AASHTO T 222-1981 Standard Method of Test for Nonrepetitive Static Plate Load Test of Soils and Flexible Pavement Components for Use in Evaluation and Design of Airport and Highway.pdf

1、Standard Method of Test for Nonrepetitive Static Plate Load Test of Soils and Flexible Pavement Components for Use in Evaluation and Design of Airport and Highway Pavements AASHTO Designation: T 222-81 (2012) American Association of State Highway and Transportation Officials 444 North Capitol Street

2、 N.W., Suite 249 Washington, D.C. 20001 TS-1b T 222-1 AASHTO Standard Method of Test for Nonrepetitive Static Plate Load Test of Soils and Flexible Pavement Components for Use in Evaluation and Design of Airport and Highway Pavements AASHTO Designation: T 222-81 (2012) 1. SCOPE 1.1. This method cove

3、rs the making of nonrepetitive static plate load test on subgrade soils and flexible pavement components, in either the compacted condition or the natural state, and is intended to provide data for use in the evaluation and design of rigid and flexible-type airport and highway pavements. 1.2. The va

4、lues stated in SI 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. residual deflectionthe difference between original and final elevations of a sur

5、face resulting from the application and removal of one or more loads to and from the surface. 2.1.3. rebound deflectionthe amount of vertical rebound of a surface that occurs when a load is removed from the surface. 3. APPARATUS 3.1. Field Test ApparatusThe required field test apparatus, part of whi

6、ch is shown in Figure 1, is as follows: 3.1.1. Loading DeviceA truck or trailer, or a combination of both, a tractor trailer, an anchored frame, or other structure loaded with sufficient mass to produce the desired reaction on the surface under test. The supporting points (wheels in the case of a tr

7、uck or trailer) shall be at least 2.4 m (8 ft) from the circumference of the largest diameter bearing plate being used. The dead load shall be at least 5675 kg (25,000 lb). 3.1.2. Hydraulic Jack AssemblyWith a spherical bearing attachment, capable of applying and releasing the load in increments. Th

8、e jack shall have sufficient capacity for applying the maximum load required and shall be equipped with an accurately calibrated gauge, or proving ring, that will indicate the magnitude of the applied load. 2015 by the American Association of State Highway and Transportation Officials.All rights res

9、erved. Duplication is a violation of applicable law.TS-1b T 222-2 AASHTO Figure 1Plate Bearing Test Equipment 3.1.3. Bearing PlateA set of circular steel bearing plates not less than 25.4 mm (1 in.) in thickness, machined so that they can be arranged in pyramid fashion to ensure rigidity, and have d

10、iameters ranging from 152 to 762 mm (6 to 30 in.). The diameters of adjacent plates in the pyramid arrangement shall not differ by more than 152 mm (6 in.) (Note 1). Aluminum alloy No. 24ST plates 38 mm (1.50 in.) thick may be used in lieu of steel plates. Note 1A minimum of four different plate siz

11、es 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 critical combination of conditions of wheel load and tire pressure. Fo

12、r 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. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved

13、. Duplication is a violation of applicable law.TS-1b T 222-3 AASHTO 3.1.4. Dial GaugesThree or more, graduated in units of 0.02 mm (0.001 in.) and capable of recording an accumulated deflection of at least 25.4 mm (1 in.), or other equivalent deflection measuring devices. 3.1.5. Deflection BeamUpon

14、which the dial gauges shall be mounted. The beam shall be a 63.5-mm (2.50-in.) standard black pipe or a 76-by-76-by-6-mm (3-by-3-by-0.25-in.) steel angle, or equivalent. It shall rest on supports located at least 1.2 m (4 ft) from the circumference of the bearing plate or nearest wheel or supporting

15、 leg. The entire deflection measuring system shall be adequately shaded from direct rays of the sun and protected from inclement weather such as rain, etc. 3.1.6. Miscellaneous ToolsIncluding a spirit level, for preparation of the surface to be tested and for operation of the equipment. 3.1.7. Conso

16、lidometer ApparatusNecessary equipment for cutting an undisturbed specimen of the soil into a consolidometer test ring. Scales, oven, and miscellaneous tools are required for determining the moisture content. 4. PROCEDURE 4.1. Where unconfined load tests are to be made, strip an area of the soil to

