Experimental Study On Pot-Cover Effect In Laboratory

In the cold winter season,the surface temperature of the soil is lower than that of the internal temperature,and the vapor in the soil migrates upward due to the temperature gradient.the vapor cannot migrates to the ground and accumulates beneath a pavement where the local surface is covered by an airport runway,highway,building foundation,Which forms pot-cover effect.During the engineering exploration of the Shenyang Taoxian International Airport runway,it was found that a large amount of moisture was accumulated in the gravel layer below the road surface,which caused the danger of frost heave cracking and uneven settlement of the road surface.laboratory tests based on this project case were carried out.The pot-cover effect apparatus with freezing-thawing cycles developed by Beihang was improved according to the needs of the tests.Experimental study on pot-cover effect in the gravel were carried out with the improved instrument,and a large amount of moisture was gathered in the gravel under the cover.Combined with the engineering case of Shenyang Taoxian International Airport,it is speculated that the moisture accumulated in the gravel of road foundation at the airport was caused by the pot-cover effect,and an laboratory test was performed to simulate the disaster process of the pot-cover effect at the airport runway,and the mechanism of the disaster was analyzed.The main conclusions of this article are:1.Analysis of back-flow principle of Mariotte bottle was carried out,the amount of water reflow to Mariotte bottle calculation equation is obtained.And the equation has been verified by experiments.The study reveals the mechanism of water reflow process in Mariotte bottle.2.The conclusions were revealed by experimental study on pot-cover effect in the gravel.the rate is relatively stable of moisture accumulation beneath a pavement of condensation or desublimation.The amount of absorbed water in the gravel is related to the temperature distribution in the soil.The higher of temperature of the soil at the top,the less amount of water was absorbed.3.The laying structure of experimental soil is similar with the structure of foundation of Shenyang Taoxian International Airport runway,and the mode of the temperature control of the freeze-thaw cycle is used to immitted to the seasonal cycle of the Airport.The test results show that the lower the controlled temperature at the top of soil,the deeper of the freezing front,and the more condensation ice and condensate generated under the cover.The amount of water supplemented by the Mariotte bottle can be considered to be equal to the amount of water generated by pot-cover effect.