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In-situ Evaluation of Design Parameters and Procedures for Cementitiously Treated Weak Subgrades using Cyclic Plate Load Tests
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2020-12-01
[PDF-5.98 MB]
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Edition:Final Report, Mar 2013 – Nov 2019
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Abstract:This study aimed at evaluating the performance-related properties (e.g., resilient modulus and permanent deformation) of cementitious treated/stabilized subgrade soils under repeated loading test conditions. For this purpose, both laboratory and field testing programs were performed on treated/stabilized specimens/test sections. The laboratory testing program comprised of two phases: Phase I focused on evaluating the resilient modulus (MR) and permanent deformation (PD) of the current subgrade treatment/stabilization schemes for hauled soils using cement and/or lime stabilizer as provided in DOTD’s standard specifications. Three soil types with different plasticity indices (PI)were used in Phase I. The results of Phase I showed that the MR for treated/stabilized soil specimens ranged from 25 ksi to 36 ksi, and that the values of PD are negligible. Phase II focused on examining the proper treatment/stabilization recipe (lime, fly ash, and cement) for very weak subgrade soils at high moisture contents, and evaluating the corresponding MR and PD. Four soil types with different — ii — PIs were considered in Phase II that were prepared at three different moisture contents correspond to a raw unconfined compressive strength (UCS) of 25 psi or less. All soil specimens in Phase II were treated with different combinations of class C fly ash (or Portland cement type I) and hydrated lime to achieve a 7-day target UCS values of 50 psi to create a working platform and 100 psi for subbase application. Repeated load triaxial tests (RLT) tests were performed in the laboratory testing program to evaluate the MR and PD of the laboratory treated/stabilized specimens. The results of Phase II demonstrated good correlation between the water/additive ratio and the MR/PD, such that the soil specimens prepared at low water/additive ratio showed better performance than those prepared at high water/additive ratio. The MR for treated/stabilized very weak soil specimens at 50 psi UCS for working platform ranged from 5.5 ksi to 11 ksi. However, for the 100 psi UCS (subbase application), the MR for treated/stabilized very weak soil specimens ranged from 9.5 ksi to 14.5 ksi. The results of laboratory tests showed that there is no correlation between MR and UCS for the treated/stabilized soils as well as no trend between MR/PD and PI. The field testing program involved constructing and performing cyclic plate load tests (CPLT) on 10 test sections at the Accelerated Load facility (ALF) site in which six sections were selected based on the results of Phase II, while the other four sections were selected from a previous study on micro cracks of cement stabilized soils. The CPLTs were performed to measure the in-situ composite resilient modulus (MR -comp) of the ten test sections at ALF site. The measured MR of the different treated/stabilized layers were back-calculated based on the assumption that ratio (E1/E2)DCP equal to the ratio (E1/E2)CPLT for the two-layer system. The results of field tests showed that the back-calculated MR values for the treated/stabilized test sections are in good agreement with the laboratory-measured MR values for Phase II.
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