With the ever increasing need for MSE walls, the study of the interaction between soil and geosynthetics has become increasingly relevant. New concepts are constantly being researched, including the use of industrial byproducts as alternative backfill materials. The idea that byproduct material could somehow be a suitable fill for these MSE walls may spark new opportunities. One such byproduct being researched is dredged material. The suitability of dredged material as a backfill would not only contribute to lower construction costs, but would also benefit local confined disposal facilities looking to reduce their already overflowing dredged material accumulation. This thesis further considers the use of dredged material by evaluating its interface shear strength with uniaxial geogrids. A series of laboratory pullout tests were conducted using two types of uniaxial geogrids (UX1400 and UX1700) embedded in three different soil types (Monterey Sand and two different dredged materials). The laboratory results are used to examine the effect on the coefficient of interaction of the various parameters governing the pullout resistance. The results of this study show that: (1) the presence of adhesion to characterize the soil-reinforcement interface shear strength causes a decrease in the coefficient of interaction with increasing normal stress, (2) the reinforcement length of the geogrid was found not to affect the coefficient of interaction; provided that boundary effects are minimized, (3) the dredged material, tested wet of optimum, showed a response consistent with an undrained behavior, which produced pullout resistances significantly lower than that of the Monterey Sand, (4) the coefficient of interaction for the UX1700 was comparatively higher than that for the UX1400; however the differences obtained when testing Monterey Sand were similar to those obtained when testing the dredged materials. / text

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 research objective was to develop a new competitively priced, high strength macrosynthetic fiber for concrete reinforcement. Mechanical bond properties were examined through aligned and inclined pullout testing. Variables involved in optimizing these properties included materials, fiber cross section, and other changes made through manufacturing processes. In addition to extensive pullout testing, improvements to fiber properties were explored through tensile testing, creep testing, and fiber performance in concrete mixtures. Practical considerations were also made, such as manufacturing processes, cost, and workability. Properties of synthetic microfibers were also considered for use in engineered cementitious composites. Synthetic macrofibers containing PVDF demonstrated high bond strength in pullout testing. Fibers demonstrating the highest performance in FRC testing were those with additional mechanical anchorage such as fibrillation or embossment. EVA as an additive did not exhibit increased interfacial bond, but further research was recommended. Further research on deformed fibers containing PVDF was also recommended.

Increasing quantities of dredged material (DM) from navigation waterways have led to a growing need to find alternative methods of disposal. Using this material in earthwork construction is a very attractive avenue, but poses concern of quality from a geotechnical standpoint. By blending DM with granular materials like industrial steel slag fines (SSF), studies have showed that the geotechnical properties of the mixture are greatly enhanced. If these materials can be proven to be competitive for use in earthwork construction, they would pose as an economically viable alternative, and would obviate the need for the relatively expensive conventional granular backfill. The scope of this project entailed the characterization of pullout interaction of SSF-DM blends in different proportions with Tensar uniaxial geogrids to determine an optimal combination for usage in earthwork construction. The media used for testing included the individual SSF and DM materials, and the 80/20, 50/50 and 20/80 blends mixed based on dry unit weights of the individual components. The SSF media comprised of particles smaller than 3/8 in. and classified as SW, while the DM was classified OH soil. Two Tensar uniaxial geogrids UX1400 and UX1700 were undertaken for the study. Pullout tests were conducted and performances of all the blends are compared with each geogrid at various normal pressures. Pullout loads and interaction coefficients give an idea of the quality of the interaction, and are studied in this thesis. Also, various variables that could potentially affect the pullout interaction are identified and investigated. Results show remarkably high pullout resistances for the 100% SSF and 80/20 SSF/DM media, and high interaction coefficients indicating excellent pullout interaction, even better than conventional sands. It was also clear that the dredged material exhibits very poor pullout interaction with geogrids. The 50/50 and the 20/80 SSF/DM media were significantly lower than the 80/20 SSF/DM blend in terms of quality of pullout interaction, but still higher than the 100% DM. The results observed with the 80/20 SSF/DM blend show that it is a suitable backfill material and also poses to be a very competitive and cost-effective alternative to be used in earthwork construction. / text

In this thesis different mechanical properties for shotcrete (sprayed concrete) such as compression strength, bond strength, bending tensile strength, elastic modulus, free and restrained shrinkage as a function of its age was investigated. One of the main issues was to investigate the difference between ordinary cast concrete and shotcrete. Reliable material data for young and hardening shotcrete is scarce which in the past have made such comparisons difficult. Also, less accurate data representative for cast concrete has often been used in numerical modelling and design analyses. The focus of the project has particularly been on the properties bond strength and restrained shrinkage for which two new testing methods has been developed and evaluated. Microstructural studies have also been performed as a complement to the bond strength testing. The bond to rock is one of the most important properties for shotcrete used as rock reinforcement. During the very first time after spraying the physical properties and the bond to the rock depend on the set accelerator and the micro structure that is formed. The investigation of early age bond strength of shotcrete is of great importance both from a production perspective and a safety perspective. The newly developed method was tested and evaluated and proved that it can be used for bond strength testing already from a couple of hours after shotcreting. The bond, or adhesion, depends on several factors such as texture of the rock, the type of accelerator, application technique, etc. In this work the development of the microstructure in the interfacial transition zone (ITZ) and strength of the bond was investigated. The results show that the bond strength is related to the hydration process, i.e. the strength gain of the shotcrete. The early development of the ITZ was here studied using a scanning electron microscope (SEM) making it possible to observe changes over time, before and after proper cement hydration. Restrained shrinkage cracking of shotcrete, especially in the case of shotcrete sprayed on soft drains that are parts of a tunnel lining not continuously bonded to the rock, can be detrimental for the sustainability of an infrastructure tunnel system. Maintenance and repair costs can be high over time. It is shown that the developed test method realistically captures the behaviour of shotcrete drains on hard rock in situ. The method can be used in the evaluation of different technical solutions for avoiding or minimizing shrinkage cracks in shotcreted soft drains. It can also be used to assess the performance of shotcrete fully bonded to a rock surface, with respect to the ability to prevent cracking or to distribute possible shrinkage damage into several fine cracks instead of one wide. / <p>QC 20140526</p>