Characteristics of Settlement Consolidation and Influencing Factors Analysis of Dredger Fill of Clay Soil Mixing Sand
Abstract
Sedimentation column that the size of 100×500mm is used to study the relationship between the self weight settlement of cohesive soil and the initial sand-mud ratio and initial water content of dredger fill of clay soil mixing sand. Test results show that: (1) the consolidation time of dredger fill of clay soil mixing sand is mainly related to the size of the settlement column, compared with the initial water content, the influence of sand-mud ratio is not significant. The larger the size of the settlement column, the longer time of gravity consolidation will be completed, and the higher initial water content, the shorter time of consolidation. (2) The settlement curve of dredger fill of clay soil mixing sand is in accordance with the relation formula S = A1e-t/t1 + A2e-t/t2 + S0. In the formula, S0 is the steady settlement. The stability time of settlement consolidation can be deduced by this formula. Under the condition of the same water content, the consolidation settlement of dredger fill of clay soil mixing sand increases linearly with the sand-mud ratio, but the amplitude of the increase is not large; (3) the logarithmic curve of consolidation settlement is basically divided into three stages: The straight line segment, the upper concave line segment and the lower concave line segment. At first, the slope of the linear section increases gradually with the increase of the initial water content; The upper concave curve gradually decreases with the increase of water content, and when the initial water content reaches a certain value, the concave curve becomes a straight line; The lower concave curve section gradually changes to the curve type, then the slope of the settlement curve decreases and finally tends to the horizontal.
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Introduction
When the filling material flows out from the blowpipe, the filling material has the characteristics of sorting and partitioning. As the distance from the distance to the fill increases, the deposited soil particles gradually become coarser. Generally, dredger fill is characterized by obvious heterogeneity, high natural water content, poor water permeability, difficult drainage consolidation, high compressibility, low shear strength, thixotropy and rheological properties. The settlement consolidation characteristics of dredger fill are related to the design of yard volume, the selection of foundation treatment method and the effect of foundation treatment. Most of the existing scholars at home and abroad are pure silt soil, the simulation is the initial stage of dredging, the water content is very high, and the study of the self weight consolidation law of sand and clay soil mixing system is not very common. Stokes[1] formula is the most classical particle settling velocity formula at present. In the aspect of settling velocity of mud water interface, IMAI[2-3] considered that there are 3 stages of consolidation of cohesive sediment suspended sediment with high water content, namely, flocculation stage, settlement stage and consolidation stage. Liangtong Zhan[4] used the 50cm high sediment column (high 50cm, inner diameter 9cm)to study muddy water mixtures. Test results show that the higher the content of fine particles (especially clay) in dredger fill, the longer the process of self weight deposition, the ratio of pore to sediment is larger, and the pore ratio of silty soil after consolidation is 1~2, while silty clay is between 2~6. Xianwei Zhang[5] took the dredger fill mud in Tianjin Binhai New Area as the object of study, and studies the rule of mud self weight settlement and consolidation of initial water content 200~2000%.The sedimentation types of dredger fill mud in Tianjin are mainly sedimentary subsidence and consolidation subsidence. The sedimentation process is divided into flocculation stage, hindered settlement stage and self consolidation stage. In the process of settlement, the consolidation settlement gradually changes with the decrease of water content. When the initial moisture content is less than 400%, consolidation settlement occurs, and sedimentation occurs when the initial water content is greater than 400%
Conclusion
1) The primary factor affecting the settlement of dredger fill of clay soil mixing sand is the initial water content. With the increase of initial water content, the settlement speed of slurry interface is faster, the settlement value increases, and the time of completion of consolidation decreases. The completion time of consolidation decreases obviously with the increase of initial water content. Settlement column size is also one of the major factors of settling stability time, as the settlement column size and drainage distance increase, the consolidation time increases.
2) The settlement curve of mixed sand and clay filled soil conforms to the relation of S = A1e-t/t1 + A2e-t/t2 + S0. In the formula, S0 is the stable settlement. According to the formula, the consolidation stability time and the consolidation settlement amount can be determined according to the percentage of completion settlement consolidation. Under the condition of certain water content, the settlement is basically linear with the sand content ratio.
3) The logarithmic time curve of consolidation settlement is basically divided into three stages: straight line section, the upper concave section and the lower concave line segment are formed. At the begin, the curve begins is linear, and with the increase of the initial water content, the slope of the straight line segment increases gradually; With the increase of water content, the upward trend of the concave curve decreases gradually, and when the initial water content reaches a certain value, the upper concave curve becomes a straight line; The lower concave curve section gradually changes to the curve type, then the slope of the settlement curve decreases and finally tends to the horizontal. In this test, when the water content is 200%, the upper concave line is close to the straight line, while in the reference [9], when the water content is 200% and the sand-mud ratio is 20% and 30%, the concave line is close to the straight line.