Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
APPENDIX G SPECIMEN PREPARATION OF COHESIVE SOIL G-1
APPENDIX G SPECIMEN PREPARATION OF COHESIVE SOIL Impact Compaction. In the impact procedure, the soil was compacted in a 4 in. diameter by 8.5 in. high cylindrical split mold. The lower 0.5 in. of the mold was used to create either flat or sloped specimen ends for Phase ~ testing by placing a 0.5 in. thick steel plate at the bottom of the mold. The flat steel plate made the extrusion of the soil sample much easier. Impact compaction was achieved using 5 layers and 22 blows per layer of a 5.5 lb hammer dropping 12 in. which was found by trial and error to produce a similar moisture density curve to the conventional T-99 procedure. Each soil specimen was prepared according to the following procedure: ~ . Weigh out 8.0 lbs of air dried soil. 2. Add the calculated mass of water to achieve the target water content. 3. Thoroughly mix the soil sample and water and then cover the container with aluminum foil for 24 hours. 4. Spray the mold with a lubricant to prevent the compacted specimen from sticking to the mold walls, and then compact the wet soil in five layers using the 5.5 lb. hammer applying 22 blows to each layer. 5. Extrude the wet soil sample using a hydraulic extruder and determine the wet weight of the sample, WT 6. Determine the water content from the remaining portion of wet soil. Kneading Compaction. The spring loaded kneading compactor, which uses a pie shaped foot, was used to compact the silty sand and clayey sand soils into a 4.0 in. diameter mold. Specimens were compacted in 10 layers with 24 tamps per layer using a 70 lb. spring. Ibis preparation procedure was determined by trial and error to give a dry density that matches the T-99 density at optimum water content. Using this compaction energy the following procedure was used: ~ . Weigh out 8.0 lbs of air dried soil. 2. Add the calculated mass of water to achieve the target water content. 3. Thoroughly mix the soil sample and water and then cover the container with aluminum foil for 24 hours. 4. 5. Spray the mold with a lubricant to prevent the compacted specimen from sticking to the mold walls, and then compact the wet soil in ten layers using the 70 lb. spring loaded hammer to apply 24 tamps to each layer. Level every layer before tamping, and generate 70 lbs. by just compressing the spring. Relevel after 12 tamps. After tamping the last layer, level the top and measure the total specimen weight. Measure the water content from the trimmings and calculate the dry density. G-2
Compaction of CohesionIess Soil All A-3 sand specimens were prepared by tamping the sand at a water content of 9.0% in eight equal layers by the following procedure using the apparatus shown In Figure G-1: Weigh out 7.0~Ibs. of air dried cohesionTess soil and mix with 286 ml of water to obtain a water content of 9.0 %. 2. Determine the weight of each layer from the relative density and the needed dry densities as follows: WT=7dxVT We, = WT / HT 3. Place a filter paper on top of the pedestal of the tnaxial cell. 4. Place each layer of sand In the split mold and tamp it as shown in Figure G 1. 5. After tamping the last layer, level Me top layer and weigh the extra soil to determine the total compacted soil weight (WT)- Take a sample from the remaining soil to find the water content. 6. Apply a vacuum of about 2 to 3 psi to the specimen base to hold the soil sample together while removing the split mold. 7. Add another membrane around the sample to prevent air leaks. 8. 9. After mounting the tnaxial cell chamber and applying the confining pressure, release the vacuum applied to the inside of the sample. Leave the base drainage valve open throughout the test. Soaking Cohesive Specimens Cohesive soil specimens were soaked by applying a back pressure of lLO psi to the specimen for about 15 days. The clayey sand (A-6) specimens were very difficult to soak because of the presence of clay. While the A-5 specimens were easier to soak, they still took about two weeks to reach a degree of saturation of more than 90%. Bow the compacted A-6 and A-5 soil specimens were soaked in the cell shown in Figure G-2 by the following procedure: I. Compact the soil specimen following the procedure for cohesive soil given earlier using a 4.0 in. diameter PVC mold. 2. After removing the base, measure the total weight of the soil specimen and the mold. Use this weight and We water content evaluated from the remaining portion of the soil to calculate We initial degree of saturation.
