Parametric Study for the Behavior of Blocks Anchor Embedded in Sand at Various Conditions

Abstract

Anchors embedded in soil are used to restrain horizontal movement of structures, especially pipelines. Block anchors are not thoroughly studied in the literature as compared to plate anchors. This research paper intended to address this gap and contribute to the field by studying various parameters influencing the behavior of block anchors embedded in sand when subjected to a horizontal load. The behavior focuses on the pullout capacity and displacements/rotation of the block anchor, and the failure mode of the soil. The parameters studied include width, depth, and thickness of the block; depth of embedment below the ground surface; location of the pulling load; and the degree of saturation of the soil. The rigorous research methodology consists of numerical, analytical, and experimental approaches. First, the analytical calculations were based on Rankine, Coulomb, and log spiral theories to obtain values for the pullout capacity, for the 3-D magnification factor, and for the mobilized friction angle. Second, the experimental work included pullout tests, made in the laboratory, on concrete block anchors of various dimensions and on steel plate anchors, embedded in sand at two different depths. The sand was deposited in a box by pluviation to ensure a uniform and reproducible density. Materials properties were determined, and instruments were calibrated. The load and the corresponding horizontal and vertical displacements were recorded, and visual observations of the failed soil surface were captured. Finally, the numerical computations used PLAXIS program for the 2-D cases to obtain the pullout capacity and the deformation for long anchors. The main findings of this study show that the block anchor has a higher pullout capacity than a plate anchor; and the depth of embedment and the moisture condition of the sand significantly affect the pullout capacity, while the thickness of the block and the exact location of the load do not significantly affect the capacity. The capacity of a short block anchor per unit width decreases with increasing width, as the 3-D effect reduces. With reference to dry sand, the capacity of the anchor is doubled if the sand is unsaturated/wet, but it is reduced to only one half if the sand is saturated. The experimental results were compared with the analytical calculations and also with the numerical computations. The analytical results were also utilized for the experimental design. The results of numerical computations were used to validate the experimental design and to explain experimental findings, especially failure mode and deformation. The findings of this research are also compared with other studies reported in the literature. These findings have very significant implications to the analysis and design of the block anchor. They also contribute to the hazard risk assessment of block anchors embedded in sand subjected to variations in the environmental condition of wetting and drying cycles.