| Soft soil is a common natural material, which is widely distributed on the surface of theearth. Its physical and mechanical properties are very complex, with high water content, highpore ratio, high compression, low strength, poor permeability and visible structure. Silt andmuddy soil are mainly composed by much fine clay particles, organic matter, oxides and solidphase material and water. Soft soil in Zhuhai is of the typical nature of the soft soil. The soilused on foundation, shows low bearing capacity, large amount of the settlement, the longertime required to stabilize. It also has a direct impact on the progress, cost and safety of theproject. The formation of soft soil engineering properties is closely related to their specifichistorical circumstances. Lots of research and practice have proved that the engineeringproperties of soft soil are related to not only the material composition, particle size, drainageconditions, depth and external loads state, but also its microscopic pores, the particlecharacteristics, the composition an arrangement of the particles and microscopic structures.For a long time the researchers studied the engineering properties of soft soil mainly from themacro level. The fundamental mechanisms and natural rule of the adverse engineeringcharacteristics cannot be explained and illustrated. Through the macro and micro perspective,this article introduced the method of studying the engineering properties of soft soil fromZhuhai and analyzed the microscopic mechanism of the engineering properties of soft soilfrom Zhuhai through a comprehensive macro-and micro-angle.The mainly research work and theoretical achievements are obtained as follows.(1) Through basic physical and mechanical properties tests of Zhuhai undisturbed softsoil with different depth in lab, it is concluded that Zhuhai soft soil particles are given priorityto fine grained soil, with high content clay mineral. Zhuhai soft soil particle is mainly of finegrained soil with clay and silt. For mineral composition, kaolinite takes the most percentageof clay mineral, followed by illite and montmorillonite. The specific surface area of Zhuhaisoft soil is large. The liquid and plastic limit show positive correlation with the specificsurface area. The specific surface area and adsorption property of clay mineral is better thannon-clay mineral, with high combined water. Specific surface area and permeabilitycoefficient present certain negative correlation. It shows that the larger specific surface area is, the lower the permeability characteristics.(2) From the conventional consolidation test and rebound test data of Zhuhai soft soil, itcan conclude that Zhuhai soft soil belong to owe consolidation soil. The consolidationcharacteristics are related to pre-consolidation pressure. When consolidation pressure waslarger than pre-consolidation pressure, the consolidation rate presented growth trend. Thehorizontal consolidation coefficient has big difference from vertical consolidation in the initialstages. As the depth increased, the final consolidation coefficient stable value presenteddecrease trend. The constitutive property of Zhuhai soft soil is strong. When consolidationpressure was greater than the overlying soil pressure, the soil was at the rebound initial stage,and the resilience curve characteristics showed relatively gentle. When consolidation pressuredischarged to less than the overlying soil pressure, soil samples were at rapid rebound stage,and the resilience curve turned steep, with rapid growth void ratio.(3) Using environmental scanning electron microscope technology to analyze Zhuhaiundisturbed and consolidated soil samples, from different depth and section direction, it isconcluded that Zhuhai natural soft soil microstructure is mainly of honeycomb structure,spongy structure and clotted structure. Soil particle is curved piece flocculence fold polymers,with large micro pore distribution. The deep microscopic particles are smaller than shallow,with high compactness and clear flocculation structure. The micro pore distribution andorientation probability entropy is large. In the process of consolidation, many big pores werepressed into small pore, the soil turn compactness. The soil particles showed no apparentdirectional property. The particle elements changed from side-surface, surface-surface toedge-edge combination, with no obvious curve sheet structure. The particle conglomerated,and closely contacted with each other. As the loading increased, the pore water reduced, andbound water membrane thinned, turned to conglomerate shape form. The big pore area andquantity reduced, small pore increasing, equivalent pore diameter decreased, and then the porechanged from inter-granular to internal. In the process of consolidation, microscopiccharacteristic of vertical direction changed more obviously than horizontal direction. The longshaft was easy to be cut into small grain. So the microscopic structure element characteristicwas mainly at the pressure direction.(4) Through the mercury injection test, it is researched that the influence of infiltration effect on microscopic pore size distribution for Zhuhai soft soil, besides the microscopic porechange rule through consolidation process. The microscopic pore of Zhuhai undisturbed softsoil mainly distributed at400nm-2500nm and30nm-400nm. The microscopic poreshowed kind of increase after penetration. The reason is that the effect of seepage force takesaway part of particle, and the concentration pore diameter is greater than undisturbed peakaperture value. At the same time, soft soil pore area reduced, and the micro pore scaledistribution showed homogenization effect. In the consolidation process, the larger poregradually changed into smaller pore of soft soil samples. As consolidation pressure increased,at the stage of consolidation pressure between100kPa and200kPa, void ratio rapidlydecreased and the average aperture also decreased rapidly. When consolidation pressureturned to more than200kPa, the pore ratio and average aperture still kept reduced, but slowdown.(5) According to the consolidation mechanisms of unidirectional universal equation andTerzaghi unidirectional consolidation theory, the corresponding relation between microscopicparameters and consolidation coefficient was analyzed, such as specific surface area,equivalent aperture, grain orientation probability entropy, and granular fractal dimension. Theconsolidation coefficient equation was given, which considered micro factors correction.Through the microscopic parameter range value, the corresponding microscopic parametersinfluencing factor value was also obtained. Through the practical engineering of vacuum jointpreloading on Zhuhai Jinwan soft soil, the analysis of the sampling image, vane shear dataand actual consolidation settlement, verified the accuracy and reliability of the analysis value,data and theory by indoor macro and micro tests. |
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