Development of a foundation model for loading test using an artificial poorly cemented sandstone
|Keywords:||人造膠結不良砂岩;軟岩;模型承載試驗;極限承載力;artificial poorly cemented sandstone;soft rock;foundation model for loading test;ultimate bearing capacity|
經研究結果顯示，人造膠結不良砂岩之比重約2.66、乾單位重約2.02 g/cm3、孔隙率約24%、單壓強度介於3~5MPa、凝聚力 = 0.06MPa及有效內摩擦角 =37.27o；其性質已接近模擬之天然岩材。
This thesis aims to investigate the engineering performance of shallow foundation in poorly cemented sandstone. In this thesis, an artificial weak rock was developed as the foundation material. The mechanical behavior of the artificial rock is analogous to the natural sandstone. A set of laboratory loading equipments for foundation model was assembled. The loading capacity of the loading facility is up to 400 tons. Then, four sets of model loading tests were performed. Based on the results of the model loading tests, the loading stress v.s. settlement curves can be divided into three parts, i.e., the incipient stage, the yielding stage, and the fracture stage. The curve of the initial stage is approximately linear. It reflects the model material is still elastic. At the yielding stage, the micro-fractures are induced and model material behavior becomes inelastic. The deformation rate increases at the fracture stage. Then, the bearing stress decreases with the increase of settlement. Based on the observation of the failure modes of the foundation model, the failure foundation model can be divided into four particular zones, i.e., the active stress zone, the passive stress zone, the shear-crack zone, and undisturbed zone. The active stress zone locates beneath the footing and was induced by the stress concentration at the corner of the footing. The passive zone was formed by the lateral expansion of the active zone. The shear fractures increase with the increase of the loads. Then, a macro shear slip surface forms and extends to the surface. Since both the shear and tensile cracks were observed in the models, the loading behavior of model foundation of poorly cemented failure mode is little difference with those for hard rocks or soils. The existing solutions for estimating foundation bearing capacity for soils or hard rocks are not suitable for weak rocks.
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