Dynamic load test is often used for bearing capacity evaluation of driven pile foundation. It is also reported the successful use of this test in bored piles and caissons. This research is mainly concerned with the adaptation, performance and interpretation of the dynamic load test in circular steel plate aiming at the verification of the bearing capacity of shallow foundations. The dynamic increasing energy test (DIET) was used. The tests were performed at the USP/São Carlos experimental foundation site, which soil profile consists of superficial unsaturated, porous and collapsible soil, and for that reason matric suction’s measurements were made, since it has strong influence on the bearing capacity. It could be verified that it is possible to make use of the dynamic load test to plates, associated with analysis methods based on the stress propagation in bars (wave equation), to infer the plate-soil system bearing capacity. Good adjustments were found from dynamic and static load tests performed in a plate tested in this research field. It was also verified that the plate penetration into the soil caused an important increase in the plate-soil system bearing capacity.
This work analyses the influence of footing size and soil matric suction on the behavior of shallow foundations on unsaturated sandy soil, in terms of bearing capacity and settlements. Fourteen plate load tests were performed at the Experimental Site of USP/São Carlos. Rigid metal plates were used, with diameters varying between 0.20 m and 0.80 m and reinforced concrete footings, with circular base diameter 1.50 m. All the plates and the footings were installed at a depth of 1.5 m. These tests were conducted either with matric suction monitoring using tensiometers installed at the bottom of the hole or with soil flooding. The important role of the matric suction was confirmed. A reduction of the matric suction close to zero causes a great decrease in the bearing capacity and a significant increase in the settlement. In relation to the footing size (B), the bearing capacity as well as the settlements did not present a constant linear increasing variation. This work also proved the importance of considering the soil collapsibility in unsaturated soil shallow foundations design. When this factor is not considered, the calculated allowable bearing capacity may cause very high settlements if soil flooding occurs.
This paper describes a mechanical device to compare the energy transference from the blow of a hammer to the stem referring to standardized and non-standardized equipment in Brazil. The device allows to measure the vertical displacement of a sleeve due to one or more blows of a hammer falling freely. Tests were carried out using three pieces of equipment for the SPT measurements, but only one was mounted on a tripod standardized by the NB 6484:2001 norm. Based on the displacement values, a comparative analysis of the available energies of the equipment was conducted. The efficiency of the standard tripod for the test performed without a strict control of the fall of the hammer relative to the transfer efficiency of the test performed with a strict control of the fall height was 82.5%, showing a significant influence of human factor on the results. The lowest coefficient of variation of the displacements (5.05%) was obtained for the test using mechanized equipment with an automatic hammer. From the standpoint of the available energy of the system, it is possible to use non-standard equipment by applying the correction factor (Cf) to SPT results. Finally, static tests were performed on the sleeve and the energy transferred to the system was calculated.
Relata-se um estudo paramétrico de grupos de 2 e 3 estacas, escavadas e cravadas, com espaçamento variando de 1 a 10 diâmetros, submetidos a carregamento horizontal em centrifugadora.
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