Study On The Mechanism And Application Of Wicking Fabric In Regulating Subgrade Moisture Field

Frost damage to highway subgrade in seasonal frozen soil areas will cause road surface damage and a lot of economic losses.The traditional methods of preventing and controlling the freezing damage of the subgrade all have various shortcomings and deficiencies,which cannot fundamentally solve the problem of freezing damage in subgrade,making the frost heave more severe.Therefore,a new type of wicking fabric is introduced to solve the moisture accumulated in unsaturated subgrades due to various environmental and climatic conditions such as rainfall infiltration or groundwater capillary rise,so that the freezing and thawing of subgrades in northern regions can be effectively resolved.Financially supported by the National Natural Science Foundation of China(No.41877240,41672280)and based on laboratory tests,model tests,numerical simulation methods,and field tests,systematic studies are conducted on the capability of the wicking fabric to drain water,the mechanism of water absorption and drainage in the subgrade,and its influencing factors.Main conclusions of the research work are given as follows:A series of tests are carried to study wicking fabric’s water absorption and drainage capacity itself,and the relationship between the free water absorption capacity and evaporation capacity of wicking fabric is investigated.The influence of the initial moisture content of soil sample,the relative humidity of the environment and the exposed area of the material on the capacity of wicking fabric in unsaturated soil is studied.In unsaturated soil,wicking fabric can discharge the water in the soil column,reducing the water content in the soil by 5% to 8%.Based on the Priestley-Taylor model,an evaluation method for the drainage capacity of wicking fabric in unsaturated soil is proposed.The drainage rate of wicking fabric is equivalent to 13%of the evaporation rate of soil surface of the same area.An optimization scheme for the arrangement of the water conducting fiber of the wicking fabric is proposed.The drainage effect will be better when the water conducting fibers are arranged in a single beam spacing of 3 mm.The regulation effect of the wicking fabric on the subgrade moisture field is studied,and the effect of the wicking fabric on the rainfall infiltration and groundwater capillary rise is investigated by the indoor model test.The influence of the number of buried layers and locations of wicking fabric on the distribution of moisture field in subgrade soil is expounded.The moisture content of the soil near the wicking fabric is significantly reduced.Each layer of wicking fabric can reduce the overall moisture content of the soil by 5%.Based on the on-site climate and subgrade design data,a hydrothermal coupled numerical simulation method is used to study the influence of capillary wicking fabric on subgrade moisture field and temperature field under rainfall conditions,and the influence range of wicking fabric on subgrade moisture field is clarified.The wicking fabric can effectively prevent rainfall infiltration and groundwater capillary rise,reducing the moisture content by 6%to 10%,keeping the subgrade water content below the initial frost heave moisture content and at the same time,the freezing depth can be effectively reduced by 0.4～1 m.The influence of the buried position and the layers of the wicking fabric on the subgrade moisture content and freezing depth is expounded,and the value of the buried depth of the material is given based on the requirements of the existing highway subgrade construction codes.The field tests further study the influence of capillary wicking fabric on the subgrade moisture field in practical engineering applications,and verify the results of laboratory tests and numerical simulation calculations.The subgrade of the field test section is drilled to take soil and test the water content.The results show that the influence range of the wicking fabric in the subgrade is 40 cm near the material,which is consistent with the numerical simulation results;the wicking fabric can reduce the water content by 5% to 8%,which is basically consistent with the results of laboratory tests and numerical calculations.The particle size analysis test and scanning electron microscopy observation of the new and on-site wicking fabric samples show its drainage mechanism from a microscopic perspective,and clarify the wicking fabric’s anti-clogging ability and long-term performance.