Load testing

Abstract: The potential benefits of geosynthetic reinforced soil foundations are investigated using large-scale model footing load tests. A total of 34 load tests were performed to evaluate the effects of single and multiple layers of geosynthetic reinforcement placed below shallow spread footings. Two different geosynthetics are evaluated: a stiff biaxial geogrid and a geocell. Parameters of the testing program include the number of reinforcement layers, spacing between reinforcement layers, the depth to the first reinforcement layer, plan area of the reinforcement, the type of reinforcement, and soil density. Test results indicate that the use of geosynthetic reinforced soil foundations may increase the ultimate bearing capacity of shallow spread footings by a factor of 2.5.

Abstract: At least two methods for using static cone data to predict settlement exist and have received extensive use—those of Terzaghi-Peck-Meyerhof and Buisman-DeBeer. Another method is presented in this paper. All three methods are then applied to 16 test cases involving either actual foundations, or plate load tests, with measured settlements. The proposed method simplifies calculations without sacrificing conservatism, yet appears most accurate over the full scope of the available test cases. These involve foundation widths of 2 ft to 184 ft. The key feature of the new method is that a single distribution of a strain influence factor is assumed for all cases. This method eliminates the need to compute the intermediate parameter of change in vertical stress with depth below a shallow footing. Also presented is a new correlation between static cone-bearing capacity and sand compressibility. Compressibility was measured in-situ by a special screw-plate form of plate-bearing load test. New data are included for the correlation between the static cone-bearing capacity and SPT blow count values in sands.

Abstract: A method is presented for evaluating the relative performance of unstabilized base course materials with respect to rutting and is then used in the evaluation of a number of materials. A general method is also proposed for calcualting rut depth occurring in flexible pavements. The proposed methods make use of the plastic axial strains obtained from the repeated load triaxial test. Cylindrical specimens 6 in. in diameter and 12 in. in height of crushed stone and soil-aggregate mixtures were placed in a conventional triaxial cell and subjected to 100,000 load repetitions using a constant confining pressure and a triangular stress pulse. Stress-strain curves giving the relationship between deviator stress, confining pressure and plastic axial strain were constructed for each material studied using the repeated load test results. The concept of a rut index was proposed which can be calculated making use of the plastic stress-strain relationship, and is approximately proportional to the rut depth that will occur in the base after a desired number of load repetitions. The rut index appears to offer a practical laboratory method for evaluating the relative performance of base materials used in pavements having similar structural configurations. An evaluation of the test results using the rut index approach indicates that under good conditions of drainage and proper maintenance of the pavement surface, carefully selected blends of 20 percent soil and 80 percent stone should perform satisfactorily. Soil aggregate blends having properties similar to the materials tested should probably not be used at all under poor drainage conditions, and 40-60 blends should not be used even under good conditions of drainage. The results further indicate that only a sufficient amount of fines should be used in a crushed stone base to permit proper compaction if the amount of rutting in the base is to be minimized. Furthermore, even though the specified gradation and density may be the same, bases constructed from aggregates obtained from different sources may exhibit different rutting characteristics. A general engineering method for estimating the rut depth in a flexible pavement after a desired number of load repetitions was proposed which utilizes nonlinear layered theory, the plastic stress-strain response of the component materials, and a hyperbolic, plastic stress-strain law. Field verification is now needed of both the proposed rut index and the general method for predicting rut depth. /Author/

Abstract: Comprehensive measurements of the effective stresses developed during the installation, equalization, and load testing of displacement piles in a loose to medium dense quartz sand are presented. The results shed new light on the mechanisms that control shaft friction in sand. First, it is demonstrated directly that the stresses developed at any given soil horizon depend strongly on both the distance of that horizon from the pile tip and the soil's initial state. Second, pile loading is shown to induce radial effective stress changes associated with the soil fabric set up by installation and dilation phenomena at pile‐soil interface. Thirdly, the operational angles of interface friction are found to be constant volume values that correlate well with the results from laboratory interface shear tests.