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Additional Resources including The Red Book, Basics of Foundation Design.

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Correlation between concrete properties and sonic wavespeed using non-destructive field testing procedures

ABSTRACT


The correlation between the sonic wave speed in concrete and its compressive strength is one that has caught the interest of many geotechnical professionals dealing with Non-Destructive Testing (NDT) of concrete foundations. The present paper reports the findings from a study carried out by AATech Scientific Inc. (ASI) Engineers. Multiple miniature concrete columns are built with different mixes varying the content of aggregates, sand, and cement materials, along with several molded cylinders of each batch. The compressive strength of the samples was determined following ASTM C39/C39M-17 and sonic wave speed was determined using low strain Pile Integrity Testing (PIT). Similar work has been published by others, however, the present study targets the effects of concrete mix proportions and age. The NDT testing method used in the present study is an industry standard Quality Control (QC) testing method used in the field, as opposed to laboratory ultrasonic testing.

Effects of freeze-thaw cycles on earth pressure acting on shoring system

ABSTRACT


A case history is presented in this paper examining two 18-m deep sheet pile cofferdams supported by four levels of wale bracing with corner struts. The performance of the shoring system during construction was continuously monitored for a period of one year using vibrating-wire strain gages at critical locations where maximum compressive stresses are expected. The monitoring data presented in this paper reflects a period of frequent temperature fluctuation cycles. The strain data shows that the stress in corner struts builds up a net increase with each freeze-thaw cycle. The measured stresses retreated to their original estimated values after the complete spring thaw which helps to isolate the frost effect on the shoring supports. The paper addresses the freeze-thaw effects and suggests practical considerations for designing safe shoring systems in such harsh unpredictable climate.

Bidirectional pile testing: what to expect

ABSTRACT


Bidirectional (BD) testing of foundation piles was first introduced by Pedro Elísio (Brazil) in 1981 and Jorj Osterberg (USA) in 1987. It is still, however, not fully embraced by the industry despite its substantial technical and economic advantage over the conventional head-down test. This article provides a brief description of the state-of-the-art in bidirectional testing of foundation piles, advantages, difficulties, and recommendations. Case histories from the authors’ experience illustrate some issues that can be encountered in BD testing. One issue being the effect of uneven shaft resistance distribution on strain gage. Also discussed is the location of strain gages, and whether strain-gage instrumentation is warranted in short piles. This is intended to raise awareness and confidence in specifying bidirectional testing as an effective tool for optimizing a piled foundation design. The authors recognize the importance of sharing experience in a field where trial and error can come at high cost and better planning can lead to more rewarding tests.

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