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Records of pile lengths are not available for several hundred high-mast light towers (HMLTs) throughout the state of Minnesota. The foundation systems, typically steel H-piles or concrete-filled steel pipe piles connected to a triangular concrete pile cap, risk overturning in the event of peak wind loadings if the foundation piles are not sufficiently deep to provide the designed uplift capacity. Without prior knowledge of the in situ pile lengths, an expensive tower foundation retrofit or replacement effort would need to be undertaken. However, the development of a nondestructive screening tool to determine the in situ pile length—compared with replacing or retrofitting all towers with unknown foundation geometries—would potentially provide significant cost savings. The main goal of the research is the development of nondestructive evaluation testing techniques for determining in situ pile lengths using steady-state vibration and hammer-impact seismic testing. The foundation testing protocol involves (1) a preliminary site investigation to determine the shallow subsurface geometry and orientation of the foundation pile cap, (2) the use of seismic cone penetrometer (SCP) attached to a cone penetration test rig to capture the induced steady-state and impact waveforms, and (3) data-driven analysis of field testing results to determine the pile lengths. [ABSTRACT FROM AUTHOR]

This document discusses a research paper that proposes a modified method for evaluating the stability of deep excavations in soft clays. The discussion raises concerns about the proposed method and questions the assumptions made by the authors. It suggests alternative explanations for the observed behavior of excavations in soft clays and criticizes the models used in the study for not accurately representing actual ground movement patterns caused by excavation. The author invites the study authors to respond to these criticisms. [Extracted from the article]

Building and ground settlement due to construction dewatering is a well-studied topic. However, most previous investigations have not considered the barrier effect of an adjacent underground structure on the drawdowns and resulting settlements. In this study, the barrier effect and its influence during construction dewatering for a metro station foundation pit is investigated. There are five aquifers at the foundation pit site, and a row of buildings supported on pile foundations, which act as an underground barrier to flow, is present on one side of the pit. On the other sides, there are no deep underground structures to impede groundwater flow. Field monitoring of the groundwater level drawdown, diaphragm wall movement, and ground and building settlements on both sides of the pit was carried out during dewatering. The results indicate that on the side with the pile foundations, the groundwater level drawdown, ground settlement, differential settlement, and angular distortion of building incurred by dewatering were relatively greater, but the diaphragm wall movements were relatively smaller. The effect of preexisting barriers should be considered in the assessment of construction dewatering-induced drawdowns, soil settlements, and building movements. [ABSTRACT FROM AUTHOR]

In the random field model's consideration of the spatial variability of soil, soil properties at different locations play different roles in the reliability analysis of the foundation. Investigating the importance distribution of the random field through reliability sensitivity analysis (RSA) is beneficial for understanding how the random field affects the reliability of the foundation. However, many existing RSA methods for the random field model are deficient in terms of efficiency, accuracy, and applicability under complex engineering conditions. Consequently, this study proposes an efficient RSA method for the random field model based on the Karhunen–Loève (KL) expansion method and the first-order reliability method (FORM) to identify the important random field domain in foundation engineering. In the proposed method, the mean reliability sensitivity index (MRSI) is extended to a random field model of continuous form to characterize the importance distribution of the random field. The MRSI is analytically derived based on the results of the KL expansion method and the FORM without additional limit state function (LSF) calculations. Subsequently, the important random field domain, in which the variation of the mean of the soil property contributes significantly to the reliability index, is identified based on the MRSI. Last, two foundation engineering examples that consider the cross-correlated random fields of cohesion and friction angle, including strip footing on single-layer soil and pile in multiple-layer soil, were used to verify the proposed method. The results showed that an important random field domain with a small area dominates the variation of the reliability index of a foundation, and important random field domain area increases with autocorrelation distance (ACD). This innovative identification method holds great engineering significance, because it allows geotechnical practitioners to gain a comprehensive understanding of the failure modes and foundation treatment areas of foundations in spatially varying soil. In the random field model's consideration of the spatial variability of soil, soil properties at different locations play different roles in the reliability analysis of the foundation. Investigating the importance distribution of the random field through RSA is beneficial for understanding how the random field affects the reliability of the foundation. However, many existing RSA methods for the random field model are deficient in terms of efficiency, accuracy, and applicability under complex engineering conditions. Consequently, this study proposes an efficient RSA method for the random field model to identify the important random field domain, in which the variation of the mean of the soil property contributes significantly to the reliability index. Two foundation engineering examples that consider the cross-correlated random fields of cohesion and friction angle, including strip footing on single-layer soil and pile in multiple-layer soil, were used to verify the proposed method. The results showed that the innovative identification will allow geotechnical practitioners to gain a comprehensive understanding of the failure modes and foundation treatment areas of foundations in spatially varying soil. [ABSTRACT FROM AUTHOR]

