Showing papers on "Foundation (engineering) published in 2008"

Three-Dimensional Seismic Response of Humboldt Bay Bridge-Foundation-Ground System

Abstract: Soil-structure interaction may play a major role in the seismic response of a bridge structure. Specifically, soil layers of low stiffness and strength may result in permanent displacement of the abutments and foundations, thus imposing important kinematic conditions to the bridge structure. A study to illustrate such phenomena is undertaken based on three-dimensional nonlinear dynamic finite-element (FE) modeling and analysis (for a specific bridge configuration under a given seismic excitation). A bridge-foundation-ground model is developed based on the structural configuration and local soil conditions of the Humboldt Bay Middle Channel Bridge. The FE model and nonlinear solution strategy are built in the open-source software platform OpenSees of the Pacific Earthquake Engineering Research Center. Based on the simulation results, the overall system seismic response behavior is examined, as well as local deformations/stresses at selected critical locations. It is shown that permanent ground deformation may induce settlement and longitudinal/transversal displacements of the abutments and deep foundations. The relatively massive approach ramps may also contribute to this simulated damage condition, which imposes large stresses on the bridge foundations, supporting piers, and superstructure.

Centrifuge modelling of normal fault–foundation interaction

Abstract: Earthquake fault ruptures may emerge at the ground surface causing large differential movements. When fault ruptures emerge at or adjacent to the position of existing foundations, significant damage can be caused. However, the study of recent faulting events revealed that in some circumstances the fault-rupture emergence is deflected by the presence of buildings leaving the buildings intact. A centrifuge modelling study has been conducted to investigate how normal faults interact with strip foundations which run parallel to the strike direction. The study confirms that fault rupture may be deviated by the presence of the foundation so that the foundation is protected from the most serious differential movements. However, whilst the fault propagates to the soil surface the foundation has to withstand initial movements before the final fault rupture emergence mechanism is activated. The centrifuge results suggest that it is the bearing pressure of the foundation which causes the deviation of the fault rather than the kinematic restraint of the foundation. The interaction between the earthquake fault and the shallow foundation depends on the foundation bearing pressure, foundation width, soil depth and position of the fault relative to the foundation and these aspects should be considered in design. Results from the tests are used to validate a series of finite element analyses as reported in an accompanying paper.

Centrifuge modelling of reverse fault–foundation interaction

Abstract: The propagation of reverse faults through soil to the ground surface has been observed to cause damage to surface infrastructure. However, the interaction between a fault propagating through a sand layer and a shallow foundation can be beneficial for heavily loaded foundations by causing deviation of the fault away from the foundation. This was studied in a series of centrifuge model tests in which reverse faults of dip angle 60° (at bedrock level) were initiated through a sand layer, close to shallow foundations. The tests revealed subtle interaction between the fault and the shallow foundation so that the foundation and soil response depend on the foundation loading, position, breadth and flexibility. Heavily loaded rigid foundations appeared best able to deviate fault rupture away from the foundation but this deviation could be associated with significant foundation rotations. However, a lightly loaded foundation was unable to deviate a reverse fault and the fault emerged beneath the foundation. This led to gapping beneath the foundation as well as significant rotations and may cause severe structural distress. As well as providing insight into the mechanisms of behaviour, the data from the tests is used to validate finite element analyses in a separate article.

Finite Element Numerical Simulation of Three-Dimensional Seepage Control for Deep Foundation Pit Dewatering

Abstract: For deep foundation pit dewatering in the Yangtze River Delta, it is easy to make a dramatic decrease of the underground water level surrounding the dewatering area and cause land subsidence and geologic disasters. In this work, a three-dimensional finite element simulation method was applied in the forth subway of Dongjiadu tunnel repair foundation pit dewatering in Shanghai. In order to control the decrease of the underground water level around the foundation pit, the foundation pit dewatering method was used to design the optimization project of dewatering, which was simulated under these conditions that the aquifers deposited layer by layer, the bottom of the aquifers went deep to 144.45 m, the retaining wall of foundation pit shield went deep to 65 m, the filters of the extraction wells were located between 44 m to 59 m, the water level in the deep foundation pit was decreased by 34 m, and the maximum decrease of water level outside the foundation pit was 3 m. It is shown that the optimization project and the practical case are consistent with each other. Accordingly, the three-dimensional finite element numerical simulation is the basic theory of optimization design of engineering structures of dewatering in deep foundation pit in such areas.

