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CHAPTER 4 : SUPPORTED EXCAVATION AND SUBSURFACE WORKS - Coggle Diagram
CHAPTER 4 :
SUPPORTED EXCAVATION AND SUBSURFACE WORKS
UNSUPPORTED EXCAVATIONS
Cut with free slopes in soft cohesive soils are limited to very shallow depths (maximum 3m)
Require protection using different technique
Slope protection against erosion using geotextile membrane
Providing a filter layer made of gravel or single-grained concrete.
Stabilising the slope by means of vacuum drainage
without additional measure
supported with timber piles and geotextile mat (intermediate excavation stage)
If berms and sloped excavations remain unprotected or unstabilised, delayed slides and mass flow can occur.
A slope up to 45o (1:1) can be used for temporary slopes without a need further verification of its safety, provided that slope is located above groundwater.
Figure
SUPPORTED EXCAVATIONS
Excavation supports structures include all means and methods of preventing a collapse of the earth walls that surround an open excavation.
Excavation support is generally required for excavations in excess of 6 ft (1.8 m) or excavation that are not sloped.
OSHA has mandated that any excavation or trenching operation that goes 5ft ≥ below ground level must utilize an acceptable excavation support technique.
Factors affecting the performance of supported excavations
Parameters under designer control
Type of support system
Stiffness of support system
Degree of wall embedment
Degree of pre-loading
Parameters partially under design control
Method of support system construction
Construction period
Method of construction of structures within excavation
Size of surcharge loads
Weather
Fixed parameters not subject to designer control
Subsoil conditions and properties
Surrounding structures
Excavation shape and depth
VERTICAL AND HORIZONTAL EXCAVATION
Horizontal excavations are performed in the construction or installation of water supply and sewage pipelines, telecommunication and electrical cables, as well as roads and rail tunnels.
Vertical excavations are mainly for constructing shafts, basements, piles, piers, wall caissons and wells.
primary differences between the vertical and horizontal excavations
Accessibility
As the working face of vertical excavation is horizontal, it is readily accessible (to be walked or driven on)
Alignment
Alignment in a vertical excavation is assisted by gravity, i.e. using dead weights as loads and reactions in soil cutting system that hung by a cable
Removal of spoils (excavated soil cuttings or muck)
for deep vertical excavations, hoist, lifts, and cranes are required to remove the spoils
Side supports
as vertical excavations can be circular, square, rectangular or simply irregular-shaped
EXCAVATION METHODS AND SPOIL REMOVAL
Small-sized excavations
Vertical circular holes
Square or rectangular trenches of similar sizes
Vertical excavation more than several meters wide
Tunnels
Excavation of river or sea beds
Types of Earth Retained Walls
Braced walls, soldier pile and lagging walls
Sheet-piling or sheet pile walls
Pile walls (contiguous, secant)
Diaphragm walls or slurry trench walls
Prefabricated diaphragm walls
Reinforced concrete (cast-in-situ or prefabricated) retaining walls
Soil nail walls
Cofferdams
Caissons
Jet-grout and deep mixed walls
Top-down construction
Partial excavation or island method
Retaining Systems for Deep Excavation (common system)
Contiguous Piles
Secant Piles
Sheet Piling
Diaphragm Wall
Vertical Soldiers And Horizontal Lagging King Post Method
Case Studies
IT Tower Lahore
Alamgir Tower Lahore
Washington Convention Center, Washington, DC