Engineering Properties of Mechanically Stabilized Subbase Material Using Natural Gravel around Jimma Quarry Sites for Unpaved Road Construction

Abstract

Unpaved roa ds are de signed with a s mall input and ar e constructed fr om the nearest available materials as possible. It r equires routine and pe riodic m aintenance, and thei r co ndition ca n be s ignificantly af fected by a peri od of e xcessive tr affic volumes or inclement weather condition. The accurate estimation of maintenance cost is difficult. Many problems occur in the economic analysis of unpa ved r oads in comparison with pa ved r oads. D efects whi ch may a ffect u npaved r oads are dusty, potholes, sto neness, corrugations, and rutting. Hence, it needs to apply sufficient stabilization method to strengthen and increase the durability of the unpaved road. Mechanical stabilization is an important application in engineering for different types of construction to improve the performance of r oad construction materials. The obj ective of this research was to determine the E ngineering properties of natural gravel materials by mechanical stabilization method to be used in subbase material for the unpaved road. The methodology carried out in this research study includes: (a) field visual inspection and sampling of natural gravel materials from three quarry sites around Jimma area; and (b) laboratory tests to identify the physical and mechanical properties of natural gravel. Based on the laboratory test results, natural gravel materials from the Seka quarry site has an excellent Abrasion resistance of 35.26%, Plasticity Index of 13% a little bit above the u pper limit, and good gradation (coarser and less subtle or bind er materials), right CBR value. While the J iren quarry site has a little Abrasion resistance of 52.09%, medium plasticity index, poor gradation (moderate fine material), CBR value of 28.90% which was below 30% minimum requirement, but had good MDD. On the other hand, the Merewa quarry site comprised of a very poor Abrasion resistance of 78.3 4%, Plasticity Index of 2 3.90% which was beyond the upper limit pl asticity index of 1 2%, and poor gradation (more fine materials), poor CBR value and poor MDD. Therefore, it is concluded that the natural gravel from the Seka quarry site is suitable for subbase course. But since road construction around Jimma is booming, the natural gravel from this quarry site would be soon depleted. About this, mechanical stabilization is recommended by blending the natural gravel from Seka quarry site with 54% by weight with Jiren natural gravel of 46% by weight to meet the minimum requirements for subbase materials.

Full document