Model Experimental Study On The Water Columns Of Soft Ground Static-Dynamic Drainage Consolidation Treatment

Soft ground with high water content and high void ratio are widely distributed in coastal areas, The bearing capacity of such a foundation is very low, so the foundation should be reinforcement for the use of building, And how to strengthening such ground has been a big problem of engineering. The static-dynamic drainage consolidation method have been widely used because of its advantages with economic, efficient and effective for dealing with such ground. This paper relies on the National Natural Science Foundation project about" Ultra-soft ground with static-dynamic drainage consolidation method for rapid reinforcement mechanism design theory and research". This paper trying to solve the mechanism of how water columns transfer tamping energy. The water columns is" Soft soil set of drainage board, The void of drainage board wrapped by soft soil formed a path, pore water penetration together formed a water column, At the moment of tamping because of nearly incompressible of water, the pore water could not back to the low permeability soil, the water columns take energy to every soil layers as a carrier of energy transfer ".This article designed a model box device for simulation foundation treatment used the static-dynamic drainage consolidation method based on the similarity theory, Use the apparatus which could provide high-energy impacted the soft soil which water content is 69.9% and void ratio is 1.87, The test confirm the presence of water columns, Also explored its role for soft soil reinforcement, and analyzes the characteristics and effects of water columns.This paper has made major achievements include:(1) Because of the chain reaction for impact load and the vertical drainage, So the water columns could formed, Water columns made the additional stress and excess pore water pressure in depth direction of foundation have a small attenuation. In the instantaneous of impact, the incremental of pore pressure changes very small follow different depths after middle layer of soil, The incremental of upper and lower of middle layer have a difference of 5.7% when tamping the fourth time, And lower section with deep difference of 10.7%.The additional stress along the depth distribution were gradual change, After tamping four times the attenuation amount of additional stress about of upper and the lower middle layer is 21.36%, the deep and lower middle layer only amount 19.38%. This value is far less than no water columns transmission more than 150%, At this time additional stress in the depth direction changes:y=19.27x"014.(2) The water columns could transfer impact load, water columns transmission power having small amount attenuation in the depth direction, Deep soil and the upper soil synchronous power transmission from the water columns, The greater the impact load the more obvious characteristics of water columns. The upper layer of siol proportion energy increment (AP.AS) more then 65% at the first tamping. But as increasing of tamping the energy increment aggregation to the down soil layer, The deep and lower middle layer proportion reached more than 70% at the fourth tamping. Water columns can made the drainage consolidation synchronization for different depths of soil, But the upper soil would complete consolidation more earlier then bottom soil, the settling of upper layer accounts for the total amount form 1/2 to 2/3 at the first and second tamping, But the deep and lower middle layer amount less than 1/3. The deep layer and lower middle layer amount more than 1/2 but the upper layer accounts less than 1/5 for the finally twice tamping.(3) Water columns have characteristics about the more bigger of impact load or more intensive of drainage board, the more uniform distribution of the tamping energy in the depth direction. When the impact load are same, drainage board density of 4cm have more earth pressure increment, more faster pore pressure dissipation capacity, and larger settlement than drainage board density of 6cm,The specific values were 13.2%,8.5% and 10.2%.(4) Used additional stress ratio to calculation the model test reinforcement depth of soil at least reach 15m deep for the actual project. Analysis the monitoring and test data get form static-dynamic drainage consolidation method practical examples treatment of soft foundation, And confirmed what the conclusion of model test demonstrated by the model experiments is correct.