| The engineering application of solid waste is one of the key and hot spots in the field of geoenvironmental engineering,which meets the strategic needs of solid waste resource in China.In view of the large volume,low utilization ratio and narrow utilization level of waste asphalt pavement in China,the recycled asphalt pavement material(RAP)is obtained by milling and screening the waste asphalt pavement materials.RAP can be used in lieu of the sand and stone as reinforced retaining wall backfill,so as to promote the diversified,refined and efficient recycling of waste asphalt pavement materials.However,the strength and creep characteristics of RAP materials are easily affected by stress and environmental temperature due to the presence of asphalt.It will cause some safety hazards if not fully considered in the design.Therefore,a series of laboratory tests including direct shear test and direct shear creep test were carried out on reinforced RAP materials for use as retaining wall backfills.The effects of stress and temperature factors on the strength and creep characteristics of reinforced RAP and its mechanisms were discussed.Based on the experimental results and theoretical analysis,the creep constitutive model for reinforced RAP materials as retaining wall backfills considering the effect of temperature was established,which can provide theoretical basis and design reference for the related retaining wall engineering using reinforced RAP as backfill.The main works and conclusions are summarized below:(1)The interface direct shear tests were conducted on non-reinforced and reinforced RAP specimens under different test temperatures and other factors.The results showed that the addition of geogrid can effectively constrain the deformation of RAP specimens and improve the interface shear strength;the lower the test temperature is,the greater is the maximum shear strength τmax for the reinforced RAP specimen;both the cohesion c and internal friction angle φ decrease with the increase of the test temperature.Compared with the internal friction angle φ of traditional reinforced sand and stone as backfills,it is found that the reinforced RAP as backfill can also meet the shear strength requirements of building materials in geotechnical engineering applications,and can completely replace the traditional sand and stone as backfills in the construction of reinforced retaining wall.(2)An improved temperature-controlled and stress-controlled direct shear creep apparatus was developed to conduct the direct shear creep test on reinforced RAP specimens under different stresses and test temperatures for investigating the influence law and action mechanism of shear stress level D on the creep characteristics of reinforced RAP specimens.Test results showed that under the same condition,the shear strain ε and the shear strain rate ε of the reinforced RAP specimens at the same creep time increase with the increase of shear stress level D.No matter what the test temperature is,there was no creep rupture for the reinforced RAP specimens when the shear stress level D≤0.8.Therefore,considering the creep characteristics of reinforced RAP retaining wall backfills,for the sake of safety,it is suggested that the strength of reinforced RAP retaining wall backfills should be reduced by 20%in the actual engineering design calculation to reduce the possibility of creep rupture.(3)Through the direct shear creep test on reinforced RAP specimens under different test temperatures,the influence law and mechanism of test temperature change on the creep characteristics of reinforced RAP as retaining wall backfills were discussed.The test results showed that under the same stress condition,the shear strain ε and shear strain rate ε of reinforced RAP specimens will increase with the increase of test temperature,and creep rupture will be more likely to happen.Therefore,it is suggested to select the season with higher temperature(such as summer)for the construction of reinforced RAP as retaining wall backfill in the actual project,so as to reduce the potential creep deformation in the early stage of operation.(4)Through the direct shear creep test on reinforced RAP backfills,the obtained lgε-lgt curves showed a good linear relationship,which conforms to the classical Singh&Mitchell three parameter creep model.The effects of test temperature on parameters A、α and m of creep model were discussed.The results showed that with the increase of test temperature,the parameters A、α and m gradually increase and can be quantitatively expressed.A creep constitutive model of reinforced RAP as retaining wall backfills considering the effect of temperature was established.The validity of the model was verified by comparing the model calculated results with the measured data. |
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