The native soil behavior of unpaved low volume roads and their mode of failure were studied to establish proper method of stabilizing native soils using local available materials. The use of lime and its positive effe...The native soil behavior of unpaved low volume roads and their mode of failure were studied to establish proper method of stabilizing native soils using local available materials. The use of lime and its positive effect to modify and stabilize Ngara soil in Tanzania is presented in this paper. There are many methods of stabilizing soil to gain required engineering specifications. These methods range from mechanical to chemical stabilization. Most of these methods are relatively expensive to be implemeted by slowly developing nations and the best way is to use locally available materials with relatively cheap costs affordable by their internal funds. Tanzania is a country having abundantly amount of Lime. Ngara native soil roads (unpaved rural roads) was studied under preliminary investigation and found to have higher plasticity, tendency of swelling and shrinking, low bearing capacity when wet, compressive strength of soil to have higher sensitivity to moisture and lower shear strength when wet. These soil behaviors deny road access to about 32 million people in Tanzania (80% of population) during rainy season. The detailed investigations is still going on at China university of Geosciences but other results from similar researches show that Ngara soils can be stabilized by lime and gain the required engineering properties.展开更多
Constructed Technosols may be an alternative for creating urban green spaces. However, the hydro-structural properties emer- ging from the assembly of artefacts have never been documented. The soil shrinkage curve （...Constructed Technosols may be an alternative for creating urban green spaces. However, the hydro-structural properties emer- ging from the assembly of artefacts have never been documented. The soil shrinkage curve （SSC） could provide relevant structural information about constructed Technosols, such as the water holding capacity of each pore system （macropores and micropores）. The objectives of this study were （i） to evaluate the SSC and water retention curve （WRC） to describe the structure of constructed Tech- nosols and （ii） to understand the influence of organic matter content on soil hydro-structural properties. In this study, Technosols were obtained by mixing green waste compost （GWC） with the material excavated from deep horizons of soil （EDH）. The CWC was mixed with EDH in six different volumetric percentages from 0% to 50% （GWC/total）. The GWC and EDH exhibited highly divergent hydro-structural properties： the SSC was hyperbolic for GWC and sigmoid for EDH. All six mixture treatments （0%, 10%, 20%, 30%, 40% and 50% GWC） exhibited the classical sigmoid shape, revealing two embedded levels of pore systems. The 20% GWC treatment was hydro-structurally similar to the 30% and 40% GWC treatments; so, a large quantity of expansive GWC is unnecessary. The relation with the GWC percentage was a second-degree equation for volumetric available water in micropores, but was linear for volumetric available water in macropores and total volumetric available water. Total volumetric available water in the 50% GWC treatment was twice as high as that in the 0% GWC treatment. By combining SSCs and WRCs, increasing the GWC percentage increased water holding capacity by decreasing the maximum equivalent size of water-saturated micropores at the shrinkage limit and increasing the maximum equivalent size of water-saturated macropores, resulting in an increased range of pore diameter able to retain available water.展开更多
文摘The native soil behavior of unpaved low volume roads and their mode of failure were studied to establish proper method of stabilizing native soils using local available materials. The use of lime and its positive effect to modify and stabilize Ngara soil in Tanzania is presented in this paper. There are many methods of stabilizing soil to gain required engineering specifications. These methods range from mechanical to chemical stabilization. Most of these methods are relatively expensive to be implemeted by slowly developing nations and the best way is to use locally available materials with relatively cheap costs affordable by their internal funds. Tanzania is a country having abundantly amount of Lime. Ngara native soil roads (unpaved rural roads) was studied under preliminary investigation and found to have higher plasticity, tendency of swelling and shrinking, low bearing capacity when wet, compressive strength of soil to have higher sensitivity to moisture and lower shear strength when wet. These soil behaviors deny road access to about 32 million people in Tanzania (80% of population) during rainy season. The detailed investigations is still going on at China university of Geosciences but other results from similar researches show that Ngara soils can be stabilized by lime and gain the required engineering properties.
基金the University of Damascus, Syria, for financial support of the Ph.D.(No.1473)
文摘Constructed Technosols may be an alternative for creating urban green spaces. However, the hydro-structural properties emer- ging from the assembly of artefacts have never been documented. The soil shrinkage curve （SSC） could provide relevant structural information about constructed Technosols, such as the water holding capacity of each pore system （macropores and micropores）. The objectives of this study were （i） to evaluate the SSC and water retention curve （WRC） to describe the structure of constructed Tech- nosols and （ii） to understand the influence of organic matter content on soil hydro-structural properties. In this study, Technosols were obtained by mixing green waste compost （GWC） with the material excavated from deep horizons of soil （EDH）. The CWC was mixed with EDH in six different volumetric percentages from 0% to 50% （GWC/total）. The GWC and EDH exhibited highly divergent hydro-structural properties： the SSC was hyperbolic for GWC and sigmoid for EDH. All six mixture treatments （0%, 10%, 20%, 30%, 40% and 50% GWC） exhibited the classical sigmoid shape, revealing two embedded levels of pore systems. The 20% GWC treatment was hydro-structurally similar to the 30% and 40% GWC treatments; so, a large quantity of expansive GWC is unnecessary. The relation with the GWC percentage was a second-degree equation for volumetric available water in micropores, but was linear for volumetric available water in macropores and total volumetric available water. Total volumetric available water in the 50% GWC treatment was twice as high as that in the 0% GWC treatment. By combining SSCs and WRCs, increasing the GWC percentage increased water holding capacity by decreasing the maximum equivalent size of water-saturated micropores at the shrinkage limit and increasing the maximum equivalent size of water-saturated macropores, resulting in an increased range of pore diameter able to retain available water.
