The electro-osmotic acceleration of infiltration into the subgrade of pavements

[摘要] ENGLISH ABSTRACT: The moisture content of road foundations plays an important role in the durabilityof the pavement and the driving comfort of the road. After a pavement has beencompleted, gradual moisture changes occur in the foundations until equilibriumconditions can be reached, and this can have negative results if expansive clays,for example, are present in the foundation. Pre-wetting of the foundationmaterial is seen as a method to minimilize moisture changes after construction,but if the pavement was already completed, it would be very difficult to change oralter the moisture content in the foundation, because water could then only beapplied to the shoulder areas of the road and horizontal infiltration in the soil isexceptionally slow.The research which is reported in this account was undertaken to determinewhether the process of electro-osmosis could be applied to accelerate waterinfiltration underneath covered areas, as in, for example, road foundationlayers. Electro-osmosis, if found to be successful, has various advantages, ofwhich the most important is that it can be applied without stopping the normaloperations of the road.This research was carried out on a mixture of G5 material (TRH14 classification)and fine material in the form of clay with a low plasticity. Firstly, tests wereperformed to determine the percentage of fines required. It was found that, if toolittle fines were present infiltration did not occur, because moisture could flowfreely through the openings between the rough aggregate. Electro-osmosis alsohad no effect on the rate of flow. The allocated amount of fines required to fillsufficient openings was about 30% (TRH14 classification of mixture is G10).Free flow was stopped and true infiltration occurred. Simultaneously, the rate ofinfiltration could be accelerated with electro-osmosis. Furthermore, a two-dimensional model of a road was constructed withelectrodes placed on both sides, with the aim to determine the infiltration patterncontrolled by electro-osmosis and what the effect of the initial moisture contentwould be on the process. Water was introduced to the one side of the modelroad and the wetting of the foundation was investigated. If the electric current forelectro-osmosis was switched off, the infiltration was mainly vertical, asexpected, but with the current switched on, there was an obvious acceleration ofinfiltration in the horizontal direction. As in the case of the initial tests, it wasfound that electro-osmosis was not very successful to accelerate horizontalinfiltration at low percentages of fines. Furthermore, it was obvious that electroosmosiswas also more effective if the initial moisture content of the soil was low.Low amounts of fines and high initial moisture contents had rather the electroosmoticflow of water passing underneath the road as a result instead ofinfiltration acceleration, with the result that the moisture content did not changemuch.The research thus showed that electro-osmosis is a possible manner in whichmoisture could be conducted into the foundation layers of roads to increase themoisture content if the appropriate amount of fines and moisture content werepresent in the foundation material. Further research could still be carried out andthe materials in each case should be practically evaluated before this methodcould be continued with.

[发布机构] Stellenbosch University