Design Of Shallow Foundations Research Articles

Assessing the effects of different foundation base shapes on settlement and heaving in expansive clay: numerical analysis

AbstractThis paper investigates the behavior of shallow foundations with different base shapes on expansive soils under various Stresses conditions and different slopes of the base. Expansive soils are soils that undergo significant volume changes due to variations in moisture content, which can cause severe damage to structures built on them. The shape of the foundation base can influence the magnitude and distribution of the soil pressures, as well as the deformation and cracking of the foundation. The paper presents a numerical analysis using a finite element method with Plaxis 3D. The paper also proposes some recommendations for the optimal design of foundation base shapes on expansive soils. The numerical results show that the foundation base shape has a significant effect on the stress and displacement distributions in the soil and the foundation and that some shapes perform better than others in terms of reducing the soil pressures. The paper provides some useful insights for the design and construction of shallow foundations on expansive soils.

Sustainable Design of Onshore Wind Turbine Foundations

In recent times, wind power has emerged as a prominent contributor to electricity production. Minimizing the costs and maximizing sustainability of wind energy is required to improve its competitiveness against other non-renewable energy sources. This communication offers a practical approach to assess the sustainability of wind turbine generator foundations from a 3-dimensional holistic point of view. Specifically, the main goal of this study is to analyse the life cycle impacts of one shallow foundation design comparing three different concrete alternatives: conventional concrete, concrete with 66-80% of blast furnace slags and concrete with 20% fly ash, and then to apply a Multi-Criteria Decision-Making model based on TOPSIS method to evaluate and compare the resulting sustainability of each alternative considered. The study results in a methodology for quantifying sustainability rather than simply qualifying it. Therefore, this methodology can be employed for design optimization, such as geometry and materials, with a sustainable perspective in mind. Specifically in this study, concrete with blast furnace slags emerges as the top-ranked sustainable alternative, followed by conventional concrete in second place, and fly ash option in third position.

Settlement prediction of shallow foundations for quality controls of sandy hydraulic fills

This paper describes a procedure for settlement prediction of shallow foundations on carbonate sands, but it is fully applicable and valid for siliceous sands. For practical purposes, the design of shallow foundations resting on medium dense and dense granular soils is typically governed by limiting settlement to tolerable values. Predicting foundation settlement is therefore important, but in standard practice it is necessarily based on indirect (and therefore often conservative) determinations of soil compressibility (or modulus), due to the intrinsic difficulties in obtaining direct measurements.While numerical analyses incorporating non-linear soil behaviour may be a preferred method for computing expected total and differential settlement of shallow foundations of given geometry and stiffness on sand under static loading, the method described in this paper consists of a simplified and expeditious method based on equivalent linear elasticity. The method uses: i) the elastic soil stiffness profile at small strain, E0(z) obtained from the shear wave velocity as the primary measurement of deformability and ii) the reduction in modulus as a function of strain magnitude, E(ε) to account for stiffness non-linearity. The beneficial effect on the soil initial stiffness of the applied footing load is also considered. The method was developed as an on-site tool for checking the compaction of hydraulic fills made of carbonate sand to form artificial islands, but its application can be extended to other natural and anthropogenic coarse-grained materials.

Integration of GIS with the Generalized Reciprocal Method (GRM) for Determining Foundation Bearing Capacity: A Case Study in Opolo, Yenagoa Bayelsa State, Nigeria

This study addresses the pressing need to assess foundation bearing capacity in Opolo, Yenagoa, Bayelsa State, Nigeria. The significance lies in the dearth of comprehensive geotechnical data for construction planning in the region. Past research is limited and this study contributes valuable insights by integrating Geographic Information System (GIS) with the Generalized Reciprocal Method (GRM). To collect data, near-surface seismic refraction surveys were conducted along three designated lines, utilizing ABEM Terraloc Mark 6 equipment, Easy Refract, and ArcGIS 10.4.1 software. This methodology allowed for the determination of key geotechnical parameters essential for soil characterization at potential foundation sites. The results revealed three distinct geoseismic layers. The uppermost layer, within a depth of 0.89 to 1.50 meters, exhibited inadequate compressional and shear wave velocities and low values for oedometric modulus, shear modulus, N-value, ultimate bearing capacity, and allowable bearing capacity. This indicates the presence of unsuitable, soft, and weak alluvial deposits for substantial structural loads. In contrast, the second layer (1.52 to 3.84 m depth) displayed favorable geotechnical parameters, making it suitable for various construction loads. The third layer (15.00 to 26.05 m depth) exhibited varying characteristics. The GIS analysis highlighted the unsuitability of the uppermost layer for construction, while the second and third layers were found to be fairly competent and suitable for shallow footing and foundation design. In summary, this study highlights the importance of geotechnical surveys in Opolo’s construction planning. It offers vital information for informed choices, addresses issues in the initial layer, and suggests secure, sustainable construction options.

