TABLE OF CONTENTS In order to perform a shoring design, it is necessary to use several engineering parameters and understand some basic concepts. Some of the parameters are measured, some developed and others are derived. Together they form the input data for the empirical and analytical methods used to design the shoring systems used today. The empirical design methods are based on the systematic collection and analysis of data obtained over many years on earth retention systems such as braced and tied-back soldier pile walls. For other systems, like soil nailed walls, analytical methods are used. Both these approaches accurately and effectively predict lateral earth pressures.
Because of layering of dissimilar soils, not all earth retention systems lend themselves to analytical methods. Lateral earth pressures can also be influenced by the types of restraint used. This is called soil-structure interaction and further confounds the solution of earth retention problems by the use of first principles. The inputs necessary for these design methods include the following.
The angle of internal friction defines the increase in shear strength of a soil with increasing confining pressure. It is calculated by plotting a series of triaxial tests as Mohr Circles on a plot of principle stress vs. shear strength. This plot is called a Mohr circle diagram (see Figure 8.1). The asymptote of several Mohr circles is called the Mohr-Coulomb envelope. The angle of internal friction is the slope of the Mohr-Coulomb envelope and is defined in degrees from the horizontal.
