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The widely differing factors of safety obtained by strength reduction and load increase in the ultimate bearing capacity of foundations have been reexamined analytically. In most cases, factors of safety based on load increase need to be higher than those based on strength reduction to achieve the same level of safety in design. The greater sensitivity of foundation systems to strength reduction over load increase may impact the choice of factors in ultimate limit state design. [ABSTRACT FROM AUTHOR]

Two geotechnical centrifuge tests were designed to elicit the influence of soil-foundation-structure interaction (SFSI) and structure-soil-structure interaction (SSSI) effects on the seismic demands of an inelastic frame structure founded on individual spread footings. Four experimental cases were considered: (1) SFSI of an individual inelastic frame structure (baseline case); (2) in-plane SSSI between the frame structure and a large elastic wall structure designed to respond predominately in a rocking mode; (3) anti-plane SSSI between the frame and wall structures; and (4) combined in-plane and anti-plane SSSI between the frame structure and two wall structures. Results from Cases 1, 2, and 4 are analyzed considering 13 demand parameters. The peak seismic demands from the baseline case are compared to the peak demands from the SSSI cases to elicit the impacts of building adjacency. The number of earthquake motions that resulted in increases or decreases in the seismic demands in the frame structure are tracked for the SSSI cases. For these tests, SSSI consistently results in increased peak foundation moment and foundation base shear demands, regardless of the geometric layout of the structures. These increases propagate throughout the superstructure, resulting in increases in moment, shear and curvature ductility demands in the structural components. SSSI effects are observed to be most significant for low-to-moderate intensity earthquake motions, suggesting that particular consideration should be given to the likelihood of SSSI for highly probable earthquakes. [ABSTRACT FROM AUTHOR]

This paper reports results from centrifuge model tests that provide insight into the behavior of rectangular foundations (representing earthmoving equipment) during penetration, with freedom in rotation, adjacent to a sand embankment (cover layer), into a weaker clay layer (representing mine tailings). A parametric study was used to explore the relevant range of the setback ratio, slope height ratio, normalized clay strength and its nonhomogeneity, and foundation base geometry. The effect of these nondimensional parameters on the penetration resistance profile is discussed in the context of the likelihood and severity of failure. The failure of a flat-based rectangular foundation was less severe than that associated with a strip foundation, and the corresponding measures reduced with the increasing setback ratio (l) and slope height ratio (h). No rotational failure occurred for λ (Su,av/γcB)cr >8 (where su,av/γcB is the average normalized strength of the lower clay layer) or η≥0:604, regardless of strength nonhomogeneity and the normalized strength of the bottom clay layer. The addition of small skirts to the base of the rectangular foundation assisted in reducing the likelihood and severity of failure significantly, with the exception of γ=0.19 and η=0.264. Expressions were proposed for calculating the modified bearing capacity factors. [ABSTRACT FROM AUTHOR]

Conventional bearing capacity analyses for shallow foundations placed on slopes use a modified set of bearing capacity factors based on soil properties, footing geometry, and slope configuration, but are restricted to purely cohesionless or purely cohesive soils. This approach is adequate for establishing bearing capacity on engineered fills with controlled foundation properties, yet does not adequately address design for bearing capacity on soils that have both cohesion and internal frictional resistance--a common scenario for native soils. This role becomes increasingly important in design for mechanically stabilized earth walls, which are often placed on slopes of native c'-φ' soils in which the bearing capacity can often be the critical design constraint. Prior approaches to bearing capacity on horizontal ground for c'-φ' soils utilize principles of limited state plasticity in their formulation, yet the most commonly applied bearing capacity approaches on slopes use semiempirical formulations that employ mutually exclusive soil strength parameters. In this work, results are attained using upper-bound limit state plasticity failure discretization scheme, known as discontinuity layout optimization (DLO), which uses nonassumptive failure geometry (under translational kinematics) in its formulation. The values presented demonstrate important components in consideration of bearing capacity for strip footings placed adjacent to slopes of c'-φ' soils, in particular, the relationship between soil strength properties, slope height to footing width ratio, slope angle, and critical collapse mechanism. A set of reduction coefficients that can be directly applied to the classical bearing capacity formulation is presented for ease of application. [ABSTRACT FROM AUTHOR]

