

There are many materials which have been investigating to stabilize of highway roads, railroads, base and sub-base materials. The present study evaluates influences of naturally rounded gravel (NG) and crushed stone angular gravel (CG) in pavement sub-base materials. A series of California bearing ratio (CBR), unconfined compressive strength (UCS), compaction, and oedometer tests were carried out. The mixtures were clay with both NG and CG materials separately at ratios of 0, 5, 10, 15, and 20% by the dry weight of specimens. Maximum CBR values are 9.3% and 9.6% of mixtures with 20% of CG and NG in clay respectively. The maximum dry unit weight and optimum water content values were changed due to changing the amount of NG and CG materials into the clay mixture. The UCS tests showed that increment of NG and CG materials content cause to increase in strength of the mixture up to 15% of gravels content, the strength of the mixture decreases at 20% to 57.54% for NG (while UCS at 15% of NG was increased by 64.42%) and UCS decreased to 61.15% for CG materials (while UCS at 15% of CG was increased by 72.60%). Also, it was deduced that adding of NG and CG gravel materials into the clay soil cause to decrease the initial void ratio (e0) in percentages of 15.62% and 10.09%, and cause to decrease compression index (cⅽ) in percentages of 31.11% and 41.66% for NG and CG materials respectively. Furthermore, increasing the amount of gravel materials resulted to decrease the swelling percentage in 54.55% and 45.45% for both NG and CG materials. Using of the gravel materials in the mixtures of clay cause to decrease the thickness of sub-base in the design of highway pavements 15% for NG and 12.5% for CG materials.