Peer-to-Peer Standards Exchange

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We are working on a project where the upper layer of existing native soil is poor, and has low bearing capacity and classifies as site class E in its native state. The geotechnical Engineer has recommended ground improvement (rigid concrete inclusions) to increase the bearing capacity and densify the soil to improve seismic site class. As part of the project, to ensure the improved ground meets Site Class D criteria, the Contract Documents from the Geotechnical Engineer require the specialty ground improvement Contractor to perform Seismic Cone Penetration Tests (SCPT) to inform their area-replacement-ratio on the rigid inclusion improvement program to achieve the minimum shear wave velocity for Site Class D. As such, since the soil is being improved to meet site class D criteria, the seismic design criteria of the building is based on the improved soil site class (i.e. Site Class D). My question: can others confirm the code (ASCE 7) allows for recognizing the improved site class of ground improved soil (especially if it is tested and shear wave velocities of said site class are confirmed)?

#ASCE7-16
#Seismic

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There is nothing in ASCE 7 that precludes the use of ground improvement techniques to change the site class of a site.  This has been done on some projects in the past, although the cost of the ground improvement technique must be balanced against the cost of designing for the poorer site class.  Often the cost of such ground improvement is found not to justify its use.

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Ronald Hamburger, SE
Consulting Principal
Simpson Gumpertz & Heger
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