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Due to the increasing necessity of building on soils with insufficient bearing capacity, the development of methods for soil improvement is an important geotechnical engineering issue. One of the innovative methods of soil stabilisation is the use of nano-additives. The paper presents the influence of nanosilica on the bearing capacity under the footing under undrained conditions. For this purpose, a simple and quick unconfined compression test was used to evaluate the undrained shear strength of selected silty soil. Tests were conducted for soil without additives and with nanosilica contents of 1, 3 and 5%. All samples were compacted to the maximum dry density in a Proctor apparatus, and strength tests were conducted after 7 days of curing. The results clearly show an increase in undrained shear strength with increasing nanosilica content. Based on these data, a parametric analysis of the bearing capacity under the strip footing was performed for 4 variants of nanosilica content and for 9 loading cases. Thus, the impact of stabilisation in a practical engineering issue was presented. For all load cases the optimal dimensions of the foundation were determined. In addition, for the selected case, calculations were made for a fixed foundation dimension. All computations were performed in accordance with Eurocode 7 with GEO5 software. [ABSTRACT FROM AUTHOR]

• Explored the influence of different UHPC-based rehabilitation forms with the post-installed rebar connection. • Clarified the mechanism of different failure modes with the different embedded depths of post-installed rebar. • Established and verified a method to determine the minimum embedded depth required for the post-installed rebar. • Characterized the force–displacement curves of the post-installed rebar connection under shear loads. • Proposed a calculation formula to estimate shear bearing capacity for post-installed rebar connection. The reliable bonding effect between the ultra-high performance concrete (UHPC) layer and the existing reinforced concrete (RC) components is always expected when UHPC is used to rehabilitate deteriorated RC structures. The post-installed rebar connection has been demonstrated to possess robust mechanical performance. However, no research to date clarifies how to design the post-installed rebar connection in engineering practice. To this end, this study conducted 34 push-out tests to investigate the interfacial shear performance of UHPC-strengthened RC structures using post-installed rebar connections. The primary variables in the tests included strengthening form, embedded depth of rebar, rebar diameter, rebar spacing, and substrate type. Based on the test results, three different failure modes were identified. The analytical results indicate that the embedded depth of the rebar has a significant influence on the performance of the post-installed connection. A formula was proposed to determine the minimum embedded depth, and its accuracy was validated by the physical experiments. The load-bearing mechanisms were revealed based on the experimentally measured force–displacement curves. The shear capacity of the connection mainly comprises the adhesive effect, rebar shearing, and friction. The connection capacity can be approximated by the rebar shear capacity due to its robust shear resistance. Also, a formula was proposed to estimate the shear capacity of the rebar. The experimental and theoretical results facilitate the design and application of post-installed rebar connections in UHPC-strengthened RC structures. [ABSTRACT FROM AUTHOR]

To advance the use of reliability-based design procedures, it is necessary to evaluate the sources of the design parameter uncertainty including inherent variability, measurement error, and transformation uncertainty. The results of a probabilistic evaluation of undrained footing bearing performance are discussed in the context of an extensive test site characterization described in a companion paper. Kriged cone tip resistance values are transformed into design parameters using a second-moment probabilistic approach and compared with the parameters obtained from the laboratory test analyses on specimens retrieved from the test site. The spatial, measurement, and transformation uncertainty are incorporated into probabilistic finite-element and bearing capacity analyses in which the results are compared against a full-scale load test performed at the test site. The results indicate that the reliable assessment of the spread footing response depends to a large degree on the assumed strength anisotropy and soil layering. A comparison of the probabilistic estimates of the bearing capacity to deterministic estimates developed from the correlations and average design parameters indicate that the consideration of uncertainty results in a desirable prediction accuracy. [ABSTRACT FROM AUTHOR]

The paper presents the performance of a square footing with a structural skirt resting on sand and subjected to a vertical load through an experimental study. A series of tests were conducted in a model test tank to evaluate the performance in terms of improvement in bearing capacity and reduction in settlement of a square footing with and without a structural skirt. The results of the study reveal that this type of reinforcement increases the bearing capacity, reduces the settlement and modifies the load settlement behaviour of the footing. The various factors influencing the bearing capacity improvements and settlement reduction using a structural skirt are identified. Skirt factors are proposed which can be introduced into the general ultimate bearing capacity equation for a square footing resting on sand. The predictions made through the modified equation are in reasonable agreement with the experimental results. The bearing capacity of square footing is increased in the range of 11.2 to 70%. The improvement in bearing capacity decreases with the increase in base roughness of the footing. Further, an equation for a settlement reduction factor is proposed which can be used to calculate the settlement of the square footing with structural skirt resting on sand. The settlement reduction factor (SRF, defined as the ratio of settlement of footing with structural skirt to the settlement of footing without structural skirt at a given load) was in the range 0.11 to 1.0 depending on applied load and skirt depth ratio with the use of a structural skirt. The results further reveal that for a given depth of the skirt, the settlement reduction factor decreases with the increase in applied load. The improvement in the bearing capacity and reduction in settlement of a square footing with a structural skirt resting on sand are dependent on the geometrical and structural properties of the skirt, footing, sand characteristics and interface conditions of the sand-skirt-footing system. [ABSTRACT FROM AUTHOR]

