CONCLUSIONS

Several conclusions were derived from this research project:

1. The cross-hole sonic logging method, despite certain limitations is; a) a valid and conclusive technique in assessing the integrity of deep concrete foundations, b) is flexibility and economical for use in deep shafts, c) is accurate and repeatable but highly sensitive to measurements errors, for example relatively minor deviations of a tube, can introduce significant deviation in the "first arrival time " picks that is related to the dynamic property of the medium as "apparent" velocity, d) is capable of locating structural defects and detecting velocity variations within a medium and, e) is a two-dimensional method and is difficult to interpret the results in terms of size and geometry of defects or lateral (in vertical cross-section perspective) variations in velocity distribution.

2. Accurate interpretation of CSL results is an important issue in evaluating the integrity of deep foundations. Tomography is a method that may overcome the limitations in CSL concerning the interpretation of results. Three-dimensional color-coded tomographic imaging adds an advantage to the CSL system output by allowing imaging with high accuracy, the location, size, and geometry of a defect.

3. Tomography software separates and presents certain specific velocities representing various questionable zones of defect geometry with high resolution.

4. An important advantage of tomography is the capability to provide a visual image of lateral variations in velocity within a structure. The process is capable of determining inter-tube velocity variations of 5 % , or better.

5. Laboratory measurements of the Ultrasonic Pulse Velocity (UPV) on samples of the same concrete mixture used in the tested foundation are effective to determine the velocity datum for accurately rating defects based on field velocity reductions.

6. UPV results can be used as the maximum velocity on the velocity scale (representing "good" concrete) for plotting tomographic imaging. Any zones with "degraded velocity" from the determined UPV value are considered either "questionable" or 'failed".

7. Zero probe-offset data produces the highest range of velocities because of the smaller path length during the CSL data collection. Best aperture and therefore highest image resolution converges when combining rays from several offsets. For tomography, CSL data collection with offsets is more effective for accurately imaging concrete structure.

8. Tomography research on Piney Creek Replacement Project has shown nonanalogy between the CSL test results, tomographic interpretation, and coring results. For this case study CSL data collection were performed four different times on the same shaft (initial test, test with the offsets, retest after 16 days of curing and retest after pressure grouting). Every time, the CSL data has detected the defect on the same horizon but with some improvement followed by the pile repair procedure. Based on the coring results the defect within the shaft better corresponded with 30 % decrease in velocity than 20 % decrease.