Research On The Application Of Foundation Treatment Technology In Large Area Dredger Fill Land Areas

As the most important form of dredger fill land area in the reclamation land engineering,the development of dredger fill land area is an effective way to solve the contradiction between the need for economic development of coastal cities and the lack of land for construction,and it is also of great significance to alleviate the shortage of land area per capita and the dredging sea lanes in China.Adopting the foundation treatment technology of dredger fill land area to treat the foundation of dredger area site is a prerequisite for the delivery of dredger area,how to choose a reasonable foundation treatment technology of dredger area to effectively strengthen the foundation of dredger area site has been a major research point for scholars at home and abroad.This paper relies on an artificial island（Phase I）foundation treatment engineering in Shandong,using field tests to study the foundation treatment method of large-area complex dredger fill land areas,and the problem of difficult precipitation in the field test process in the thousand-layer cake area,proposed the bright-blind combined with precipitation dynamic compaction method,using the finite difference software FLAC^3Dto establish an numerical model,systematic analysis and study of the reinforcement effect of this new process,the main research contents and results are as follows:（1）According to the soil properties and distribution characteristics of dredger fill site,analysis of blowing filler,filling process,hydraulic gravity sortability and filling mouth placement position and other factors on the distribution characteristics of the dredger fill soil layer influence law.The results show that:the dredger fill site can be divided into sandy soil area,soft soil area and thousand-layer cake area according to the distribution of soil layers,and its corresponding filling location is the filling mouth,Silting area and back silting area,according to the above-mentioned characteristics of the distribution of soil layers in the dredger fill land area,it can be used for preliminary judgment of the geological situation of the large area filling site,which has certain engineering practicality.（2）Based on the distribution characteristics of the soil layer of the dredger fill site,through the analysis of the applicability of foundation treatment technology,we propose to choose the high energy level dynamic consolidation method in the sandy soil area,the straight-line vacuum-surcharge preloading method in the soft soil area and the precipitation dynamic compaction method in the thousand-layer cake area for field test research respectively.The results show that:after treatment,the characteristic value of bearing capacity of sandy soil area and thousand-layer cake area reached 120 k Pa and effectively eliminated the liquefaction potential of saturated sandy soil and saturated silty soil,the characteristic value of bearing capacity of soft soil area reached 80 k Pa,the average shear strength of cross plate reached 15 k Pa and the soil consolidation degree was above 95%,all the indexes met the design requirements value,which proved the applicability of the selected foundation treatment technology for dredger fill land area and determined the reference significance for the selection of foundation treatment technology and design parameters for similar dredger fill land area.The applicability of the selected foundation treatment technology in the dredger fill land area was demonstrated,and the technical solution and design parameters of the foundation treatment technology in the dredger fill land area were determined,which provided practical guidance for the reinforcement plan of the foundation treatment engineering of the artificial island（Phase II）and also provided reference for the selection of foundation treatment technology for similar dredger fill land area.（3）The effect of soft layer and high groundwater level on the reinforcement effect of dynamic compaction method on the treatment of dredger fill land area was studied experimentally,and the effect of no soft soil layer,surface soft soil layer,middle soft layer and underlying soft soil layer on the reinforcement effect of dynamic compaction in sandy soil area was analyzed,and the effect of precipitation and no precipitation on the reinforcement effect of dynamic compaction was analyzed.The results show that:soft soil layer will obviously hinder the dynamic energy transfer,soft soil layer distribution location of different degrees of impact on the effect of dynamic reinforcement,the deeper the distribution of soft soil layer,the greater the attenuation of dynamic compaction energy after penetrating the soft soil layer,it is recommended that when the soft soil layer is shallow,can increase the effective reinforcement depth by increasing the dynamic compaction energy level,when the soft soil layer is deep,increase the effective reinforcement depth by increasing the dynamic compaction energy level is not suitable,then should choose other foundation high water table will obviously lose the dynamic energy,it is recommended that when using dynamic compaction treatment in the blowing land area with high water table,water reduction measures should be taken,which provides an important practical basis for the dynamic compaction method to treat the dredger fill land area foundation with soft soil layer and high water table.（4）Based on the problem that it is difficult to precipitate water in some areas during the field test of the precipitation dynamic compaction method to treat the thousand-layer cake area,this paper proposes a new process of"bright-blind with precipitation dynamic compaction method"to treat such foundations,and uses the finite difference software FLAC^3Dto establish a dynamic simulation numerical model of the bright-blind with precipitation dynamic compaction method to simulate the continuous dynamic compaction test to obtain the pore water pressure,the effective stress of the soil layer and the displacement and settlement for change law.The results show that:in the process of one ramming cycle,when the impact load is over,the pore water pressure and the effective stress in the soil change in accordance with the principle of terzaghi principle of effective stress,,which proves the reasonableness of the numerical model.In the process of multiple ramming,one click settlement gradually decreases and stabilizes,which proves that the number of ramming is not as many as possible,and there exists an optimal number of ramming to meet the reinforcement effect while ensuring the economic efficiency of the project.In the process of multiple ramming,compared with the side without drainage ditch,the pore water pressure value on the side near the bright-blind drainage ditch is smaller,and the effective stress value of the soil body is larger and the influence range is wider,which proves that the bright-blind drainage ditch can accelerate the pore water pressure dissipation and increase the reinforcement range of the soil body in horizontal and vertical directions.It provides an important theoretical basis for the engineering application of the bright-blind combined with precipitation dynamic compaction method.