Elastic Settlement Analysis of Rigid Footings Relying On The “Characteristic Point” Concept

In the present paper, the problem of finding the location of the so-called “characteristic point” of flexible footings is revisited. As known, the settlement at the characteristic point, is equal to the uniform settlement of the respective rigid footing. The cases of infinitely long strips and circular footings are studied fully analytically. For the case of rectangular footings, analytical results (for flexible footings) are compared with the respective numerical results (for rigid footings) obtained from 3D finite element analysis (210 cases were examined). As shown, the location of the characteristic point may greatly deviate from the well-known values reported in the literature, as it strongly depends on the thickness and Poisson’s ratio value of the compressible medium. For rectangular footings this location also depends on their aspect ratio, L/B. The location of the characteristic point with respect to the center of footing for the various cases examined is given in tabular form. Strain influence area values (Aj=ρjEs/qB) are also given for the convenient calculation of the settlement (ρj) of footings, especially the rigid, rectangular ones; q is the uniform surcharge of footing and Es the soil modulus.

Numerical Modelling Observations of Settlement for Pad Footings Supported on Soft Clay Soil

Settlement calculation is an important part in the design of shallow foundations resting on soft soils. The size of the foundation, the depth of the footings, and the rise in ground water level are thought to influence settlement and have been the subject of much research for many years. Thus, this study compared several pad footing sizes using numerical techniques as the basis. The first objective of this study was to analyse soil and pad footing settlement, and to determine the optimal size of footing that withstands excessive settlement due to variation in the water table and the depth of the foundation. Three footing embedment depths of 1.5, 2, and 3m with three water table positions, at the GL (0m), 1.5, and 3m with an applied foundation concentrated load of 440 kN using five footing models of 1.5mx1.5m, 2mx1.5m, 2 m x 2 m, 2.5x1.5m, and 2.5x1.5m pad footing with a uniform thickness of 0.5m were considered. In this study, a 3D Plaxis simulation is used for predicting the settlement of shallow foundations on soft clay soils. Settlement results were discovered at various water table positions and foundation depths. The study found that the 2.5x2m footing was deemed the best among the simulated foundations, and the 3m foundation embedment was considered the best at shallow depths due to less excessive settlement than the other tested foundations. The settlement had a significant impact on the size of the foundation and the depth of the footing. The depth of the water table has a small impact on the settlement. Parametric analysis is also being used to gain a better understanding of the behaviour of the elastic settlement of various shallow foundations. It is found that the footing area increases, settlement decreases and vice versa.

Comparative Analysis of Kazakhstani and European Design Specifications: Raft Foundation, Pile Foundation, and Piled Raft Foundation

The introduction of Eurocode in Kazakhstan allows for the application of modern technological innovations and the elimination of technical barriers for the realization of international projects. It is significant to study the international standards and design requirements provided in Eurocode. This study presents a comparative analysis of Kazakhstani and European approaches for the geotechnical design of foundations and provides the design methods in the considered codes of practice. Three different types of foundations (i.e., raft, pile, and piled raft foundations) were designed following SP RK 5.01-102-2013—Foundations of buildings and structures, SP RK 5.01-103-2013—Pile foundations, and Eurocode 7: Geotechnical design for the Nur-Sultan soil profile. For all three types of foundations, the calculated results of bearing resistance and elastic settlement showed the conservativeness of Eurocode over SNiP-based Kazakhstani building regulations, as the values of bearing resistance and elastic settlement adhering to Kazakhstani code exceeded the Eurocode values. The difference between the obtained results can be explained by the application of higher values of partial safety factors by Eurocode 7. Sensitivity analysis of the bearing resistance on foundation parameters (i.e., raft foundation width and pile length) for the Kazakhstani and European approaches was performed to support the conclusions of the study.

Elastic Settlement Analysis of Rigid Rectangular Footings on Sands and Clays

In this paper an elastic settlement analysis method for rigid rectangular footings applicable to both clays and sands is proposed. The proposed method is based on the concept of equivalent shape, where any rectangular footing is suitably replaced by a footing of elliptical shape; the conditions of equal area and equal perimeter are satisfied simultaneously. The case of clay is differentiated from the case of sand using different contact pressure distribution, whilst, additionally, for the sands, the modulus of elasticity increases linearly with depth. The method can conveniently be calibrated against any set of settlement data obtained analytically, experimentally, or numerically; in this respect the authors used values which have been derived analytically from third parties. Among the most interesting findings is that sands produce “settlement x soil modulus/applied pressure” values approximately 10% greater than the respective ones corresponding to clays. Moreover, for large Poisson’s ratio (v) values, the settlement of rigid footings is closer to the settlement corresponding to the corner of the respective flexible footings. As v decreases, the derived settlement of the rigid footing approaches the settlement value corresponding to the characteristic point of the respective flexible footing. Finally, corrections for the net applied pressure, footing rigidity, and non-elastic response of soil under loading are also proposed.

Comparative Analysis of Kazakhstani and European Approaches for the Design of Shallow Foundations

The design of shallow foundations is performed in accordance with different building regulations depending on geotechnical and geological conditions. This paper involves the design calculations applying Kazakhstani and European approaches. The design of shallow foundations in Nur-Sultan city in Kazakhstan was implemented by the calculation of bearing capacity and elastic settlement in accordance with the design procedures provided in SP RK 5.01-102-2013: Foundations of buildings and structures, and Eurocode 7: Geotechnical design. The calculated results of bearing capacity and elastic settlement for two types of shallow foundations, such as pad foundation and strip foundation, adhering to Kazakhstani and European approaches are relatively comparable. However, the European approach provided higher values of bearing capacity and elastic settlement for the designed shallow foundation compared to the Kazakhstani approach. The difference in the results is explained by the application of different values of partial factors of safety for the determination of bearing capacity and different methods for the calculation of the elastic settlement of shallow foundations (i.e., elasticity theory and layer summation method).

Reducing Statistical Uncertainty in Elastic Settlement Analysis of Shallow Foundations Relying on Targeted Field Investigation: A Random Field Approach

The present paper deals with the practical problem of reducing statistical uncertainty in elastic settlement analysis of shallow foundations by relying on targeted field investigation with the aim of an optimal design. In a targeted field investigation, the optimal number and location of sampling points are known a priori. As samples are taken from the material field (i.e., the ground), which simultaneously is a stress field (stresses caused by the footing), the coexistence of these two fields allows for some points in the ground to better characterize the serviceability state of structure. These points are identified herein through an extensive parametric analysis of the factors controlling the magnitude of settlement; the number of different cases considered was 3318. This is done in an advanced probabilistic framework using the Random Finite Element Method (RFEM) properly considering sampling of soil property values. In this respect, the open source RSETL2D program, which combines elastic finite element analysis with the theory of random fields, has been modified as to include the function of sampling of soil property values from the generated random fields and return the failure probability of footing against excessive settlement. Two sampling strategies are examined: (a) sampling from a single point and (b) sampling a domain (the latter refers to e.g., continuous cone penetration test data). As is shown in this work, by adopting the proper sampling strategy (defined by the number and location of sampling points), the statistical error can be significantly reduced. The error is quantified by the difference in the probability of failure comparing different sampling scenarios. Finally, from the present analysis, it is inferred that the benefit from a targeted field investigation is much greater as compared to the benefit from the use of characteristic values in a limit state design framework.