Limerock Bearing Ratio Technician Training Course

Transcription

1 Limerock Bearing Ratio Technician Training Course Module 5: Soaking, Draining, Penetration LBR Technician Release 10, Module This section will cover the physical procedure of the LBR test. We will begin by discussing preparing the sample for testing, soaking the specimen, allowing for specimen drainage, and penetration of the specimen for bearing ratio determination. 5-1

2 Preparation for Soaking FM section 4: Specimen received following completion of FM 1 T 180. Specimen should be trimmed, mass obtained (if tare performed with spacer disk inserted), and ready for inversion. Tip: Recommended method to inverting the specimen: Remove locking ring (if applicable). Slide cylinder off baseplate ensuring spacer disk does not fall out. Place on edge of flat surface and place filter paper on surface of specimen. Clean off baseplate and place upside down on top of the specimen. Using both hands, one on top of the baseplate, one under the spacer disk, flip the mold. Replace locking ring, remove spacer disk, replace filter paper if necessary. LBR Technician Release 10, Module Once compaction per FM 1-T 180 is completed, and the sample is trimmed and the wet mass is obtained, the specimen is then handed over to the technician who will be performing the FM test (if different than the technician who compacted the material, in most cases it will be the same person assuming they have the CTQP Aggregate Base Testing Technician and LBR technician qualifications). - The technician should first look over the specimen to ensure there are no voids in the surface of the material or damage to the mold during compaction. Voids will warrant repair by the compaction technician and re-weighing of the wet mass (to account for added material). - LBR technician will invert the mold cylinder so to have access to the spacer disk. The inverting method above is recommended, but NOT require. It is considered the best practice method, but other methods of inverting are allowed as long as they do not cause damage to the specimen or a loss of material. - Once the specimen is inverted, the technician should inspect the surface of the material and the filter paper, replace if damaged, and take to the soaking tank. 5-2

3 FM section 5.1: Soaking Place swell plate on top of sample. Place specimen in soaking tank for 48 ± 4 hours. Water level shall be maintained within 0.25 inch (6.35 mm) of the top of the soil. Tank shall be appropriate size of amount of testing performed by lab. Overflow shall be used to prevent water level from getting too high. Water should be topped off each day to replace loss due to evaporation. LBR Technician Release 10, Module Immediately before placing the specimen in the soaking tank, the technician should place a swell plate on the sample. This should be done BEFORE the mold is placed in the tank because free-draining soils with a lot of pore spaces can quick become inundated with water once in the tank resulting in the surface of the soil becoming uncompacted if the swell plate is not in place. - The size of the soaking tank should be comparable with the amount of testing the lab performs. - An overflow should be used to keep the water level from going above the top of the soil (which can result in damage to the surface), and the water level should be topped off each day to replace any water lost due to evaporation. - Specimens should be allowed to soak to within 48 ± 4 hours, that is, between 44 and 52 hours. 5-3

4 Draining FM section 5.2: Remove mold from tank and place on flat surface that allow for free drainage from the bottom of the mold. Example: plate of LBR loading frame. Drain for 15 ± 2 minutes. Penetrate immediately after drainage. Tip: Prepare the specimen for penetration a few minutes before drainage time ends so penetration can begin immediately at completion of drainage. LBR Technician Release 10, Module Once soaking time is reached the specimen shall be removed and placed on a flat surface to allow drainage. This is the function of the holes in the baseplate. - The flat surface shall be one which allows free drainage of the mold (i.e. not a solid countertop surface). The platen on LBR test frames should have ridges and valley which are ideal for drainage. - Allow the material to drain (with swell plate in place) for 15 ± 2 minutes. - In order improve efficiency, and begin penetration at as soon as possible within the end of the allowable drainage time, the technician may set up the specimen in the load frame with a few minutes left to drain. Remove the swell plate, plate the surcharge weights, and get the piston in position for penetration. Apply the seating load (if necessary) immediately before penetrating. 5-4

5 Unsoaked LBR FM section 5.3: Soaking (and drainage) steps can be skipped if permitted by specification or as required by engineer. Proceed directly to penetration testing (section 6). LBR Technician Release 10, Module Unsoaked LBRs are uncommon but they are sometimes requested. In this scenario, the LBR technician will take the specimen immediate from inversion and removal of the spacer disk directly to penetration without soaking or draining of the specimen. - Unsoaked LBRs are permitted in certain FDOT specifications or as required by the engineer. 5-5

