AASHTO T208:2015 Standard Method of Test for Unconfined Compressive Strength of Cohesive Soil.
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-controlled 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 oniy to cohesive materials that will not expel bleed water (water expelled from the soil due to deformation or 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 compressive strength values.
Note 1—The 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.
4. SIGNIFICANCE AND USE
4.1. The primary purpose of the unconfined compression test is to quickly 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 bess, very soft clays, dry and crumbly soils and varved materials, or samples 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.
4.3. If both an undisturbed and a rernolded test arc 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 remoldcd state.
Note 2 For soils that will not retain a stable shape, a vane shear test or T 223 can be used to determine sensitivity.
5.1. compression Device— The 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 capacity and control to provide the rate of loading prescribed in Section 7.1. For soil with an uncon lined 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 compressive 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.AASHTO T208 pdf download.