Study On Drainage Reinforcement Methods And Consolidation Mechanisms Of Calcareous Soft Soil

In recent years,China one belt,one road initiative has accelerated the construction process of artificial island reefs.Layered deposition of coarse and fine soil particles exists during the natural deposition of marine soil,while the crushing of corals by large cuttersuction dredgers is not uniform during the filling process of offshore artificial island reefs,which provides a material prerequisite for this layered deposition.Soils with particle size less than 0.075 mm and a proportion more than 50% are called calcareous soft soils,which have small particle size,high water content and low permeability,so that drainage consolidation time is longer.It is a problem that needs to be solved and few people study to adopt appropriate drainage consolidation method to reinforce it quickly.In this paper,through laboratory tests and numerical simulation,electro-osmotic consolidation,vacuum preloading consolidation,surcharge preloading consolidation and their combined methods were used to discuss the drainage consolidation method and mechanism of calcareous soft soil.The main research results and conclusions are as follows:(1)A set of laboratory test device for drainage and consolidation of soft soil has been designed independently.The device consists of model bucket,vacuum pipeline of electrode circuit part,data measurement part and other parts.The electroosmotic,vacuum and preloading tests of calcareous soft soil can be carried out simultaneously.The test results show that the consolidation effect of calcareous soft soil is good.(2)The electroosmotic consolidation laboratory tests of calcareous soft soil with electrode material,voltage and power-on mode as variables can reduce the initial water content of 60% calcareous soft soil to about 36-40% within 29-36 h,and the treatment effect is uniform.(3)The combined vacuum preloading and electro-osmosis consolidation laboratory tests of calcareous soft soil with electroosmosis start time and mode as variables can reduce the initial water content of 60% calcareous soft soil to about 23-26% within 7 h.It is a drainage consolidation method with high efficiency and uniform treatment effect,and most of its contribution comes from vacuum preloading.Vacuum preloading contributes a lot in this method.(4)After the vacuum preloading of 4.5 h for calcareous soft soil,the vacuum combined preloading consolidation tests of the surcharge preloading 6 h for 15 k Pa were compared with the same long vacuum preloading.The consolidation settlement of the soil increases by 12% and the drainage volume increases by 8%.For high load cases which can not be carried out by laboratory tests,a numerical model was established to predict the results,in which the elastic modulus E has a greater influence on the final consolidation settlement and the permeability coefficient k has a greater influence on the rate of consolidation.When the pressure is changed to 75 k Pa,the moisture content of the soil can be reduced to about 16.4%,which is an effective treatment method.