1、Standard Method of Test for Repetitive Static Plate Load Tests of Soils and Flexible Pavement Components for Use in Evaluation and Design of Airport and Highway Pavements AASHTO Designation: T 221-90 (2012)1ASTM Designation: D1195/D1195M-09 American Association of State Highway and Transportation Of
2、ficials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1b T 221-1 AASHTO Standard Method of Test for Repetitive Static Plate Load Tests of Soils and Flexible Pavement Components for Use in Evaluation and Design of Airport and Highway Pavements AASHTO Designation: T 221-90 (2012)1
3、ASTM Designation: D1195/D1195M-09 1. SCOPE 1.1. This test method covers a procedure for making repetitive static plate load tests on subgrade soils and compacted pavement components, in either the compacted condition or the natural state, and is to provide data for use in the evaluation and design o
4、f rigid and flexible-type airport and highway pavements. 1.2. The values stated in inch-pound units are to be regarded as the standard. 2. TERMINOLOGY 2.1. Definitions: 2.1.1. deflectionthe amount of downward vertical movement of a surface due to the application of a load to the surface. 2.1.2. rebo
5、und deflectionthe amount of vertical rebound of a surface that occurs when a load is removed from the surface. 2.1.3. residual deflectionthe difference between original and final elevations of a surface resulting from the application and removal of one or more loads to and from the surface. 3. APPAR
6、ATUS 3.1. Loading DeviceA truck or trailer or a combination of both a tractor-trailer, an anchored frame, or other structure loaded with sufficient weight to produce the desired reaction on the surface under test. The supporting points (wheels in the case of a truck or trailer) shall be at least 8 f
7、t (2.44 m) from the circumference of the largest diameter bearing plate being used. 3.2. Hydraulic Jack Assemblywith a spherical bearing attachment, capable of applying and releasing the load in increments. The jack shall have sufficient capacity for applying the maximum load required, and shall be
8、equipped with an accurately calibrated gauge that will indicate the magnitude of the applied load. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 221-2 AASHTO 3.3. Bearing PlatesA set of circula
9、r steel bearing plates not less than 1 in. (25.4 mm) in thickness, machined so that they can be arranged in pyramid fashion to ensure rigidity, and having diameters ranging from 6 to 30 in. (152 to 762 mm). The diameters of adjacent plates in the pyramid arrangement shall not differ by more than 6 i
10、n. (152 mm) (Note 1). Note 1A minimum of four different plate sizes is recommended for pavement design or evaluation purposes. For evaluation purposes alone, a single plate may be used, provided that its area is equal to the tire-contact area corresponding to what may be considered as the most criti
11、cal combination of conditions of wheel load and tire pressure. For the purpose of providing data indicative of bearing index (for example, the determination of relative subgrade support throughout a period of a year), a single plate of any selected size may be used. 3.4. Dial Gaugestwo or more, grad
12、uated in units of 0.001 in. (0.02 mm) and capable of recording a maximum deflection of 1 in. (25 mm) or other equivalent deflection-measuring devices. 3.5. Beam for Mounting Dial GaugesA beam upon which the dial gauges shall be mounted. The beam shall be a 21/2-in. (63.5-mm) standard black pipe or a
13、 3-by-3-by-1/4-in. (76-by-76-by-6-mm) steel angle, or equivalent. It shall be at least 18 ft (5.5 m) long and shall rest on supports located at least 8 ft (2.44 m) from the circumference of the bearing plate or nearest wheel or supporting leg. The entire deflection measuring system shall be adequate
14、ly shaded from direct rays of the sun. 3.6. Miscellaneous Toolsincluding a spirit level, for preparation of the surface to be tested and for operation of the equipment. 4. PROCEDURE 4.1. Carefully center a bearing plate, of the selected diameter, under the jack assembly. Set the remaining plates of
15、small diameter concentric with, and on top of, the bearing plate. Set the bearing plate level in a thin bed of a mixture of sand and plaster of paris, or plaster of paris alone, or of fine sand, using the least quantity of materials required for uniform bearing. To prevent loss of moisture from the
16、subgrade during the load test, cover the exposed subgrade to a distance of 6 ft (1.83 m) from the circumference of the bearing plate with a tarpaulin or waterproof paper. 4.2. Where unconfined load tests are to be made at a depth below the surface, remove the surrounding material to provide a cleara
17、nce equal to 11/2-plate diameters from the edge of the bearing plate. For confined tests, the diameter of the excavated circular area shall be just sufficient to accommodate the selected bearing plate. 4.3. Use a sufficient number of dial gauges, so located and fixed in position as to indicate the a
18、verage vertical movement of the bearing plate. When using two dial gauges, they shall be set near each extremity of a diameter of the bearing plate, 1 in. (25.4 mm) from the circumference. When three gauges are employed, they shall be set at an angle of 120 degrees from each other, and equidistant f
19、rom the circumference of the bearing plate. Each individual set of readings shall be averaged, and this value is recorded as the average settlement reading. 4.4. After the equipment has been properly arranged, and with all of the dead load (jack, plates, etc.) acting, seat the bearing plate and asse
20、mbly by the quick application and release of a load sufficient to produce a deflection of not less than 0.01 in. (0.25 mm) nor more than 0.02 in. (0.51 mm), as indicated by the dial gauges. When the dial needles come to rest following the release of this load, reseat the plate by applying one half o
21、f the recorded load producing the 0.01- to 0.02-in. (0.25- to 0.51-mm) deflection. When the dial needles have again come to rest, set each dial accurately at its zero mark. Note 2The use of additional dial gauges, placed on the surface of the material being tested at one-half, one, one-and-one-half,
22、 etc. bearing plate diameters from the edge of the bearing plate, is optional. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 221-3 AASHTO 4.5. Apply a load giving a deflection of about 0.04 in.
