ST8201-CS 890706GINN, INC.
CONSULTING ENGINEERS
July 6, 1989 ~.
Re: Denton Tap Road Improvements from ~elt Line Rood to Sandy
Lake Rood - Concrete Riprap failure beneath the north ends of the
Grapevine Creek bridge structttres.
Nr. Scott Belch,
L. H. Lacy company
P.O. Box 541297
Dallas, Texas 75354-1297
Dear Hr. Belch:
a _ Ho daY,_J.t .e 6,._1909 ~r.. ~tsn Reed, P.Z. and myself visited
~.~_~£ .~ne ~azAure ~ ooserved the exposed full depth of
in-~~ ~flcre~e. In seve~aA areas along the Bain failure crack.
· uur ooserva=ion we no=ed that no steel re~nfor~tnfl
In the concrete. On Wednesday, ..... ~
June 28, 1989 I revisited the
~ite.and~p~n .fur~h~r_ex~..~tion of the failed concrete r~rap
=ou~.~ a?~..p~o=ngrel~led evidence of horizontal reinforcing steel
~.r~.~__~_~m__~f_ ~ ~ncrs}eI ~non~o~.li.a~cs notice regarding
_ - ~y~urmAuy Or =ne relnzorclng s~eel with the Drawi~s
~pec1Elca=ions was aerv~ June 28, 1989.
The above and a description by our resident project
~~v~fo&iath~on~ccrt~e.od !o~ concrete placement used An the
steel .....r ~e r~prap leads us to believe that the
re~n~orclng ~ars are Improperly located beneath the
. a~ ~nls par~icuiar case, It is our belief that the
concre=e rzprap (RRB) on the north bank of Grapevine Creek under
the bridge st.r~.ot~res is unsuitable a~d not in conformance with
the Specifications.
C--~=-~ .... In accordance with the Contract ~neral
~,uauzu~s ox.&greement, Article 2.14 DEF~CTSANDTHEIR
--OU ....... °, -- ......
~ a~ hereby alrec=e~ to remove
~ ........ the concrete ripraD ~ the
~ sl~e o£ Grapevine Creekand rebuild it in accordance
e Drawings and S~ecificationS, or Provide an acce table
p remedy
which will bring this item into confor~ity with the Drawings and
Specifications.
A~}er ~te~tng and photographing the failed ripra~ durino several
szce visits, and cOnferring with our structural ~ncrt..o.'
concluded that --.= .... , wa have
the failure is attributable to fact that
??rewat?r low.e Anto voids at the top of the concrete riprap
~e=ween r~e ~wo ~ridge structures and filled an extensive ~work
of voids present beneath the riprap (which your subcontractor had
~reviously tried to fill with concrete) and =ressurized th- ~i~-
o a higher pressure than that Of the flow~in the creek'd~in~
the high,water. As the high water in the creek reoeded, the
17103 Pres~onRo~d · Su~ i00 · sn]18 · [~llas. Tesas 752,18 · .Pbonc214/248-49GO
water behind ~he riprap could not escape ~nd · differential
pressure developed which was sufficient to fail the l~pra~rly
reinforoed concrete riprap. A rapid loss of the water which had
occupied the voids beneath the riprap occurred at failure'of the
concrete and probably generated flow velocities within the void
network eufficieat to further erode the earth beneath the riprap.
Additionally, the degree of apparent rotation of the lower
por~ions of the failed riprap may indicat~ weakened or failed
toe-wall sectione. :
Xt ia our opinion that the failure of the concrete riprap is due
to the means and methods employed in its construotion.
Therefore, since similar Beans and methods were used by your
subcontractor on the balance of the concrete riprap on ~h/s.and
the adjacent project, we will require that sections of each panel
of concrete ripr&p (including toe walls) on both projects,
exclusive of the north side of Grapevine Creek, be exposed for
examination by Ginn, Inc. and Reedcon, Inc., our structural
engineer.
Zn accordance with Division 1, Section 01010 - SUMMARY OF WORK,
1.13 INSPECTION ~OF WORK, Paragraph C, all of the costs of
examination, including testing and analysis, will be berne by the
Contractor If the re-examined work fails to meet the requirements
of the Contract Drawings and SPeCifications. If the Re-exa~ined
work complies with the Drawings and Specifications, the Owner
shall bear the costs of re-exalination, testing and analysis and
restoration of the work.
we will be happy to meet with you at the project site to indicate
the areas which are required to be exposed for re-examination.
Please respond to this letter in writing indicat~ng your plan of
action regarding the above including a ti~e and place convenient
for a meeting regarding the above.
Sinoerely,
John C. K~rlaruher, P.E.
Project Engineer
CC:
Russell R. Doyle, P.E.
H. Wayne Ginn, P.E.
Randy Fleming
Stan Reed,
File 378 (a:378rip)