The San Jacinto Monument was built in 1936 to celebrate the 100 year anniversary of the battlefield victory that gave Texas its freedom. Ray Dawson was in charge of the foundation design and decided to instrument the foundation to monitor the settlement of the Monument. The settlement has been recorded since 1936 and provides a very valuable long-term record. This settlement and other geotechnical data were studied and reported by Briaud and his co-authors in 2007. That study was based on data available at the time, which was primarily from a 61-m-deep boring in 1953. In 2007, Fugro and Texas A&M University drilled a new boring with sampling to a depth of 78 m, conducted in situ tests to 36 m, and laboratory tests on the samples recovered. Updated settlement calculations are provided using this new data; they show reasonably good agreement with modern settlement techniques. One of the issues possibly affecting the settlement readings is the subsidence of the ground surface, which can reach 3 m in that area of Houston. A second part of this article presents calculations and numerical simulations to evaluate the influence of subsidence on the recorded settlement of the Monument. It is shown that the true settlement of the SJM is 295 mm while the measured settlement is 328 mm. The reduction is due to the different influence of the subsidence on the settlement of the shallow benchmark and of the Monument. [ABSTRACT FROM AUTHOR]

This paper presents the results of a series of shake table tests of two 460-mm-diameter columns supported on 1.5-meter-square shallow rocking foundations. The tests were conducted using the Large Outdoor High-Performance Shake Table of the Network for Earthquake Engineering Simulation at the University of California at San Diego. The first specimen was aligned with the uniaxial direction of shaking, and the second was positioned in a skew configuration. The specimens were placed inside a soil-confining box 10.1 m long and 4.6 m wide with a 3.4-m height of clean sand compacted at 90% relative density. Three series of tests were performed; each had different groundwater and backfill conditions. The test protocols included up to six historical ground motions and resulted in peak drift ratios up to 13.8%. For peak drift ratios up to 6.9%, the rocking foundations performed very well, with residual drift ratios between 0.5 and 0.9% depending on the backfill conditions and with minimal settlements and no structural damage. [ABSTRACT FROM AUTHOR]

Scour is the removal of soil around bridge supports due to water flow during floods. One of the major problems with scour is in the case of unknown bridge foundations. Bridges with unknown foundations are listed in the National Bridge Inventory as having insufficient data for scour evaluation, particularly regarding foundation depth. Knowing the foundation depth is a critical component of scour risk assessment. Multiple nondestructive testing methods are currently used to determine the depth of unknown bridge foundations; however, many methods are hindered by the type of substructure. An advantage of using near-surface geophysical methods, specifically electrical resistivity (ER) and induced polarization (IP) imaging, is that the inversion processes yield subsurface images, thereby allowing the depth and, to a lesser extent, the foundation type to be seen. Unlike a majority of existing testing methods, ER and IP imaging do not physically use the structure so they are applicable to simple and complex foundation structures. In this paper, results of ER and IP imaging tests performed at the Texas A&M University National Geotechnical Experimentation Site, on a bridge with known foundation depth and a bridge with unknown foundation depth are presented. The applicability of ER and IP imaging to determine substructure characteristics for unknown bridge foundations is also discussed. A probability of nonexceedance estimate for predictions using IP is given to quantify IP imaging reliability. [ABSTRACT FROM AUTHOR]