Abstract: The bearing capacity of shallow foundations resting on a modified Hoek–Brown rock mass is investigated within the framework of the kinematic approach of limit analysis theory. At the rock material nivel, closed-form expressions are obtained for the support functions of the rock failure criterion. These expressions of the Π-functions are then applied to derive upper bounds estimates of the load-bearing capacity by implementing two classes of failure mechanisms. The numerical results are first compared to existing limit analysis solutions, showing the efficiency of the present approach. The effects of the loading parameters are then discussed at the light of these preliminary results. The results are compared with finite element limit analysis solutions, emphasizing the efficiency of the present approach. Design tables are finally presented for practical use in rock engineering. [Copyright &y& Elsevier]

Abstract: Most conventional computer codes, design practice and standards in rock engineering are formulated in terms of a linear Mohr–Coulomb (MC) failure criterion. However, experimental data shows that the failure of almost all types of rock masses follows a modified Hoek–Brown (HB) failure criterion that is non-linear. In order to avoid the difficulty resulting from the non-linearity of the strength envelope of rock masses in calculation of bearing capacity, the equivalent MC strength parameters from the modified HB failure criterion are developed for practical use in engineering. From the results, it is found that the equivalent strength parameters depend on not only the non-linear HB failure criterion but also the surcharge load and self-weight, which is different from the published results. [Copyright &y& Elsevier]

The authors have derived the bearing capacity factor Nq on sloping ground based on the slip line method and have verified it using finite difference analysis. The bearing capacity factor Nγ on sloping ground is obtained by an iterative finite difference solution of the slip line equations, and the results are close to those from laboratory testing. Design figures for Nγ on sloping ground are prepared for rapid engineering use. For earthquake loading, the authors have applied the concept of equivalent horizontal acceleration and have derived Nq and Nγ based on slip line analysis. [ABSTRACT FROM AUTHOR]

The underlying mechanisms governing the behaviour of displacement piles in sand are not well understood, leading to unreliability in design methods. A series of plane- strain calibration chamber tests has been conducted in order to quantify the penetration mechanism around the pile tip, and the response of the interface layer adjacent to the shaft during further penetration. A series of eight tests is reported, examining the influence of soil type, initial state, pile breadth and the use of a driving shoe. A novel image-based deformation measurement technique has been used to observe the displacement and strain paths, which are found to be relatively independent of soil type. The measured strain paths are similar to predictions made by the strain path method, and contrast sharply with assumptions implicit in cavity expansion solutions. An interface zone adjacent to the pile shaft comprising fine broken soil particles was observed to contract while shearing along the pile-soil interface. This mechanism offers an explanation for the degradation of shaft friction at a given soil horizon with increased pile penetration ('friction fatigue'), and a subsequent recovery of capacity over time ('set-up'). [ABSTRACT FROM AUTHOR]

A three-dimensional finite element modeling of high damping rubber bearings is studied. At first, the constitutive model of high damping rubber materials proposed by the writers is formulated in order to derive the constitutive tensor, which is required in the application of the finite element method. Second, a mixed finite-element method consistent with the proposed constitutive model is described. In this method, slightly compressible materials with rate form constitutive models are applied. Then, using the constitutive model and the finite-element method, a three-dimensional finite element model of high damping rubber bearings is constructed. The simulations by the model are found to be in good agreement with the experimental results of the bearing. Finally, complex deformation such as torsional or rotational deformation of the bearing are simulated by the finite-element model, and the design equations for these deformation are proposed on the basis of the simulations or experimental results. [ABSTRACT FROM AUTHOR]

An attempt is made to refine an engineering method of determining the limiting pressure on sandy beds of shallow foundations. Additional factors affecting Pu have been accounted for sufficiently correctly and successfully, and included in the same algorithm, presenting the computational results in a form that is convenient and customary for practical utilization. First results of comparison between computed and experimental pu values suggest their rather good correspondence. [ABSTRACT FROM AUTHOR]

The bearing capacity of shallow foundations is a classical problem with widespread applications, particularly in modern offshore engineering. Design is typically based on limit solutions for plane strain situations and vertical loading, with semi-empirical adjustments to allow for shape, inclination and eccentricity of the applied load, and for situations where the soil strength varies with depth. The ultimate accuracy of this approach is questionable, and indeed has been shown to be non-conservative where moment loading is involved. Although numerical techniques such as the finite element method are capable, in principle, of providing accurate solutions to specific situations, they are cumbersome to use for parametric studies, and also can lead to unacceptable errors for inexperienced users. The present paper presents new upper bound solutions for circular foundations on clay under general loading conditions. Computation of the three-dimensional mechanisms has been simplified through recent theoretical developments, and the derived failure envelopes offer good accuracy in comparison with finite element solutions. The approach not only provides a relatively simple computational basis for foundation design, regardless of the strength profile with depth, but also opens the door to novel upper bound solutions for a variety of geotechnical problems. [ABSTRACT FROM AUTHOR]