Laboratory And Field Investigations To Address Erosion, Volume Change And Desiccation Cracking Of Compost Amended Expansive Subsoils

Desiccations cracks are formed during drying process of fine grained cohesive soils in summer and these cracks often appear on unpaved subgrades due to direct exposure to sun. These cracks allow surface runoff infiltration into subsoils and eventually weaken adjacent base and subgrade layers. The loss of support from these underlying layers results in both longitudinal and transverse cracks in paved shoulders and pavements. Composting is a successful method of recycling organic waste material into stabilized materials that could be used for erosion control and landscaping applications. Since compost is rich in fibrous material and exhibits moisture affinity characteristics, it is theorized that compost material can be used to stabilize expansive soils in order to control desiccation or shrinkage cracks in them during dry seasons, which lead to considerable reductions in pavement distresses caused by longitudinal and transverse cracks. In order to verify the compost stabilization process, a comprehensive research study was conducted at four distinct test sites near Stephenville, Lubbock, Bryan and Corpus Christi cities of the state of Texas, respectively. Composts comprising of biosolids, dairy manure, cotton burr, cow manure, feedlot manure and wood compost were considered for stabilizing local expansive soils of these four sites. Laboratory studies were first conducted on the compost materials and compost amended soils to address their volume change and strength behaviors. These studies were used to establish compaction moisture content and dry unit weight conditions for the construction of compost amended covers for further field verification studies. In field investigations, a control plot with no composts as cover and several test plots with Compost Manufactured Topsoils (CMTs) as cover materials were designed and constructed. Both quantitative and qualitative data was collected from moisture and temperature sensors embedded in test plots, digital imaging related surface cracking studies, elevation surveys, visual observations of paved shoulder crack patterns and vegetation growth on the plots. The collected data was analyzed with statistical comparison t-tests, which indicated that majority of compost test plots showed that they had lesser moisture and temperature variations than those of the Control Plots. This indicates the ability of composts to insulate soils from surficial temperature changes and thus maintain uniform moisture levels in the subsoils. Majority of CMT plots constructed at four sites were able to retain moisture contents close or above the initial compaction moisture contents. This resulted in lesser desiccation cracks in CMT test plots. The reduction in desiccation cracking was attributed to the presence of fibrous materials in composts, which serve as natural reinforcements in the CMTs. Thus, the CMTs were able to withstand tensile forces generated from drying of the subsoil. Other recommendations related to CMT types and field compaction densities as well as erosion potentials of the test plots are explained. Causes for pavement distress resulting from both shoulder and subsoil cracking are identified and potential mitigation methods using compost stabilization techniques are described.