This study describes an experimental investigation of the methylene blue test to determine the methylene blue value (MBV) and quantitatively generate the soil-water characteristic curve (SWCC) for unbound aggregate material based on the predicted percent fines content (PFC). The traditional methylene blue test has been improved significantly in terms of time, sample size, and method for analyzing the results. These improvements enable the methylene blue test to be not only a laboratory test but also a field test. This improved methylene blue test methodology is used to generate the SWCC for unbound aggregate material. The relationship between the MBVand the PFC value is established. The principles of unsaturated soil mechanics are taken into account to develop regression models for determining the four fitting parameters in a previously developed SWCC equation by using the predicted PFC value, which are then used to generate the SWCC for the unbound aggregates. The proposed method is validated by a comparison between the measured and predicted suction values for various unbound aggregate materials. This method is capable of generating the SWCC far more efficiently than any previous laboratory method, and it can even be used in field investigations because the methylene blue test requires limited portable test equipment. These improvements widen methylene blue test applications and allow for the development of the SWCC without requiring difficult laboratory experiments. Finally, the slope parameter, bf, in the SWCC equations is found to be associated with the moisture susceptibility of flexible base materials. A higher bf value indicates that the material is more moisture susceptible. This finding is successfully validated by the results from the permanent deformation test. [ABSTRACT FROM AUTHOR]

The present research intends to study the effects of the seismic soil-pile-structure interaction (SSPSI) on the dynamic response of buildings with various heights by conducting a series of shaking table tests on 5-, 10-story, and 15-story model structures. Two types of foundations for each case are investigated, including (1) a fixed-base structure, representing the situation excluding the soil-structure interaction; and (2) a structure supported by an end-bearing pile foundation in soft soil. An advanced laminar soil container has been designed that uses three-dimensional numerical modeling to minimize the boundary effects and to simulate free-field motion during the shaking table tests. Four real earthquake events, including Kobe 1995, Northridge 1994, El Centro 1940, and Hachinohe 1968, are imposed to each model. According to the experimental measurements, it is observed that the SSPSI amplifies the maximum lateral deflections and in turn interstory drifts of the structures supported by end-bearing pile foundations in comparison with the fixed-base structures. The rocking component plays an important role in increasing the lateral deflection of the superstructures, which can shift the performance level of the structures to near collapse or even collapse levels and as a result should be assessed precisely in the seismic design of buildings resting on soft soils. [ABSTRACT FROM AUTHOR]

Scouring is a significant problem on river bank and coastal protection systems. Severe scouring can cause damaging consequences to geotextile tube embankment structures. In this study, five case scenarios of an embankment system supported by stacked geotextile tubes were analyzed using a commercially available finite-element analysis software. These case scenarios include (1) conventional geotextile tube stacking on ground base foundation; (2) geotextile tube stacking on gravel bedding foundation; (3) geotextile tube stacking on excavated foundation; (4) geotextile tube stacking on excavated foundation with gravel bedding; and (5) fortification of stacked geotextile tubes by riprap protection. Each case scenario is simulated under normal loading and critical loading conditions with and without scouring at the base toe of the embankment system. Results suggest that the potential problems that occur during scouring and critical states of the embankment system instigate failures that could destabilize the geotextile tube retaining structure. Among all the case scenarios considered, additional fortification by riprap increases the performance and global stability of the geotextile tube embankment system. [ABSTRACT FROM AUTHOR]

Ground movements observed during foundation installation and basement construction of a residential 53-story RC tower are presented. The One Museum Park West building is located in Chicago, Illinois, and was developed using a combination of bottom-up methods, used for the construction of a central concrete core of the building, and top-down methods to build five levels of basements. The excavation extended 13-15 m below grade and was made through soft to medium-stiff clays. The building was supported by drilled shafts and a perimeter wall formed by secant piles that transitioned to tangent piles below the bottom of the cut. The system was laterally braced with RC floor slabs structurally connected to the secant pile walls and the RC core. Field performance data were collected by means of settlement points and inclinometers located close to the walls on two sides of the excavation. The construction sequence and attendant ground movements during each main activity are summarized. As much as 160 mm of settlement was recorded in the adjacent streets throughout construction. Wall and foundation installation accounted for approximately 35% of the total settlements during construction, whereas top-down construction of the basement resulted in approximately 40% of the total settlements. These data emphasize the importance of considering all construction activities when making predictions of ground movements adjacent to deep supported excavations. [ABSTRACT FROM AUTHOR]