Pile foundations supporting high-rise buildings are generally subject to cyclic loading because of dynamic loading. The corrosion of steel materials in pile foundations is another major concern, especially for piles in a marine environment. In this study, a series of cyclic and static loading tests on model piles made of fiber-reinforced polymer (FRP) and seawater–sea sand concrete (SSC) and ended in a rock socket were reported. Three structural configurations (FRP tube–confined, FRP rebar cage–reinforced, and centered FRP rebar–reinforced) were adopted for the model piles. Strain along the depth of the piles was measured using fiber Bragg grating (FBG) optic sensors and an advanced distributed optical sensing technique known as optical frequency domain reflectometry (OFDR). Strain distribution, axial cyclic stiffness, and shaft friction mobilization of the piles under static and different modes of axial cyclic loading were analyzed and explored in detail. The test results indicated that the FRP tube–confined model pile showed higher confinement and cyclic capacity and lower stiffness degradation, leading to relatively more stable behavior. A high level of cyclic loading can cause microcracks to form and grow within the pile material, thereby decreasing pile stiffness. The strain profile of all the piles along the depth appeared to follow a similar trend, and fluctuations at certain points led to failure. Cyclic stiffness showed gains initially when cyclic load conditions were below a certain threshold level but degraded when loading was increased beyond it. Moreover, shaft resistance gradually increased with cycles, causing higher mobilization in the upper portion of the socket. The experimental results have provided the first systematic study on the performance of the FRP-SSC composite model piles ended in rock sockets under axial cyclic and static loadings. This will contribute to development of a potential predictive method for pile settlement and capacity for the better design of rock-socketed piles. [ABSTRACT FROM AUTHOR]

Existing simplified procedures for evaluating soil liquefaction potential or for estimating excess pore pressures during earthquakes are typically based on undrained cyclic tests performed on saturated soil samples under controlled loading and boundary conditions. Under such conditions, the effect of excess pore pressure (ue) dissipation and redistribution to neighboring soil layers cannot be accounted for. Existing simplified procedures treat liquefiable layers as isolated soil layers without any boundary conditions even if dense and loose layers are very thin, permeable, and adjacent to each other. However, redistribution is likely to increase and decrease ue in the neighboring dense and loose layers respectively. Until now, no procedure short of fully coupled numerical analysis is available to estimate the importance of redistribution. This paper presents an approximate analytical procedure for assessing the effects of ue redistribution in (1) soil layers that would have liquefied if they were undrained, and (2) soil layers that would have not liquefied even if undrained. It is found that a layer that is initially assumed liquefied under undrained conditions might not even liquefy accounting for the ue redistribution to neighboring layers. On the other hand, a layer initially assumed to not liquefy can develop significant ue and can even liquefy due to pore pressure migration from the neighboring layers. Thus, accounting for redistributed ue is important for liquefaction consequence assessment quantification, particularly in systems that span the depth of these effects like deep foundations. Migration of u toward the tip of a pile can reduce its capacity, even if the tip is embedded in a dense sand layer. On the other hand, if redistribution can result in the reduction of ue in initially assumed liquefied layers, risks associated with liquefaction might be avoided. A criterion is also developed to evaluate the thicknesses of a layer below which redistribution could prevent liquefaction even if the layer is deemed liquefied according to the existing liquefaction-triggering procedures. Finally, the proposed procedure is illustrated by application to selected shaking events of centrifuge tests involving liquefaction of layered soil profiles. The predictions from the procedure matched the centrifuge test results reasonably. [ABSTRACT FROM AUTHOR]

