Construction & Contractors/Query.

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Question
Good day
With reference to foundations on buildings I have the following questions:
1. How does one determine if cracks on walls and post are surface based or structural based? Are there tests for the layman who knows little about construction to determine if cracks are structural or artificial
2.In purchasing a used home, how does a layman assess the soundness and quality of foundation ie. how much load can take etc... What tests and methods are available for assessing and quantifying the foundation of any structure (after a building is constructed)

Answer
There are a few references that are available to interpret the causality of cracking.  Some books have been written on the subject (e.g., Oriard's book on environmental effects on structures, which is highly recommended and understandable even to the layperson) and there are some papers and other information that try to give characteristics of different kinds of cracking (for example, http://inspectapedia.com/structure/Concrete_Settlement_vs_Shrinkage.htm).  However, the interpretation of cracking is in general something that requires a trained eye -- someone who has looked at a lot of cracks.

There are no easy visual tests to determine the adequacy of a house foundation.  This is because the foundation design is related to geological conditions that are not discernable visually, especially from the ground surface.  Most foundations have cracks.  Cracks in foundations in terms of bearing capacity are not worrisome unless they are very numerous and/or are wide (greater than 5-10 mm or so).  The best way to assess the adequacy of a foundation after it has been constructed is to asssemble as-built information, so that you know what is there, and perform subsurface exploration by advancing borings or test pits  adjacent to the foundation, to a depth at least equal to the foundation depth plus three times the foundation width, and getting a geotechnical engineer to evaluate the bearing materials and perform whatever tests -- usually density, plasticity, swelling, moisture content, gradation, and specific gravity -- are required to estimate the strength and stability of the bearing substrate.  

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Robert Cummings, P.E.

Expertise

I can answer questions related to rock blasting, rock and soil excavation (such as tunnels and highway cuts), stability of such excavations, and foundations in rock and soil. I can also answer questions related to geology and mining.

Experience

30+ years as a geotechnical engineer and minerals engineer. Active consulting practice in rock blasting, geotechnical engineering, and rock mechanics for mining and heavy construction.

Organizations
Society of Mining Engineers, Deep Foundations Institute, Association of Engineering Geologists, and International Society of Explosives Engineers.

Publications
Mining Engineering, AEG Bulletin.

Education/Credentials
BS and MS Geological Engineering

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