1、Standard Method of Test for Unconfined Compressive Strength of Cohesive Soil AASHTO Designation: T 208-15 ASTM Designation: D2166-00 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-1a T 208-1 AASHTO Standard Method
2、 of Test for Unconfined Compressive Strength of Cohesive Soil AASHTO Designation: T 208-15 ASTM Designation: D2166-00 1. SCOPE 1.1. This test method covers the determination of the unconfined compressive strength of cohesive soil in the undisturbed, remolded, or compacted condition, using strain-con
3、trolled application of the axial load. 1.2. This test method provides an approximate value of the strength of cohesive soils in terms of total stresses. 1.3. This test method is applicable only to cohesive materials that will not expel bleed water (water expelled from the soil due to deformation or
4、compaction) during the loading portion of the test and that will retain intrinsic strength after removal of confining pressures, such as clays or cemented soils. Dry and crumbly soils, fissured or varved materials, silts, peats, and sands cannot be tested with this method to obtain valid unconfined
5、compressive strength values. Note 1The determination of the unconsolidated, undrained strength of cohesive soils with lateral confinement is covered by T 296. 1.4. This test method is not a substitute for T 296. 1.5. The values stated in SI units are to be regarded as the standard. 1.6. This standar
6、d may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of whoever uses this standard to consult and establish appropriate safety and health practices and determine the applic
7、ability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 145, Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes M 231, Weighing Devices Used in the Testing of Materials T 88, Particle Size Analysis of Soils T 89, Determining
8、 the Liquid Limit of Soils T 90, Determining the Plastic Limit and Plasticity Index of Soils T 100, Specific Gravity of Soils T 207, Thin-Walled Tube Sampling of Soils T 223, Field Vane Shear Test in Cohesive Soil 2015 by the American Association of State Highway and Transportation Officials.All rig
9、hts reserved. Duplication is a violation of applicable law.TS-1a T 208-2 AASHTO T 265, Laboratory Determination of Moisture Content of Soils T 296, Unconsolidated, Undrained Compressive Strength of Cohesive Soils in Triaxial Compression 2.2. ASTM Standards: D653, Standard Terminology Relating to Soi
10、l, Rock, and Contained Fluids D4220/D4220M, Standard Practices for Preserving and Transporting Soil Samples 3. TERMINOLOGY 3.1. Refer to ASTM D653 for standard definitions of terms. 3.2. Description of Terms Specific to This Standard: 3.2.1. Unconfined Compressive Strength (qu)The compressive stress
11、 at which an unconfined cylindrical specimen of soil will fail in a simple compression test. In this test method, unconfined compressive strength is taken as the maximum load attained per unit area or the load per unit area at 15 percent axial strain, whichever is secured first during the performanc
12、e of a test. 3.2.2. Shear Strength (su)For unconfined compressive strength test specimens, the shear strength is calculated to be one half of the compressive stress at failure, as defined in Section 3.2.1. 4. SIGNIFICANCE AND USE 4.1. The primary purpose of the unconfined compression test is to quic
13、kly obtain the approximate compressive strength of soils that possess sufficient cohesion to permit testing in the unconfined state. 4.2. Samples of soils having slickensided or fissured structure, samples of some type of loess, very soft clays, dry and crumbly soils and varved materials, or samples
14、 containing significant portions of silt or sand, or both (all of which usually exhibit cohesive properties), frequently display higher shear strengths when tested in accordance with T 296. Also, unsaturated soils will usually exhibit different shear strengths when tested in accordance with T 296. 4
15、.3. If both an undisturbed and a remolded test are performed on the same sample, the sensitivity of the material can be determined. This method of determining sensitivity is suitable only for soils that can retain a stable specimen shape in the remolded state. Note 2For soils that will not retain a
16、stable shape, a vane shear test or T 223 can be used to determine sensitivity. 5. APPARATUS 5.1. Compression DeviceThe compression device may be a platform weighing scale equipped with a screw-jack-activated load yoke, a hydraulic loading device, or any other compression device with sufficient capac
17、ity and control to provide the rate of loading prescribed in Section 7.1. For soil with an unconfined compressive strength of less than 100 kPa (1.0 ton/ft2), the compression device shall be capable of measuring the compressive stress to within 1 kPa (0.01 ton/ft2). For soil with an unconfined compr