Cyclic behavior of laterally loaded concrete piles embedded into cohesive soil

Abstract: Modern seismic design codes stipulate that the response analysis should be conducted by considering the complete structural system including superstructure, foundation, and ground. However, for the development of seismic response analysis method for a complete structural system, it is first imperative to clarify the behavior of the soil and piles during earthquakes. In this study, full-scale monotonic and reversed cyclic lateral loading tests were carried out on concrete piles embedded into the ground. The test piles were hollow, precast, prestressed concrete piles with an outer diameter of 300 mm and a thickness of 60 mm. The test piles were 26 m long. Three-dimensional (3D) finite element analysis was then performed to study the behavior of the experimental specimens analytically. The study revealed that the lateral load-carrying capacity of the piles degrades when subjected to cyclic loading compared with monotonic loading. The effect of the use of an interface element between the soil and pile surface in the analysis was also investigated. With proper consideration of the constitutive models of soil and pile, an interface element between the pile surface and the soil, and the degradation of soil stiffness under cyclic loading, a 3D analysis was found to simulate well the actual behavior of pile and soil.

Tsunami scour around a square structure

Abstract: Tsunami-induced local scour around a land-based square structure on a sand foundation was investigated with laboratory experiments and numerical simulations. The laboratory experiments revealed tha...

Reliability of Conventional Settlement Evaluation for Circular Foundations on Stone Columns

Abstract: The unit cell idealization has been long adopted in the settlement prediction of stone column-reinforced soils. This paper tests the accuracy of this modeling concept against trusted settlement values of engineering foundations. It is believed that in order to bestow the outcome of this study adequate generality different soil properties and foundation geometries need to be considered. It was, nevertheless, found impracticable to collect field settlement records for all the analyzed cases. The authors, therefore, appealed to the back analysis concept to construct a reliable mathematical model, calibrated against settlement records of full-scale field load test. This model, which is capable of reproducing the real field settlements, is then employed as a generic tool to obtain trusted settlement values for a variety of cases with essential geometrical similarity. The investigation revealed that the unit cell analysis may, in some cases, lead to erroneous estimation for the settlements of foundations with limited extents. Correction factors, dependent on the treated soil properties as well as the foundation size, are introduced.

A macro-element for a circular foundation to simulate 3D soil–structure interaction

Abstract: This paper presents a non-linear interface element to compute soil-structure interaction (SSI) based on the macro-element concept. The particularity of this approach lies in the fact that the foundation is supposed to be infinitely rigid and its movement is entirely described by a system of global variables (forces and displacements) defined in the foundation's centre. The non-linear behaviour of the soil is reproduced using the classical theory of plasticity. Failure is described by the interaction diagram of the ultimate bearing capacity of the foundation under combined loads. The macro-element is appropriate for modelling the cyclic or dynamic response of structures subjected to seismic action. More specifically, the element is able to simulate the behaviour of a circular rigid shallow foundation considering the plasticity of the soil under monotonic static or cyclic loading applied in three directions. It is implemented into FedeasLab, a finite element Matlab toolbox. Comparisons with experimental monotonic static and cyclic results show the good performance of the approach.

Effect of Soil — Structure Interaction on Seismic Isolated Bridges

Abstract: The role of soil–structure interaction (SSI) on the response of seismically isolated bridges is studied. A generic bilinear hysteretic model is utilized to model the isolation system. The behavior of the pier is assumed to be linear and the foundation system is modeled with frequency-dependent springs and dashpots. Two bridge systems were considered, one representative of short stiff highway overpass systems and another representative of tall flexible multispan highway bridges. Nonlinear time history analyses were employed with two sets of seismic motions; one containing 20 far-field accelerograms and one with 20 near-fault accelerograms. The results from these comprehensive numerical analyses show that soil–structure interaction causes higher isolation system drifts as well as, in many cases, higher pier shears when compared to the fixed-pier bridges (no SSI).

