UFC 3-220-01N
15 AUGUST 2005
CHAPTER 8
EXCAVATIONS, FILL, BACKFILL, AND SOIL STABILIZATION FOR STRUCTURES
8-1
EXCAVATIONS
8-1.1
Introduction and Scope
This chapter covers the methods of evaluating the stability of shallow and deep
excavations. There are two basic types of excavations:
"open excavations" where stability is achieved by providing stable side
slopes
"braced excavations" where vertical or sloped sides are maintained
with protective structural systems that can be restrained laterally by
internal or external structural elements. Guidance on performance
monitoring is given in Logging the Mechanical Character of Rocks,
Chapter 2.
8-1.1.1
Methodology. In selecting and designing the excavation system, the
primary controlling factors will include:
soil type and soil strength parameters
groundwater conditions
slope protection
side and bottom stability
vertical and lateral movements of adjacent areas, and effects on
existing structures
8-1.1.2
05, Dewatering and Groundwater Control.
8-1.2
Open Cuts
8-1.2.1
Sloped Cuts. Depth and slope of an excavation, and groundwater
conditions control the overall stability and movements of open excavations. In granular
soils, instability usually does not extend significantly below the excavation, provided
seepage forces are controlled. In rock, depths and slopes of excavation, particular joint
patterns, in situ stresses, and groundwater conditions control stability. In cohesive soils,
instability typically involves side slopes but may also include materials well below the
base of the excavation. Instability below the base of excavation, often referred to as
bottom heave, is affected by soil type and strength, depth of cut, side slope and/or berm
geometry, groundwater conditions, and construction procedures. Methods for
controlling bottom heave are given in UFC 3-220-10N.
8-1
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