| At present, with the ever-accelerating development process of Binhai New Area in Tianjin, the slogan of "green city","eco-livable city" came into being. Shortage of land resources is the main bottleneck restricting the development of coastal areas. Directly using of sea mud dredger fill for the landscaping not only solved the dredged sediment occupation of land resources, pollution of the environment, but also solved the garden soil scarcity problem. With systematic, comprehensive measurement of Tianjin mud blowing soil on physical and chemical properties, and the analysis of internal coupling mechanism, the conclusions are as follows:(1) Tianjin marine dredger fill is very sticky. Judging from the whole, the sand content is extremely low, only about10%of the total mass, silt is the most abundant matter which is up to50%to60%, followed by clay, accounting for35%, which are classified as poorly graded soil. The more common texture type is silty clay loam than the individual clay loam and silty clay due to the source of dredger fill and reclamation process. On the whole,the soil is tight with poor permeability (average permeability coefficient is5.6×10-5cm/s) and1to2orders of magnitude worse than ordinary farmland soil.(2) The fertility and CEC value of the soil in this area turned out to be low(13.96g/kg and8.61cmol/kg for means of organic matter and CEC, respectively). CEC value increased with greater organic matter content, and both of them are relatively related with the composition of soil particles. Both organic matter and CEC are positively correlated with clay content, but there is no direct linear relationship between them.(3) The salinity of marine dredger fill is between9.6to33.01g/kg in Tianjin, with the mean value22.21g/kg,,is far beyond the salt tolerance of garden plants. The mean value of pH is7.89performing weakly alkaline which represented typical sodium chloride heavy saline-alkali soil.We found that viscous and high salt content are the main reasons restricting the Tianjin mud dredger fill improvement by investigating and analysising its physico-chemical properties. Further experiments-mixing sand soil improvement of indoor soil column leaching salt test is conducted to get optimum ratio of sand-doped from the study of water movement law, salt transport, the desalting rate and desalination of irrigation water use, leaching solution salinity and ionic composition changes, changes of soil column and leaching solution pH after desalination. The test results are as follows:(4) The wetting is significantly exponentially related with infiltration time from the condition of water infiltration. The infiltration depth increase negatively correlated with increase in infiltration time. The greater ratio of sand, the faster water infiltration and the greater the slope we got. They spent34days,16days,7days and1.5days from the beginning of infiltration to just water leaking in control group, treatment1, treatment2, and treatment3, respectively. It indicated that, the permeability of soil can be effectively improved with mixing of sand and soil improvement.(5) Leaching and desalinization rate will significantly increase and salt peak depth will deepen with the increase of doped proportion of sand. It is the best effect of desalination when the proportion of mixing sand is40%with about9days and no salt peak phenomenon existing in the40cm layer which is beneficial for plants growth. However, soil alkalization phenomenon occurred during mixing sand improving soil leaching and desalinization process. For this reason, it is not enough simply using mixing sand to improve soil structure, and leaching and desalinization alkalization issues are left to be resolved. |
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