Hazard Curves for Reliability Assessment of Strip Footings on Spatially Varying Cohesive Soils

The present study aimed to create a series of hazard curves against maximum total settlement and angular rotation of strip footings for probabilistic shallow foundation design on clays. Random field finite element method (RFEM) was adopted with elasto-plastic clay-like soil behavior, deformation modulus (Ed) and shear strength parameters (c and ) were employed as random field inputs. Parameters were defined and assigned to the analysis models with varying correlation lengths (h, v). Models have been iteratively solved one thousand times, and output distributions of maximum settlement and angular rotations were recorded. Probability density functions (PDF) were fitted to the outputs, and probability of failure (Pf) for footing deformation limits was subsequently estimated. Proposed hazard curves for two anisotropy and three variability categories were developed employing the estimated Pfs. The method proposed has been validated using an independent database of in-situ results, and a worked example was provided to illustrate the implementation of the process. The key contribution of the research is to form hazard curves for shallow foundations considering elasto-plastic soil behavior with the impact of all influencing parameters, respecting the limit values for foundation deformation in the design codes. The proposed technique offers a probabilistic evaluation of strip footings with spatial variation of clayey soils and a valid method for the reliability-based design of foundations in the serviceability limit state.

Using GIS for the allowable soil bearing capacity estimation according to the Terzaghi (1943) equation in Eskişehir city center, Türkiye

In foundation engineering, it is necessary to calculate the bearing capacity of soils. The allowable soil bearing capacity required for foundation design is calculated through various empirical methods using geotechnical parameters such as specific gravity and angle of internal friction. Standard Penetration Test (SPT) values of the soil are used in these calculations. Therefore, soil tests which engineers need, are costly and time-consuming. This study aims to determine the soil bearing capacity of Eskişehir city according to the Terzaghi (1943) equation and present soil bearing capacity maps for shallow foundations. The geotechnical parameters of the soil were obtained from 40 borehole data made in the field. Within the scope of the study, according to the Terzaghi (1943) equation bearing capacity maps were created for 0-5 m depth to provide an overview of the bearing capacity of Eskişehir soil. These maps were made in the Geographic Information System (GIS), which has a database that stores and analyses regular data. In addition, these maps can assist engineers working on shallow foundation design on the site.

Quantile-Based Design and Optimization of Shallow Foundation on Cohesionless Soil Using Adaptive Kriging Surrogates

Quantile-Based Design and Optimization of Shallow Foundation on Cohesionless Soil Using Adaptive Kriging Surrogates

Combined rupture mechanism of shallow foundations under drained conditions

Current technical standards and codes of practice for shallow foundation design at the ultimate limit state require the analysis of rupture mechanisms that involve only the soil by assuming that the foundation structure does not undergo any yielding or rupture, but do not consider the case of combined rupture mechanisms in the soil and in the foundation structure, a situation that was recently observed in experiments on wind turbine foundations. By means of special numerical techniques for the analysis of soil–foundation interaction at the ultimate limit state under drained conditions, this work extends previous numerical investigations on undrained conditions and shows that the internal actions, the bearing contact pressures and the contact shear stresses beneath a yielding, flexible shallow foundation are much different with respect to those evaluated under undrained conditions. In any case, it is shown that foundation plasticisation leads to a potentially strong reduction of the bearing capacity depending on the loading condition. This work draws attention to some possible design situations that may be relevant for the optimised structural design of shallow foundations and paves the way to the development of simplified approaches that could be used in the usual design practice.