18、essive strength of 100 kPa (1.0 ton/ft2) or greater, the compression device shall be capable of measuring the compressive stress to the nearest 5 kPa (0.05 ton/ft2). 5.2. Sample ExtruderHand-operated, mechanical, and hydraulic extruders are acceptable provided the device (1) is capable of extruding
19、the soil core from the sampling tube in the same direction of 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 208-3 AASHTO travel in which the sample entered the tube, (2) has a length of travel
20、at least equal to the required untrimmed test length of the sample and permits the extrusion to occur in one operation without resetting the piston or extrusion mechanism, (3) can be operated at a relatively uniform rate, and (4) causes negligible disturbance of the sample. 5.3. Deformation Indicato
21、rThe deformation indicator shall be a dial indicator graduated to 0.02 mm (0.001 in.) or better and having a travel range of at least 20 percent of the length of the test specimen, or some other measuring device, such as an electronic deformation measuring device, meeting these requirements. 5.4. Di
22、al Comparator, or other suitable device, for measuring the physical dimensions of the specimen to within 0.1 percent of the measured dimension. Note 3Vernier calipers are not recommended for soft specimens, which will deform as the calipers are set on the specimen. 5.5. TimerA timing device indicati
23、ng the elapsed testing time to the nearest second shall be used for establishing the rate of strain application prescribed in Section 7.1. 5.6. BalanceThe balance shall have sufficient capacity, be readable to 0.1 percent of the sample mass, or better, and conform to the requirements of M 231. 5.7.
24、Equipment, as specified in T 265, for drying moisture content samples. 5.8. Miscellaneous Apparatus, including specimen trimming and carving tools, remolding apparatus, data sheets, and water content cans, as required. 6. PREPARATION OF TEST SPECIMENS 6.1. Specimen SizeSpecimens shall have a minimum
25、 diameter of 30 mm (1.3 in.) and the largest particle contained within the test specimen shall be smaller than one-tenth of the specimen diameter. For specimens having a diameter of 72 mm (2.8 in.) or larger, the largest particle size shall be smaller than one-sixth of the specimen diameter. If, aft
26、er completion of a test on an undisturbed specimen, it is found, based on visual observation, that larger particles than permitted are present, indicate this information in the remarks section of the report of test data (Note 4). The height-to-diameter ratio shall be between 2 and 2.5. Determine the
27、 average height and diameter of the test specimen using the apparatus specified in Section 5.4. A minimum of three height measurements (120 degrees apart) and at least three diameter measurements at the quarter points of the height shall be made to determine the average height and diameter of the sp
28、ecimen. Note 4If large soil particles are found in the sample after testing, a particle-sized analysis performed in accordance with T 88 may be performed to confirm the visual observation and the results provided with the test report. 6.2. Undisturbed SpecimensPrepare undisturbed specimens from larg
29、e undisturbed samples or from samples secured in accordance with T 207 and preserved and transported in accordance with the practices for Group C samples in ASTM D4220/D4220M. Tube specimens may be tested without trimming except for the squaring of ends, if conditions of the sample justify this proc
30、edure. Handle specimens carefully to prevent disturbance, changes in cross section, or loss of water content. If compression or any type of noticeable disturbance would be caused by the extrusion device, split the sample tube lengthwise or cut it off in small sections to facilitate removal of the sp
31、ecimen without disturbance. Prepare carved specimens without disturbance, and whenever possible, in a humidity-controlled room. Make every effort to prevent any change in water content of the soil. Specimens shall be of uniform circular cross section with ends perpendicular to the longitudinal axis
32、of the specimen. When carving or trimming, remove any small pebbles or shells encountered. Carefully fill voids on the surface of the specimen with remolded soil obtained from 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violati
33、on of applicable law.TS-1a T 208-4 AASHTO the trimmings. When pebbles or crumbling result in excessive irregularity at the ends, cap the specimen with a minimum thickness of plaster of paris, hydrostone, or similar material. When sample condition permits, a vertical lathe that will accommodate the t
34、otal sample may be used as an aid in carving the specimen to the required diameter. Where prevention of the development of appreciable capillary forces is deemed important, seal the specimen with a rubber membrane, thin plastic coatings, or with a coating of grease or sprayed plastic immediately aft
