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By Barry C. Roth

A Real Time Automated Remote Reading Electrolytic Tilt Monitoring System was effectively deployed for monitoring an existing five story brick building during underpinning, shoring and excavation operations for a directly adjacent thirty-foot deep excavation. The monitoring system was comprised of four sets of uniaxial electrolytic tilt meters connected to a Campbell datalogger with multiplexer, cellular modem and solar power. The excavation was for the foundation and underground parking as part of a new 55 story tower complex. Challenges to the contractors and to our monitoring personnel which were addressed included a tight urban site contemplating property line to property line new construction with directly adjacent old existing buildings, buried concrete foundations from former site use, cohesionless pervious sandy soils and high groundwater. Highly variable and diurnal ambient temperature regimes due to adjacent building shadows required careful corroboration and application of temperature corrections to the raw data. Earth tides were suspected on a very small scale and investigated by correlation between the data and the local sinusoidal tidal ephemera. Incidental inadvertent contractor interference with the instruments during underpinning due to site constraints was readily detected.

Jan 1, 2007

By B. Francis

Literature provides only limited information regarding the behaviour of laterally loaded piles socketed into weak rock masses. A laboratory program, comprising a number of tests of scaled models of the pile/rock mass system has been conducted. A synthetic rock, known as Johnstone was used to simulate a naturally weathered and fractured siltstone. The load-deflection behaviour of the test piles was measured, and strain gauges were fixed to the model piles to assess the bending moments. The laboratory results are compared with the results from several theoretical models, some of which are in the form of commercial software packages. This study highlights the inadequacy of existing methods to adequately model the influence of rock joint orientation in geotechnical design. Additionally, numerical modelling of the pile/rock mass system was carried out using the discrete element program UDEC. The importance in modelling the system using discontinuum mechanics is highlighted, particularly to capture the anisotropy of the rock mass.

Jan 1, 2004

By H. (Sam) Salem

A site investigation for a wide and tall hotel building, in the San Juan Bay area, Puerto Rico, indicated a soil profile of silty clay on sand, soft and loose enough to require piled foundations. The apparent uniformity of the soil profile across the site indicated that a single pile driving and termination criterion could be applied to the installation of the piles ? driven precast concrete piles. Because of the size of the site and importance of the project, the project also included a static and dynamic testing programme. The dynamic monitoring using the Pile Driving Analyzer (PDA) verified a consistent hammer operation. However, the results of the static loading tests showed significant and inconsistent variation in pile capacity between locations and little correlation between end-of-driving and restrike penetration resistances (blow-counts) and pile capacity. Therefore, it was not possible to rely on a simple depth and blow-count termination criterion for the site. In contrast, pile driving response in terms of measured reflected force and mobilized resistance coupled with CAPWAP analysis gave a reliable correlation to the results of the static loading tests. As presented in the paper, the dynamic testing programme was enlarged and used to develop and verify a complex set of termination criteria tailored for the multitude of conditions encountered across the site to achieve and ensure economical and safe pile installation.

Jan 1, 2008

By Stephen T. Bloomer

The application of a direct current electrical potential between a metallic pile and a fine grained soil results in an almost instantaneous change in the magnitude of the forces acting on the pile. During installation, with the pile connected as a cathode, the driving force needed can be reduced dramatically. Reversal of the polarity results in an increase in ultimate bearing capacity. The cause of the aforementioned phenomenon has been investigated and found to be two-fold; ie the electro-osmotic transport of pore-water and the electro-chemical hardening of the clay in close proximity to the pile. In the case of the former effect, the pore-water is transported towards the cathodic pile resulting in a temporary, reversible change in the engineering properties of the clay surrounding the pile. This effect is represented by a change in Skempton's Adhesion Factor (a). A total of one hundred and forty eight model tests was undertaken to study the change in the a valve using different types of metallic pile. The tests revealed changes in bearing capacity related to embedded length, skin-friction, end bearing and electro-osmotic gradient. It was shown in skin-friction-only tests that variations in soils strength across the soil profile caused by the electro-osmosis caused resultant changes in bearing capacity. This work is being carried out with the collaboration of Hercules Piling, a subsidiary of Stent Foundation Ltd.