Seasonal Subsidence and Heave Recorded by Borehole Extensometers in Houston

Seasonal ground movements, particularly subsidence and heave, present a great challenge for the design of roadways, parking lots, underground utility lines, and buried culverts. The US Geological Survey has been operating 13 deep borehole extensometers in Houston, Texas, for land subsidence monitoring since the 1970s and the early 1980s. The half-century extensometer datasets provide direct and continuous measurements of seasonal ground movements in the vertical direction. The Houston global positioning system (GPS) network (HoustonNet) provides independent measures for the timely evaluation of extensometer data. According to this study, shallow expansive soils can induce up to 4 cm (peak-to-trough) seasonal subsidence and heave, and deep sediments can further produce up to 2 cm seasonal subsidence and heave. The latter is primarily caused by the seasonal fluctuations of hydraulic heads in the lower Chicot and upper-Evangeline aquifers, varying considerably over time and space. The results from this study are important for determining potential vertical movement (PVM) for the design of pavements and shallow foundations and for the optimization of groundwater management in the Houston region.

Undrained strength of clay determined from simple shear test

The undrained shear strength of clay is an important parameter for the design of embankments, shallow foundations, and pile foundations. Among the various methods of testing undrained strength, the simple shear is essential when the shearing mode of the soil surrounding the pile is similar to that in a simple shear test. This study employs a series of undrained strength tests with a Berkeley simple shear apparatus. Three reconstituted natural clays and one artificial clay were tested with a range of coefficients of consolidation. The influence factors, including sample pre-consolidation pressure, saturation back pressure, shearing rate, height of specimen, consolidation stress, and lateral stress ratio, were investigated in undrained simple shear tests. The failure mode in simple shear and corresponding strength parameters are also examined. Based on the test data set, models for describing the undrained strength with simple shear for high plasticity clays are developed and compared to test data for normally consolidated reconstituted clay. Good agreement between models and intact Onsoy clay is also observed when allowance is made for the coefficient of consolidation and strength parameters of undisturbed clay and in situ stress state.

Bearing behaviour of shallow foundations for wind energy converters on sandy soils under cyclic eccentric loads

ABSTRACT For wind energy converters (WECs), the behaviour under cyclic loading is critical to the operation and lifetime, especially because the cyclic load is associated with eccentricity. In various geotechnical design standards, the eccentricity of shallow foundation for WECs is supposed to be limited. In the German geotechnical design standards, it is specifically required that no gapping shall occur under quasi-static eccentric load. This verification is often decisive in practical design and leads to potential over-dimensioning. The one possible favourable effect of limiting the gapping of WECs on non-cohesive subsoils is to limit the accumulation of permanent rotation under cyclic loads indirectly. In this article, the experimental results of cyclic rotation accumulation of shallow foundation on non-cohesive subsoils from literatures and own medium scale tests are discussed. It is shown that the gapping has no direct influence on the rotation accumulation rate, instead it is the load magnitude relative to the bearing capacity of foundation that is decisive to the cyclic rotation accumulation behaviour. Based on these observations, the verification ‘no gapping under quasi-static eccentric load case’ seems dispensable in the design of WEC shallow foundations on non-cohesive subsoils.

Effect of structural inertia on liquefaction-induced settlements of shallow foundations

The majority of published research on the performance-based design of shallow foundations on liquefiable soil focuses on seismic settlement accumulation by neglecting soil-structure-interaction (SSI) effects. On the other hand, SSI effects prove dominant when the foundation soil is non-liquefiable. Thus, the aim of this paper is to investigate the dynamic response of structure-foundation-soil (SFS) systems by examining the role of structural inertia on the performance of shallow foundations on liquefied soil, through a series of 3D fully coupled nonlinear numerical analyses of SFS systems. As a first step, the nonlinear fundamental period of vibration of the SFS system is correlated to the key system and excitation parameters. Next, in order to isolate the effects of structural inertia, shear-induced seismic settlements of SFS systems in liquefied soil are compared with the respective settlements of conjugate foundation-soil (FS) systems that apply the same static contact pressure on the foundation soil. Finally, approximate relations are proposed for the effects of structural inertia on liquefaction-induced settlements of shallow foundations, based on a multivariable statistical analysis of the numerous parametric numerical estimates.

