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Re: Landslide[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org, seaoc(--nospam--at)seaoc.org
- Subject: Re: Landslide
- From: John Buchanan <jjb(--nospam--at)scruznet.com>
- Date: Fri, 13 Mar 1998 06:35:07 -0800
To all, As an example of the soils settlement problem, I have included a portion of the geotechnical report. "Considering the seismic setting including the potential for ridge top shattering, the site history, soil characteristics, and site preparation recommendations, it is our opinion that an appropriate foundation system to support the proposed structures will consist of an interconnected reinforced concrete grid system. The grid system should consist of continuous exterior spread footings interconnected with interior continuous footings. Isolated spread footings fire not recommended for this site due to the possibility of ridge top shattering. The grid footings should be embedded into the sandstone/ siltstone bedrock and below the lowest adjacent grade not less than 18 inches. Footing widths should be based on the allowable bearing value but not less than 12 inches for I story and 15 inches for 2 story structures. Footing excavations must be observed by the Geotechnical Engineer before steel is placed and concrete is poured to insure bedding into proper material. The footing excavations should be saturated prior to placing concrete. The foundation grid system should be designed so that the building moves as a unit and is capable of spanning cracks and differential ground movement which may occur during ridge top shattering. The grid system should be able to span a void appearing anywhere under the building with a diameter of 10 feet. In Addition, the footings of the grid system should be able to resist the tensile forces applied to the foundation system from cracks appearing and opening beneath the footings. Continuous spread footings should contain tensile reinforcement sufficient to resist tensile forces of 1000 pounds per lineal foot of footing for it distance of 1/1 the footing length. For example, a 20 foot long footing should contain tensile reinforcement able to withstand 10,000 pounds of tensile force. As a minimum, footing should be reinforced with 4 #4 bars, 2 at the top and 2 at the bottom." This particular foundation system recommended a "conventional foundation system". Does any one have any comments regarding this type of system? These types of recommendations are starting to become more prevalent around this area. Some times the geotechnical engineers require a pier and grade beam system. My problem with these recommendations is how to economically design a foundation system so the project owners may still be able to afford to build with out dumping a tremendous amount of money into the foundation. I do appreciate the comments regarding the drilled piers. I personally do not use any thing less than an eighteen inch drilled pier and a minimum of eight number five bars with ties at 10" o.c. I do now I have lost clients to the other engineers that use 12" piers with one number 6 bar. Just as well, I refuse to become what is termed a lick and stick engineer! John Buchanan
- Re: Landslide
- From: Arvel L. Williams, P.E.
- Re: Landslide
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