Building Design and Construction Handbook - Merritt - Ventech!

SOIL MECHANICS AND FOUNDATIONS 6.23
termine the foundation type (shallow versus deep foundation), calculate the amount
of settlement of the structure, evaluate the effect of groundwater on the project and
develop recommendations for dewatering of underground structures, perform slope
stability analyses for projects having sloping topography, and prepare site development
recommendations.
6.3 LABORATORY TESTING
6.3.1 Introduction
In addition to document review and subsurface exploration, an important part of
the site investigation is laboratory testing. The laboratory testing usually begins
once the subsurface exploration is complete. The first step in the laboratory testing
is to log in all of the materials (soil, rock, or groundwater) recovered from the
subsurface exploration. Then the geotechnical engineer and engineering geologist
prepare a laboratory testing program, which basically consists of assigning specific
laboratory tests for the soil specimens. The actual laboratory testing of the soil
specimens is often performed by experienced technicians, who are under the supervision
of the geotechnical engineer. Because the soil samples can dry out or
changes in the soil structure could occur with time, it is important to perform the
laboratory tests as soon as possible.
Usually at the time of the laboratory testing, the geotechnical engineer and engineering
geologist will have located the critical soil layers or subsurface conditions
that will have the most impact on the design and construction of the project. The
laboratory testing program should be oriented towards the testing of those critical
soil layers or subsurface conditions. For many geotechnical projects, it is also important
to determine the amount of ground surface movement due to construction
of the project. In these cases, laboratory testing should model future expected conditions
so that the amount of movement or stability of the ground can be analyzed.
Laboratory tests should be performed in accordance with standard procedures,
such as those recommended by the American Society for Testing and Materials
(ASTM) or those procedures listed in standard textbooks or specification manuals.
For laboratory tests, it has been stated (M. J. Tomlinson, ‘‘Foundation Design
and Construction,’’ 5th ed., John Wiley & Sons, Inc., New York):
It is important to keep in mind that natural soil deposits are variable in composition
and state of consolidation; therefore it is necessary to use considerable judgment based
on common sense and practical experience in assessing test results and knowing where
reliance can be placed on the data and when they should be discarded. It is dangerous
to put blind faith in laboratory tests, especially when they are few in number. The test
data should be studied in conjunction with the borehole records and the site observations,
and any estimations of bearing pressures or other engineering design data obtained
from them should be checked as far as possible with known conditions and past
experience. Laboratory tests should be as simple as possible. Tests using elaborate
equipment are time-consuming and therefore costly, and are liable to serious error
unless carefully and conscientiously carried out by highly experienced technicians. Such
methods may be quite unjustified if the samples are few in number, or if the cost is
high in relation to the cost of the project. Elaborate and costly tests are justified only
if the increased accuracy of the data will give worthwhile savings in design or will
eliminate the risk of a costly failure.