35、er preparation and during the entire testing cycle. Determine the mass and dimensions of the test specimen. If the specimen is to be capped, its mass and dimensions should be determined before capping. If the entire test specimen is not to be used for determination of water content, secure a represe
36、ntative sample of cuttings for this purpose, placing them immediately in a covered container. The water content determination shall be performed in accordance with T 265. 6.3. Remolded SpecimensSpecimens may be prepared either from a failed undisturbed specimen or from a disturbed sample, providing
37、it is representative of the failed undisturbed specimen. In the case of failed undisturbed specimens, wrap the material in a thin rubber membrane and work the material thoroughly with the fingers to assure complete remolding. Avoid entrapping air in the specimen. Exercise care to obtain a uniform de
38、nsity, to remold to the same void ratio as the undisturbed specimen, and to preserve the natural water content of the soil. Form the disturbed material into a mold of circular cross section having dimensions meeting the requirements of Section 6.1. After removal from the mold, determine the mass and
39、 dimensions of the test specimens. 6.4. Compacted SpecimensSpecimens shall be prepared to the predetermined water content and density prescribed by the individual assigning the test (Note 5). After a specimen is formed, trim the ends perpendicular to the longitudinal axis, remove from the mold, and
40、determine the mass and dimensions of the test specimen. Note 5Experience indicates that it is difficult to compact, handle, and obtain valid results with specimens that have a degree of saturation that is greater than 90 percent. 7. PROCEDURE 7.1. Place the specimen in the loading device so it is ce
41、ntered on the bottom platen. Adjust the loading device carefully so the upper platen just makes contact with the specimen. Zero the deformation indicator. Apply the load so as to produce an axial strain at a rate of 0.5 to 2 percent per minute. Record load, deformation, and time values at sufficient
42、 intervals to define the shape of the stressstrain curve (usually 10 to 15 points are sufficient). The rate of strain should be chosen so the time to failure does not exceed about 15 min (Note 6). Continue loading until the load values decrease with increasing strain, or until 15 percent strain is r
43、eached. The rate of strain used for testing sealed specimens may be decreased if deemed desirable for better test results. Indicate the rate of strain in the report of the test data, as required in Section 9.1.7. Determine the moisture content of the test specimen in accordance with T 265, Laborator
44、y Determination of Moisture Content of Soils, using the entire specimen unless representative cuttings are obtained for this purpose as in the case of undisturbed specimens. Indicate on the test report whether the water content sample was obtained before or after the shear test, as required in Secti
45、on 9.1.2. Note 6Softer materials that will exhibit larger deformation at failure should be tested at a higher rate of strain. Conversely, stiff or brittle materials that will exhibit small deformations at failure should be tested at a lower rate of strain. 7.2. Make a sketch, or take a photo, of the
46、 test specimen at failure showing the slope angle of the failure surface if the angle is measurable. 7.3. A copy of a sample data sheet is included in the Appendix. Any data sheet can be used, provided the form contains all the required data. 2015 by the American Association of State Highway and Tra
47、nsportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-1a T 208-5 AASHTO 8. CALCULATIONS 8.1. Calculate the axial strain,1, to the nearest 0.1 percent, for a given applied load, as follows: 1 = L/Lo(1) where: L = length change of specimen as read from deformation
48、indicator, mm (in.); and Lo= initial length of test specimen, mm (in.). 8.2. Calculate the average cross-sectional area, A, for a given applied load, as follows: A = Ao /(1 1) (2) where: Ao= initial average cross-sectional area of the specimen, mm2(in.2); and 1= axial strain for the given load, perc
49、ent. 8.3. Calculate the compressive stress, c, to three significant figures, or nearest 1 kPa (0.01 ton/ft2), for a given applied load, as follows: 1000cPA= (3) where: P = given applied load, N; and A = corresponding average cross-sectional area m2(ft2). 8.4. GraphIf desired, a graph showing the relationship between compressive stress (ordinate) and axial strain (abscissa) may be plotted. Select the maximum value of compressive stress, or the compressive stress at 15 percent axial strain, whichever is secured first, and report as th
