Calculation methods, installation and quality control principles for barrette piled foundations

Nowadays, need for the residential areas are increasing in the cities due the population growth. In order to compensate this growth, number of constructions for high-rise buildings, heavy bridges, viaducts and structures of these kinds are increasing day by day. Transferred load from all these kind of super structures to the soils reaches high degrees. Transmission of this load with shallow foundations is usually insufficient considering settlement and bearing capacity criterias. Deep foundation systems are applied for the cases in which shallow foundations are uneconomical for depth reasons, bearing capacity of soil layers close to the surface are low, construction of the proposed structures are prone to total and/or different settlement, there is a high horizontal load transfer from upper layers of soil to the foundation, liquefaction of upper surface layers due to earthquakes. The most popular deep foundation system in our country is reinforced concrete piles. Characteristics of planned construction, structure loads and execution conditions affects foundation cost. It is expected to make this cost as suitable as possible like all other construction practices. When planned construction requirements and bored piles are uneconomical, it is preferred to use barrette piles. Barrette piles can simply be defined as rectangle section bored pile. The term 'barrette' originates from the French language. In existing literature on civil engineering, 'barrette' refers to a concrete replacement pile formed in a short and deep trench excavated under bentonite or polymer slurry by diaphragm walling equipment. A barrette is also known as a diaphragm wail bearing element or a strip pile. Barrettes are generally of rectangular section. Composite cross-sectional shapes, e.g., cruciform, T-, L-, H-, Y- and I-shapes etc., are occasionally specified in practice to suit the pattern of loading or the layout of the columns supported by the barrette foundations or the shapes at the comers of a basement. Conventional circular piles often become impractical and uneconomical when very heavy column loads are to be transmitted to a very deep bearing stratum. Barrettes provide an alternative to large diameter bored and cast-in-place piles or drilled shafts. This is because a rectangular barrette has a higher specific surface (i.e., surface area to mass ratio) than a circular pile for resisting larger vertical loads by shaft resistance. In addition to this, from a structural point of view, a barrette can be properly dimensioned and orientated to satisfy the required moment of inertia, and hence flexural rigidity in a preferential direction. This would benefit the barrette in its capacity for resisting relatively larger lateral loads or bending moments. Quality control tests are also important for the barrette pile constructions as the same with bored pile system. A reaction system should be constructed to provide required test load in conventional pile load tests. Reaction system construction is time-consuming and costly process in high test loads. Additionally, safety problems may occur during the construction. The Osterberg Cell method, improved as an alternative procedure to the conventional pile load tests, was first introduced in the late 1980's. As a result of the bidirectional loading of piles with Osterberg cell, loss of time and safety risks are minimized, high test loads could be applied on the test piles in accordance with the design loads of barrette. Since the end bearing and skin frictions are measured independently, test results are evaluated more reliable with the design values. Osterberg method pile load tests are widely used for the quality control of barrette pile constructions. This thesis covers the literature review of vertical bearing mechanism and the settlement behavior of barrette piles. Site applications, installation principles, advantages and limitations compared to other bored pile system of barrette piles are researched. The Osterberg Cell method pile load test is detailed in quality control tests of barrette piles. A barrette pile application project as a case-study is evaluated and presented in the final part. Calculated theoretical bearing capacities and settlement of barrette piles are compered to results obtained from Osterberg cell method pile load tests. Pile load test is also modeled with Plaxis 3D Foundation finite elements program and test performance is assessed.