Determination of dynamic cone penetration index (DCPI) of borrow pit materials for construction of low volume roads in Dodoma Tanzania

Abstract

The study for determination of dynamic cone penetration index (DCPI) of borrow pit materials for construction of low-volume roads was conducted in the Dodoma region in Tanzania. Samples for tests were collected from five borrow pits, which are Nkulabi, Zuzu, Mahomanyika, Dinda, and Ntyuka. Results of plasticity indices were 14%, 11%, 10%, 16%, and 13% for Nkulabi, Zuzu, Mahomanyika, Dinda, and Ntyuka borrow pits, respectively. Results of grading coefficients and shrinkage products were 33.7 and 148.1 units for Nkulabi, 19.9 and 295.9 units for Zuzu, 32.3 and 56.0 units for Mahomanyika, 25.4 and 391.3 units for Dinda, and 32.8 and 111.2 units for Zuzu borrow pits, respectively. Results of dynamic cone penetration indices were 5.8 mm/blow, 5.2 mm/blow, 4.7 mm/blow, 6.0 mm/blow, and 4.5 mm/blow for Nkulabi, Zuzu, Mahomanyika, Dinda, and Ntyuka borrow pits, respectively. Specifications require DCPI values for the tested material not to exceed 5.69 mm/blow in order to be suitable for use as gravel-wearing course material. Therefore, these results indicate that materials from Zuzu, Mahomanyika, and Ntyuka borrow pits have satisfied the requirement and hence qualify to be used as gravel-wearing course material. However, materials from Dinda and Nkulabi borrow pits have DCPI values above the limiting value of 5.69 mm/blow, and therefore they did not meet strength requirements as gravel-wearing course material. Based on grading coefficient, shrinkage product, and strength parameters, which are used for the selection of suitable materials, only Zuzu borrow pit materials qualified for the construction of the gravel wearing course. Therefore, engineering properties of materials from Dinda, Mahomanyika, Nkulabi, and Ntyuka need to be improved through the blending process.