Guidelines and Equipment for basic on site soil stabilizing compression strength testing
The Imants Quakemeter is inexpensive, easy to transport and can be used for compressive strength testing at a variety of different depths.
For site testing prior to stabilizing use the quakemeter to check the strength of the areas below the layer to be stabilized. This will indicate any structural problems that may require further investigation.
After stabilizing, and compaction, place the point of the quakemeter in the centre of a 25mm disc or coin and apply pressure. The load bearing capability of the stabilized soil can then be calculated from the Imant pressure indicator.
All standard testing equipment including Troxler nuclear density and Cone Penetrometer equipment can also be used.
During the stabilizing process treated soil samples can also taken and compacted into a container /mould for laboratory testing.
On-site core sampling is not recommended for stabilized soils.
All samples must be sealed with AggreBind prior to a water uptake test for 3 minutes in a 12ml depth of water.
The AggreBind surface seal will normally cure within 2 hours.
Unconfined Compressive Strength Tests (UCS) on stabilized soils should only be carried out after 28 days.
It is recommended that a full soil analysis should always be carried out before any soil stabilizing project is implemented.
Thin Layer Nuclear Density Gauge Performance Test Results
Troxler Electronic Laboratories, Inc. is the only manufacturer of a true thin layer density gauge. Troxler Models 4640 and 3450 both feature the patented technology to measure the density of thin layer asphalt and concrete overlays from 2.5 to 10 cm (1 to 4 inches) without influence from the underlying material. This testing method determines density through the backscatter method. Photons from the source are scattered through the material being tested. Two sets of photon detectors are present in the gauge base to read those photons scattered back toward the gauge from differing depths. The difference in the depth of material measured by each system, factory calibration, and the mathematical models allow the thin layer gauges to determine the density of the top layer of asphalt.
The state of Virginia has devised a specification to determine that a nuclear density gauge is a true thin layer gauge. The test procedure for this specification is called, “Virginia Test Method for Thin-Lift Nuclear Density Gauge Performance Requirements” designation: VTM-81. The equipment necessary to perform this test includes:
2 base blocks (each 22”L x 14”W x 8”D minimum); one with density between 100 – 120 PCF density and the other with density between 155 – 170 PCF density
4 thin layer metal plates; two Aluminum (22”L x 14”W x 1.25”D and 22”L x 14”W x 2”D) and two Magnesium (22”L x 14”W x 1.25”D and 22”L x 14”W x 2”D)
The procedure for this test involves placing each of the thin layer plates on each of the base blocks, placing the gauge upon the plate, taking four readings and finding the average of the four. The instructions for this test are as follows:
Place the 1.25” Aluminum plate on top of one of the base blocks. Check to make sure that it is resting squarely and does not rock. Set the nuclear gauge on the 1.25” Aluminum plate. Check to see that it does not rock. Set the gauge thickness to match the plate thickness (for thin layer gauges). Take four one-minute readings and record them and their average on the attached form. Repeat this process using the same 1.25” Aluminum plate placed on the other base block. The following steps require that this procedure be repeated with each of the other thin layer plates. The results of the density of the same plate tested on the different base blocks should not vary if tested with a true thin layer gauge due to the fact that the underlying material density does not influence the reading. Therefore, limits are set by this test to determine how much the two tests may vary.
List of Tests and Testing Equipment
- Compressive Strength (ASTM C109)
Load capacity is from 2,500lb to 250,000lbsTest specimen: 2”x 2”x 2”
- Flexure Strength (ASTM C348)
Load capacity is up to 1,000 lbTest specimen: 1.57”x 1.57”x 6.30”
This report will give the results obtained when following this test procedure using a Troxler Model 3440 gauge, Model 3450 gauge and Model 4640 gauge. The Model 3440 gauge does not offer a thin layer mode and therefore was used in the backscatter position in asphalt mode. The Model 3450 was used in thin layer mode, and the 4640 (a thin layer only gauge) was also used in this mode. The test results shown below prove that the standard surface moisture/density gauge, does not pass the criteria of a thin layer gauge and that the readings are greatly influenced by the underlying material density. The Model 4640 and Model 3450 in thin layer mode easily fall within the limits stated by this test. These two density gauges pass the test of a true thin layer density gauge, proving that the underlying material density does not influence the readings of the thin layer gauges.
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Notes on the Cone Penetrometer Test
GE 441: Advanced Engineering Geology & Geotechnics, Spring 2004
The standardized cone-penetrometer test (CPT) involves pushing a 1.41-inch diameter 55o to 60o cone (Figs. 1 thru 3) through the underlying ground at a rate of 1 to 2 cm/sec. CPT soundings can be very effective in site characterization, especially sites with discrete stratigraphic horizons or discontinuous lenses. Cone penetrometer testing, or CPT (ASTM D-3441, adopted in 1974) is a valuable method of assessing subsurface stratigraphy associated with soft materials, discontinuous lenses, organic materials (peat), potentially liquefiable materials (silt, sands and granule gravel) and landslides. Cone rigs can usually penetrate normally consolidated soils and colluvium, but have also been employed to characterize d weathered Quaternary and Tertiary-age strata. Cemented or unweathered horizons, such as sandstone, conglomerate or massive volcanic rock can impede advancement of the probe, but the author has always been able to advance CPT cones in materials of Tertiary-age sedimentary rocks. The cone is able to delineate even the smallest (0.64 mm/1/4-inch thick) low strength horizons, easily missed in conventional (small-diameter) sampling programs. Some examples of CPT electronic logs are attached, along with hand-drawn lithologic interpretations.
Most of the commercially-available CPT rigs operate electronic friction cone and piezocone penetrometers, whose testing procedures are outlined in ASTM D-5778, adopted in 1995. These devices produce a computerized log of tip and sleeve resistance, the ratio between the two, induced pore pressure just behind the cone tip, pore pressure ratio (change in pore pressure divided by measured pressure) and lithologic interpretation of each 2 cm interval are continuously logged and printed out.
The tip resistance is measured by load cells located just behind the tapered cone (Figure 4). The tip resistance is theoretically related to undrained shear strength of a saturated cohesive material, while the sleeve friction is theoretically related to the friction of the horizon being penetrated (Robinson and Campanella, 1986, Guidelines for Use and Interpretation of the Electric Cone Penetration Test, 3rd Ed.: Hogentogler & Co., Gaithersburg, MD, 196 p.). The tapered cone head forces failure of the soil about 15 inches ahead of the tip and the resistance is measured with an embedded load cell in tons/ft2 (tsf).
The local friction is measured by tension load cells embedded in the sleeve for a distance of 4 inches behind the tip (Figure 4). They measure the average skin friction as the probe is advanced through the soil. If cohesive soils are partially saturated, they may exert appreciable skin friction, negating the interpretive program.