172 haened. HIGHWAY BRIDGE FOUNDATIONS [Ch. 9 



plosive percussion blow (Creager, Justin, and Hinds, 1945, p. 19). The 

 resistance the sediment offers to tool penetration and extraction is com- 

 monly an important measurement of sediment character. This is 

 particularly true when procedures are standardized and measurements 

 are recorded by properly calibrated gages as attested to by results of 

 the standard penetration test (Terzaghi and Peck, 1948, p. 265). 



Undisturbed sediment or soil samplers capable of delivering samples 

 in a reasonably undisturbed state are essential if some of the more 

 significant soil mechanics tests are to be conducted. Of the many types 

 of samplers on the market, the thin-walled types, in general, meet 

 most of the sampling requirements. Certain situations, however, such 

 as the procurement of samples of very soft mud, clean uniform sat- 

 urated sand, or the sampling of sediment at the proposed tip elevation 

 for bearing piles, may require the use of special-purpose sampling 

 spoons. It should be kept in mind at all times that no amount of un- 

 disturbed sampling or testing is of any great significance if the sampling 

 procedure does not, or cannot on an economic basis, result in the pro- 

 curement of representative samples of the sediment in a sufficiently un- 

 disturbed condition to permit accurate evaluation of the control criteria 

 by means of standard testing procedures. It is the engineering geolo- 

 gist's job to determine whether or not the samples are representative 

 of the true conditions. If the site is one of such complexity that 

 samples are not diagnostic, the recognition of this fact is extremely 

 important, and the problem may then be handled by means of an ad- 

 justment in the safety factor or by incorporating extra flexibility in the 

 contract specifications. 



The large array of boring-tool types, samplers, penetrometers, and 

 other special tools designed for the foundation study purpose furnishes 

 ample evidence of the fact that there is no universal tool panacea for 

 work of this nature. Among the control factors regarding the choice 

 and extent of tools are the amount of foundation investigation work 

 to be done by any specific agency, the degree of geologic complexity 

 or variability of the general area and specific site of operation, and 

 the size of the project. Many thousands of dollars have been wasted 

 for the want of proper equipment to conduct efficient foundation 

 studies. Numerous attempts have been made to solve the problems 

 presented by complex or erratic conditions of sedimentation by liter- 

 ally drilling the site full of holes, taking continuous undisturbed 

 samples, and conducting innumerable shear, unconfined compression, 

 consistency limits, moisture, density, permeability, consolidation, etc., 

 tests, when possibly all that was required to be determined was how 