The design of rock-socketed pile foundations requires careful consideration of critical construction aspects such as the socket roughness and smear for accurately estimating the shaft load capacity. Despite the effect of smear being investigated extensively over the years, previous studies are limited in accurately characterizing the effect of smear on the shaft response. This paper presents a comprehensive investigation on the load-bearing mechanisms of model smeared rock-socketed piles with different smear fabrics (configurations) at the pile-rock interface. These model piles were loaded into synthetic soft rocks while being intermittently subjected to three-dimensional (3D) X-ray computed tomography (CT) imaging. Interpretations from the X-ray CT images were correlated with the pile-head load-displacement behavior to gain insights into the load transfer attributes between the pile, smear, and rock. The various interactions between these components were deduced by monitoring the micromechanics at the pile-rock interface through shaft energy utilization, interface void volume, smear volume, and sand density mapping. Based on the observations, it was inferred that the load transfer between the smear and the rock is primarily dependent on the percentage and position of smear occupancy at the interface. Results indicated that for the partially smeared interfaces, the interface mechanics are a combination of smeared and clean shafts with the residual resistances dependent upon the combined compression of smear and rock debris at the interface. Moreover, it was observed that the continuous presence of smear for more than half area of the leading faces of the pile asperities results in the smeared regions of the pile taking precedence over the unsmeared regions in governing the load-carrying capacity of the shaft. The discussions presented in this study can provide a strong base to further study the smear effect, subsequently aiding in enhancing the existing design guidelines to economically construct piles in soft rock. [ABSTRACT FROM AUTHOR]

Interactions between adjacent piled-raft foundations may induce additional settlement and cause the tilt of the structure. This case study investigates the long-term performance of a large piled-raft foundation system supporting high and heavy alumina solution storage tanks based on field measurements and three-dimensional (3D) numerical simulations. To properly consider the interactions among rafts, piles, and soils; the elastoplastic behavior of clayey and sandy soils; and the consolidation behavior of soil after construction, a 3D finite-difference code was utilized for the numerical modeling. Two undrained mechanical analyses were conducted to simulate the installation of foundations/tanks and the filling of alumina solution into the tanks, while two coupled hydromechanical analyses were performed to model the period between the two undrained stages and the stage after tank filling, respectively. The predictive capability of the numerical model was checked by comparing the simulation results first with single pile load test data and then with in situ settlement measurements at different locations of the piled-raft foundations. The long-term behavior of the piled-raft foundations was further investigated by analyzing various aspects including the axial force variation along the pile at different locations, the time-settlement relation at monitoring locations, the vertical effective stress increment and displacement of soil, and the differential settlement between monitoring locations. Based on the simulations, the tilt of the platform was mainly due to the superposition of additional stresses near the centerline of the two rows of piled-raft foundations. Finally, parametric studies were conducted to investigate the interactions among the piled-raft foundations at different pile length configurations. The results show that by properly increasing the length of the piles near the centerline of the two rows of piled-raft foundations, the differential settlement of the platforms can be mitigated. [ABSTRACT FROM AUTHOR]

Shake table experiments are conducted to assess the potential of the polymer injection technique as a liquefaction countermeasure. A large 2.9 m high (10 ft) laminar soil container on a 3.9×1.85 m (13×6 ft) shake table is employed. Mitigation of liquefaction-induced settlement for a shallow foundation is explored. In a series of two shake table experiments, the system response is studied first without (baseline) and subsequently with polymer injected into the liquefiable stratum. Each test is densely instrumented to provide insights into the dynamic response of the soil and foundation system. Furthermore, cone penetration tests (CPTs) are performed pre- and postinjection to assess the extent of soil improvement. Strong base excitation is imparted by the shake table, resulting in liquefaction and excessive foundation settlement in the original baseline test. In the second test, with the polymer injection countermeasure, a significant reduction is observed in the tendency for liquefaction and the resulting foundation settlement. After this test, careful excavation provided additional insights into the polymer's configuration within the deposit, increasing overall soil relative density, confinement and creating solidified paths for the shallow foundation load toward the lower, more competent stratum. As such, these mechanisms have the potential to allow for: (1) an increase in soil resistance to liquefaction, and (2) a significant reduction in settlement of overlying shallow foundations. [ABSTRACT FROM AUTHOR]

