Determining and evaluating the pile bearing capacity via static pile load test and statical formulas

With the increase in the needs of human kind the weight of the buildings increase too. The shallow foundations become incapable of carrying the weight of the buildings (except the ones that are built on solid rock soils) and this lead engineers to develop deep foundations. Also building structures on soils which can not be defined as building materials have triggered the need of deep foundations. The mostly used deep foundation type in Turkey and all around the world is foundations with piles. Piles are classified according to the material that are made by, the way of casting and the way they carry the buildings' loads. Reinforced concrete, steel and wood are the main materials that the piles are made with. The most used type is the reinforced concrete type. In Turkey, wooden piles were used before 20th century. The mostly used way of pile casting in Turkey is the bored piles while the interest in vibrex piles are increasing day by day. The interest towards vibrex piles is increasing because this way of pile installation is much more economic and faster. The disadvantage of the vibrex piles is that they can not be installed in every type of soil. The classification according to the way that piles carry the load is done in two; friction piles and tip piles. A pile is called "friction pile" if it transfers the building loads to the soil via its surfaces. On the other hand, piles are called "tip piles" if they transfer the load to the soil via its tip at the bottom of the pile. Piles transfer the building loads to the soil by interacting with it. There are two factors that determine the load which a pile can carry; the statics of the pile and the load that a pile can transfer by interacting with the soil. The statics of the pile is designed so that it can carry the related loads. Therefore the statics of the pile is not a limiting factor. However, the strength of a pile is determined by the amount of weight it can bare by interacting with the soil. Pile bearing capacities are calculated (determined) by various methods. The rarest method used for determining the pile bearing capacity is the field experiments. Pile bearing capacity could be calculated by correlating the data obtained from the field experiments. Empirical formulas are being used for this method. The most commonly used pile bearing capacity calculation is done with statical equations. This method is done by using the soil parameters of the project field and the equations that the scientists have developed. Unless the project field is filled very tediously this method does not give realistic results. Despite the fact that this is the most commonly used method, the deep foundation projects that are designed this way are generally overdesigned. This is clearly seen when the results are compared with the pile load test results. Calculating the bearing capacity less than the reality causes the piles' radius, length and/or quantity to be more than necessary. Safety factor (3) is one of the main reasons why this method's results are far away from the reality. The most accurate pile bearing capacity calculation method is the pile load test. By this way the relevant piles are actually installed, the necessary loads are actually applied via hydraulic systems and the settlements of the pile is tediously observed. Therefore bearing capacity calculations which are done with this method give the most accurate results. Despite the fact that pile load tests are the most accurate bearing capacity calculation method, it is not used as much as needed. The reason of this is the price of the test. However the deep foundations designed with the results of the pile load tests are usually much more economic than the ones that are designed with the other methods. Pile load tests should be done before starting the installation of the actual project piles. Since the tests are done before the actual project piles, it seems like an extra cost. But, the decrease in the radius, length and/or quantity of the project piles leads to a serious cost saving. Pile load tests have many advantages. Most of all the project costs decrease when it is desgined with the results obtained from the tests. The reason of the decrease is the decrease in the radius, depth and/or quantity of the piles. Since the results are more precise when compared with the statical equations, almost every project designed with the test results causes a significant saving. By decreasing the radius, depth and/or quantity also enables so many time saving. The time spent for the geotechnical executions and design seriosly decreases, because the projects are drawn with more accurate data. Savings made during the design process also cause environmental friendly results. Because less pile execution means less gas consumption, less interaction between soil and concrete, less smoke production, less consumables, etc. Also the cocnrete and rebars are produced by using chemicals. Therefore, by decreasing the amount of piles to be executed, a serious environmental help occurs. Another advantage of pile tests is decreasing the import amount of the country. Nearly all the materials, machines and equipments used during pile execution is imported to Turkey. By decreasing the pile works, current deficit also decreases. Thus, this helps the economics of the country. In the scope of this thesis pile load test setup, problems faced during the setup, how the test is done, loading steps, loading weights, test results, bearing capacity calculation via the test results, the comparison of the results with the other methods and the advantages of the pile load tests are studied in detail also with the subjects stated above. 16 tests that were done within the Sakarya, Kırklareli, Konya, Bakü and İstanbul Projects are dealt in detail within the scope of this thesis. 2 tests at Sakarya, 1 test at Kırklareli, 8 tests at Konya, 4 tests at Bakü and 1 test in İstanbul were held between the years 2012 and 2014. 1 of the tests were applied to a tip pile and 15 tests were applied to friction piles. Every single test is examined elaborately under specific titles. Bearing capacity calculations done via static equations and pile load tests are compared and significant differences were observed. According to the comparisons, pile load tests' results lead to a higher bearing capacity calculation result. Pile load tests which should be done during the deep foundation design and before installing the actual piles so that it leads to financial and time-wise savings. By using the pile load test data, an equation was generated for calculating the bearing capacity of friction piles. The relating equation and its accuracy with the real results are explained.