Dynamics of Structure and Foundation - A Unified Approach: 2. Applications

Abstract: Designed to provide engineers with quick access to current and practical information on the dynamics of structure and foundation, this 2-volume reference work is intended for engineers involved with earthquake or dynamic analysis, or the design of machine foundations in the oil, gas, and energy sector. Whereas Volume 1 (ISBN 9780415471459

Cyclic softening of low plasticity clay and its effect on seismic foundation performance

Abstract: During the 1999 Chi-Chi earthquake (Mw = 7.6), significant incidents of ground failure occurred in Wufeng, Taiwan, which experienced peak accelerations of about 0.7 g. We describe the results of field investigations and analyses of a small region within Wufeng along an E-W trending line 350 m long. The east end of the line has single-story structures for which there was no evidence of ground failure. The west end of the line had 3-6 story reinforced concrete structures that underwent differential settlement and foundation bearing failures. No ground failure was observed in the free-field. Surficial soils consist of low-plasticity silty clays that extend to 8-12 m depth in the damaged area (west side), and 3-10 m depth in the undamaged area (east side). A significant fraction of the foundation soils at the site are liquefaction-susceptible based on several recently proposed criteria, but the site performance cannot be explained by analysis in existing liquefaction frameworks. Accordingly, we use an alternative approach that accounts for the clayey nature of the foundation soils. Field and laboratory tests are used to evaluate the monotonic and cyclic shear resistance of the soil, which is compared to the cyclic demand placed on the soil by ground response and soil-structure interaction. Results of the analysis indicate a potential for cyclic softening and associated strength loss in foundation soils below the six-story buildings, which contributes to bearing capacity failures at the edges of the foundation. Similar analyses indicate high factors of safety in foundation soils below one-story buildings as well in the free field, which is consistent with the observed field performance.

Foundation particularly for a wind turbine and wind turbine

Abstract: A foundation, particularly a foundation of a wind turbine, is provided. The foundation includes a central foundation member and a plurality of foundation segments which are segments of a circular, ring shaped or polygonal foundation element and which are connected to the central foundation member using a plurality of locking elements.

Cyclic softening of low plasticity clay and its effect on seismic foundation performance - eScholarship

Abstract: During the 1999 Chi-Chi earthquake (Mw = 7.6), significant incidents of ground failure occurred in Wufeng, Taiwan, which experienced peak accelerations of about 0.7 g. We describe the results of field investigations and analyses of a small region within Wufeng along an E-W trending line 350 m long. The east end of the line has single-story structures for which there was no evidence of ground failure. The west end of the line had 3-6 story reinforced concrete structures that underwent differential settlement and foundation bearing failures. No ground failure was observed in the free-field. Surficial soils consist of low-plasticity silty clays that extend to 8-12 m depth in the damaged area (west side), and 3-10 m depth in the undamaged area (east side). A significant fraction of the foundation soils at the site are liquefaction-susceptible based on several recently proposed criteria, but the site performance cannot be explained by analysis in existing liquefaction frameworks. Accordingly, we use an alternative approach that accounts for the clayey nature of the foundation soils. Field and laboratory tests are used to evaluate the monotonic and cyclic shear resistance of the soil, which is compared to the cyclic demand placed on the soil by ground response and soil-structure interaction. Results of the analysis indicate a potential for cyclic softening and associated strength loss in foundation soils below the six-story buildings, which contributes to bearing capacity failures at the edges of the foundation. Similar analyses indicate high factors of safety in foundation soils below one-story buildings as well in the free field, which is consistent with the observed field performance.

Foundation for monopole wind turbine tower

Abstract: An innovation is disclosed which relates to a wind turbine foundation. A circular foundation using fiber reinforced concrete has optional circular reinforcement rods. The foundation includes a vertical stanchion that rests in the bottom of an excavated hole and supports anchor bolts and reinforcement bars in a predetermined configuration while concrete is poured into the hole. All the necessary foundation materials can be combined in a simple and compact kit which can be shipped to a customer.

Foundation Design for the Burj Dubai – the World’s Tallest Building

Abstract: This paper describes the foundation design process adopted for the Burj Dubai, the world’s tallest bui lding. The foundation system is a piled raft, founded on deep deposits of carbonate s oils and rocks. The paper will outline the geotechn i al investigations undertaken, the field and laboratory testing programs, and the design process, and will discuss how various design issues, including cyclic degradation of skin friction due to wind loading, w ere addressed. The numerical computer analysis that was adopted for the original design together with the check/calibration analyses will be outlined, and then the alternative analysi s employed for the peer review process will be described. The paper sets out how t he various design issues were addressed, including ultimate capacity, overall stability under wind and seismic loadings, and the settlement and differential settlements. The comprehensive program of pile load testing that w s undertaken, which included grouted and non-gro uted piles to a maximum load of 64MN, will be presented and “Class A” predi ctions of the axial load-settlement behaviour will be compared with the measured behavior. The settlements of the towers observed du ring construction will be compared with those predi cted.