This document is a discussion of a research paper titled "Numerical Study of the Effect of Ground Improvement on Basal Heave Stability for Deep Excavations in Normally Consolidated Clays" by Ari Surya Abdi and Chang-Yu Ou. The authors conducted a three-dimensional finite-element method analysis to investigate the impact of ground improvement on the stability of deep excavations in soft clays. They proposed a modified Terzaghi's method based on their findings. However, the discussion raises concerns about the reliability of the authors' numerical simulation results and suggests the need for validation through field or experimental data. It also questions the use of an elastic-perfectly plastic Mohr-Coulomb model and the absence of mention of dewatering in the original paper. The discussion further examines the displacement patterns and deflection profiles of retaining walls during excavation. The author requests a response from the original authors. [Extracted from the article]

The damage caused by seismic shaking and liquefaction-induced permanent ground deformation has conventionally been assessed as two separate problems often by different engineers. However, the two problems are inherently linked, since ground shaking causes liquefaction, and liquefaction-induced soil softening affects ground shaking. Modelling both problems within a single numerical model is complex for both the engineer and the software, and most finite element software only have the capabilities to address one of them. To improve the estimates of the seismic performance of buildings on liquefiable soil, a new sub-structuring approach is proposed called the macro-mechanism approach. This approach allows the soil-liquefaction-foundation-structure interaction to be considered in a series of sub-models accounting for the major nonlinear mechanisms of the system at a macro level. The proposed approach was implemented in the open-source finite element software OpenSees and then applied to a case study of a building where significant liquefaction- and shaking-induced damage was observed after the 1999 Mw 7.4 Kocaeli Earthquake. The case study building was also simulated using two different commercial software programs, the finite difference software FLAC, and the finite element software PLAXIS, by two different research teams. A comparison between the results from the macro-mechanism approach compared to full numerical models shows that the macro-mechanism approach can capture the extent of the foundation deformation and provide more realistic estimates of the building damage than full approaches since the FLAC and PLAXIS models consider elastic elements for the building. [ABSTRACT FROM AUTHOR]

Excavation-induced ground movements can have a detrimental influence on adjacent structures and services. These complex soil–structure interactions are affected by a range of factors such as ground conditions, excavation sequence, and the characteristics of the structures. Considerable prior research has been concerned with understanding the ground response during excavation and in evaluating the potential damage to adjacent facilities. A number of case histories have been reported worldwide. Finite-element analysis can be effective in providing insight into the response of the ground and adjacent structures during the entire construction process. Previous studies have shown that observed excavation behavior (e.g., ground movements and retaining wall deformations) can be captured reasonably well in finite-element analysis, provided that certain key modeling aspects are appropriately addressed. This paper extends a previous deep excavation case study in greenfield conditions (i.e., without adjacent buildings and utilities included in the analysis), focusing particularly on the excavation-induced settlements of nearby buildings and buried pipelines. Sensitivity analyses have been conducted to investigate the effects of several aspects on the computed settlements of buildings and pipelines, such as (1) building weight, (2) building stiffness, (3) building foundation type, (4) ground improvement measures, and (5) geometries and material properties of pipelines. Conclusions are drawn for future applications. [ABSTRACT FROM AUTHOR]

Time-dependent response of piled raft foundations (PRFs) in saturated, normally consolidated and moderately overconsolidated clayey soils under the single-drainage condition is investigated using three-dimensional, elastoplastic finite-element (FE) analysis with the modified cam clay (MCC) soil constitutive model. Four different types of clay (Boston Blue Clay, San Francisco Bay Mud, London Clay, and Shanghai Clay) with different values of overconsolidation ratio (OCR) (OCR=1 , 2, and 5) and 20 different configurations of rectangular PRFs are considered for the study. The settlement response and load sharing of PRFs are investigated. Regression analyses are performed with the FE analysis results to obtain fitted equations for immediate settlement, primary consolidation settlement, and degree of consolidation of PRFs. These equations are applicable to PRFs with cast in situ bored piles similar in size to those considered in this study. The proposed equations can be used to estimate time-dependent PRF settlement in normally consolidated and moderately overconsolidated clay as part of preliminary design calculations. [ABSTRACT FROM AUTHOR]