23、 (1.02 mm), start a stopwatch, and maintain the same load constantly until the rate of deflection is 0.001 in. (0.03 mm) per minute or less for 3 successive min. Then completely release the load, and observe the rebound until the rate of recovery is 0.001 in. (0.03 mm) per min or less, for 3 success
24、ive min. Apply and release the same load in this manner six times. Record the reading of the dial gauges resting on the bearing plate at the end of each minute; record the readings of the dial gauges set beyond the perimeter of the bearing plate just before the application, and just before the relea
25、se of load, for each repetition. To ensure good contact between the gauges and the bearing plate or other surface on which they are resting, briefly buzz an electric bell attached to the deflection beam 10 s before the dial gauges are to be read. 4.6. Increase the load to give a deflection of about
26、0.2 in. (5.08 mm) and proceed as directed in Section 4.5. 4.7. Increase the load to give a deflection of about 0.4 in. (10.2 mm) and proceed as directed in Section 4.5. 4.8. In all cases, the standard end point shall be a rate of 0.001 in. (0.03 mm) per minute or less for 3 successive min. 4.9. From
27、 a thermometer suspended near the bearing plate, read and record the air temperature at half-hour intervals. 5. RECORD OF TESTS 5.1. In addition to the continuous listing of all load, deflection, and temperature data, as prescribed in Section 3, a record shall also be made of all associated conditio
28、ns and observations pertaining to the test, including the following: 5.1.1. Date; 5.1.2. Time of beginning and completion of test; 5.1.3. List of personnel; 5.1.4. Weather conditions; 5.1.5. Any irregularity in routine procedure; 5.1.6. Any unusual conditions observed at the test site; and 5.1.7. An
29、y unusual observations made during the test. 6. CALCULATION AND PLOTTING OF LOAD-DEFLECTION RELATIONSHIPS 6.1. For each repetition of each load, determine the deflection at which the rate of deflection is exactly 0.001 in. (0.03 mm) per minute. This is termed end-point deflection and can be determin
30、ed with sufficient accuracy from visual inspection of the deflection data for each repetition of load recorded. 6.2. Correct the recorded loads, as read from the pressure gauge of each hydraulic jack employed, by means of the calibration curve for each jack and pressure gauge used. 2015 by the Ameri
31、can Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 221-4 AASHTO 6.3. Determine graphically the zero point corrections for both applied load and deflection. This requires taking into account the weight of the hydraul
32、ic jack, that of the pyramid of bearing plates, etc., and that of the corrected jack loads at which the dial gauges were set to zero at the beginning of the test. 6.4. Plot the corrected deflection at which the rate of deflection is exactly 0.001 in. (0.03 mm) per minute versus the number of repetit
33、ions of each corrected load. Similar graphs may be prepared in which corrected residual deflection and rebound deflection are plotted versus the number of repetitions of each corrected load. 7. PRECISION AND BIAS 7.1. The precision and bias of this test method for making repetitive static plate load
34、 tests on subgrade soils and flexible pavement components has not been determined. Soils and flexible pavement components at the same location may exhibit significantly different load-deflection relationships. No method presently exists to evaluate the precision of a group of repetitive plate load t
35、ests on soils and flexible pavement components due to the variability of these materials. The subcommittee is seeking pertinent data from users of this method that may be used to develop meaningful statements of precision and bias. 1This method is technically equivalent to ASTM D1195/D1195M-09. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.