6 Surcharge Weights FM section 6.1: Apply surcharge weights to surface of soil: Base Materials: No surcharge required. Stabilized subgrade: 15 lbs. (6.8 kg) required. Embankment: 20 lbs. (9.1 kg) required. LBR Technician Release 10, Module The amount of surcharge weight depends on the usage of the material. - For Base Materials: no surface shall be applied. - For Subgrade Materials: 15 lbs. of surcharge is applied (3 5 lb. disks). - For Embankment Materials: 20 lbs. of surcharge is applied (4 5 lb. disks). 5-6

7 Using Loading Devices FM section 6.2 Manual Loading Devices Apply 10 lb (4.54 kg) seating load to specimen. Zero deflection and load gauges. Apply load to specimen at 0.05 ± inches (1.3 ±.12 mm) per minute. LBR Technician Release 10, Module For manual Loading devices, once the specimen is in place on the frame, a 10 lb. seating load should be applied to the specimen. - Once applied zero out the displacement and load gauges. - Rate of penetration is 0.05 ± inches per minute. Ensure a consistent rate of penetration throughout the whole test. Manual machines may require two technicians, one to load the specimen, the other to read and record the load and displacement values. 5-7

8 Using Loading Devices FM section 6.2 Automatic Loading Devices No seating load required. For strip char recorders: zero recording pen. Apply load to specimen at 0.05 ± inches (1.3 ±.12 mm) per minute. LBR Technician Release 10, Module Automatic loading devices generally automatically zero themselves once a set load is reached. For this reason a seating load is not required. Most machines these days are equipment with data acquisition units that record load and displacement data automatically and plot the graph. Some even monitor the data and stop the test when an LBR value can be determined, and will even provide that value at the end of the test. - As with a manual machine, if a chart recording device is being use the pen should be zeroed. - Load shall be applied at a consistent rate of 0.05 ± inches per minute through the entire test. 5-8

9 Recording Load Readings FM section 6.3: Record every inch up to inches. Record every inches up to inches. Record every inches up to inches. Test can be ended early if LBR value can obviously be obtained from data recorded. LBR Technician Release 10, Module Load and displacement should be recorded at a minimum the intervals required in FM section Automatic machines will usually record at a higher frequency obtaining a larger dataset. - The test should be run to a displacement of 0.5 inches, however, if the LBR penetration curve clearly shows an LBR value can be determined the test can be stopped early. 5-9

10 Recording Load Readings FM section 6.3: Convert Load to Unit Load by dividing by the area of piston. LBR Technician Release 10, Module To determine LBR values, the load, as measured by the load cell on the loading device, needs to be converted in to a Unit Load (mass per area). - The area the load is being applied to is the area of the head of the piston (3.0 in2). - Unit Load = the recorded load divided by the area of the head of the piston. - For a load of 12 lbs., what is the Unit Load? - 12 lbs / 3.0 in2 = 4 lbs/in2 - For a load of 21 lbs., what is the Unit Load? - 21 lbs / 3.0 in2 = 7 lbs/in2 - We can do this for the entire dataset getting unit loads for each displacement measurement. 5-10

11 Plotting Load Readings FM section 6.3: Plot unit load on Y axis Plot penetration on X axis Obtain one plot for each specimen penetrated to determine individual LBR values. LBR Technician Release 10, Module The next step is to plot the data to obtain our LBR penetration curve. - These plots will be used to find the Unit Load for each specimen penetrated and calculate individual LBR values. These individual LBR values for each specimen will be plotted and used to determine the sample s LBR value. - Plot the Unit Load on the Y-axis and the displacement on the X-axis. 5-11

12 Plotting Load Readings LBR Technician Release 10, Module Here is the data from the previous table plotted on an LBR penetration curve. - Notice the typical S shape of the curve. Most LBR curves will show this shape. - Sometimes, particularly if a seating load is applied, the plot may not have the bottom curve of the S and will start right with the highest sloped part of the curve. - Sometimes, particularly very strong materials, may not have the top curve of the S and will continue as a diagonal line all the way through 0.5 inches. - Determining the specimen s Unit Load and LBR values will be covered in the next section. 5-12

13 ANY QUESTIONS? LBR Technician Release 10, Module