An innovative yet extremely simple approach to reduce the seismic vulnerability of existing buildings on shallow foundations is to remove the lateral contact between the embedded foundation and the surrounding soil. This paper compares the dynamic response of two identical one-degree-of-freedom reduced-scale model sway frames tested in a geotechnical centrifuge. One of the models was founded on fully embedded shallow strip footings, whereas the foundations of the other were disconnected from the soil laterally. Both models were constructed in dry medium density sand whose strength and small strain shear stiffness profiles were obtained by cone penetration and air hammer tests carried out in flight. Various tools were used to monitor the displacements and accelerations both in the structure and in the soil, including micro-electro-mechanical systems (MEMS) accelerometers, piezoelectric accelerometers, LVDTs, and a high-frequency camera. The experimental results demonstrate that the lateral disconnection of the foundation from the adjacent soil significantly reduces the foundation translational and rotational stiffness, which results in a larger predominant period of the structure and a reduction of the absolute floor accelerations obtained for different sinusoidal input signals. The lateral disconnection also mitigates floor drift and story shear forces. The trade-off is the lower radiative damping observed for the laterally disconnected foundation, which results in a larger number of post-earthquake oscillations of the structure. [ABSTRACT FROM AUTHOR]

The rigid inclusion technique has been used worldwide to reinforce soft soil for road and railway embankments and deep building foundations. This technique is studied through field tests and physical and numerical models. Most studies focus on embankments or slabs on soils reinforced with rigid inclusions. Previous research based on numerical modeling demonstrated that the load-transfer mechanisms for a rigid slab differ from those for an embankment. Here, a simplified physical model was developed to assess the load-transfer mechanism between the inclusion head and the load-transfer platform (LTP) under a rigid slab. This research focused on the use of an alternative material for the LTP, which is a compacted soil with or without cement. When the reinforced soil contribution is neglected, the LTP weight and applied load are transmitted completely to the inclusion cap (load-transfer efficiency of 100%). As the LTP material stiffness increases, the settlement magnitude decreases considerably. The experiments demonstrated that the applied load was transferred to the inclusion head through an inverted truncated load-transfer cone (LTC) over the inclusion; the external angle depended on the LTP material strength in accordance with Coulomb's theory. The principal stress state at the base of the LTC also was determined. Equations are proposed to determine LTP thickness and inclusion spacing. [ABSTRACT FROM AUTHOR]

Based on the recommended range of HT ht by Basile ([2]), HT ht and HT ht are assumed for the present calculations. The interaction factor HT ht is defined in such a way that it decreases with an increase in the raft thickness HT ht but increases with an increase in the raft Young's modulus HT ht [Figs. The induced vertical stresses in the soil reduce to 10% of the applied vertical load HT ht at a depth HT ht three to four times the width of the raft HT ht . [Extracted from the article]

Excavation induces stress changes and soil movement on existing floating piled rafts and elevated pile groups. Limited investigation of the effects of deep excavations has resulted in an incomplete understanding of pile foundation performance at the serviceability state. A series of three-dimensional (3D) centrifuge model tests and numerical simulations are conducted in this study to investigate the influence of raft contact on the response of an existing 2×2 piled raft in comparison to that of an elevated pile group when subjected to an adjacent multipropped deep excavation in dry sand. After rising g , an applied axial load was supported by 18% by the raft and 82% by the piles in the piled raft foundation prior to excavation. Owing to stress release and soil movement caused by the 8-m-deep excavation, the pile head load increased by 21% and 3% for the pile closer to the excavation for the piled raft and pile group foundations, respectively. Analysis of pile–soil relative settlement and raft contact pressure shows that a gap formed between the raft and ground surface in the piled raft, resulting in a load transfer from the raft to the embedded piles. A 20% larger settlement was seen in the piled raft foundation than in the pile group, to further mobilize shaft and end bearing resistances for the maintenance of vertical equilibrium. Moreover, 30% additional pile bending moment was induced due to excavation. [ABSTRACT FROM AUTHOR]