Design and Performance Verification of Ultra-High Performance Concrete Piles for Deep Foundations

Abstract: The strategic plan for bridge engineering issued by AASHTO in 2005 identified extending the service life and optimizing structural systems of bridges in the United States as two grand challenges in bridge engineering, with the objective of producing safer bridges that have a minimum service life of 75 years and reduced maintenance cost. Material deterioration was identified as one of the primary challenges to achieving the objective of extended life. In substructural applications (e.g., deep foundations), construction materials such as timber, steel, and concrete are subjected to deterioration due to environmental impacts. Using innovative and new materials for foundation applications makes the AASHTO objective of 75 years service life achievable. Ultra High Performance Concrete (UHPC) with compressive strength of 180 MPa (26,000 psi) and excellent durability has been used in superstructure applications but not in geotechnical and foundation applications. This study explores the use of precast, prestressed UHPC piles in future foundations of bridges and other structures. An H-shaped UHPC section, which is 10-in. (250-mm) deep with weight similar to that of an HP10×57 steel pile, was designed to improve constructability and reduce cost. In this project, instrumented UHPC piles were cast and laboratory and field tests were conducted. Laboratory tests were used to verify the moment-curvature response of UHPC pile section. In the field, two UHPC piles have been successfully driven in glacial till clay soil and load tested under vertical and lateral loads. This report provides a complete set of results for the field investigation conducted on UHPC H-shaped piles. Test results, durability, drivability, and other material advantages over normal concrete and steel indicate that UHPC piles are a viable alternative to achieve the goals of AASHTO strategic plan.

Method of constructing an insulated shallow pier foundation building

Abstract: A method of constructing a shallow pier foundation building that includes a) placing a plurality of insulating pier forms along a perimeter of the building; b) placing a plurality of insulating concrete forms between the insulating piers to form a continuous insulating surface to the surrounding soil and a continuous forming surface to provide a slab form; c) placing a concrete composition in the insulating piers and insulating concrete forms and allowing the concrete composition to cure and harden; and d) placing a concrete slab composition in the slab form and allowing the concrete composition to cure and harden.

Connectable drainage device

Abstract: A drainage tile used on a footing of a foundation to promote drainage of water along the footing and away from a foundation wall. The drainage tile comes in lengths that are less than the length of the footing. The drainage tile can be secured together with other drainage tiles to span the length of the footing.

In situ soil testing for foundation performance prediction

Abstract: Our understanding of non-linear soil behaviour at small strains hinges on laboratory static and dynamic element testing of ideal undisturbed samples. However such samples are prohibitively expensive for day to day geotechnical engineering projects, especially in sandy soils. In addition to soil’s complex nature, construction processes also have an important effect on foundations’ behaviour under working load. This is especially true in piling engineering. It is well acknowledged that the base stiffness of a displacement pile is much higher than that of an equivalent bored pile. To be able to understand and predict such effects of geotechnical processes on soil-foundation performance, it is necessary to develop practical techniques to measure both the in situ non-linear soil behaviour and any construction-induced changes. This thesis presents an attempt at fulfilling both of these objectives within the limited scope of wished-in and pressed-in model piles in a dense silica sand. Simplified methods of pile base settlement prediction are then developed using the analogy with spherical cavity expansion. To measure monotonic soil properties in situ, a new miniature pressuremeter was developed for the centrifuge. The design successfully avoided any installation disturbance by adopting a wished-in installation process, and produced repeatable results in the small to intermediate strain rage. However, membrane penetration errors proved severe for the current design at small strains. The large-strain cross-hole method of Salgado et al. (1997a) was successfully implemented in the centrifuge. Small-strain stiffness and its dependency on mean stress level were successfully measured and compared well against data obtained from triaxial tests. The dynamic shear stiffness-strain relationship was also estimated assuming a power law constitutive model of Bolton & Whittle (1999). The in situ shear stiffness field around a penetration pile was measured directly using the large-strain seismic method both during pile jacking and after pile unloading. An estimate of the corresponding in situ stress field was made from the stiffness field, giving direct evidence of stiffer soil behaviour and the existence of large locked-in stresses after pile jacking. These higher values of shear stiffness and large locked-in stress are shown to be the main reason behind the stiffer load-settlement behaviour of a displacement pile vs a non-displacement pile. The effect of soil densification due to the action of pile penetration does not contribute significantly to the above difference in behaviour.