SW4210801_Schedule of Compliance_20220421

C❑ESIGN &
ENGINEERING, RLLC
CLIENT -FOCUSED • COMPREHENSIVE • COST-EFFECTIVE
December 20, 2021
Ms. Jamie Hayes
Assistant District Engineer
NCDOT— Division of Highways
Division 7 — District 1
336-570-6833
RE: 24" and 18" Pipe Crossings at Holt Farms Sub -Division
4601 Mt. Hermon Rock Creek Road — Snow Camp, NC 27349
Dear Ms. Hayes,
2537 E. L YON STATION RD, STE f02
PO BOX 361
CREEDMOOR, NC 27522
9f9 230-0996
Per phone correspondence with you, Mr. Chuck Edwards, PE, and myself on Wednesday,
December 15th, I am providing herein information regarding the sufficiency of the proposed piping
material for the referenced crosslines. As you are aware there are two crossings on this project: 1) A
24" storm drain that conveys stormwater runoff from the proposed road and adjacent lots and 2) An 18"
storm drain that conveys runoff from the lots along Mt. Hermon Rock Creek Road along with the existing
road and right of way improvements adjacent to lots 1-4.
1.
60LF 24"
RM PIPE
The 24" class III NCDOT certified reinforced concrete
pipe (rcp) at +/- STA: 12+70 is currently proposed to
have +/-2.33' of cover to finished surface. As
discussed, NCDOT cover requirements are from top of
pipe to top of subgrade and does not include the
pavement or stone, also referred to as the "pavement
structure". However, per the manufacturer's
recommendations and the American Concrete Pipe
Association acceptable cover requirements, the Class
III RCP will provide the required HL-93 rating at 1' of
cover (see chart below). Therefore, the 2' of cover
proposed exceeds this minimum standard and the
required strength rating will be achieved.
J:\DD-PROJECTS\2020\20-085\CIVIL - 20-085\Submittals\2021-12-20 NCDOT - Letter for Pipe\2021-12-20 Holt Farms - Pipe
Certification.docx 1

CSOESIGN &
ENGINEERING, I-LLC
CLIENT -FOCUSED a COMPREHENSIVE • COST-EFFECTIVE
640
'
SOLF 18"
TORM PIPE
2537 E, L YON STATION RD, STE 102
PO BOX 361
CREEDMOOR, NC 27522
919-230-0996
The 18" class IV NCDOT certified rcp at +/-STA: 10+40 is
currently proposed to have +/-1' of cover to finished surface.
Using the same resources and table below, this pipe is rated
for the HL-93 loading with a min. of 1' of cover. As previously
noted, whether the fill above the pipe is embankment or
"pavement structure", the loading and allowable fill heights
are considered the same for pipe strength rating. Therefore,
using a type IV pipe will provide the minimum strength rating
required at this crossing. The contractor has been advised to
increase cover of the 18" pipe by any means available, even if
but a few inches and has agreed to do so during installation.
It should be noted that the chart below is for a "TYPE 1" Bedding and Backfill which implies there is little
to no support from the surrounding soils and a classified material is to be used for backfill to achieve the
strength rating. Per Sheet 2 of NCDOT STD Drawing 300.01, Rigid Pipe is not required to have a Type 1
backfill below the springline, but is required to have a Type 1 bedding. However, in each of the proposed
scenarios herein, Type 1 Backfill/Bedding shall be used for the bedding and all fill up to the springline
All bedding thicknesses and excavation dimensions shall meet NCDOT STD Drawing 300.01
Requirements.
The following Fill Height Tables have been developed by the American Concrete Pipe Association (ACPA) using the indirect design method in accordance with Section
12.10.4.3 o1 the AASHTO LRFD Bridge Design Specification, 61h Edition, 2012 with 2013 Interim Class I Class IV
I Height120 ewes are based on: D-Load (Ib/ft/it) for Type 1 Bedding 8 Class 11 class v
.� = tzo pcf
2. AASHTO HL-93 live load Class III Special Design
3. Positive Projecting Embankment Condition - this gives conservative results in comparison to trench conditions
4. A Type 1 installation requires greater soil stiffness from the surrounding soils than the Type 2, 3, and 4 installations. and is thus harder to achieve.
Therefore. field verification of sod properties and compaction levels should be performed.
Fill Height in Feet_
Pipe Size (m)
1
2
3
4
5
6
7
8
9
10
11
12
13-7
14
12
1612
1399
888
695
633
620
635
661
544
603
662
721
780
839
15 _
1546
1344
_856
673
614
602
617
6"
532
589
646
704
761
818
18
1462
1307
836
660
604
593
608
634
526
583
639
696
752
_809
21
1309
1281
823
653
598
588
604
630
525
581
637
693
749
805
24
1287
1262
814
648
595
587
603
629
527
583
638
694
750
805
27
t230
1217
789
636
587
582
600
627
530
586
642
697
753
809
C3 sincerely appreciates the opportunity to present this information for the referenced pipe crossings.
Please don't hesitate to call with any questions, comments, or input that you may have.
Re s,
Chad E. Abbott, PE
Principal Engineer
C3 Design & Engineering, PLLC
[e-mail]
J:\DD-PROJECTS\2020\20-085\CIVIL - 20-085\Submittals\2021-12-20 NCDOT - Letter for Pipe\2021-12-20 Holt Farms - Pipe
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