<p><p><strong>Reference(s):</strong></p><p><em>Casagrande (1952)</em></p><p><strong>Method Summary</strong></p><p><strong> </strong>Plate load tests are performed using static loads or dynamic impulse loads. Casagrande (1952) documented use of plate load tests to evaluate the bearing capacity of soils treated (with electro-osmosis) and untreated embankments. The test procedure and equipment used are not described in that reference.</p><p>Static plate load tests involve obtaining load versus deflection curves to determine soil elastic modulus or soil bearing capacity. The test is conducted by increasing a static load on the soil and continuously monitoring the plate deflections. Early work by Terzaghi included using a 760-mm (30-inch) diameter plate, but more commonly a 300-mm (12-inch) diameter plate is used. The larger the plate, the deeper the measurement influence depth. A 300-mm (12-inch) diameter plate is sufficient for pavement construction working platforms and pavement foundation layer stabilization applications. Large plate diameters are required to evaluate soils at deeper depths; however, this requires high reaction forces to obtain desired loads. ASTM D1195 describes the test method to perform repetitive static plate load tests of soil for evaluation and design of airport and highway pavements. A 300-mm (12-inch) diameter plate (stepped with small plates on the top to reduce plate deflections) is used in the ASTM D1195 test procedure.</p><p>Light Weight Deflectometers (LWD) and Falling Weight Deflectometers (FWD) can be used to perform dynamic plate load tests. These tests are performed by obtaining plate deflections under dynamic impulse loading. LWD testing involves applying relatively low contact stresses (about 0.2 MPa or less) compared to FWD testing (applied contact stresses up to 1.0 MPa). FWD tests can also be performed with an array of deflection sensors spaced away from the loading source to develop deflection basin data to assess the stiffness/modulus of the subsurface layers down to a depth of about 2 meters. FWD equipment is trailer-mounted and pulled with a van or a truck. LWD devices come in an enclosed box and can be carried in a truck. LWD and FWD devices are commonly used in evaluating pavement foundation layers. Although the methodology of the two tests is similar, different manufacturers use different type of measurement sensors to measure deflections (e.g., geophones, accelerometers, sensiometers, etc.). For LWD testing, some devices assume a constant assumed load while some devices use a load cell to measure the applied load. These differences between device configurations affect the modulus value. LWDs are generally setup with 200- and 300-mm diameter plates, while FWDs are setup with 300- and 450-mm diameter plates. The modulus values are affected by the plate diameter and applied contact stresses.</p><p>Applicability of LWD and FWD tests on projects where electro-osmosis treatment is applied has not been previously evaluated.</p><p><em> </em><strong>Accuracy and Precision</strong></p><p>Accuracy of these test methods is not known. ASTM D1195 indicates that the precision and bias of the static plate load test method has not been determined due to the variability associated with soils.</p><p><strong>Adequacy of Coverage</strong></p><p>Sufficient evaluation requires many tests. The number of tests depends on the variability observed on-site.</p><p><strong>Implementation Requirements </strong></p><p>Experience and special equipment are necessary. For static plate load tests, special equipment may be necessary to produce enough reaction force for the required applied stresses. Typically, a heavy truck or a dozer or any similar heavy construction equipment may be used as a reaction force. A trained field engineer is required to analyze load-deflection curves. FWD is relatively more expensive than LWD or PLT but special training is required to conduct the test. A FWD is trailer mounted and is pulled with a truck while an LWD can be enclosed in a box and carried in a truck.</p><p><strong>General Comments</strong></p><p>This test method provides a direct measure of modulus and/or bearing capacity and can be an effective method for QA.</p></p>