Cover both ends with Alter paper. 4. Saturate the drainage line going into the bottom of the base before screwing it into the base . Also saturate the porous stones. 5. Fix the bottom base to the mold which contains the soil specimen after positioning the O-ring to prevent leakage. 6. Attach the top end plate having a hole pattern and size similar to the one used when soaking CBR specimens and screw it on tightly. 7. Apply a back pressure of 10 psi to the specimen base using a biaxial pressure board. To reduce the tone required for saturation, a larger back pressure could be used for production work. 8. 9. Monitor the amount of water flowing to the soil specimens with the help of the pressure board burettes. Make sure that the lines and the burettes do not run out of water while · ~ soa sing specimens. 10. After two weeks disassemble the setup and find the weight of the soaked sample. The increased weight of the soil sample equals the weight of water that flowed into the soil specimen. Calculate the degree of saturation of the soaked sample. Specimen End Preparation To give better contact between the top and bottom plates and the specimen, the ends of selected specimens were grouted with hydrostone I-. The clamps used to grout the specimen ends are shown in Figure G-3. The grouting procedure is shown in Figure G-4 and described as follows: . Mix 28 ml of water with 70 gm of hydrostone cement until it becomes a liquid. The water-hydrostone cement (W/C) ratio is 0.4 by weight. 2. Let the mixture hydrate for about 15 min. as to become a paste. 3. Pour the paste into the aluminum split clamps around the pedestal shown in Figure G-4(a). Place the sample on top of the hydrostone grout. 4. Center the sample vertically by using an acrylic plate with a 5.0 in. diameter hole in Me middle and supported horizontally on three steel rods Elxed to the base of the biaxial cell as shown in Figure G-4(b). 5. Remove the clamps from around the bottom of the sample 10 min. after pouring the grout into the mold. 6. Repeat steps ~ and 2. Place the clamps around the top end of the sample using the acrylic plate as a support as shown in Figure G-4(b). G-4
8 9e Repeat step 3. Place the top cap on the top of the hydrostone paste and center it in the direction to fit the EVDT clamps. Place a rubber membrane around the specimen and form a seal using two rubber O-rings. Leave it for about two hours to allow the hydrostone paste to reach its required strength. I. Fix the EVDT rod carriers to the bottom of the tr~ax~al cell and attach the EVDT's to them. The specimen is now ready for testing. Attaching EVDT Clamps Figure G-5 shows the Inside EVDT clamps (Figure G-5a) used in Phase ~ and He alignment supports (Figure G-5b) developed to install these clamps. Four steel arms carry the four clamps and each clamp is fixed by a screw to the end of the arm. Me arms are connected to two horizontally fixed bars which are cattier on a veridical steel rod and kept a fixer} distance apart. The vertical steel bar is supported by a steel base to give stability. The alignment support device maintains the four clamps on He middle of the sample at a fixed separation distance equal to half of the total specimen height. The clamps are fixed to the sample by rubber bands. References Gut. Pezo, R.F., CIaros, G., Hudson, W.R., and Stoke, K.H., (1992), "Development of a Reliable Resilient Modulus Test for Subgrade and Non-Granular Subbase Materials For Use in A Routine Pavement Design", Research Report ~ 177-4F. (prepared for Texas DOT), University of Texas-Austin, January. G-S
1 ' ~ 1' o - - ~ ~ Ple glass Coil , ~ __ , ~ ~ ~ Plexiglas Split Sold Hem; ~9 `` ~ ~ C oh 4t ~ ~ _ o Collar Figure G- 1. Setup for preparing cohesionless soil specimen G-6 Vacuum Tribal Cell Base
Holes Similar to Those of CBR Soaking Plate _ :/ I Tl 11 11 1~lL / . Back Pressure \ Soil Specimen D = 4.0 in. H = 8.0 in. 11 ~ '\ 11 ~ c- ~ ~N ' O-Ring Screws . ~ Figure G-2. Setup used to soak cohesive soil specimens G-7 Filter Paper PVC Mold Filter Paper
~ D.4.0~. Hi_ A// = 0.1 ~ Spat ~ Hy~tone Grout ~ Space 1 '' - _ ~ ~C~8~ . ~ Figure G-3. Clamps used in grouting the ends of the test specimen G-8
- ~ - - ~ .~ E ~ ~ .Y - . _ ,6 < ~ ~-L,~' \ , ~ ' ._ _F Cat 11 - C} C ~ ^l By ' 1 to c .= E NO ~ C: y o . _ S _ a _ \1 i - - i i ~ ~ 73 | ELF ~ .= I ~ I Fin 1 _ , ~ ~ ~ 1 3 F A. Ha mar. 'a /~/~' ~' at ~F. ___ ~,~_F_ ~- ~S X C~ 11 t1 C' ~ = J G-9 o oo ·3 o D _F o o D ._ o _` C~ _F ·_ C U] - ·_ o U] · _ V, . ~ o C~ C~ o C~ ~: ~ - - o D C~ .S S: ._ ~0 o - o · _
Al sat // // LOOT Hole 3\~\ Lt~ R"1 Hole R ~ 2 0 loch ~ JO (a) One pair of internal LVDT clamps 1 1 1 - ~ ' _ 1 , ~ , ,, , i, 1 1 (b) Side view of alignment support device Figure G-5. Eternal L~VDT clamps and alignment support device C-10