Proceedings of DFI of India 2015 Conference, Bengaluru, India, (DFI)
Driven Piles Hollow Concrete Spun Piles – The Brazilian Experience
Mario Medrano, Ms.
Brazil has a highly variable geology all along its coast that directly influence the choose of foundation type, being too employed the use of reinforced spun concrete piles initially ranged in diameter from 60 to 80 cm. Over the past 10 years with the advent of investment in marine works projects began to demand a new range of piles with diameters greater than 100 cm and in the absence of amendments. On land is also very remarkable the presence of regions with large layers of soft clay, in prime areas that have been explored. A classic example is the Barra da Tijuca in Rio de Janeiro that has suffered from the housing boom growing toward these regions. In these regions it has been very common driven lengths of about 40.0 meters, which basically go through thick layers of soft material or unconsolidated and they will find strength in depth with residual soil layers or even the bedrock. The spun concrete has great qualities for application in deep cuttings resulting from the production process, which gives a redistribution of fresh concrete mass collaborating with the particle size distribution effective loss of water that is thrown to the center stake being subsequently discarded. Consequently this contributes to a reduction in the factor a/c that is directly connected to increase strength. The fact that there is a sort of concrete helps to reduce voids in the mixture, which increases the durability characteristics. This condition made it possible to employ the spin technique on poles, which are directly linked to aggressive media in large urban centers. Another very attractive feature is that the centrifuge process can work with concrete with the lowest percentage of mortar and more gravel. This concrete mix directly contributes to increasing the specific modulus of elasticity, thus allowing a greater capacity to absorb the energy of the blows transferred with less deformation. Despite the great potential of land application of prefabricated spun concrete stakes there are only three factories and its limitation is the cost of transporting manufactured for the various regions, since all transportation is done by road. For its transportation is carried out exclusively by trucks, this limits the size of cuttings being produced commonly in length from 11.0 to 12.0 meters in length and smaller compositions. For use in long piles of works is resorted to amendments in the form of metal rings, concreted near the ends of the stakes, with the transfer through steel bars in CA-50 welded to the ring. Usually run in steel ASTM A-36. Later in the work these rings are welded with coated electrode. In the case of maritime stakes are very used to drowned splicing technique, which basically consists during the spin process leave one end with the armor of the apparent stake and work together two elements and make specific, with superior resistance to the prefabricated stake. This study in addition to briefly introduce the process of manufacturing, design and logistics presents a detailed study of application of different types of stakes in Brazilian land, ranging from application in extremely soft soils as the port of Navegantes and Guaruja, applying examples land in the Steel Plant in Santa Cruz / RJ and Barra da Tijuca. These cases were employed foundations solution with the spiking over a stake element, presenting data spiking diagram scams counts, elastic denies records and peal extracted during execution and end with the execution of strokes with variable power - DIET methodology which allows to set a displacement-load curve mobilized and thus estimate the breaking load. This curve obtained is compared with results from dynamic loading tests performed at the end of riveting, and results in other age (time elapsed between the end of the crimping and test performance), thereby evaluate the resistance gain effect over of the time. After that will be presented a comparative study of spun piles with a diameter of 70 cm, with wall thickness of 11 cm, tested with dynamic load tests with variable power methodology performed with hydraulic hammer 80 kN which saw the maximum stroke energy a mobilized load stabilization without actually achieve the expected minimum capacity. Later the stake was tested with free-fall hammer with 110 kN. In such cases will be compared the two curves resistance mobilized by displacement in order to investigate the influence of the crimping system in relation to the resistance offered by the ground. In parallel to the results measured by field trials from the records of denying and elastic rebound are estimated in the field mobilized resistance that allow on-site evaluation of crimping system and resistant surface of the ground. It is understood by resistant surface the tip of the quota of driven piles that has the load capacity required in design and is directly dependent on the type of land and its stratification. To estimate the field turn up the dynamic formulas, being employed to successfully control due to various calibrations already made by the S & D method proposed by Aoki et al. (2014) and Energy Approach. Through these considerations and application examples are intended to contribute to the solution of foundations for prefabricated spun concrete piles.
|article #2196; publication #1015 (India2015)|