Since the last three decades, several studies have been conducted related to improvement in bearing capacity of pavements, embankments, and shallow foundations resting on geosynthetic reinforced soil. Most of the work has been carried out on single layer soil e.g., sand or clay layer only. Very few studies are available on a double layer soil system; but no study is available on the local soil of Carbondale, Illinois. The present study investigates the physical and engineering properties of a local soil and commonly available sand and improvement in the bearing capacity of a local soil for a rectangular footing by replacing top of the local soil with sand layer and placing geogrids at different depths. Seven tests on the model footing were performed to establish the load versus settlement curves of unreinforced and reinforced soil supporting a rectangular foundation. The improvement in bearing capacity is compared with the bearing capacity of the local soil and double layer unreinforced soil system. The test results focus on the improvement in bearing capacity of local soil and double layer unreinforced soil system in non-dimensional form i.e., BCR (Bearing Capacity Ratio). The results obtained from the present study show that bearing capacity increases significantly with the increasing number of geogrid layers. The bearing capacity for double layer soil increases, by placing three inch sand layer at the top of local soil, was not significant. The bearing capacity of the local soil increased at an average of 7% with three inches sand layer. The bearing capacity for the double layer soil increases with an average of 16.67% using one geogrid layer at interface of soils (i.e., local soil and sand) with u/B equal to 0.67. The bearing capacity for the double layer soil increases with an average of 33.33% while using one geogrid in middle of sand layer having u/B equal to 0.33. The improvement in bearing capacity for double layer soil maintaining u/B equal to 0.33 and h/B equal to 0.33; for two, three and four number geogrid layer were 44.44%, 61.11%, 72.22%, respectively. The results obtained from this research work may be useful for the specific condition or similar type of soil available anywhere to improve the bearing capacity of soil for foundation and pavement design.

[pt] Os projetos de capacidade de suporte de estacas estão baseados em dados de ensaio de campo de maneira direta ou indireta. Devido a sua praticidade, os métodos empíricos são amplamente utilizados. No Brasil os métodos de Decourt e Quaresma (1978, 1982) e de Aoki e Velloso (1975) se destacam. Este trabalho procura avaliar o uso de dados de SPT e CPT para estimativa de parâmetros geotécnicos necessários na previsão de capacidade de suporte de estacas através de métodos teóricos. São apresentadas e avaliadas formulações empíricas de estimativa de parâmetros para materiais granulares e materiais argilosos. Outro elemento importante na previsão da capacidade de suporte é o estado de tensões atuante em torno da estaca que é analisado através de considerações a respeito do coeficiente de empuxo. Finalmente, são mostrados alguns resultados de provas de carga para a análise da seleção de parâmetros e do estado de tensões, além de uma avaliação dos métodos empíricos de previsão de capacidade de suporte. / [en] The main objective of this thesis is to discuss the applicability of in-situ tests like the Standard Penetration Test (SPT) and the Cone Penetration Test (CPT) to determine directly the design parameters to predict the bearing capacity of pile foundations. In case it will be considered the use of empirical correlation to indicate the mechanical properties of the soil in terms of shear resistance, and the application of these values directly in the classic formulation based on the theory of equilibrium limit to evaluate distinctly the shaft and the base resistance of piles. Adaptations of these values will be proceeded considering aspects related with the non-linear behavior of the soil; the mechanism of load transfer and the influence of the constructive aspects.The results obtained through this new methodology will be compared with experimental results, obtained from static and dynamic load tests and also with other empiric procedures that use the results obtained from in-situ tests to evaluate directly the bearing capacity of deep foundations.