To evaluate the effect of soil-foundation interaction on the earthquake response of structures, centrifuge tests were performed using an in-flight earthquake simulator. The test specimen was composed of a single-degree-of-freedom structure model, a shallow foundation, and subsoil deposits in a centrifuge container. The test parameters were the dynamic period of the structure model, the centrifugal acceleration level, and the type and level of input earthquake accelerations. The test results showed that the lateral forces of the structures were limited by the soil-bearing strength (i.e., ultimate moment capacity of the foundation) and the damping effect owing to the rocking motion of the foundation. Thus, even when the periods of the structures were close to the site periods, the lateral forces did not significantly increase. However, it should be noted that, because of the damping effect of the foundation, the maximum seismic lateral load of the structures exceeded the load statically determined by the soil-bearing strength. This issue should be addressed for the safe design of structures and members. In this test, the maximum damping ratio for rocking due to the rocking motion was estimated to be 0.31. [ABSTRACT FROM AUTHOR]

A new concept with respect to offshore wind turbines, the bucket foundation, is known in the oil and gas industry, although the load conditions for wind turbines are significantly different. An extensive number of loading tests with small-scale bucket foundations subjected to combined loading were carried out in the geotechnical laboratory at Aalborg University in Aalborg, Denmark. Tests were performed on buckets of various sizes, embedment ratios, and load paths on saturated dense Aalborg University Sand No. 1. The experimental results were used to evaluate the behavior of the bucket foundations in accordance with the macromodel approach. An expression to describe the combined capacity of bucket foundations was developed by calibrating the failure criteria for bucket foundations. [ABSTRACT FROM AUTHOR]

This paper reports advances in the prediction of spudcan resistance profiles during installation and preloading, based on the soil flow mechanisms observed in model tests and numerical analysis, and taking into account strain softening and rate dependency on the soil strength. Deep penetration of spudcan foundations was simulated for 14 case histories reported from different locations in the Gulf of Mexico, where the soils were single layer, predominantly normally to lightly overconsolidated clay. Axisymmetric and three-dimensional analyses were carried out using two large deformation finite-element (LDFE) approaches, modifying the simple elastic-perfectly plastic Tresca soil model to allow strain softening and strain-rate dependency of the shear strength. The field data were compared with the results of the finite-element analyses and with predictions using various design approaches. Excellent agreement was found, particularly when a mechanism-based design approach was used that differentiated between conditions before and after backflow of soil above the penetrating spudcan. [ABSTRACT FROM AUTHOR]

Previous numerical analyses of the bearing capacity of embedded footing under combined vertical, horizontal, and moment loading have been based on the assumption that the foundation is wished-in-place, surrounded by undisturbed soil. Under these conditions, the large displacement and remolding of the soil during the footing installation are not accounted for. This assumption results in an overestimation of the capacity. This paper presents results of the size and shape of the bearing capacity surface of spudcan footing in soft clay that accounts for the effects of installation in the modeling. Results for soil sensitivities between one and five and for embedment depths up to three diameters are provided. The findings have practical application in the site-specific assessment of mobile jack-up platforms in soft clay. [ABSTRACT FROM AUTHOR]

Based on the estimated HT ht , the average PRF settlement HT ht . The average elastic settlement HT ht obtained directly from FE analysis is 19.5 mm. The maximum PRF settlement HT ht obtained directly from FE analysis is 20.4 mm. [Extracted from the article]

The article discusses research on design methodology for stiffened slabs-on-grade usually used as foundation support for residential and commercial buildings. Other topics include the most common methods for sizing stiffened slabs-on-grade, geostructural problem posed by the suggested processes, and factors that affect the shape of the mound.

The article offers the authors insights on the article "Interaction between Laterally Loaded Pile and Surrounding Soil," by Lusu Ni, Hai Lin, Anne Raich, and Muhannad T. Suleiman. Topics discussed include the use of tactile pressure sheets of measure stresses, soil pressure, and the measurement of horizontal soil stress distribution.

