The Research On Amelioration Of Mud Dredger Fill In Tianjin And Breeding Technology Of Tamarisk

With the development and urbanization process of Tianjin Binhai New Area, the urgency of the construction land shortage and the marine land reclamation stretched out particularly.As the important land resource to expand the construction of coastal city, marine mud dredger fill was called "green restricted area" by the domestic and foreign experts because of its bad structure, heavy texture, high salinity and poor permeability.In order to solve the the worldwide technical problem of the reclaimed soil greening, in this paper, on the basis of water movement law, salt transport, the improvement result of industrial and agricultural waste,the physical and chemical properties of marine mud dredger fill can be determined further. The right amount of mixed material was added to marine mud dredger fill by the combination of physical,chemical and biological methods to carry out soil column simulated experiment for improvement of saline soil. And through the experiment by indoor breeding of Tamarisk, the fast greening system of theory and technology of original marine mud dredger fill can be established,and the new techniques and technologies of directly greening Tamarisk vegetation and ecological restoration in inshore sea mud reclaimed soil area can be explored for the formation of Tamarisk forest green landscape on the heavy saline plate ground as soon as possible.The main research results are as follows:(1)The marine mud dredger fill in Tianjin is heavy and clay,the content of sand is little,only account for 15.27% of the total mass;the content of powder is the most,accounting for 70.15% of the total mass; the content of clay is the least,accounting for 14.58% of the total mass.The marine mud dredger fill in Tianjin belongs to poor graded soil,and the texture type of the soil is silty clay.The structure of the soil in this area is tight, the bulk density is between 1.21 g/cm3and1.63g/cm3,with an average of 1.42g/cm3. The soil porosity is between 40.17% and 51.05%, with an average of 47.01%.The permeability coefficient of marine mud dredger fill is from 7.4×10-5cm/s to 1.4×10-4cm/s, with an average of 5.6×10-5cm/s, lower than the ordinary farmland 1 to 2 orders of magnitude,the permeability is weak, and the ventilation of water permeability is poor.(2)The salt content of the marine mud dredger fill in Tianjin is high,with the average of 18.38g/kg,and showing the law of the highest salinity in the surface and the lowest salinity in the bottom,this may be caused by water evaporation and the soil salinization to the surface.The p H of the marine mud dredger fill in this area is high, the minimum value is 8.23 and the maximum value is 8.68,which belongs to alkaline soil. The content of organic matter is low,with the average of 14.76g/kg,which is relatively barren,and it also shows the law that the content of organic matter is the highest in the surface, and the content of organic matter is the lowest in the bottom.(3)The source of heavy metal pollution in this area are mainly composed of As, Hg, Cd, and the single factor pollution index is Cd > Hg > As from large to small, it can be seen that the heavy metal pollution is given priority to Cd, and the content of Cd is more than four times than the standard value.(4) The mixed adding of desulfurization gypsum, rice husk and sand can significantly improve the water vapour permeability and desalting efficiency of the marine mud dredger fill;the effect of treament 2(20% sand + 20% rice husk + 1% desulfurization gypsum) is best, with only 6.5 h to reach the soil column bottom,and the infiltration rate of treament 2 is 7.69 cm/h, ahout 24.7 times of that of the control group.In the control group the wetting front migration is slow, in which the penetration rate of the above 25 cm was greater than the following 25 cm, about 6.95 times of the that.(5) To analysis the conductivity and total salt of the leaching solution of each treament, the end of the leaching process was composed by rapid desalination, slow desalination and basically stable desalination, and the first stage had cleared large amount of salt.The p H change rule was roughly the same trend under different processing conditions of leaching solution, namely the p H value were increased gradually from partial acid to weak alkaline, but in the end was stable under 8.0.(6) At the end of the leaching, the leaching efficiency of total salt of each treatment was over 88%, among them the content of Na+ and Cl– slashed sharply, whose leaching efficiency was more than 88% and 88% respectively; the p H value of each treatment after leaching was between7.18 and 7.33, it means that adding desulfurization gypsum inhibited the phenomenon of salinization significantly.(7) The leaching effect of treament 2 was the best, reaching the end of the leaching process just used 30 h, and the consumption of total water was 7055 m L, the soil and water ratio was 1:1.59. Perennial ryegrass pot experiment was carried out on the improved soil, the growth was in good condition, it showed that the ecological condition of the improved marine mud dredger fill has been improved.(8) The methods of transplanting, artificial planting, water planting, cutting(local content) and other methods was adopted to breed the Tamarisk indoor, and it was found that the survival rate of artificial planting was not high, so it was not suitable to build large-scale Tamarisk forest; the method of transplanting was strict to transplanting process and final-period management, and it was limited in the field;the method of Tamarisk cutting was simple and easy, and the survival rate of Tamarisk cutting(local content) reached 70%, which was economically feasible.