Classification of Marl Soils

Field and laboratory tests were conducted to investigate the degree of uniformity and quality that is obtained with chemical treatment of the subgrade with LKD using current construction techniques. An INDOT road project under construction was selected for the research. A 140-m long subgrade section was chemically treated with LKD with a target thickness of 16 inches, which is the current standard practice, while another 140-m long section was treated with a target thickness of 14 inches. DCP tests were done at each section to obtain the stiffness (or strength) of the chemically-treated and natural (untreated) subgrade soil layers. LWD tests were performed at the same locations where the DCP tests were done to estimate the stiffness of the treated subgrade layer. Nuclear gauge and sand cone tests were carried out to obtain the water content and dry density of the chemically treated subgrade. XRD and TGA tests were performed on soil samples collected in the field to identify and quantify the minerals contained in the soil. XRD and TGA laboratory tests show an adequate presence of lime in the subgrade, with somewhat better uniformity for the test site with 14 inches target thickness for the subgrade. Field tests, namely density, DCP and LWD, show consistently better and more uniform results for the 14 inches target thickness site than for the 16 inches target site. As a result of the research, it is recommended: (1) to increase for design the CBR of the subgrade treated with LKD by 25% over that of the natural soil; (2) to implement recommendation for a target thickness of the treated subgrade of 14 inches; (3) to introduce special, one type project where QC/QA is done by the contractor for design and construction, where full advantage of the subgrade improvement may be taken into consideration to minimize pavement thickness.