Calibration of resistance factors for design of shallow foundations against sliding

The design of shallow foundations typically proceeds by using the load and resistance factor design (LRFD) methodology to avoid various limit states with some probability. This paper looks at the sliding limit state of shallow foundations, and the sliding resistance factors required for the LRFD approach are estimated using reliability analyses of surface strip foundations. Cohesive and frictional soils are separately studied under wind loading conditions. Monte Carlo simulations are used to estimate the sliding failure probability of foundation designs on cohesive soils, and an analytical method is developed for frictional soils. The results indicate the existence of a “worst case” correlation length for cohesive soils, and the sliding resistance factor required to achieve target maximum lifetime failure probabilities is around 0.4–0.65 for moderate soil variability. For frictional soils, the required sliding resistance factor is about 0.5–0.85 for ν ϕ′ = 0.15. Overall, the sliding resistance factors recommended here agree well with the resistance factors of ϕ gu = 0.6 for cohesive soils and ϕ gu = 0.8 for frictional soils stipulated by geotechnical LRFD code provisions in Canada. The analyses can be used to estimate the reliability of current designs and can also aid the calibration of geotechnical design codes.

Sub-Surface Geotechnical Data Visualization of Inaccessible Sites Using GIS

Geotechnical investigation, in hilly areas, for high-rise projects, becomes a problematic issue and costly process due to difficulties in mobilization and assembling the drilling equipment on mountainous terrains. The objective of this study is to map soil properties of study areas, especially at inaccessible sites, for reconnaissance. Digital soil maps for Tehsil Murree, Pakistan, have been developed using the emerging Geographical Information System (GIS). The research work involved the creation of an exhaustive database, by collecting and rectifying geotechnical data, followed by the digitization of the acquired data through integration with GIS, in an attempt to visualize, analyze and interpret the collected geotechnical information spatially. The soil data of 205 explanatory holes were collected from the available geotechnical investigation (GI) reports. The collection depth of soil samples, which were initially used for the design of deep and shallow foundations by different soil consultancies in the Murree area, was approximately 50 ft. below ground level. Appropriate spatial interpolation methods (i.e., the Kriging) were applied for the preparation of smooth surface maps of soil standard penetration tester number values, soil type and plasticity index. The accuracy of developed SPT N value and plasticity maps were then evaluated using the linear regression method, in which the predicted values of soil characteristics from developed maps and actual values were compared. SPT N value maps were developed up to a depth of 9.14 m below ground level and at every 1.52 m interval. The depth of refusal was considered in the developed maps. Soil type and plasticity maps were generated up to 15.24 m depth, again at every 1.52 m intervals, using color contours, considering the maximum predicted foundation depth for high-rise projects. The study has implications for academics and practitioners to map the soil properties for inaccessible sites using GIS, as the resulting maps have high accuracy.

Spatially variable soils affecting geotechnical strip foundation design

Natural soil variability is a well-known issue in geotechnical design, although not frequently managed in practice. When subsoil must be characterized in terms of mechanical properties for infrastructure design, random finite element method (RFEM) can be effectively adopted for shallow foundation design to gain a twofold purpose: (1) understanding how much the bearing capacity is affected by the spatial variability structure of soils, and (2) optimisation of the foundation dimension (i.e. width B ). The present study focuses on calculating the bearing capacity of shallow foundations by RFEM in terms of undrained and drained conditions. The spatial variability structure of soil is characterized by the autocorrelation function and the scale of fluctuation ( δ ). The latter has been derived by geostatistical tools such as the ordinary Kriging (OK) approach based on 182 cone penetration tests (CPTs) performed in the alluvial plain in Bologna Province, Italy. Results show that the increase of the B / δ ratio not only reduces the bearing capacity uncertainty but also increases its mean value under drained conditions. Conversely, under the undrained condition, the autocorrelation function strongly affects the mean values of bearing capacity. Therefore, the authors advise caution when selecting the autocorrelation function model for describing the soil spatial variability structure and point out that undrained conditions are more affected by soil variability compared to the drained ones. • RFEM is able to consider the soil variability structure in strip foundation design. • Bearing capacity mean value is affected by soil spatial variability. • Bearing capacity is affected by autocorrelation function model. • Coefficient of variation COV reduces as the foundation size increases. • Both drained and undrained soil conditions show similar COV reduction.

Load and resistance factor design versus reliability-based design of shallow foundations

ABSTRACT The load and resistance factor design (LRFD) approach employed in geotechnical design codes is often calibrated using the reliability-based design (RBD) method. However, the LRFD may not achieve the target safety level exactly. This paper makes comparisons between the LRFD and RBD by considering the ultimate and serviceability limit state design of strip foundations. The RBD is carried out via the Random Finite Element Method. It is found that the failure probability and the resulting foundation width for ULS obtained using the RBD increase with the soil spatial correlation length, gradually reaching a plateau. The comparison between the LRFD and RBD results for ULS suggests that the LRFD is conservative for low to medium soil variability, particularly at smaller correlation lengths. The reliability-based SLS design is less dependent on the soil correlation length, particularly for lower coefficients of variation of the soil elastic modulus. However, a resistance factor of 1.0 for SLS is unconservative, and resistance factors of 0.65, 0.7 and 0.8 are better aligned with the RBD when the target failure probabilities are 1×10−3, 1×10−2 and 1×10−1. The current study can be used to guide the design of shallow foundations and the calibration of the LRFD approach.

