| In recent years, with the development constructions in coastland and seaport, artificial hydraulic fill technology is widely used in civil engineering projects. In the point view of project built on the soft soil region, the main problem is how to improve the foundation bearing capacity of the aritficial dredger fill and the weak foundation soil under the dredger fill.Vacuum pre-consolidation method is a good method to reinforce soft foudation and the method has been used in many engineering projects in our country. However, when the dredger fill is part of super soft soil, drainage and consolidation effect was always unsatisfactory, the rate of growth of soil strength was very low. In order to improve the bearing capacity of the foundation of super soft soil, to seek a reasonable treatment method, to save project cost, it is necessary to make further study.The reinforcement effect of large area dredger fill is evaluted in this paper associated with the project of"Study on The Influence of Organic Matter in The Progress of Marine Soft Soil Foundation Consolidation"(No.40372122) and Haixi Bay ship building project. The study focused on solving the regional problem of the low bearing capacity of the surface soil. In this paper, according to the analysis of the vacuum pre-consolidation monitoring data, we study the influence of foundation reforce in many aspects on surface settlement, lamination stettlement, deep displacement, the film under vacuum delivery, the pore water pressure dissipated and underground water line. Through the analysis of the detect data of the strengthening area, study the reasons for the low soil bearing capacity of surface soil, and to raise the second ground treatment programme and the implementation methods. It selected cross-shear test index and indoor soil test index to study the reinforcement of regional stability.First of all, it considered that vacuum pre-consolidation is the best method from economic, technology, project period and etc. The problems of the design of vacuum pre-consolidation system will be discussed:â‘ The project demands the vacuum equipment must work in water because the base in the seaside, two pumps which are pump-engine and pump-engine split should be work together. The wax well can solve the shallow airproof problem triumphantly.â‘¡The responsibility of partition large area dredger fill is extremely important, so the vacuum pre-consolidation design of the whole project will be divided into four regions and a number of areas. A3, A4, B2-3 and B2-4 area are the typical regional district and analyse monitoring results of the four areas.Secondly, in line with the existing literature and the works of some of the scene measured data, the pre-engineering vacuum pressure reinforcing effect analysis and made the following points:â‘ The scene of the data indicate that a vacuum-pressure method of improving soft-obvious effects, Reinforcement of each district in a week reached a pre-designed pressure load 80kPa.â‘¡The reinforcement area in the 90 to 115 days of the degree of consolidation have reached more than 85 percent, the average surface subsidence in about 1 m, the settlement was mainly due to differences in wind Filled with mud or uneven distribution of the foundation of the heterogeneity of the soil caused.â‘¢Provisions of the proposed norms stop the vacuum to make a standard: "to meet the requirements of the vacuum, the exhaust should be continuous, when settlement Stability, the pump stopped before unloading. Vacuum-pressure stability standards for the settlement: the measured rate of land subsidence in a row 5~10days average settlement of less than or equal to 2mm/d; on the settlement after the demanding work in five consecutive 5~10days average settlement of less than or equal to 2mm/d on the basis of continuing vacuum greater than or equal to 30days".â‘£It will be vacuum-pressure water table under the conditions defined as: soil water table is the role of gravity in the water because of the pressure of the line of 0, 0 hydrostatic pressure to the line.Third, because of dredger fill sources, such as hydraulic fill of the condition of the area blowing fill the following characteristics: clay particles in different, the clay content of 20% to 41.3% between the high water content, than the intensity low soil composition and strength in space on the distribution is uneven, the detection point of cross-shear strength of large difference. After vacuum-pressure soft-law reinforcement, through soil tests and cross-cut test pilot, B-bearing capacity of the land surface area does not meet design requirements, the paper through on-site testing and engineering experience of reasons, and the second by ground treatment programmes And the implementation methods:â‘ The vacuum after the pre-pressure, A majority of the regional district soil moisture content of less than 36 percent in the south east corner of the upper 2.5m of mud around silty clay layer moisture content of 38% to 44.3%, close to the design Requirements; area B most of the region around the upper 3m of silt layer of clay moisture content of 43% to 60.1%, with the design requirements of large difference;â‘¡3.5 points after test and analysis of engineering experience, area B of soil bearing capacity of lower The main reason for the two areas: First, the flow of soil particles in less than 0.002 mm in the proportion of larger particles, the sewer would be easy to plug the vacuum-pressure performing poorly. Second, in the soil by the shear role, because particles of water lubrication, resulting in low shear strength of the soil.â‘¢In order to increase the surface area B of the regional land-bearing capacity, design of the two options: Excavation replacement programme; mixing treatment options. Comparing the merits of the programme, the area B by mixing the surface replacement, that is, in a surface of about 2.5m, "mixing the surface layer", of which the upper 1.5m, the lower 1.0m not doped stones. To ensure that the excavation pit area B dock at the slope and the slope stability, in the second foundation construction, adopted the provision of temporary pavement approach.â‘£Static load test by test, A vacuum-pressure area after reinforcement after the foundation bearing capacity to achieve the design features of not less than 80 kPa requirements; B vacuum-pressure area after reinforcement and surface mixing replacement treatment, the foundation bearing capacity eigenvalue to meet the design of not less than 120 kPa requirements.Finally, making use of the cross-shear test index and indoor soil test index, the paper study the slope stability. After stability analysis, area B1 designed 1:2 slope grade, and the stability safety quotiety is 0.8, the slope is instability. Afer adjusting the slope grade to 1:3.5, slope stability safety quotiety is greater than 1.15, as a result, the holistic slope are stability. |
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