This paper investigates the response of framed buildings on raft foundations to tunnel construction using geotechnical centrifuge testing. Five framed building models were considered, and the influence of building configuration, weight, eccentricity, and soil density were evaluated. Soil and foundation displacements, frame deformed shape, maximum structure deformation parameters (deflection ratios and angular distortions), and associated modification factors are illustrated. Results indicate that unlike equivalent isotropic plates, framed buildings primarily exhibit shear behavior and a semi-flexible response. Building deformed shapes indicate that angular/shear distortions (considering bay slope and local tilt) are more appropriate for quantifying framed building distortions than deflection ratios. A relative stiffness parameter is suggested to relate maximum angular distortions to the greenfield settlement slope. Moreover, the efficiency of the available relative stiffness parameters for the deflection ratio modification factors is confirmed. Limitations of the equivalent plate approach and practical implications of the results for framed buildings are discussed. [ABSTRACT FROM AUTHOR]

In Example 2, HT ht should be 0.849 instead of 1.52 as reported in the paper, HT ht should be 0.021 instead of 0.032 as reported in the paper, and HT ht should be recalculated after revising the HT ht in the equation from 18,816 to HT ht (after performing the previous revisions). The authors have established a simplified method to predict settlement of piled raft foundations using a finite-element-derived database and statistical methods. In Example 1, HT ht should be 1.308 instead of 1.89 as reported in the paper and HT ht should be 0.525 instead of 0.475. [Extracted from the article]

In this study, the uplift load-carrying capacity of micropiles was investigated, focusing on the effect of various installation conditions including installation angle (θ), spacing (S), and group configuration. For this purpose, a series of uplift model load tests was conducted using single micropiles (SMP) and group micropiles (GMP). The uplift load capacity of both SMP and GMP increased with θ up to 30° but decreased for a higher installation angle of θ = 45°. Micropile spacing had less effect on the uplift load capacity for GMP. The uplift loadcarrying mechanism of inclined micropiles is proposed based on decomposed axial and lateral loads and resistance components. Based on the proposed load-carrying mechanism, axial and lateral load capacity ratios were proposed and adopted to formulate the uplift load-capacity equation for inclined micropiles. For GMP, the group-effect factor was proposed based on the reduction effect of group micropiles on the overall uplift load capacity. Full-scale uplift load tests were conducted to check the validity of the proposed method. Both SMP and GMP were constructed and tested. It was observed that the estimated results using the proposed method were in good agreement with the measured results. [ABSTRACT FROM AUTHOR]

Difficulties in obtaining high-quality soil samples from offshore sites and heavy involvement of lab testing and engineering judgment have necessitated increasing reliance on in situ penetrometer tests, giving continuous penetration resistance profiles. This paper reports a framework for estimating spudcan penetration resistance directly from continuous resistance profile of a full-flow penetrometer (T-bar) test in single-layer clays and calcareous silts. The framework was validated chiefly against centrifuge test data, supplemented by some reported field data. [ABSTRACT FROM AUTHOR]

This work provides a detailed description of the full-scale experimental tests performed on the dynamic behavior of a shallow foundation under intermediate strains. Awind tower supported by the foundation was subjected to a snap-off test, i.e., it was first pulled with a cable and then suddenly released, thus inducing free oscillations of nonnegligible amplitude in the whole system. The motion induced was measured with a digital camera, seismometers, and accelerometers attached to the surrounding ground surface and to the wind tower. An innovative interpretation technique based on optimizing a few meaningful parameters obtained from the recorded time histories was required by the heterogeneity of the data collected and the accuracy needed to deduce the behavior of the foundation plinth. The analyses showed that the rotational stiffness of the foundation plinth was approximately 10 times greater than that of the base joint, which in turn was approximately one order of magnitude greater than that of the wind tower. As a result, the vibration phenomenon was driven by the wind tower, which induced a sort of forced, damped, harmonic excitation in the foundation such that the tower's oscillations and the foundation's rocking were decoupled from one another. Seismometer measurements performed on the ground surrounding the foundation plinth enabled an assessment of the geometrical attenuation of the surface vibrations induced by foundation rocking. To the best of the authors' knowledge, the geometrical attenuation assessments reported in this study are the first to be published on the deformations of the ground surrounding a rocking foundation, and could serve as a useful reference to validate constitutive models for simulating small-strain soil response. [ABSTRACT FROM AUTHOR]

