Theses and Dissertations at Montana State University (MSU)
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Item Aggregate piers: stress transfer mechanism and construction effect(Montana State University - Bozeman, College of Engineering, 2022) Gamboa, William; Chairperson, Graduate Committee: Mohammad KhosraviThis thesis is a compilation of two different papers based on the behavior of aggregate piers which is a soil improvement method used to increase the bearing capacity and reduce the expected settlements of soils in which different types of structures are supported. The first paper describes the results of two modulus load tests and a dimensional finite difference analysis (FDA) conducted to evaluate the load-displacement response of isolated aggregate piers. Load test aggregate piers were constructed with two different materials: the first one with 38 mm base coarse and the second one with 75 mm subbase coarse materials. The numerical analyses provided reasonable predictions of the load-displacement response of the isolated aggregate piers. Parametric analyses using the validated numerical model illustrate that the lateral stress increment on the soil around the pier during the installation process of the pier should be considered in the numerical analysis, otherwise the settlement can be overestimated. The second paper is based on two full-scale load tests that were conducted to examine the load transfer mechanisms of end-bearing single and group aggregate piers. The first included a load test on a 0.76 m diameter isolated aggregate pier. The length of the aggregate pier was 4.3 m. The second test included a 2.1 m square reinforced concrete footing supported by four 0.76 m diameter aggregate piers of 4.3 m long. The soil consists of soft to medium stiff layers of sandy and clayey silt overlain by a 2-m-thick, softer silty clay layer. At the bottom, weathered rock was found. The load transfer mechanism within the length of the piers was examined using a series of load cells and tell-tale reference plates installed at different depths of the aggregate piers. Additionally, the installation effect was investigated using Cone Penetration Tests (CPT) conducted prior and after construction of the aggregate piers and inclinometers installed at multiple locations around the aggregate piers. The results of the experiments were compared with those in the literature to provide insights on the performance of aggregate piers with different configurations (single vs. group) and depths (floating vs end-bearing) in different soil profiles.Item Effectivenes of desiccation in densifying a series of sand-clay mixtures(Montana State University - Bozeman, College of Engineering, 1961) Donley, Howard F.Item Effect of compaction and water content on swell of clays(Montana State University - Bozeman, College of Engineering, 1948) Fistedis, Stam H.Item Interaction of superstructure, foundation, and soil(Montana State University - Bozeman, College of Engineering, 1981) Hightower, John JosephItem Axial capacity of piles supported on intermediate geomaterials(Montana State University - Bozeman, College of Engineering, 2008) Brooks, Heather Margaret; Chairperson, Graduate Committee: Robert L. MokwaPile foundations used to support bridges and other structures are designed and installed to sustain axial and lateral loads without failing in bearing capacity and without undergoing excessive movements. The axial load-carrying capacity of a driven pile is derived from friction or adhesion along the pile shaft and by compressive resistance at the pile tip. There are well established analytical methods for evaluating pile capacity and for predicting pile driving characteristics for cohesive soil, cohesionless soil, and rock. However, past experience indicates these methods may not be reliable for piles driven into intermediate geomaterials (IGMs), which often exhibit a wide array of properties with characteristics ranging from stiff or hard soil to soft weathered rock. Methods to determine the axial capacity, driving resistance, and long-term resistance of piles driven into intermediate geomaterials are not well established. Nine projects, in which piles were driven into IGMs, from the Montana Department of Transportation were analyzed. Each project contained information from CAPWAP dynamic analyses, construction records, and design reports. The purpose of any analyses, of the nine projects, was to better predict the behavior of piles in IGMs. IGMs were divided into two broad types, cohesive and cohesionless. The computer program DRIVEN is often used to predict the axial capacities of piles; however, in IGMs the design method is unreliable. Attempts were made to determine trends within the available data. Normalized resistances for shaft and toe capacities did yield slight correlations of shaft resistance to pile length in IGMs. Iterative solutions using DRIVEN to match the CAPWAP ultimate capacity did not provide meaningful trends or correlations. Slight modification of MDT's original DRIVEN inputs was required in most cases to match the CAPWAP ultimate capacity. Because no meaningful trends were found from analysis, other capacity calculation methods were used to determine other methods that accurately predict pile capacity within IGMs. The Washington Department of Transportation Gates formula is the most accurate method of those attempted. More research is required for further analysis of piles in IGMs.