Search

This document is a closure to a previous paper titled "Foundation Settlement and Tilt of Millennium Tower in San Francisco, California." The authors respond to comments and questions raised by discussers regarding the design, construction, and analysis of the tower's foundation movements. They emphasize that their goal was to objectively document the data and provide interpretations of the soil deformation mechanisms that caused the settlements. They encourage further investigation and analysis of the case history to advance foundation engineering practices in dense urban environments. [Extracted from the article]

Existing projects indicate that a large number of pile boreholes formed via cement fly ash gravel (CFG) pile construction in soft soil could produce a borehole group effect in the absence of timely backfilling. The borehole group effect could cause ground settlement and threaten the safety of adjacent buildings, tunnels, and pipelines. However, the mechanism of the borehole group effect, causing serious deformation in surrounding soil, has seldom been studied, and there exists no simple simulation method to predict the borehole group effect. In this study, a case involving CFG pile boreholes in a soft soil area causing a significant settlement of surrounding buildings was introduced. Based on this case, a centrifuge test was designed to simulate the influence of a single borehole and multiple boreholes on the surrounding soft soil. The mechanism of the borehole group effect was investigated via centrifuge tests and the finite-element method. In the case of a single borehole, a horizontal circumferential stress arch and vertical stress transfer arch were formed in the soil, which effectively limited the shrinking deformation of the borehole wall. In the case of a large number of boreholes with a small spacing, the horizontal and vertical stress arches around the boreholes affected and weakened each other. As a result, the shrinking deformation of the borehole group was greater than that of the single borehole. In other words, the borehole group effect was found to cause serious deformation in the surrounding soil. To overcome the difficulty in the simulation of a large number of pile boreholes in engineering, the borehole-type conversion and multihole merging method was proposed. The simulation results indicated that the simplified method was reasonable. [ABSTRACT FROM AUTHOR]

A hand-calculation method for estimation of nonlinear load–settlement response of piled raft foundations (PRFs) embedded in sandy soils is developed using three-dimensional finite-element (FE) analysis in which the elastoplastic constitutive behavior of the soil is modeled using the unified Clay And Sand Model (CASM). Three types of PRFs with rectangular, strip, and circular rafts and with a variety of pile dimensions and arrangements are considered in the study. The PRFs are assumed to be embedded in five different sands (Ottawa sand, Erksak sand, Sacramento sand, Portaway sand, and Decomposed Granite sand) with different elastic properties, critical state parameters, and relative densities. Systematic parametric studies are performed to develop equations for the estimation of the average nonlinear settlement of PRFs. The maximum and differential settlements are also estimated from the average settlement. The proposed equations require the relative density, elastic constants, and critical state friction angle of sand, and the piled raft geometry and properties as inputs. The settlement equations are applicable to PRFs of sizes similar to those considered in the study and can be used by practitioners for quick, initial estimation of PRF settlement as part of design calculations. [ABSTRACT FROM AUTHOR]

Time-dependent settlements of piled raft foundations embedded in consolidating clays were studied using three-dimensional (3D) finite-element analysis and critical state-based soil constitutive modified Cam-Clay (MCC) model. In this study, different small to large rectangular rafts connected to circular bored cast-in-situ piles resting on four different types of clays and with varying overconsolidation ratios (OCRs) (1, 2, and 5) for each clay under a single drainage condition were analyzed. The influence of various piled raft parameters (pile length, pile spacing, pile diameter, raft thickness) and soil parameters (Poisson's ratio of soil, soil critical state parameters, stress history of soil or OCR) on immediate and consolidation settlements of piled rafts were investigated. The detailed parametric study shows that critical state parameters and soil elastic properties have important roles in piled raft immediate and consolidation settlements. However, the pattern of parametric influence on immediate settlement and consolidation settlement is different. To capture the total settlement at the end of primary consolidation, a simple and quick calculation method for estimating the average soil subgrade modulus below the piled raft in consolidating clays is proposed through regression analysis and defining a combined influence parameter based on soil parameters, area ratio, and normalized loading. The results of the proposed method were compared with five case studies of piled raft foundations in various normally or overconsolidated clays showing satisfactory matches. It is believed that the proposed method will be very useful for design practitioners to get a quick estimate for the overall settlement of piled raft at the initial design stage. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to establish a complete analytical solution concerning the linear pressure distribution under rigid rectangular spread footings. An eccentricity diagram is developed to map the unique footing deformations and compression zones in each one of five distinct regions. For each region, the linear soil pressure, neutral axis position, and pressure values at the four corners are expressed in closed forms. The accuracy and consistency of the explicit expressions are verified by presenting several special boundary cases, whereas the physical interpretation is brought out by analyzing the eccentricity diagram. A generic nomogram providing the maximum soil pressure is also formed to promote efficient structural footing design. The developed analytical formulas for responses and resultants enable algorithmic implications without iterations and offer high computational efficiency. Proper examples, generated via developed computer software, exhibit how the theoretical content of this article is applied in practice. The software enables three-dimensional (3D) viewing of the deformed and undeformed physical and mathematical model of the structure, allowing detailed visual inspection of the results. [ABSTRACT FROM AUTHOR]

In the present paper, the response of cylindrical storage tank foundation resting on stone column-reinforced ground has been studied considering the separation between the bottomraft and ground under liftoff condition. The bottomraft of the tank is idealized by a circular plate. The stone column-reinforced ground ismodeled as a tensionless foundation. Soft foundation soil and granular fill are idealized as a spring-dashpot element and Pasternak shear layer, respectively. Stone columns are modeled as stiff nonlinear springs. The stone columns are converted into equivalent concentric rings with one stone column at the center to simulate the axisymmetric condition for the analysis. The governing differential equations are derived fromthe classical theory of thin plate and solved using the finite-difference technique. A parametric study is performed to investigate the differences between the response of tensionless and conventional elastic foundation systems. It is observed that tensionless foundation idealization is essential to analyze the liftoff and avoid erroneous design of the raft for the cylindrical storage tank. Recommendations are also suggested to avoid possible liftoff. [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 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]

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]

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 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.