HomeMy WebLinkAboutSanitary Sewer DeflectionJuly 26, 2010
Ms. Carol Cotter, PE
City of College Station Public Works Department
1101 Texas Avenue
College Station, TX 77842
Re: Sanitary Sewer Deflection in Boring Across WD Fitch
CSISD Transportation Center
College Station; Texas
Gessner Engineering Job No.: 09-0317
Dear Ms. Cotter:
The purpose of this letter is to address concerns regarding the deflection of
the eight (8) inch sanitary sewer pipe and the steel casing pipe in the bore
across WD Fitch.
The S" SDR-26 pipe is manufactured by Certinteed and it is the eight (8)
and installer. According to the manufacturer, this pipe has an allowable
bending radius of 200 fleet. This would allow a twelve (12) inch deflection
for each twenty (20) foot section of pipes for a total allowable deflection of
three (3) feet over 60 linear feet of bore. The on -site deflection according
to the City Inspector occurs in the last sixty (60) feet of boring and is two
(2) feet five (5) inches which is within the allowable deflection tolerance.
The schedule 80 steel casing pipe used in the boring
has an allowable deflection of five (5) percent which
would give three (3) feet of allowable deflection over
sixty (60) feet of bore. The onsite deflection is two (2) essner
feet five (5) inches over sixty (60) feet of pipe,
according to the City Inspector. Therefore, the steel Engineering
casing pipe is within allowable deflection tolerances.
2501 Adrford Duce
Sincerely,
GESSNER ENGINEERING, LLP F-7451
1 = I ='
Melissa P. Thomas; P.E.
Suite 102
College Station,'P ss 77840
20. Box 10763, 77842
979.680.8840
f.,, 979.680.884t
2204 S. Chappell 1101 Sncee
Brenham.; Teas 77833
979.836.6855
&x 979.836.6847
June 29, 20' -);
Ms. Carol Cc':er, PE
City of Collet � Station Public Works Department
1101 Texas i',venue
College Station, TX 77342
Re: Sanit- y Sewer Deflection in Boring Across WD Fitch
CSIS'i Transpciation Center
Collet Station. Texas
Gess r Engin wring Job No.: 09-0317
Dear Ms. Cc; :_�r.
The purpose of this letter is to address concerns regarding the deflection of
the eight. 8) inch sanitary sewer pipe and the steel casing pipe in the bore
across V Fitch. _
The SDR-26 pipe is maKufactured by Certinteed and it is the eight (8)
inch low Cer'a-Lok e with couplings, according to the manufacturer ` u
and alter. r cc
" g to the manufacturer, this pipe has ale b
bend J radius of et. This would allow atwely 12) nth deflection
for e, twenty (20) foot section of pipe, for a total allo a le deflection of
eight ' 3) feet over the 160 total linear feet of bore. The actual on -site
deflec:'on of two (2) feet five (5) inches is well below that value.
Acco-c'Ing to Join Wright Construction, who drilled
the b rng, the .velds in the steel casing did not give
durin the bor',ig operation. This was a gradual
deflec on through -out the boring process due to soil
frictie- and not the result of hitting something
unde und. in addition, the schedule 80 steel
casir; pipe u ed in the boring has an allowable
defle: ,n of fiv=: (5) percent. The current deflection is
one a half /) percent, well within the deflection
limit c ;hhe pipe
Sincerely,
GESSNER GINEE "iNG, LLP F-7451
Melissa P. T .-�mas, P E.
2501 &J,Iord Drive
suite lot
Colkga Station. T,sa 77840
EO. Bm 10763, 77842
979.680.8MC
fay 979.6S0.8841
2204 S. Chappd Hill Srren
Brenham, "ltsu 77833
979.836.6855
C. 979.836.6847