17、be tested to the proposed elevation of the subgrade surface. The stripped area should be at least twice the diameter of the plates to eliminate surcharge or confining effects. If the subgrade is to be composed of fill material, construct a test embankment at least 762 mm (30 in.) in height using the

18、 proposed fill material compacted to the moisture content and density that will be required during construction. Clear the area to be tested of any loose materials and make it level. Extreme care should be taken not to disturb the soil in the test area, especially in granular material. For confined

19、tests, the diameter of the excavated circular area shall be just sufficient to accommodate the selected bearing plate. Carefully center a bearing plate of the selected diameter under the jack assembly. Set the remaining plates of smaller diameter concentric with, and on top of, the bearing plates. S

20、et the bearing plate level in a thin bed of a mixture of sand and plaster of paris, of 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 subgrade during the load test, cover the exposed subgrade to a dist

21、ance of 2.0 m (6 ft) from the circumference of the bearing plate with a tarpaulin or waterproof paper. 4.2. Seat the 762-mm (30-in.) diameter bearing plate on the Ottawa sand or plaster of paris. Turning or working the plate back and forth will help to provide uniform seating of the plate. Center th

22、e 610-mm (24-in.) and 457-mm (18-in.) diameter plates on the 762-mm (30-in.) diameter plate, and center the hydraulic jack on the 457-mm (18-in.) diameter plate. If cribbing is needed, crib between the top plate and the jack. If a steel proving ring is being used to measure load, it should be placed

23、 on top of the jack and the ball joint used between the proving ring and the load reaction device. For safety reasons, shims should not be used between the ball joint and the reaction device. The load reaction device must be long enough so that its supports will be at least 2.4 m (8 ft) from the bea

24、ring plate. A steel beam between two loaded trucks provides a good load reaction device. Three dial gauges shall be used to measure deformation of the soil under load. Place these gauges so that the dial stems rest on the bottom 762-mm (30-in.) diameter plate not more than 6 mm (0.25 in.) from the o

25、uter edge, spaced 120 degrees apart. Fasten the gauges to a frame whose supports are at least 1.22 m (4 ft) from the edge of the 762-mm (30-in.) diameter plate. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicabl

26、e law.TS-1b T 222-4 AASHTO 4.3. Use one of the following initial procedures: 4.3.1. Seating Procedure No. 1Seat the loading system and bearing plate by applying a load of 321 kg (707 lb), 6.9 kPa (1 psi) when the design thickness of the pavement will be less than 380 mm (15 in.) or a load of 642 kg

27、(1414 lb), 13.8 kPa (2 psi) when the design thickness of the pavement is 380 mm (15 in.) or more. Allow the seating load to remain in place until practically complete deformation has taken place. Then take a reading on all three dial gauges, which will be used as the “zero” reading. The seating load

28、 is also considered to be the “zero” load. Cyclic loading under the seating load may be used to assure good seating of the apparatus and bearing plate. 4.3.2. Seating Procedure No. 2After the equipment has been properly arranged, with all of the dead load (jacks, plates, etc.) acting, seat the beari

29、ng plate and assembly by the quick application and release of a load sufficient to produce a deflection of not less than 0.25 mm (0.01 in.) or more than 0.50 mm (0.02 in.) as indicated by the dials. When the dial needles come to rest following release of this load, reseat the plate by applying one h

30、alf of the recorded load producing the 0.25- to 0.50-mm (0.01- to 0.02-in.) deflection. When the dial needles have then again come to rest, set each dial accurately at its zero mark. 4.4. Without releasing the seating load, Load Application Procedure No. 1 or 2 shall then be followed. 4.4.1. Load Ap

31、plication Procedure No. 1Apply loads at a moderately rapid rate in uniform increments. The magnitude of each load increment shall be small enough to permit the recording of a sufficient number of load-deflection points to produce an accurate load-deflection curve (not less than six). After each incr

32、ement of load has been applied, allow its action to continue until a rate of deflection of not more than 0.02 mm/min (0.001 in./min) has been maintained for 3 consecutive min. Record load and deflection readings for each load increment. Continue this procedure until the selected total deflection has

33、 been obtained, or until the load capacity of the apparatus has been reached, whichever occurs first. At this point, maintain the load until an increased deflection of not more than 0.02 mm/min (0.001 in./min) for 3 consecutive min occurs. Record the total deflection, after which release the load to

