Stabilisation des sols traités à la chaux et leur comportement au gel

Abstract : The present work deals with the behaviour of fine-grained silty and clayey soils treated with lime under frost. Those soils are frequently encountered in earthworks. Three soils corresponding to A1, A2, A3 classes according French NF P 11-300 standard were chosen for this study. These soils were treated with 3 lime dosages corresponding to three objectives: 1) improvement (minimum dosage), 2) stabilization and insensitivity to water (intermediate dosage), 3) stabilization and frost resistance (highest dosage). Lime-treated soils were subsequently cured for different times: 7, 28, 90, 365 days. Two frost processes, frost heave and freeze-thaw cycles, were applied in parallel with the assessment of mechanical, hydraulic and microstructural properties. Experimental results evidenced that it is the hydraulic properties (suction at frost front, sp and unsaturated hydraulic conductivity, kunsat) that govern the frost heave phenomenon of soils, treated or not. In addition, this study demonstrates the direct link between the microstructure (the pore size distribution) and the hydraulic properties (water retention curve and hydraulic conductivity). The treatment on one hand improves the mechanical performances of soils, and on the other hand modify their microstructure, and thus changes their frost sensitivity. The frost susceptibility increases directly after treatment, and then decreases with curing time. Based on the suction at frost front and the unsaturated hydraulic conductivity, a simple model was proposed and validated allowing to estimate the frost heave. Considering that the determination of unsaturated hydraulic conductivity is not a test commonly performed by most laboratories, a criterion based on the suction at frost front and the saturated hydraulic conductivity was proposed to estimate the frost sensibility of soils. The second frost resistance test consists of measuring the retained strength factor after 10 freeze-thaw cycles, RFT (%). The results obtained show that RFT of lime treated soil varies from 0% (when soil specimen completely loses its resistance and collapses after 10 freezethaw cycles) to 90%. When RFT is higher than 60%, no visual damage was observed on the specimen surface; consequently, this value is proposed as a criterion for acceptance of lime treated soil in capping layer before covering. In addition, the study of effect of freeze-thaw cycles showed a significant decrease of mechanical performance (RFT) during the first three cycles, and a stabilization after 10 cycles. Using X-ray Tomography, the intern damage of specimens due to freeze-thaw cycles was quantified. A correlation between the decrease of mechanical performance and the increase of damage index was evidenced. A model was then developed to evaluate the degradation of mechanical performance with the increase of damage index
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Thi Thanh Hang Nguyen. Stabilisation des sols traités à la chaux et leur comportement au gel. Autre. Université Paris-Est, 2015. Français. ⟨NNT : 2015PESC1064⟩. ⟨tel-01191696⟩

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