City of Frisco Engineering Standards

Engineering Standards
c. Major stream crossings (over channels more than 200’ wide) require borings in the
channel. A site inspection by the driller or logger is necessary to evaluate site
accessibility and special equipment needs.
d. Minor stream crossings over channels less than 200’ wide shall provide a boring on each
bank as close to the water’s edge as possible. If boring information varies significantly
from one side of the channel to the other, a boring in the channel may be required by the
Director of Engineering Services.
e. Grade Separations. If the borings indicate soft surface soils (fewer than 10 blows per
foot), additional borings and testing shall be required for the design of the bridge
approach embankments.
3. Retaining Walls Obtain soil borings for walls taller than 3-ft.
a. Obtain soil borings at 200’ spacing unless site conditions or the design engineer requires
closer spacing. A greater spacing may be allowed by the Director of Engineering Services
only if recommended in writing by the geotechnical engineer of record.
b. Fill Walls. For spread footing walls and MSE walls, the depth of the boring shall be a
minimum of as deep as the wall height depending on the wall type and existing and
proposed ground lines. The minimum boring depth is 10’ below the bottom of the
proposed wall unless rock is encountered (see Section 9.03.H.4). Extend borings at least
5’ into rock for fill walls unless additional depth is recommended by the geotechnical
engineer.
c.
Cut Walls. For drilled shaft walls, tied-back walls, and soil and rock nail walls, the depth
of the boring is based on the proposed ground line. Cantilever drilled shaft walls require
the depth of boring to extend the anticipated depth of the shaft below the cut, which is
typically between one and two times the wall height unless additional depth is
recommended by the geotechnical engineer of record. Borings for soil nail and rock
nailed walls need to be advanced through the material that is to be nailed. The minimum
boring depth is 15’ below the bottom of the proposed wall. Borings for proposed cut
walls may need to penetrate rock significant distances depending on the depth of the cut
and wall height.
d. Provide additional testing for taller walls, walls on slopes, or walls on soft founding strata
as necessary, or recommended by the geotechnical engineer of record, to completely
evaluate wall stability.
4. Borings Encountering Rock
a. Based on the geotechnical engineer's experience and engineering judgment, if rock is
encountered the minimum boring depths specified above may be reduced but only at the
direction of the geotechnical engineer.
9.04 Bridge Design
A. The structural engineer shall be responsible for selecting the appropriate bridge foundation. The
engineer shall consider the following factors in that selection:
1. Design load. The magnitude of the design load dictates the required size of the foundation.
Section 9 – Structural Design Requirements May 2012 Page 9-5