Jan 1, 1996

By Paul W. Mayne

The axial load-displacement-capacity and load-transfer response of deep foundations can be conveniently assessed by geophysical piezocone tests that provide four independent readings with depth, including tip stress (qt), sleeve friction (fs), porewater pressures (ub), and shear wave velocity (Vs). The penetration data (qt, fs, and ub) of the CPT are utilized to obtain the pile side friction (fp) and end bearing capacity (qb) while the shear wave measurements provide the initial stiffness. Within an elastic continuum framework, the axial pile deflections are calculated and an approximate nonlinear response is obtained by modulus degradation from small-strain response (G0) to intermediate- and large-strains (G). The continuum solution permits separation of load transfer along the sides and proportion to the base. Applications are shown for case studies involving an end-bearing drilled shaft, two friction-type drilled shafts in Alabama and Georgia, and a "Class A" prediction involving driven pipe piles in residuum of the Atlantic Piedmont geology. Load-transfer data were available for the drilled shaft foundations.

Jan 1, 2002

By Dan Brown

Renewal and revitalization of transportation presents a challenge in the need for replacement, repair, and improvements of existing bridges, as well as increased construction of transit systems within existing transportation rights of way. Difficulties with conventional deep foundation systems occur because of the limited site access, adjacent structures, the need to maintain traffic, and other constraints on construction activity. Major projects are often performed in a design-build contract environment in which the schedule is aggressive, and where speed and reliability represent major considerations. Foundation designers are confronted with a need to solve problems with a construction-oriented mindset, where typical experience with lowest cost solutions may not reflect the most effective approach. This presentation presents an overview of the challenges that may affect design and construction of deep foundations in this environment and the methods that have successfully been employed on several large transportation projects in the U.S.

Jan 1, 1900

By Andrew Baxter

The Crystal Bridges Museum of American Art in Bentonville, Arkansas is a beautiful glass and concrete structure cut into a valley that mingles with water ponds spanned by multiple bridges with suspended roofs. Or, at least it will be when completed in 2009. At Crystal Bridges, most of the proposed buildings involve cuts up to 50 ft high to be retained by the building structures. This requires the construction of retaining walls adequately founded to support lateral loads of up to 70 kip/ft. To add to this difficulty, the site is within a karst region with all the variability and irregularities associated with solutioning and erosion of the parent rock in this environment. The irregular rock profile made it virtually impossible to conceive a predictable arrangement of shallow footings and shear keys for the retaining walls. The existence of layers of soft soils within a hard rock formation made a caisson foundation impractical. The authors developed an innovative solution based on micropiles, which proved to be invaluable from a cost and schedule point of view. In areas where rock was shallow, micropiles were used as ?shear pins? to transfer the horizontal loads to the rock. In areas with significant overburden, a system of vertical and battered micropiles was devised to carry vertical and horizontal loads from the retaining walls. This paper presents a detailed description of the design and installation of the micropiles used as shear pins, and includes the results of lateral load tests performed on full-scale models of the grade beams on shear pins. The work performed shows that micropiles in rock can be effectively utilized for support of significant lateral loads provided that an adequate arrangement of suitably sized micropiles is provided, and that micropiles used as shear pins may develop significant tensile stresses when loaded laterally.

Jan 1, 2008

By Peter Iovino

Unfortunately, I don't know the unit cost per cubic yard of treatment. I reflected on that yesterday and I don't think that we considered the use of micropiles. They could have been an option. The challenge may have been picking up some of the lateral load but I think the micropiles could have been installed on a batter and perhaps extended to rock. We could have considered them, but I do not believe we explored micropiles as an option for this project.

Feb 10, 2003

By Lois G. Schwarz

I did not make studies about this parameter but I can say that some researchers recommend using low C3A cements to repair masonry mortar in order to reduce a possible combination with sulphate that can be present in old mortars.

Feb 10, 2003