Belled piers are widely applied in Gobi gravel to withstand axial tensile loads for transmission towers in Northwest China. This study evaluates the pullout performance of belled piers in Gobi gravel. Forty-one full-scale belled piers were installed at seven sites, and pullout load testing was conducted for each foundation. In general, the uplift load – shaft-head displacement curves of the belled piers in Gobi gravel approximately exhibited an initial linear, a curvilinear transition, and a final linear region, and their capacities should be interpreted from the load test results. Four representative uplift interpretation criteria (Chin, slope tangent, tangent intersection, and L1–L2) were used to evaluate the capacity of each belled pier. The results were interrelated to establish a generalized correlation among these interpreted capacities using a mean normalized uplift load–displacement curve. Based on these analyses, the relative interrelationships of these criteria were established, and the use of these methods was suggested.
Surface protection has been accepted as an effective way to improve the durability of concrete. In this study, nanosilica (NS) was used to improve the impermeability of cement-fly ash system and this kind of material was expected to be applied as surface protection material (SPM) for concrete. Binders composed of 70% cement and 30% fly ash (FA) were designed and nanosilica (NS, 0–4% of the binder) was added. Pore structure of the paste samples was evaluated by MIP and the fractal dimension of the pore structure was also discussed. Hydrates were investigated by XRD, SEM, and TG; the microstructure of hydrates was analyzed with SEM-EDS. The results showed that in the C-FA-NS system, NS accelerated the whole hydration of the cement-FA system. Cement hydration was accelerated by adding NS, and probably, the pozzolanic reaction of FA was slightly hastened because NS not only consumed calcium hydroxide by the pozzolanic reaction to induce the cement hydration but also acted as nucleation seed to induce the formation of C-S-H gel. NS obviously refined the pore structure, increased the complexity of the pore structure, and improved the microstructure, thereby significantly improving the impermeability of the cement-FA system. This kind of materials would be expected to be used as SPM; the interface performance between SPM and matrix, such as shrinkage and bond strength, and how to cast it onto the surface of matrix should be carefully considered.
The purpose of the study described in this paper was to investigate the load–movement behaviour of uplift-loaded bell pier foundations in Gobi gravel. In total, 40 full-scale field tests were carried out in Gobi gravel at seven sites in China. Both the site conditions and the load tests were documented comprehensively. Under tensile loading, the behaviour of the foundations followed a typical two-phase pattern. Normalising the measured load–displacement curves reduced the scatter in the curves. Furthermore, it was found that the normalised uplift load–movement behaviour of the foundations could be characterised by a hyperbolic model. Explicit hyperbolic curve-fitting constants were suggested for the foundations at the 50% and 95% confidence levels. The hyperbolic curve of the normalised load–displacement relationship for the foundations revealed a substantially stiffer response than that of spread footing foundations in backfilled soil.
Lightweight sand–EPS soil (LSES) is regarded as a kind of sustainable geomaterial for providing a way to reutilize fast-growing waste expanded polystyrene (EPS) packages. It is usually applied in marine geotechnical engineering to solve the excessive settling of soft ground or bumps at bridge heads due to its merits such as low density, high strength, and adjustability. Aiming to investigate the dynamic shear strength of LSES made from marine sand, a series of laboratory dynamic triaxial experiments was conducted on LSES with different proportions and control sand (CS). The influences of cement content, EPS bead content, and confining pressure on dynamic shear strength were analyzed, as were comparisons with the material sand. It was found that the dynamic strength of LSES increased with the increase in cement content and confining pressure. The bonding function of cement hydration products contributed to the dynamic strength of LSES; however, the work required a certain content of cement. The dynamic strength of LSES decreased with the increase in EPS bead content due to the low particle strength and smooth surface of EPS beads. The cyclic number of failure (Nf) of both LSES and CS decreased linearly with the increase in dynamic shear stress in semilogarithmic coordinates. Both the slopes and the intercepts increased with the increase in cement content and confining pressure. However, they decreased with the increase in EPS bead content.
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