In geotechnical engineering, the stability of strip footings under eccentrically inclined coupled loads is a major concern. The objective of this paper was to estimate the ultimate bearing capacity ...of a rigid strip footing, subjected to eccentrically inclined loads resting on cohesive-frictional soil, using the rigid plastic finite element method (RPFEM). In the numerical analysis, an interface element was introduced to properly evaluate the interaction between the footing base and the soil. The footing base was assumed to be rigid and rough, as it most often is in reality. Focus was placed on the effect of the soil properties (cohesive strength c, internal friction angle ϕ, and unit self-weight γ) and footing width B on the loading planes of the V-H-M limit load space (vertical load-horizontal load-moment) in order to consider the uniqueness of this limit load space. In particular, the effect of the two directions of the horizontal load, namely, positive and negative horizontal loads, on the V-H-M limit load space was clarified. The numerical results of the RPFEM showed that the negative horizontal load had a positive effect on supporting a higher bearing capacity than the positive horizontal load in the presence of a small eccentricity length. However, the results also showed a negligible effect on the bearing capacity for both directions of the horizontal load in the presence of a large eccentricity length. New equations were proposed to determine the V-H-M limit load space, predicted as functions of c/γB and ϕ, by taking into account the direction of the horizontal load. The applicability of the V-H-M limit load space was widely examined for several loading paths with different prescribed loads for V, H, and M. Consequently, the limit load space of the strip footing was clearly found to be unique for each value of c/γB and ϕ.
Abstract
This study widely investigates the ultimate bearing capacity of a rigid footing on the free surface of sand overlying clay using the rigid-plastic finite-element method (RPFEM). Interface ...elements were introduced with the new constitutive equations developed by the authors to properly evaluate the interaction between the footing and the soil because these elements greatly affect the failure mechanism of the footing–soil system. Two friction conditions were employed for the footing surface, namely, the perfectly rough condition and the perfectly smooth condition. The RPFEM was extended to calculate the distribution of contact normal stress along the footing base corresponding to changes in the thickness of the sand layer. Several design charts were developed to directly determine the ultimate bearing capacity by increasing the internal friction angle, the thickness of the sand layer, and the shear strength of the clay layer. Two cases were considered for the clay layer below the sand layer, namely, a weak layer and a stiff layer. The failure mode of two-layered soils was found to change from the general shear mode to the punching shear mode for both friction conditions by a reduction in the shear strength of the clay layer. The sheared area of the ground was limited to the sand layer in the general shear mode, while the sheared area was distributed throughout the two layers in the punching shear mode. New bearing capacity formulas during the punching shear mode were proposed for the two friction conditions in a wide range of strength and geometric parameters, which were in close agreement with the experimental studies and are efficient enough to be used in practice.
Most of the contemporary ultimate bearing capacity (UBC) formulas assume a linear yield function in shear stress-normal stress space. However, experimental investigations have corroborated the ...non-linearity in the failure envelopes of sandy soils. This study focused on the assessment of the stress level effect on the UBC of surface strip footings ascribed to the soil unit weight (γ), footing size (B), and uniform surcharge load (q). The rigid plastic finite element method (RPFEM) was employed for the analysis. The analysis method was validated against the centrifuge test results from the published references in the case of various sandy soils with different relative densities. The RPFEM, using the mean confining stress dependence property of Toyoura sand, is utilized in non-linear finite element analysis of model sandy soil. The normalized ground failure domains in the case of the non-linear shear strength model are gleaned smaller than those in the case of the linear shear strength one. The numerical results are compared with the guidelines of the Architectural Institute of Japan (AIJ) and the Japan Road Association (JRA). The modification coefficients are ascertained for the frictional bearing capacity factor (Nγ) and surcharge bearing capacity factor (Nq), and a modified UBC formula is proposed. The performance of the proposed UBC formula is examined against the analysis results and various prevailing UBC guidelines.
On October 23, 2004, an earthquake with a moment magnitude of 6.8 occurred in the Chuetsu area of Niigata prefecture in Japan. This earthquake is known as the 2004 Mid-Niigata prefecture earthquake; ...the event was followed by severe aftershocks and caused many types of landslides such as surficial slides, shallow slides, and deep slides. A large number of landslides occurred in the upland village of Yamakoshi, destroying the entire village; in addition, a huge number of houses collapsed in Kawaguchi town. This study investigates the correlations between each type of landslide and the bedding plane orientation and dip, and other geomorphologic conditions. The landslide occurrence ratio (LOR) is used as an index to determine the correlation between the 2004 Mid-Niigata prefecture earthquake-induced landslides and the slope angle, slope aspect, rock type, and bedding plane orientation and dip. This work also proposes a methodology to determine the geometric alignment between the topography and the orientation of geological bedding planes. The method provides an efficient means of estimating the topography/bedding plane relationship over large areas.
