Quantifying the Influence of Geosynthetics on Pavement Performance (2017)

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153 ATTACHMENT A. STANDARD METHOD OF TEST FOR DETERMINING THE PERMANENT DEFORMATION PROPERTIES OF GEOSYNTHETIC-REINFORCED AND UNREINFORCED GRANULAR MATERIAL

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155 4.2. Loading Device—The loading device shall be a top-loading, closed-loop, electro-hydraulic, or electro-pneumatic testing machine with a function generator that is capable of applying repeated cycles of haversine-shaped load pulse with 0.1-second loading and 0.9-second unloading periods. 4.3. Specimen Response Measuring Equipment—The measuring system for all materials shall consist of two linear variable deformation transducers (LVDTs) mounted on the top or both sides of the specimen. The LVDT requirement shall be as described in T 307. 4.4. Specimen Preparation Equipment—Use of different methods of compaction is necessary to prepare specimens of different materials and to simulate desired field conditions. The specimen compaction equipment and compaction procedures shall be as described in T 307. 5. PREPARATION OF TEST SPECIMENS 5.1. Use 150-mm-diameter and 150-mm-height (or 300-mm-height) specimens for tests on granular material specimens. 5.2. Cut the geosynthetic product in a circle with a diameter of 150 mm. 5.3. Prepare laboratory-compacted specimens/reconstituted test specimens of granular materials to approximate the in-situ wet density and moisture content. Place the geosynthetic at a certain location during compaction. 5.4. Ensure that the moisture content of the laboratory-compacted specimen does not vary by more than ± 0.5 percent for granular materials from the in-situ moisture content obtained. 5.5. Protect the prepared specimens from moisture change by applying the triaxial cell or the triaxial membrane and testing within five days of completion. Prior to storage, and directly after removal from storage, weigh the specimen to determine if there was any moisture loss. If moisture loss exceeds 0.5 percent, then do not test the prepared specimen. 6. PROCEDURE 6.1. Place the laboratory-compacted geosynthetic-reinforced or unreinforced specimens in the triaxial chamber. 6.2. Connect the air pressure line to the triaxial chamber and apply the specified preconditioning confining pressure of 41.4 kPa to the test specimen. Maintain a contact stress of 10 percent ± 0.7 kPa of the maximum applied axial stress during each stress level. 6.3. Begin the test by applying 500 repetitions of a load equivalent to a maximum axial stress of 103.4 kPa and 103.4 kPa confining pressure according to Stress Level 0 in Table 1. This is a preconditioning step to eliminate the effects of the interval between compaction and loading and to eliminate the initial loading versus reloading. 6.4. Apply a specified axial load to the top of the triaxial cell piston rod for 10,000 cycles according to the stress level shown in Table 1. 6.5. Test each granular material specimen for only one stress level. Condition the specimen by Stress Level 0 in Table 1 prior to the permanent deformation test.

156 Table 1—Permanent Deformation Testing Protocol for Geosynthetic-Reinforced and Unreinforced Granular Material Stress Level Confining Pressure Max. Axial Stress Cyclic Stress Contact Stress No. of Load Applications kPa psi kPa psi kPa psi kPa psi 0* 103.4 15 103.4 15 93.0 13.5 10.3 1.5 500 1 27.6 4.0 192.9 28.0 173.6 25.2 19.3 2.8 10,000 2 48.2 7.0 130.9 19.0 117.8 17.1 13.1 1.9 10,000 3 68.9 10.0 68.9 10.0 62.0 9.0 6.9 1.0 10,000 4 48.2 7.0 192.9 28.0 173.6 25.2 19.3 2.8 10,000 5 68.9 10.0 192.9 28.0 173.6 25.2 19.3 2.8 10,000 6 89.6 13.0 192.9 28.0 173.6 25.2 19.3 2.8 10,000 *Note: Stress Level 0 is for preconditioning of granular material. 7. CALCULATION OF RESULTS 7.1. Perform the calculations to obtain the curves of permanent strain versus the number of load cycles for each tested stress level. 7.2. Determine the permanent deformation properties in Equations 1 to 3 using the least square error criteria.    0 2 1m nNp e J I K          (1)   2sin 3 3 sin    (2)   6cos 3 3 sin c K     (3) where: 2J = the second invariant of the deviatoric stress tensor; 1I = the first invariant of the stress tensor; 0 ,  ,  , m , and n = permanent deformation properties; c = cohesion of granular material; and  = internal friction angle of granular material. 8. REPORT 8.1. The report shall include the following: 8.1.1. Source of granular material. 8.1.2. Type of geosynthetic. 8.1.3. Geosynthetic location. 8.1.4. Permanent strain curve for each tested stress level. 8.1.5. Determined permanent deformation properties and fitted permanent strain vs. load repetition curves.