HomeMy WebLinkAboutCT 14-10; POINSETTIA 61; SLOPE STABILITY CONSIDERATIONS; 2015-03-06A,u<CUPDELTA
March 6, 2015
Lennar Homes
25 Enterprise, Suite 300
Aliso Viejo, California 92656
Attention: Mr. Andrew Han
SUBJECT:
Reference:
Mr. Han:
SLOPE STABILITY CONSIDERATIONS
Poinsettia 61 Development
Carlsbad, California
Group Delta Consultants (2014). Report of Geotechnical Investigation, Poinsettia
61 Development, Carlsbad, California, Document No. 14-0188, November 20.
In accordance with the request of Mr. Tim Carroll with O'Day Consultants, we have prepared
this letter regarding the need for benches within the slopes at the Poinsettia 61 development in
Carlsbad, California. A variety of new slopes will be constructed as part of the planned
subdivision. The slopes will be inclined no steeper than 2:1 (horizontal to vertical), and will
have a maximum height of SO-feet or less (typically less than 40 feet). Slope stability was
discussed in Sections 4.4, 6.3.9 and Appendix C of the referenced report (GDC, 2014). Our slope
stability analyses indicated that the proposed 2:1 (horizontal to vertical) cut and fill slopes at
the site should possess an adequate factor of safety against deep-seated failure (FS>l.5) for the
planned heights. However, various buttresses and subdrains were recommended in the
referenced report in order to help reduce the potential for future slope instability.
It should be noted that providing benches within a slope will increase the calculated safety
factor against slope failure. This is primarily due to the overall decrease in slope inclination
resulting from the benches. For example, a 40-foot high 2:1 slope will cover 80 horizontal feet.
If a 10-foot wide flat bench is added to the 40-foot high slope, the horizontal length of the slope
increases to 90 feet, and the overall slope inclination is effectively decreased to 2X:1. This
results in an increased safety factor calculated using a global limit equilibrium analysis.
However, as noted above, it is our opinion that the proposed slopes at the site will already
possess an adequate safety factor at a 2:1 inclination (provided that our geotechnical
recommendations are implemented during grading). Therefore, it is our opinion that slope
benches are not needed for the proposed slopes at the subject site.
•
Slope Stability Considerations
Poinsettia 61 Development
Lennar Homes
GDC Project No. SD412
March 6, 2015
Page 2
We appreciate this opportunity to be of continued professional service.
office with any questions or comments, or if you need anything else.
Feel free to contact the
GROUP DELTA CONSULTANTS
Matthew A. Fagan, G.E. 2569
Senior Geotechnical Engineer
Distribution: (1) Addressee, Mr. Andrew Han (andrew.han@lennar.com)
(1) Addressee, Mr. Tim Carroll (timc@odayconsultants.com)
t:~ GRCUP CEL TA N:\Projects\SD\50412 Lennar Poinsettia Geotechnical lnvestigation\15-0029\15-0029.doc