resulted in a unit end bearing resistance of 330 ksf (15.8 MPa), which was significantly higher than design expectations. A rock soc- ket unit side resistance of 4.5 ksf (215 kPa) and an average overburden unit side resistance of 1.7 ksf (81 kPa) were mea- sured. The total side resistance for the entire shaft was in excess of 2,600 kips (11.6 MN) at less than 1/10 in (2.5 mm) of displace- ment. Although designed for end bearing, the service load would have been supported in side resistance, and it was unlikely the load would ever make it to the shaft base. San Diego project trestle bridge work area Load-displacement relationship for bi- directional test in Atlanta, Ga. In many cases, wet excavations are still evaluated with a simple weighted tape. However, other sensor-based methods exist for QA assessment of the shaft base that do not require downhole entry. The most common are penetrometer systems, such as SQUID and Mini-SID type devices. Although these methods have the obvious advantage of keeping personnel out of deep excavations, they too introduce difficulties related to needed preparations (e.g., set up, materials, etc.) and interpretation. On a recent project in San Diego, Calif., evaluation of the cleanliness of the bottom of the test shaft using a Mini-SID was specified. The excavation was accomplished using a spherical grab. The results of the Mini-SID indicated some sediment remained in the bottom of the shaft. However, in our experience, few or no uniform numerical criteria or standards exist to assess this type of excavated shape. The shaft was load tested by LTC using the bi-directional test method. The load test measured a higher-than-expected end bearing resistance, with no indications of soft toe in the load-displacement curve. Load-displacement relationship for bi- directional test in San Diego Use and Interpretation of QA Data With advancements in shaft bottom test methods and load testing performed on shafts that have employed these tech- nologies, project specifications should be re- evaluated and adjusted with respect to acceptable bottom cleanliness criteria. Specifications should present a method for evaluating bottom cleanliness but should also include rational procedures if the criteria are not achieved. If end bearing is not a design component, expending con- siderable time testing and evaluating bottom cleanliness need not be specified. In addi- tion, rejecting a shaft solely on a bottom cleanliness measurement, without consider- ing all the observational data and design requirements, can lead to poor decisions resulting in large expense, delays, etc. Typical drilled shaft integrity test methods include cross-hole sonic logging (CSL), gamma-gamma logging, (GGL), thermal integrity profiling (TIP) and low-strain dynamic testing (PIT). The chosen method is typically one favored by the engineer or contractor or based on local practice. Frequently, if the favored method produces an undesirable result, the first instinct is to reject the shaft and call for a remediation plan. Remediation measures may include coring and grout injection or a complete replacement. Fortunately, a secondary method can often be used for additional evaluation, which may confirm or refute the original results. On the same project in San Diego men- tioned above, the test shaft included nine 2 in. (51 mm) PVC access pipes for GGL. The GGL results indicated several zones of DEEP FOUNDATIONS • MAY/JUNE 2019 • 87
