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Drilled shafts are cast-in-place concrete, deep foundation elements that require high levels of quality control to ensure the borehole does not become unstable either during excavation or during concreting. Bentonite slurry is a popular choice among state DOT officials nationwide to maintain borehole stability as it has a long history with reasonable load carrying performance. However, specifications developed to replicate successful shaft construction are largely based on empirical data. Further, as slurry construction is a blind process, the final as-built shaft is rarely visually inspected and much of the perceived concrete flow and slurry interaction with rebar and the soil interface are largely unverified. This thesis presents the wide range of nationwide specifications for slurry viscosities (upper and lower) and notes that in only one case out of a hundred (50 states with an upper and lower viscosity limit) is there a rational basis for setting the limit. To this end, the objective of this thesis was to provide compelling evidence to support or dispute present upper viscosity limits. The study was part of a larger scope to show the effects of high viscosity slurry on concrete / soil interface and rebar bond. However, this thesis addresses only the latter via large scale testing to show concrete flow patterns, the build-up of bentonite slurry on rebar, and the degradation of rebar pull-out capacity as a function of bentonite slurry viscosity. Pull-out test results from 126 specimens, comprised of No. 8 rebar embedded in 42in diameter shafts, showed that rebar bond degraded as much as 70%#37; and more when in the presence of bentonite slurry that conformed to most state viscosity specifications (40 to 90 sec/qt). Visual inspection which is rarely possible on drilled shafts showed convincingly that the concrete that flowed through the cage to form the cover concrete does not fully encapsulate the rebar. In most cases a void/crease was formed reflecting the cage grid and which would provide a pathway from the soil pore water directly to the reinforcing steel. While present specifications nationwide dictate bentonite slurry ranges from a minimum of 28 to a maximum of 60 sec/qt, the study findings indicate that only viscosity levels of 30 sec/qt and below are reasonable from both a bond and durability stand point. As pure water has a viscosity of 26 sec/qt, this leaves only a very slight window of acceptability which is unlikely to provide sufficient lateral borehole stability.

The first part of our study introduces a new method for rapidly generating an "improved" Stribeck curve (i.e. Stribeck+ curve) that, compared to traditional Stribeck curves, shows a more complete tribological picture of the chemical mechanical planarization (CMP) process. The method significantly reduces the consumables and time required to obtain the curve compared to traditional means. Results of the Stribeck+ curve are consistent with individual tests using several different consumables combinations. All copper CMP Stribeck+ examples clearly indicate the lubrication mechanism and transitions thereof between different polishing conditions. Variability in COF as well as a much wider range in U/P are also explored. In the second part of our study, the Stribeck+ curve is successfully applied to silicon dioxide CMP processes to characterize the tribology of such processes under different process conditions and consumables. Results show our Stribeck+ curve methodology to be capable of rapidly determining and differentiating the tribological mechanism among all cases studied. The Stribeck+ curve helps indicate process stability as shown by the spread of the COF vertical clusters. The Stribeck+ curve also confirms a previously known effect that the greater the ratio of pad’s up-features to the total pad area, the greater the probability of wafer hydroplaning. As the third part of our study, we investigate the effect of different pad surface micro-textures on the tribological, thermal and kinetic attributes during copper CMP. Different micro-textures are generated by two different chemical vapor deposited (CVD) diamond-coated conditioner discs (i.e. Disc A and Disc B). Results show that while pad temperature and removal rate increase with polishing pressure and sliding velocity on both discs, Disc B generates consistently lower removal rates and COF than Disc A. To fundamentally elucidate the cause(s) of such differences, pad surface contact area and topography are analyzed using laser confocal microscopy. The comparison of the pad surface micro-texture analysis indicates that Disc A causes a pad surface with a smaller abruptness (λ) and much more solid contact area which results in a higher removal rate. In contrast, Disc B generates less contact areas and COF. A two-step modified Langmuir–Hinshelwood model is employed to simulate copper removal rates as well as chemical and mechanical rate constants. The simulated chemical to mechanical constant ratios indicate that Disc A produces a more mechanically limited process under all conditions tested. In the fourth part of our study, the position of a slurry injection system (SIS) is optimized to achieve a more cost-effective and environmentally benign CMP process using a widely-adopted ceria-based "reverse slurry". Here, SIS is configured with different angles in order to investigate slurry dilution characteristics caused by residual pad rinsing with ultrapure water (UPW) that is known to affect silicon dioxide removal. UPW dilution effect on removal rate, coefficient of friction and pad surface temperature is explained by maintaining a constant dilution ratio for each of the SIS configuration tests. Results indicate that SIS negative rotation angles increase the actual slurry dilution ratio on top of the polishing pad. This generates more Ce3+ which boosts removal rates. Application of negatively rotated SIS allows significantly lower slurry flow rates and/or shorter polishing times leading to more environmental friendly semiconductor manufacturing processes. Finally, it is confirmed that variations in SIS configuration has no impact on silicon dioxide to silicon nitride removal rate selectivity. In the fifth and final part of our study, the silicon dioxide removal rate using a "reverse" ceria-based slurry is investigated under four different combinations of conditioning modes and slurry application methods. In a “reverse” slurry, addition of water acts to promote material removal. Overall, the process using ex-situ conditioning with the SIS results in the highest removal rate, while the process using in-situ conditioning with the conventional point application (PA) generates the lowest removal rate. This study explains the differences in silicon dioxide removal rate based on the variations of the actual slurry dilution ratio on the pad associated with conditioning and slurry application methods. Frictional analysis and Stribeck+ curves are employed to elucidate the tribological characteristics. Results show that the conditioning modes and the slurry application methods vary the extent of the polishing vibrations. Silicon dioxide removal rate is found to linearly correlate with the extent of COF fluctuation. The work underscores the importance of optimum slurry flow dynamics and injection geometry to obtain a more cost-effective and environmentally benign CMP process.

In recent years drilled shafts have become the preferred foundation method for marine bridges. Typically, the drilled shaft is selected over traditional driven piles due to soil strata encountered, construction economy, increased lateral stiffness requirements, and/or vibration control considerations. The most critical component in drilled shaft construction is borehole stabilization. Wall sloughing or groundwater inclusion can have devastating effects on the strength of the finished shaft however recent research has shown that the materials, more specifically the slurry, used to accomplish stabilization may be having a negative impact on the durability of the finished product. This thesis investigates the durability of drilled shaft specimens as it relates to the slurry type and viscosity. Electrochemical corrosion potential test results from 23 lab cast specimens showed that the shafts cast using bentonite slurry were 54% more likely to exhibit corrosion potential crossing the ASTM threshold of -350mV. The laboratory setting allowed for visual inspection of each shaft. This inspection showed reflective quilting on all bentonite cast shafts, this quilting was visible to a lesser degree on select polymer cast shafts and not present on shafts cast in water. This creasing appears to be directly related to the slurry used and the resulting decrease in durability. While current construction practice favors the use of bentonite slurry, the study indicates that both polymer slurry and the casing method are more advantageous from a durability standpoint.

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