The design of pile foundations in conventional geotechnical engineering practice is based on the soil mechanics principles for saturated soils. These approaches are also extended to pile foundations that are placed totally or partially above the ground water table (i.e., vadose zone), where the soil is typically in a state of unsaturated condition. Such approaches lead to unrealistic estimations of the load carrying capacity and the settlement behavior of pile foundations. Some studies were undertaken in recent years to understand the influence of the matric suction towards the bearing capacity of model pile foundations placed in unsaturated fine-grained and coarse-grained soils. The conventional   and methods were modified to interpret the contribution of shaft carrying capacity of single piles in fine-grained soils (e.g., Vanapalli and Taylan 2011, Vanapalli and Taylan 2012). Also, the conventional method has been used to understand the contribution of matric suction towards the shaft resistance in unsaturated sands (Vanapalli et al. 2010). One of the key objectives of the present research study is directed to determine the contribution of matric suction towards the bearing capacity and settlement behavior of model single pile foundations in unsaturated sands. A series of single model pile load tests were performed in a laboratory environment to study the contribution of the matric suction towards the total, shaft, and base bearing capacity of the model piles with three different diameters (i.e., 38.30, 31.75, and 19.25 mm) in two unsaturated sands (i.e., a clean commercial sand and a super fine sand). Hanging column method (i.e., plexi glass water container) was used to control the matric suction values in the compacted sands in the test tank by varying the water table. The results of the testing programs indicate the significant contribution of the matric suction towards the bearing capacity of single model piles (i.e., 2 to 2.5 times of base bearing capacity and 5 times of shaft bearing capacity under unsaturated conditions in comparison with saturated condition). The test results were interpreted successfully by modifying the conventional methods for estimating the pile shaft bearing capacity (i.e., β method) and base bearing capacity (i.e., Terzaghi 1943, Hansen 1970 and Janbu 1976). In addition, semi-empirical methods were proposed for predicting the bearing capacity of single model piles using the effective shear strength parameters (i.e., c' and ϕ') and the soil-water characteristic curve (SWCC). There is a good agreement between the measured and the predicted bearing capacity of single model piles using the semi-empirical models proposed in this study. In addition, numerical investigations were undertaken using the commercial finite element analysis program SIGMA/W (Geostudio 2007) to simulate the load-displacement (i.e., p-δ) behavior of the single model piles for the two sands (i.e., clean commercial sand and super fine sand) under saturated and unsaturated conditions. An elastic-perfectly plastic Mohr-Coulomb model that takes into account the influence of the matric suction was used to simulate the load-displacement (i.e., p-δ) behavior. The numerical approach proposed in this thesis is simple and only requires the information of the effective shear strength parameters (i.e., c' and ϕ'), the elastic modulus (i.e., Esat) under saturated conditions, the soil-water characteristic curve (SWCC), and the distribution of the matric suction with respect to depth. The approaches proposed in this thesis can be extended to determine the in-situ load carrying capacity of single piles and also simulate the load-displacement (i.e., p-δ) behavior. The studies presented in this thesis are promising and encouraging to study their validity in-situ conditions. Such studies will be valuable to implement the mechanics of unsaturated soils into geotechnical engineering practice.

It is evident from several studies that ultimate bearing capacities calculated by traditional methods are conservative and subjective. For large civil structures founded on spread footings, cost-effective and safer foundation could be achieved by adopting optimum ultimate bearing capacity values that are based on an objective and pragmatic analysis. There is a pressing need to modify the existing methods for accurate estimation of the bearing capacities of rocks for spread footings. In practice, foundation bearing capacities of rock masses are often estimated using the presumptive values from Building Officials Code Administrators, National Building Code, and methods adopted by the American Association of State Highway and Transportation Officials. However, the estimated values are often not realistic, and site-specific analyses are essential. In this study, geotechnical reports and drill-log data from successful geotechnical design projects founded on a wide range of granites in eastern Tennessee were consulted. Different published methods were used to calculate ultimate bearing capacity of rock mass. These methods included Peck, Hansen and Thornburn, Hoek and Brown, Army Corps of Engineers, Naval Facilities Engineering Command, and Terzaghi's general bearing capacity equations. Wide variation was observed in the calculated ultimate bearing capacity values, which ranged over about two orders of magnitude. Only two of the methods provided realistic results when validated with plate-load test data from similar rocks.

The design of foundation in normal soil conditions is governed by bearing capacity, minimum depth of foundation and settlement. However, foundation design in karst regions needs to consider an additional criterion associated to the possibility of subsurface subsidence and ravelling sinkholes. Under this environment, alternative techniques are needed to improve the subsurface soil. In this study general background information is given to understand the geological characteristics of Central Florida and why this area is considered to be a karst region and susceptible to sinkholes formation. Traditional foundation design techniques on karst regions are addressed in this paper. Finally, the use of a network of three subsurface horizontal piles is proposed and the effect on stress increase and soil bearing capacity for footing due to the horizontal piles is investigated. Finite element computer software is used to analyze the stress distribution under different conditions and the results are discussed. The objective of this study is to determine whether or not horizontal piles under a circular footing at the sinkhole site is a viable solution to reduce the stress increase in the soil induced by the footing load. The horizontal piles located at a certain depth below the center of the footing intercepts the cone of pressure due to the footing load. Also, it is the purpose of this research to determine the effect on the soil bearing capacity for footing due to the proposed horizontal piles at the sinkhole prone area. In 1983 Baus, R.L and Wang, M.C published a research paper on soil bearing capacity for strip footing above voids. In their research, a chart for soil bearing capacity for strip footing located above a void was presented. However, in this paper we present a chart for circular footing size as a function void location and a design chart for circular footing size with a network of three underground piles. The result indicates that with the horizontal piles placed above the cavity, the stress increase caused by the footing load substantially decreases as compared to the situation of no horizontal piles, thus increases the soil bearing capacity for the normal design of footing size. The approach of using the horizontal piles placed in between the footing and the subsurface cavity is a new concept that has not been experienced previously. The results are strictly based on the analytical model of finite element program. Before full implementation for the construction practice, further research and experimental work should be conducted.

No / Laboratory scale model slopes reinforced with waste carpet fibers were made in a rigid tank with dimensions of 800 mm x 300 mm x 500 mm. Bearing capacities of the strip footing rested on non-reinforced and fiber-reinforced model slopes with 1%, 3% and 5% fiber content were compared at 20% footing displacement ratio. The influence of location of footing on the bearing capacity was studied with placing the footing at different edge distances from the crest of the footing (i.e., 150 mm, 100 mm and 0). Suction probe sensors were installed at appropriate locations on the rear side of the model slope to measure the pore-water pressure generated due to the footing pressure. Results showed that fiber reinforcement increased the bearing resistance of the model slopes significantly. Inclusion of 5% fiber increased the bearing resistance by 271% compared to that of non-reinforced model slope at the footing edge distance ratio of 3. The location of footing was found to affect the load-carrying capacity of the fiber-reinforced model slope. The increase in the edge distance ratio of the footing increased the load-carrying capacity of the model slope.