An experimental program of large-scale direct shear tests was conducted to evaluate shear strength of a composite liner consisting of a textured geomembrane (GMX) over a hydrated needle-punched geosynthetic clay liner (GCL) for a wide range of normal stress, including high-stress conditions (>4 MPa). Tests were conducted with specimens placed between hard backing plates (single-interface) as well as between sand and gravel layers (multi-interface) to investigate the effects of local stress concentrations from coarse soil particles. Single- and multi-interface specimens experienced similar transitions from GMX=GCL interface failure at low normal stress to GCL internal failure at high normal stress. Failure surfaces for the single-interface specimens were essentially planar. Failure surfaces for the multi-interface specimens exhibited out-of-plane deformation (i.e., dimpling) that occurred because of variation in contact stress from the overlying gravel layer and increased with increasing normal stress. This deformation yielded modest percentage increases in peak shear strength and large percentage increases in large displacement shear strength and produced changes in local thickness and local bentonite dry mass per unit area for the GCL specimens. Direct shear tests conducted on single-interface GMX=GCL composite liners placed between hard backing plates are unlikely to reveal geomembrane out-of-plane deformation and damage effects but are likely to yield conservative (low) shear strengths for GMX=GCL composite liners that are placed in close proximity to coarse soils in the field. [ABSTRACT FROM AUTHOR]

This paper presents a case history of the successful application of observational method to instruction microtunneling with successive pipe-jacking. The microtunneling project is the construction of four parallel pipes under Guan River in Jiangsu, China. Four parallel tunnels with external diameter of 4,160 mm and horizontally spaced at 4.8 m apart were jacked over 450 m in cemented silty clay and sand by two slurry-balance microtunnel boring machines (MTBM) at a depth of 4.6 m under the river bed. Since the overburden soil is very thin, proper control of tunneling operations was of utmost importance for maintaining the stability of the river bed. In order to optimize the operation parameters prior to construction under the river bed, a field trial was conducted, which included measurement of ground surface settlement, subsurface settlement, and lateral displacement of the subsurface soils, as well as excess pore water pressure and earth pressure. The relationship between ground response and construction operation parameters is summarized. Appropriate operation parameters were applied during tunneling under Guan River. Although tunneling and pipe jacking under the river was successfully carried out, a difficulty was encountered when the MTBM reached the opposite bank and large settlements were observed. This paper discusses the technical issues faced and lessons learnt from interpretation of the monitoring data collected. [ABSTRACT FROM AUTHOR]

Failure of foundations induced by earthquakes occurred many times in the past. There is a general lack of data recorded during earthquakes in the field about seismic response of such foundations. According to the results of some previous laboratory tests and numerical analyses, anisotropy of fabric of soil grains has significant influence on dynamic soil response. However, there is hardly any realistic physical data available to analyze the influence of fabric anisotropy on the response of foundations during earthquakes. Centrifuge tests are small scaled model tests which have been widely used to study the mechanism of response and to verify and validate design methods and numerical simulations. In this study, 12 centrifuge tests were carried out to study the effect of fabric anisotropy on seismic response of foundations. Important parameters in the response are evaluated and implications for design are discussed. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

The discussers considered two possibilities: (1) 10% of the pile load transferred to the pile toe and 90% to the pile shaft and (2) 50% of the pile load transferred to the pile toe and 50% to the pile shaft. With the loading carried by the raft and the pile group, the settlement of the piled raft could be simply evaluated by the Aoki and Lopes ([1]) equations. The calculation of the raft and pile group stiffness allowed the estimation of the load shared by the raft and that shared by the pile group. [Extracted from the article]

Tables 2 and 3 list the calculated results of HT ht obtained by the discussers, along with the values of HT ht , HT ht , HT ht , and the shape factor HT ht for the piled raft foundation cases listed in Tables 1 and 2, respectively, in the original paper. None of the calculated values of HT ht are greater than 1.15. [Extracted from the article]

What will be the limiting condition for the maximum number of piles in a raft that can be used for the reliable and accurate calculations of HT ht and HT