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CHAPTER 4 : SUPPORTED EXCAVATION AND SUBSURFACE WORKS - Coggle Diagram
CHAPTER 4 :
SUPPORTED EXCAVATION AND SUBSURFACE WORKS
Type of Wall Support
Soldier beam and lagging
Pairs of soldier beams are driven to a depth slightly below the final excavation.
Their spacing is in the order of 6 to 10 feet so that available timber can be used for lagging.
Soldier Pile - Tremie Concrete (SPTC)
SPTC is used for very difficult conditions in soft ground with a high water table.
Soldier piles are set in predrilled holes, and the space between flanges of adjacent soldier piles is excavated and filled with bentonite slurry.
For very wide excavations, raker bracing is used.
Soil Nailing
Soil Nailing is an in situ reinforcing of the soil while it is excavated from the top down.
Soil nailing requires a unusual amount of hand work, craftsmanship and geotechnical knowledge to construct
Examples
North West Animal Facility, University of California at Berkeley
Chemistry Building, Washington State University, Pullman, Washington
The Beckman Center, University of California San Diego
Excavation Bracing
For narrow excavations, internal struts are most appropriate.
Before struts are installed, a horizontal member called waler is placed against the soil support.
Tieback Systems
Tiebacks (or anchors) are structural system which acts in tension and receives its support in earth or rock.
They consist of rods that extend well beyond any potential failure surface into firm undisturbed soil or rock.
Some tiebacks are made with high tensile cables grouted into rock and prestressed against a wale, and others utilizing ordinary steel rod or reinforcing steel.
Examples
Two Renaissance Square, Phoenix, Arizona
MODES OF FAILURE FOR EXCAVATION SUPPORT SYSTEMS
Overturning
Sliding
Overstresse of foundation
Overstress of wall
General stability
Berm and simple slope failure
Bottom heave
Bulked struts
Steps of Excavation
Clearing
if your excavation site has vegetation or tree roots that have to be removed, this happens during the clearing phase.
Excavation
any building that requires a basement will have to be excavated, and the dirt which is removed will have to go somewhere.
Rough-Grading
some of the dirt which was removed during excavation can be back-filled around the home to establish the right pitch toward the curb, for drainage purposes.
Erosion Control
some locations have regulations about not allowing topsoil to be eroded away by run off from heavy rains, so you may have to investigate local restrictions on this.
Rough-Staking
this process is necessary to identify approximately where a home or other building will be situated.
EXCAVATING AND EARTH MOVING EQUIPMENT
Drag line
The drag line is so name because of its prominent operation of dragging the bucket against the material to be dug.
Type of Drag Line
Crawler mounted - low travel speed, soft ground, large projects
Wheel mounted - high travel speed, firm ground & scattered job
Truck mounted - high travel speed, firm ground & scattered jobs
Walking draglines
Power shovel
To excavate the earth and to load the trucks
For Excavation above its own track or wheel level.
For cutting and for loading.
Suitable for heavy positive cutting in all types of dry soil.
Suitable for heavy positive cutting in all types of dry soil
Type of Power Shovel
Crawler mounted - low travel speed and on soft grounds.
Wheel mounted - high speed and on hard ground.
Hoes
Also known as hoe, back shovel and pull shovel
To excavate below the natural surface on which it rests.
Clam shell
The name the machine is derived from the shape of its bucket.
The shape of bucket is that of the shell hinged at the top which can be closed and opened in two parts.
Selection depends largely on the requirement of the job.
Trenching machines
Excavate all type of soils except rocks.
Mostly crawler mounted.
Excavating trenches for water, oil, gas
Used where control on depth and width is required.
Type of Trenching Machine
Wheel type - can cut trench of width up to 30 to 150 cm & Maximum cutting depth 2.5 – 3.0 m.
Ladder type - maximum cutting width up to 360 cm & Maximum cutting depth 9.0 to 10.0 m.
Vertical boom type - modified of ladder type & trench width ranges from 40 to 70 cm.
Tractors
Bull dozer
Rippers
Scrapers
Bucket
Consists of two shells with hinged at the top and provided with sharp edges at the bottom.
Heavy types of buckets with sharp cutting edges are used for hard soils and light buckets with plane edges for loose soil.
Used mostly in lifting the heavy rock pieces.
