| 1. |
The term post-grouting, or tip or base grouting, refers to a variety of practices related to injection of grout under pressure below the tip of a drilled shaft foundation to improve performance when subjected to compressive axial load. |
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True |
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False |
| 2. |
Although post-grouting of drilled shafts has been performed for nearly four decades in Europe, there has been limited application of post-grouting in the United States (U.S.). Variations of post-grouting have received increased interest within the United States private and public sectors following research supported by the Florida Department of Transportation (FDOT) in the early 2000s. Additional research has also recently been conducted for other state Departments of Transportation (DOTs) to evaluate the effectiveness of post-grouting for improving the performance of drilled shafts as structural foundations. |
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True |
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False |
| 3. |
Which one of the following are claimed by post-grouting a the tip of the drilled shaft? |
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Increase the tip resistance of drilled shafts, thereby allowing design lengths of drilled shafts to be shortened. |
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"Stiffen" the load-deformation response of a shaft by pre-mobilizing side and tip resistance. |
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Verify a "lower-bound" load carrying resistance of a drilled shaft as a function of the maximum sustained grout pressure. |
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Reduce the effects of, and risk associated with, bottom cleanliness and potential "soft-bottom" conditions. |
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All of the above |
| 4. |
Grout is a broad term that describes construction material used for a variety of functions. Which one of the functions below can grouting help? |
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Permeating the ground to fix soil/rock in place, |
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Densifying loose soils |
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Displacing soft soils |
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Filling voids |
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All of the above |
| 5. |
Chemical grout is typically used in cohesionless soils and rock for creating water barriers, sealing leaks, and filling small voids and fissures. In addition, chemical grouts may be used as an improvement mechanism for bearing capacity and excavation support. Chemical grouts are soluble in water and may consist of one or more components, including sodium silicate or acrylamide. |
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True |
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False |
| 6. |
Cement-based particulate grouts __________________ because of their cost effectiveness, and because the methods used to prepare and place the grout are widely known and readily available throughout the construction industry. |
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are most commonly used |
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are seldom used |
| 7. |
Cement-based particulate grouts have different classifications depending on the particle size and composition of the cement. There are five types of Portland cement (ASTM Standard C150, 2012). Type I cement is most common and represents most of the cement production in the U.S. Type II cement provides protection against moderate sulfate exposure and is suitable for use when the concrete is placed in direct contact with sulfate-containing soil or in regions where aggregates susceptible to alkali-silica reactivity are employed. For PGDS applications, neat grouts comprised of water and Type I/Type II Portland cement (often found as a combination Type I/II) are common. Type III cement is known for having “high early strength.” Type IV cement has a “low heat of hydration,” and has been utilized for grouting in and beneath dams, and/or when careful control of hydration is needed. Type V cement is used where high sulfate resistance is required. |
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True |
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False |
| 8. |
The particle size distribution of the cement ______________ in determining whether a grout can penetrate a specific soil formation. The size of cement particles also has an important effect on the rate at which the particles will hydrate when mixed with water. |
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Plays a major role |
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Does not play any role |
| 9. |
Bleed is the separation of water from the grout solution. Bleed can be reduced by thorough mixing and use of a lower water-to-cement ratio. Bleed development for neat cement grouts is related primarily to the fineness of the cement and the water-to-cement ratio. |
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Lower water- to cement ratio |
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Higher water to cement ratio |
| 10. |
In this course PGDS stands for |
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Post grouted drilled shaft |
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Prior ground design schematics |
| 11. |
Use of PGDS has expanded in states where drilled shaft construction is common. The most prevalent use of PGDS has been for projects with large axial loads that require relatively large diameter shafts with lengths exceeding ____________. |
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50 ft or more |
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5 ft or more |
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10 ft or more |
| 12. |
Several different devices have been used for post-grouting of drilled shafts. These devices can be classified as open-type systems or closed-type systems. An open-type system is an apparatus for delivering grout at the shaft tip without any means to contain the grout or provide separation between the grout and the surrounding ground. In an open-type system, the grout is directly injected into the surrounding ground and is free to flow along the path of least resistance. |
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True |
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False |
| 13. |
A closed-type system is an apparatus with a barrier (e.g., flexible rubber membrane) that is intended to contain the grout and provide separation between the grout and the surrounding ground. Barring rupture of the separation barrier, grout will be contained within the apparatus. |
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True |
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False |
| 14. |
There are numerous reported cases where load tests have been performed on comparable ungrouted and post-grouted drilled shafts at the same site. Results of most of these tests consistently demonstrate that post-grouting improves the axial load-deformation response of drilled shafts either by “stiffening” the response of the shafts, by increasing the ultimate axial resistance, or both. However, the scatter present in the load test measurements _____________, which makes it difficult to develop methods for predicting the improved performance of PGDS. |
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Is substantial |
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Is minor |
| 15. |
Such scatter is not uncommon in results of load tests of ungrouted drilled shafts and of many other deep foundation element types, but is possibly aggravated by the use of different grouts, grout delivery systems, and grouting procedures across the various reported cases, as well as by different shaft construction and load testing methods. |
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True |
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False |
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