In geotechnical engineering, the stability of rigid footings under eccentrically inclined loads is an important issue. This is because the number of superstructures has increased and the situation of ...structures being subjected to eccentrically inclined loading is occurring more and more frequently. The objective of this paper was to evaluate the bearing capacity of a rigid footing on the free surface of uniform sandy and clayey soils under the action of eccentric and inclined loading using a finite element analysis by assuming that the soils follow the Drucker-Prager yield function. In the two-dimensional analysis of the footing-soil system, the rigid plastic finite element method (RPFEM) was applied to calculate the ultimate bearing capacity of the eccentric-inclined loaded footing. In the numerical analysis, an interface element was introduced to simulate the footing-soil system with the rigid plastic constitutive equation developed by the authors. The footing was considered to be rigid and rough, as it most often is in reality. This study thoroughly considered the effect of the soil properties on load inclination factors iγ and ic in order to investigate the validity of the current design methods. In particular, the effects of the horizontal load in two directions on the ultimate bearing capacity of the footing and the failure envelopes in the V-H-M space were clarified, namely, positive and negative horizontal loads. The results showed that the positive horizontal load had a negative effect on the bearing capacity, while the negative horizontal load had the opposite effect in the presence of eccentrically inclined loading. The failure mode of the footing-soil system was clearly seen in the difference between the two directions of horizontal load. Through a series of numerical analyses, new equations were proposed for load inclination factors iγ and ic, and for the failure envelopes in the V-H-M space, taking into account the direction of the horizontal load. The obtained limit load space was proved to be rational in comparison to those given in the literature. Furthermore, the applicability of the limit load space to different loading paths, and moreover, to the independently prescribed loads of V, H, and M, was examined. Consequently, the failure envelope for each type of soil in the V-H-M space was clearly seen to be unique.
Seismic design employs the seismic-intensity method. In this study, the ultimate vertical bearing capacity of building foundations on sandy soils subjected to inclined and moment loads is evaluated ...using the rigid plastic finite element method. The study takes into account the size effect of the foundation to assess its stability during earthquakes. The ultimate bearing capacity is simulated by gradually increasing vertical and horizontal loads simultaneously, aiming to ascertain the impact of inclined load. The analysis findings suggest that a high-order function can effectively describe the foundation size effect. Discrepancies between the analysis results and the AIJ evaluation formula are discussed. The findings of the study revealed that the reduction formula, which utilizes the ultimate bearing surface by Nova, aligns well with the obtained analysis results while considering the influence of eccentricity and inclined loads.
The long-term settlement of the ground after the Niigataken Chuetsu-oki Earthquake in 2007 was observed at Shinbashi in Kashiwazaki city. To study the seismic deformation mechanism and long-term ...post-earthquake settlement, this study carried out ground investigations such as drilling survey on the observation site and indoor element tests for sampled soil. The results showed that the sampled soil was very soft, strongly compressible, and relatively highly-structured. Subsequently, the ground subsidence behavior was simulated through soil-water coupling elastoplastic finite element (FE) analysis using the Transformation Stress-Cyclic Mobility (TS-CM) constitutive model developed by Zhang et al. (2007). The FE simulation results were in good agreement with the on-site site subsidence observation data and the subsequent settlement was predicted forward. Based on the simulation results, sensitivity analysis was conducted on two key parameters λ and κ, and it was concluded that λ is more sensitive to the subsidence amount. In addition, the impact of parameter uncertainty on model uncertainty was also discussed and it was concluded that both λ and κ are moderately conservative and nearly low dispersion for subsidence results, but the dispersion of parameter λ was relatively lower than κ, although parameter λ was more sensitive to the subsidence.
In geotechnical engineering, the stability of rigid footings under eccentric vertical loads is an important issue. This is because the number of superstructure buildings has increased and the ...situation of structures being subjected to eccentric vertical loading is occurring more and more frequently. In this study, focus is placed on the ultimate bearing capacity of a footing against the eccentric load placed on two types of soil, namely, sandy soil and clayey soil, using a finite element analysis. For the sandy soil, the study newly introduces an interface element into the footing-soil system in order to properly evaluate the interaction between the footing and the soil, which greatly affects the failure mechanism of the footing-soil system. For the clayey soil, the study improves the analysis procedure by introducing a zero-tension analysis into the footing-soil system. Two friction conditions between the footing and the soils are considered; one models a perfectly rough condition and the other models a perfectly smooth condition. For a two-dimensional analysis of the footing-soil system, the rigid plastic finite element method (RPFEM) is applied to calculate the ultimate bearing capacity of the eccentrically loaded footing. The RPFEM is extended in this work to calculate not only the ultimate bearing capacity, but also the distribution of contact stress along the footing base. The study thoroughly investigates the effect of the eccentric vertical load on the ultimate bearing capacity in the normalized form of V/Vult and e/B where e is the length of the eccentricity and B is the width of the footing. Vult indicates the ultimate bearing capacity of the centric vertical load. The failure envelope in the plane of V/Vult and M/BVult is further investigated under various conditions for the sandy and clayey soils. M is the moment load induced by the eccentric vertical load. This study examines the applicability of the failure envelope obtained for the eccentric vertical load to the cases where two variables, V and M, are independently prescribed. The obtained results are coincident and indicate the wide applicability of the failure envelope in the normalized V-M plane in practice. Finally, in a comparison with previous researches, the numerical data in the present study lead to the derivation of new equations for the failure envelopes of both sandy and clayey soils.
The old movable weir at Shinano River Ohkouzu in Nagaoka city was demolished owing to aging of structure, after construction of the new movable weir. This study reports the rapid loading test results ...of wooden piles installed below the foundation of movable weir and discusses the design method of foundation. Ground survey clearly illustrated the geological structure of the ground and indicated the wooden piles of 13m in length below the pillar was supported by the dense sandy layer. On the other hand, the wooden piles of 7m in length at the channel was shown to be supported by the thin dense sandy layer. Ultimate bearing capacity of wooden pile was estimated by the in-situ rapid loading test of piles. It matched with the design value in case of the channel, but it was smaller than that in case of the pillar. The foundation design of the pillar was found based on the piled raft foundation theory. Wooden piles had maintained the integrity of material, although it was constructed before about 80 years.
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