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STRUCTURAL INSPECTIONS & DEFECTS
AGE of a BUILDING - how to determine
BRICK FOUNDATIONS & WALLS
CHIMNEY INSPECTION DIAGNOSIS REPAIR
COLD POUR JOINTS, CONCRETE
COLUMNS & POSTS, DEFECTS
DISASTER BUILDING INSPECTION & REPAIR
EARTHQUAKE DAMAGED FOUNDATIONS
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
FLOOD DAMAGE TO FOUNDATIONS
FOOTING & FOUNDATION DRAINS
FOOTINGS EXPOSED, Repair Methods
FOUNDATION BULGE or LEAN MEASUREMENTS
FOUNDATION CONSTRUCTION TYPES
FOUNDATION CONTRACTORS, ENGINEERS
FOUNDATION CRACKS & DAMAGE GUIDE
FRAMING DAMAGE, INSPECTION, REPAIR
GRADING, DRAINAGE & SITE WORK
GUTTERS & DOWNSPOUTS
INSECT INFESTATION / DAMAGE
MOBILE HOMES, DOUBLEWIDES, TRAILERS
MODULAR HOME CONSTRUCTION
MOISTURE CONTROL in BUILDINGS
RETAINING WALL DESIGNS, TYPES, DAMAGE
RETAINING WALL GUARD RAILINGS
STRAW BALE CONSTRUCTION
STRUCTURAL DAMAGE PROBING
STRUCTURAL WOOD ASSESSMENT
THERMAL EXPANSION of MATERIALS
TIMBER FRAMING, ROT
WATER BARRIERS, EXTERIOR BUILDING
WATER ENTRY in BUILDINGS
WINTERIZE A BUILDING
This article explains Concrete block or "cinder block" or concrete masonry unit (CMU) foundation inspection procedures and the diagnosis of cracks, bulges, leaning, bowing, and settlement in concrete block foundations and building walls such as damage due to impact, settlement, frost or water damage, and other causes.
Types of foundation cracks, crack patterns, differences in the meaning of cracks in different foundation materials, site conditions, building history, and other evidence of building movement and damage are described to assist in recognizing foundation defects and to help the inspector separate cosmetic or low-risk conditions from those likely to be important and potentially costly to repair.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
How to Identify, Diagnose, & Evaluate Masonry Block (concrete & "cinder block") Foundation & Wall Damage
How the history of building construction, movement, events can help diagnose concrete block foundation cracks & damage
Bulged, collapsing concrete block walls
The masonry block foundation at the house in these photographs collapsed after a period of heavy rain. The underlying problem was in-slope grade at the rear of the home and trapped roof spillage there, causing lots of heavy wet earth pressure on the wall.
The home inspector had previously observed water damage at the wall and had correctly assessed the outside conditions. The owners had deferred action to prevent further water damage, leading to an unexpected and sudden precipitous collapse of the foundation after a period of unusually wet weather. [Left hand photograph courtesy of Alan Carson, Carson Dunlop, Toronto. These photos are of two different buildings.]
If a foundation wall crack is vertical and fairly uniform in width, but the wall on one side of the crack is higher than on the other, we're looking at differential settlement which will probably be traced to the footings.
If a foundation wall crack is vertical and wider at its top than its bottom, we may be looking
at footing settlement in which the footings have "bent" and settled unevenly, such as when a footing has been placed
over unevenly compacted fill or where there was bedrock or a large boulder under a portion of the footing permitting
settlement such that the footing has settled down on one or both sides of this "high point".
At least one author also posed that a concrete masonry unit wall which has a vertical crack near its center and whose crack is wider at its top than bottom has cracked due to wall shrinkage along its length. His explanation was that the top of the wall was free to shrink but its bottom was held in place by the footing, making a crack wider at top than bottom. However other experts (D.Wickersheim) assert that concrete block walls do not shrink significantly during curing, though wet masonry blocks might change a bit in dimension during drying.
Crack patterns in concrete or other masonry foundation walls can occur as vertical, diagonal, stair-stepped, or horizontal patterns which we discuss and among which we distinguish in more detail at FOUNDATION CRACK EVALUATION
Missing components such as headers where the wall has been modified, steel reinforcement wire or re-bar (if required by local codes).
Questions & answers or comments about damaged concrete block foundations: causes, crack & movement patterns, diagnosis, repair, inspection procedures..
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The frost heaving forces developed under a 1 ft. (30.5 cm) diameter steel plate were measured in the field throughout one winter. The steel plate was fixed at the ground surface with a rock-anchored reaction frame. heave gauges and thermocouples were installed at various depths to determine the position and temperature of the active heaving zone. The general trend was for the surface force to increase as the winter progressed. when the frost line approached the maximum depth the force was in excess of 30,000 lb (13,608 KG). Estimates of the heaving pressure at the frost line ranged from 7 to 12 psi (0.49 to 0.84 KG/cm) square during this period. The variation of surface heaving force was closely associated with weather conditions. Warming trends resulting in a temperature increase of the frozen layer caused the forces to decline.
Leda clay slopes in the Ottawa valley are vulnerable to catastrophic landslides. More than 250 landslides, historical and ancient, large and small, have been identified within 60 km of Ottawa. Some of these landslides caused deaths, injuries, and property damage, and their impact extended far beyond the site of the original failure. In spectacular flowslides, the sediment underlying large areas of flat land adjacent to unstable slopes liquefies. The debris may flow up to several kilometres, damming rivers and causing flooding, siltation, and water-quality problems or damaging infrastructure. Geologists and geotechnical engineers can identify potential landslide areas, and appropriate land-use zoning and protective engineering works can reduce the risk to property and people.
Deposits of Leda clay, a potentially unstable material, underlie extensive areas of the Ottawa-Gatineau region. Leda clay is composed of clay- and silt-sized particles of bedrock that were finely ground by glaciers and washed into the Champlain Sea. As the particles settled through the salty water, they were attracted to one another and formed loose clusters that fell to the seafloor. The resulting sediment had a loose but strong framework that was capable of retaining a large amount of water. Following the retreat of the sea, the salts that originally contributed to the bonding of the particles were slowly removed (leached) by fresh water filtering through the ground. If sufficiently disturbed, the leached Leda clay, a weak but water-rich sediment, may liquefy and become a 'quick clay'. Trigger disturbances include river erosion, increases in pore-water pressure (especially during periods of high rainfall or rapid snowmelt), earthquakes, and human activities such as excavation and construction.
After an initial failure removes the stiffer, weathered crust, the sensitive clay liquefies and collapses, flowing away from the scar. Failures continue in a domino-like fashion, rapidly eating back into the flat land lying behind the failed slope. The flowing mud may raft intact pieces of the stiffer surface material for great distances.