Limerock Bearing Ratio Technician Training Course

Transcription

1 Limerock Bearing Ratio Technician Training Course Module 6: Calculating and Reporting LBR Technician Release 10, Module This section will cover the how to use LBR penetration data to determine individual LBR values for each specimen. This section will also cover developing an LBR curve, determining the LBR value for the whole sample and reporting of LBR test data. This section completes the actual training for LBR testing. 6-1

2 Determining Individual LBR Values Find point of greatest slope on the line and draw a tangent line to the X axis. Shift over 0.1 inches penetration from X axis point of tangent line. Go up to the original plotted curve to determine corrected unit load. Unit Load (psi) Corrected Unit Load 360 psi Displacement (inches) LBR Technician Release 10, Module Penetration of the piston is measured and labeled as Displacement. The penetration/unit load curve is used to determine individual LBR values for each specimen compacted for the LBR sample. In most cases the penetration curve will need to be corrected. This correction shift the origin of the curve to the point where the tangent of the steepest slope of the curve crosses the X-axis. - Begin by identifying the steepest slope on the penetration curve and draw a line tangent to that slope crossing the X-axis. - This point is considered your new origin. - The LBR is calculated from the Unit Load at a penetration depth of 0.1 inches. From this new origin point move over 0.1 inches to the right, and go up vertically to the point on the penetration curve at that displacement. - The Unit Load at this penetration depth (displacement) is the value needed to calculate LBR. - For this specific plot, the tangent line shift the origin over to about 0.08 inches. If you more over 0.1 inches you end at 0.18 inches. Going up to the curve (the blue dotted curve, NOT the black tangent line), you read a Unit Load of 360 psi. - In some cases, especially if you start with a seating load, the points recorded may not show a ramping up phase on the curve. If the tangent line to this type of graph goes through the existing origin, then no correction is necessary and the unit load needed is at 0.1 inches. See Appendices I-K of FM for examples. 6-2

3 Determining Individual LBR Values Corrected Unit Load 360 psi 400 Unit Load (psi) Displacement (inches) LBR Technician Release 10, Module The Unit Load is NOT the LBR value. This value needs to be recorded. - To calculate the LBR, the corrected Unit Load must be divided by the reference Unit Load for limerock (800 psi, or MPa), then multiplied by The LBR value is a ratio of the unit load of the sample to the unit load of the reference material (limerock). - The result is unitless, but it can be considered a percentage (the unit load is X percent of the standard). For example, if the unit load of the material is 400 psi, 400 psi / 800 psi X100 = 50. The material with a unit load of 400 has 50% the strength of the reference limerock material. For this example, our corrected unit load is / 800 X 100 = So this material has 45% the strength of the reference standard limerock. However, LBR is never reported as a percentage. 6-3

4 Determining Sample LBR Value Determine LBR values for each specimen compacted for a sample. Plot LBR values on a semi log plot: Moisture Content on X axis LBR Values on Y Axis Draw a smooth curve through the points. Determine maximum LBR value on the curve. LBR Technician Release 10, Module Individual LBR values are calculated from the corrected unit load for each specimen compacted. - As shown in this table, the LBR values are recorded with the compaction data as well as a Record Number which related to the file or location of the raw LBR penetration data (it is important to be able to access this data in the event of machine malfunction and manual LBR determination is necessary). - The individual specimen LBR values shall be plotted on a semi-log plot against the moisture content. Typically, if hand drawn, you will see the LBR curve plotted on a separate plot just above the compaction curve. This is good for reference since the Moisture Content on the X-axis is the same for both sets of data (Compaction and LBR). Also so the technician can quickly see the link between compaction data and LBR data. 6-4

5 Determining Sample LBR Value Determine LBR values for each specimen compacted for a sample. Plot LBR values on a semi log plot: Moisture Content on X axis LBR Values on Y Axis Draw a smooth curve through the points. Determine maximum LBR value on the curve. LBR Technician Release 10, Module Individual LBR values are calculated from the corrected unit load for each specimen compacted. - As shown in this table, the LBR values are recorded with the compaction data as well as a record number which related to the file or location of the raw LBR penetration data (it is important to be able to access this data in the event of machine malfunction and manual LBR determination is necessary). - The individual specimen LBR values shall be plotted on a semi-log plot against the Moisture Content. Typically, if hand drawn, you will see the LBR curve plotted on a separate plot just above the compaction curve. This is good for reference since the X-axis is the same for both sets of data (Compaction and LBR), and also so the technician can quickly see the link between compaction data and LBR data. 6-5

6 Considerations When drawing the LBR curve by hand, be careful not to over extrapolate the curve. If the two highest LBR points are not above 90% of the minimum LBR needed per FDOT specification you cannot extrapolate a curve the results in a passing value. Compact and penetrate additional specimen as needed. LBR Value Maximum LBR Value Moisture Content (%) LBR Technician Release 10, Module If we assume 100 to be the minimum passing value, we can see that only 96 is over 90% of is close, but not over 90%. Therefore the curve shown is NOT a valid curve. And no maximum LBR value can be reported as a final result. - In this example, the technician should compact and penetrate an additional point at exactly 12.5% moisture content to determine if the point will fall on the curve that is show and a passing value can be reported. 6-6

7 FM section 8: Report Moisture Density Plot. Report LBR Plot. Report maximum Density to nearest 0.1 lb/ft3 (kg/m3). Report Optimum Moisture to nearest 0.1%. Report maximum LBR to nearest whole number. FM 1 T 180 Results: % FM Results: LBR: 89 Reporting LBR Technician Release 10, Module When reporting LBR data, both the FM 1-T 180 data and well as the LBR data needs to be reported. - Report the Moisture-Density plot from the FM 1-T 180 test, as well as the LBR plot from the FM test. The can be reported as shown or side-by-side with independent X-axes. Ensure LBR is a semi-log plot. - Report the maximum dry density (to the nearest 0.1 lb/ft 3 (kg/m 3 ) and optimum moisture content from FM 1-T Report the maximum LBR value from the curve to a whole number. - Note: Maximum LBR does not always coincide with the optimum moisture content and maximum density. The maximum LBR can be shifted to either side based on the type of material tested. 6-7

8 ANY QUESTIONS? LBR Technician Release 10, Module