CHAPTER 4 EXPERIMENTAL VARIABLES AND PROCEDURES
4.4 Standard Proctor Compaction Curves
4.5.2 Saturation of Ceramic Plate and PPE Specimen Preparation
Saturation of the 15-bar ceramic plate is initiated by soaking the plate in a pan with de-aired potable water having less than 2 mg/L of dissolved oxygen concentration. After soaking for at least 24 h, the ceramic plate is transferred to a sealed chamber containing de-aired water with a small headspace above the water.
A vacuum exceeding 90 kPa is applied to the head space for 2 h. After 2 h, the vacuum is completely removed and the plate allowed to sit submerged for ẵ h. The vacuum is then immediately increased to 90 kPa and held for another 2 h. While under vacuum, the plate is inspected intermittently for escaping air bubbles. This
process is repeated until no air bubbles are observed for at least two consecutive applications of vacuum. The PPE device developed herein can be used to test undisturbed specimens or specimens that are compacted or reconstituted.
For clay, compaction tools, hammer, and a custom-made compaction ring (figure 4.9) were needed. The necessary amounts of water, by dry weight of soil, were calculated to attain optimum moisture content (w = 20%). Dry soil was first thoroughly mixed with the required amount of water until ensuring homogeneity, and then this soil mix was compacted into the 2.8-in diameter, 1-in height steel ring.
Specimens were compacted in two equal layers with 16 uniformly distributed blows of a 2-lb, 12-in drop, hammer (figure 4.10). Then the soil specimens (figure 4.11) were extruded and transferred into the confining ring over the ceramic plate.
Figure 4.9 Clayey Specimen Compaction Tools for PPE Testing
Figure 4.10 Compaction of Clayey Specimen for PPE Testing
Figure 4.11 Compacted Clayey Specimen for PPE Testing
For sand, specimens were prepared directly into the custom-made confining ring. During compaction, the confining ring remains seated on top of the saturated 15-bar ceramic plate. A known mass of soil corresponding to optimum gravimetric moisture content is placed in the confining ring and compacted in three lifts using in- place tamping compaction, as shown in figure 4.13. The number of blows is also adjusted so that the desired unit weight is achieved.
Figure 4.12 Confining Ring Seated on the Ceramic Plate
Figure 4.13 Tamping Compaction for Sand
After either compaction method is completed, saturation of the specimen is immediately initiated by placing a coarse porous stone on top of the ring and soaking the full arrangement of ceramic plate, ring, specimen, and stone was submerged in a pan of de-aired potable water. A thin hollow stainless steel plate was placed on top of the porous stone to prevent the loss of soil during soaking as shown in figure 4.14. Soaking is allowed for 24 h in sandy soils and 48 h in clayey soils. After saturation of specimen is complete, the confining ring is fully assembled into the PPE vessel.
Figure 4.14 A Full Soaking Arrangement with Stainless Steel Setup 4.6 Filter Paper Testing Measurement
Specimens compacted at 20% moisture content and used for RC and BE tests, were cut in two halves for matric suction measurement with filter paper. The specimens were trimmed to easily fit into a clean glass jar making sure that the surfaces of the sample are smooth and flat enough to establish an intimate contact with the filter paper for accurate matric suction measurement. Figure 4.15 shows the specimen cut in two halves with filter paper supplies.
In order to get soil suction values at low moisture contents (high suction), however, the specimens were left air-drying in opened glass jars at room temperature (25°C), to allow for some moisture to evaporate at the same dry density. After a moisture content was reached at the approximately desired amount of water (3% ≤ w ≤ 15%), then suction measurement was initiated via filter paper.
Figure 4.15 Two Halves Soil Specimens with Filter Paper Apparatus
Figure 4.16 Schleicher&Schuell No. 589-WH Filter Paper in between Two Larger Protective Filter Papers
For matric suction measurements, a single Schleicher&Schuell No. 589-WH filter paper was inserted in between two protective filter papers larger in diameter (figure 4.16). After that, the other half of the soil sample was put on top, keeping the sandwiched filter papers in between and in intimate contact with the soil samples.
The two pieces of soil were then taped together, as shown in figure 4.17.
Figure 4.17 Two Pieces of Soil Samples Taped Together
For total suction measurements, after the two halves of the soil specimens were carefully put in the glass jar, a piece of rolled stainless steel net was placed on top of the specimen, as shown in figure 4.18. Then, dry filter paper, 5.5-cm diameter, was removed from the box using tweezers and placed on top of a piece of rolled stainless steel net that has the sharp edge facing up in order to minimize the contact area (figure 4.19). Next, the lid was closed and secured tightly in order to prevent any moisture exchange between the air inside and the air outside of the glass jar (figure 4.20). The jar was then left in a controlled temperature room for 3 weeks.
Figure 4.18 Soil Specimen in Glass Jar with Rolled Stainless Steel Net on Top
Figure 4.19 Filter Paper Resting on Top of Rolled Stainless Steel Net Using Tweezers
Figure 4.20 Glass Jar Secured Tightly with Lid
After the three-week equilibrium period, the glass jar is opened and the filter paper quickly and gently carried with a pair of tweezers (figure 4.21) in less than a few seconds. Subsequently, filter paper was directly put on a moisture tin and the weight measured with a balance to the nearest 0.0001 gram accuracy (figure 4.22).
Figure 4.21 Filter Paper Removed from Glass Jar Using Tweezers
Figure 4.22 A tin with Wet Filter Paper inside Small Scale Balance
Then, the tin with the wet filter paper was transferred to a hot oven and left in the oven for at least 10 hours. After that, the weight of the fully dry filter paper was measured using the same balance. Soil moisture and the moisture content of each filter paper were then calculated. Suction values were obtained accordingly from the appropriate calibration curve, as shown in figure 3.49.
Chapter 5 describes the experimental program followed in this work and a comprehensive analysis of all test results.
CHAPTER 5