The article presents a response from the author of a study on design methodology for stiffened slabs-on-grade usually used as foundation support for residential and commercial buildings. Other topics include recommendations for determining depth of the active zone when there is insufficient soil and climatic information on a particular site, and applicability of the new design to basement floor slabs.

A review of the article "Shielding Piles from Downdrag in Consolidating Ground," by S.Y. Lam, C.W.W. Ng, and H.G. Poulos, which appeared in the periodical Journal of Geotechnical and Geoenvironmental Engineering on June 2013, is presented.

The article the authors insights on the article "Interaction between Laterally Loaded Pile and Surrounding Soil," by Lusu Ni, Hai Lin, Anne Raich, and Muhannad T. Suleiman. Topics discussed include the use of the pressure distribution to simplify the analysis about pile rotation, the use of pressure sensors to measure soilpile interaction pressure, and the procedure of soil preparation.

A fully instrumented experiment was conducted to investigate the soil-structure interaction of single short, stiff laterally loaded piles. A hollow steel pipe pile with a diameter of 102 mm, a thickness of 6.4 mm, and a length of 1.524 m was installed in well-graded sand and subjected to increasing lateral load. The pile and surrounding soil were fully instrumented using advanced sensors, including flexible shape acceleration arrays, thin tactile pressure sheets, and in-soil null pressure sensors. The sensors attached to the pile were used to develop the compressive soil-pile interaction pressures and the lateral displacement along the pile length. The tactile pressure sheet sensors provided the soil-pile interaction compressive pressures on the circumference of the pile at a specific depth and along the length of the pile. The measured soil-pile interaction compressive pressures combined with the measured lateral displacement along the pile length were used to develop the soil-pile interaction force-displacement relationships ( curves) using direct measurements. In addition, the in-soil null pressure sensor measurements were used to develop the distribution of horizontal stress changes around the pile as the lateral pile displacement increased. When appropriate, the measured results were compared with data and methods available in the literature. [ABSTRACT FROM AUTHOR]

Twenty-seven wall-splice specimens reinforced with number (No.) 15 (0.6 in.) deformed bars were tested to evaluate the effect of transverse bar spacing on the tensile resistance of the lap-spliced reinforcement. All specimens were blocks wide and 13 courses tall and were constructed in running bond with all cells fully grouted. In all cases, the lapped bars were located within a single block cell and were either spaced 0, 25, or 50 mm (0, 1, or 2 in.) apart. It was determined that the calculated tensile resistance of the reinforcement was greater for bars that were in contact and furthermore, is insensitive to the magnitude of the transverse spacing provided in the case of noncontact lap splices. It would appear that both the American and Canadian provisions are appropriate for both contact and noncontact lapped bars given the resulting levels of conservatism. [ABSTRACT FROM AUTHOR]

The article discusses the response of researchers to a review of their study on implications of shielding effects to negative skin friction (NSF) published in the June 2013 issue of the periodical "Journal of Geotechnical and Geoenvironmental Engineering." Topics covered include the relationship between the drag load and piles, various ways of evaluating NSF and the relevance of the research to bearing capacity.

The authors discuss research on the cyclic response of reinforced concrete walls with different anchorage details. They reference the study "Cyclic Response of Reinforced Concrete Walls With Different Anchorage Details: Experimental Investigation" by Sriram Aaleti and colleagues published in the journal in 2014. Topics discussed include the loading history for applying lateral load to wall specimen of a test, horizontal sliding shear cracks and the mechanism of instability of wall specimens.

The author discusses the paper "Shaft Resistance of Drilled Shafts in Clay" by Tanusree Chakraborty, Rodrigo Salgado, Prasenjit Basu and Mônica Prezzi. He commends the paper for examining the influence of the method of pile installation on the alpha factor used in determining the unit shaft resistance. He also describes the process of removal and reinsertion of the auger during the installation.