Development of a Cost-Based Design Model for Spread Footings in Cohesive Soils

The use of cost-effective construction design approaches is an emerging concept in the field of sustainable environments. The design of the foundation for the construction of any infrastructure-related building entails three basic requirements, i.e., serviceability limit state (SLS), ultimate limit state (ULS), and economics. Engineering economy coupled with safety are the two main essentials for a successful construction project. The conventional design approaches are based on hit and trial methods to approach cost-effective design. Additionally, safety requirements are prioritized over the economic aspect of foundation design and do not consider safety requirements and cost simultaneously. This study presents a design approach that considers foundation construction costs while satisfying all the technical requirements of a shallow foundation design. This approach is called an optimization process in which the cost-based isolated foundation design charts were developed based on the field SPT N data. The design charts are the first of their kind for the robust design of foundations and can be used to compare the economic impact of different bearing capacity models. Furthermore, the design framework considers the quantitative impact of the different applied factors of safety values in terms of cost. The results show that Vesic’s equation yields higher values of bearing capacities than Terzaghi and Meyerhof. On the other hand, Vesic’s theory offers a 37.5% reduction in cost as compared to the conventional design approach of the foundation for isolated footing.

Seismic Reliability-Based Design Versus Safety-Factor Based Design of Shallow Foundation Near a slope

Seismic Reliability-Based Design Versus Safety-Factor Based Design of Shallow Foundation Near a slope

Effective Hybrid Soft Computing Approach for Optimum Design of Shallow Foundations

In this study, an effective intelligent system based on artificial neural networks (ANNs) and a modified rat swarm optimizer (MRSO) was developed to predict the ultimate bearing capacity of shallow foundations and their optimum design using the predicted bearing capacity value. To provide the neural network with adequate training and testing data, an extensive literature review was used to compile a database comprising 97 datasets retrieved from load tests both on large-scale and smaller-scale sized footings. To refine the network architecture, several trial and error experiments were performed using various numbers of neurons in the hidden layer. Accordingly, the optimal architecture of the ANN was 5 × 10 × 1. The performance and prediction capacity of the developed model were appraised using the root mean square error (RMSE) and correlation coefficient (R). According to the obtained results, the ANN model with a RMSE value equal to 0.0249 and R value equal to 0.9908 was a reliable, simple and valid computational model for estimating the load bearing capacity of footings. The developed ANN model was applied to a case study of spread footing optimization, and the results revealed that the proposed model is competent to provide better optimal solutions and to outperform traditional existing methods.

Application of wave equation theory to improve dynamic cone penetration test for shallow soil characterisation

Among the geotechnical in situ tests, the dynamic penetration test (DPT) is commonly used around the world. However, DPT remains a rough technique and provides only one failure parameter: blow count or cone resistance. This paper presents an improvement of the dynamic cone penetration test (DCPT) for soil characterisation based on the wave equation theory. Implemented on an instrumented lightweight dynamic penetrometer driving with variable energy, the main process of the test involves the separation and reconstruction of the waves propagating in the rods after each blow and provides a dynamic cone load-penetration (DCLT) curve. An analytical methodology is used to analyse this curve and to estimate additional strength and deformation parameters of the soil: dynamic and pseudo-static cone resistances, deformation modulus and wave velocity. Tests carried out in the laboratory on different specimens (wood, concrete, sand and clay) in an experimental sand pit and in the field demonstrated that the resulting DCLT curve is reproducible, sensitive and reliable to the test conditions (rod length, driving energy, etc.) as well as to the soil properties (nature, density, etc.). Obtained results also showed that the method based on shock polar analysis makes it possible to evaluate mechanical impedance and wave velocity of soils, as demonstrated by the comparisons with cone penetration test (CPT) and shear wave velocity measurements made in the field. This technique improves the method and interpretation of DPT and provides reliable data for shallow foundation design.