This paper presents results of a comprehensive investigation undertaken to quantify the efficiency of using reinforcement layers in order to enhance the bearing capacity of soils that are characterised by the existence of localised soft pockets. Small-scale model experiments using two dimensional tank were conducted with beds created from well graded sand with mean particle size of 300 μm but prepared with different dry densities. A relatively softer material was embedded at predetermined locations within the sand beds so as to represent localised soft pockets. Various arrangements of soil reinforcement were tested and compared against comparable tests but without reinforcement. In total 42 tests were carried out in order to study the effect of the width and depth of the soft pocket, the depth of one reinforcing layer and the length and number of reinforcing layers on the soil bearing capacity. The results show clearly that the ultimate bearing capacity reduces by up to 70% due to the presence of a soft pocket. It was also noted that the proximity of the soft pocket also influenced the bearing capacity. Reinforcing the soil with a single layer or increasing the length of reinforcement is not as effective as was anticipated based on previous studies. However, bearing capacity increased significantly (up to 4 times) to that of unreinforced sand when four layers of reinforcement were embedded. The results suggest that rupture of the bottom reinforcement layer is imminent in heavily reinforced sand beds overlying soft pockets and therefore its tensile strength is critical for successful reinforcement.

This thesis presents experimental work and numerical analysis that has been undertaken to assess the bearing capacity of perforated offshore foundations. Perforated foundations may be used to support subsea infrastructure, including as mudmats into which a number of perforations have been made, or as grillages which consist of a series of structurally connected strip footings. Larger gravity base foundations, such as for offshore wind turbines or oil and gas platforms, may adopt a single central perforation. The advantages of using perforated foundations can include reduced material requirements and easier offshore handling as a result of smaller weight and lower hydrodynamic forces during deployment. Limited guidance currently exists for assessing the bearing capacity of these foundation types. Bearing capacity of perforated foundations has been examined in this thesis under conditions of combined vertical, horizontal and moment loading which is typical in offshore settings. Undrained soil conditions have been considered, except for the case of grillages in which drained conditions are often most relevant. Experimental work has included centrifuge testing of ring and square annular foundations on clay, and 1g testing of grillage foundations on sand. Finite element modelling has also been undertaken to assess perforated foundation capacity. A Tresca material subroutine (UMAT) and an adaptive meshing scheme have been developed to improve the accuracy of the finite element analysis carried out. The results showed that perforated foundations can be an efficient foundation solution for accommodating combined loading. As a ratio of their vertical load capacity, perforated foundations may be able to withstand higher moment and horizontal loads compared with unperforated foundations. The experimental and numerical results have been used to develop design expressions that could be employed by practitioners to estimate the vertical and combined load bearing capacity of these foundation types.

O presente trabalho tem como objetivo avaliar a utilização de um penetrômetro manual para quantificar a resistência à penetração em um solo poroso e não-saturado. Os ensaios foram efetuados com monitoração de sucção, obtendo-se assim correlações entre resistência à penetração do penetrômetro e a sucção do solo. Os valores de tensão de ruptura obtidos nos ensaios penetrométricos foram comparados com valores de capacidade de carga de ensaios de placa e de provas de carga em sapatas realizados à mesma profundidade, no mesmo local, com medidas simultâneas de sucção. Finalmente, o trabalho comprova a influência da sucção nos resultados dos ensaios realizados / The objective of this work is to evaluate the use of a hand penetrometer to quantify the penetration resistance of a porous and unsaturated soil. The tests were done with suction monitoring, thus, it was obtained correlation between resistance of the penetrometer penetration and the soil suction. The values of rupture pressure obtained by the penetrometer tests were compared with values of bearing capacity of plate load tests and footing load tests, that were done at the same deep and at the same location, with suction measurement. Finally, this work proves the influence of the suction on the tests results

Large diameter piles are widely used as foundations to support buildings, bridges, and other structures. As a result, it is critical for the field to have an optimized approach for quality control and efficiency purposes to measure the suggested number of load tests and the required measured capacities driven piles. In this thesis, an analysis of a load test program designed for proposed bridge replacements at Kentucky Lake is performed. It includes a detailed site exploration study with in-situ and laboratory testing. The pile load test program included monitoring of a steel H-pile and steel open ended pipe pile during driving and static loading. The pile load test program included static and dynamic testing at both pile testing locations. Predictions of both pile capacities were estimated using commonly applied failure criterion, and a load transfer analysis was carried out on the dynamic and static test data for both piles. The dynamic tests were then compared to the measured data from the static test to examine the accuracy. This thesis concludes by constructing t-z and q-z curves and comparing the load transfer analyses of the static and dynamic tests.