34、 that at which the dial gauges were set at zero, and maintain the zero-setting load until the rate of recovery does not exceed 0.02 mm (0.001 in.) for 3 consecutive min. Record the deflection at the zero-setting load. Each individual set of readings shall be averaged, and this value is recorded as t

35、he average settlement reading. 4.4.2. Apply two load increments of 1605 kg (3535 lb), 34.5 kPa (5 psi) each with load increment being held until deformation averages less than 0.02 mm/min. (0.001 in./min) for 10 consecutive min. Read all three dial gauges at the end of each load increment. Following

36、 the completion of the 3210-kg (7070-lb), 69.0-kPa (10-psi) load increment, determine the average deflection by averaging the total movement between the “zero” and 69.0-kPa (10-psi) increment for each dial. 4.5. Compute a value of ku(uncorrected modulus of soil reaction) using the following formula:

37、 69 0 kPa (10 psi)average deflection =.uk (1) If the value of kuis less than 54.3 kPa/mm (200 psi/in.), the test is considered complete and the load may be released. Should the value of kube 54.3 kPa/mm (200 psi/in.) or greater, apply load increments of 1605 kg (3535 lb) 34.5 kPa (5 psi) until a tot

38、al load of 9630 kg (21,210 lb) 207 kPa (30 psi) is reached, allowing each load increment to remain until the deformation averages less than 0.02 mm/min (0.001 in./min) for 10 consecutive min. Read all three dial gauges at the completion of each load increment. 4.6. Obtain an undisturbed sample of th

39、e foundation material for laboratory testing to determine the saturation correction to apply to the field test value. The undisturbed sample must be large enough to obtain two consolidometer specimens side by side (i.e., at the same elevation). Take the sample 2015 by the American Association of Sta

40、te Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 222-5 AASHTO in a container suitable for sealing to preserve the moisture content until the laboratory correction tests can be performed. When the plate-bearing test is performed directl

41、y on cohesive subgrade material, obtain the undisturbed specimen from the foundation at the same elevation at which the test is performed, but alongside rather than under the plates. When the test is performed on a granular base course material that is underlaid by a cohesive material, and when the

42、base course is less than 1.9 m (75 in.) in thickness, take the undisturbed sample from the cohesive material at the bottom of the base course. 4.7. From a thermometer suspended near the bearing plate, read and record the air temperature at 30-min intervals. 5. RECORD THE TESTS 5.1. In addition to th

43、e continuous listing of all load, deflection, and temperature data, as prescribed in Section 3, a record shall also be made of all associated conditions 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 pers

44、onnel; 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. Any unusual observations made during the test. 6. CALCULATIONS AND PLOTTING OF LOAD DEFLECTION RELATIONSHIPS 6.1. When the kuvalue, as computed in Secti

45、on 4.5, is less than 54.3 kPa/mm (200 psi/in.), load-deformation curves need not be prepared. However, when the kuvalue is 54.3 kPa/mm (200 psi/in.) or greater, it is necessary to plot the load-deformation curve and correct the curve for such things as poor seating of the plates, nonlinear load-defo

46、rmation relations, or shear failure; the unit load (kPa lb/in.2) on the plate is plotted versus the average deflection for each load increment. The average deflection is the average of the three dial readings between the “zero” and the end of each load increment. When averaging the three dial gauge

47、readings, the data should be carefully examined to ensure that a reasonable average is being computed. If the load-deformation relation does not plot a straight line passing through the origin, the curve is corrected, as shown in Figure 2. Generally, the load-deformation curve will approximate a str

48、aight line between the unit loads of 69.0 and 207 kPa (10 and 30 psi). The correction consists of drawing a straight line, parallel to the straight-line portion of the plotted curve, through the origin. When correcting the load-deformation curve, good engineering judgment will be required. If the cu

49、rve is nonlinear through its length, the straight-line correction will be based on the average slope of the curve through at least three points in the region of the curve having the least curvature. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1b T 222-6 AASHTO 6.2. An uncorrected modulus of soil reaction kuis computed from the field test data using the formula: ( )69.0 kPa 10 psiaverage deflection =uk (2) When a load-deformation curve is unnecessary, as o