Chapter 4
Bench Checks
Chapter 4- Bench Checks
1
•Before construction begins the BMs
need to be checked.
•Why?
•From Design Phase to actual
construction could have been 3-5
years or longer.
•Who will check the Benches?
Chapter 4- Bench Checks
2
• BMs are shown on
proposed plans of
construction.
• BM number, station,
offset and elevation
are shown.
• Check every Bench
listed in plans.
• Third order accuracy.
Chapter 4- Bench Checks
3
Preparation and Documentation
Manual
• 8.4.5 Check Levels, a complete set of levels
from the first to the last bench mark on the job,
turning through all existing bench marks, without
adjusting H.I.’s or “correcting up” for any
differences at individual benches. If the Check
Levels are within third order accuracy, no
additional check levels will need to be run. Third
Order Accuracy requires the closure to be within
12.0 mm x square root of the distance in km (.05
feet x square root of the distance in miles).
Chapter 4- Bench Checks
4
• Plans with BMs.
• Set up Field Book.
• Peg Test Level.
Chapter 4- Bench Checks
5
Peg Test
Chapter 4- Bench Checks
6
Chapter 4- Bench Checks
7
Chapter 4- Bench Checks
8
B.M.
B.M.
#20
TP #1
B.S.
+
5.68
5.38 = 5.38
5.08
16.14
H.I.
F.S
-
ELEV.
47.86
B.M.
ELEV.
42.48
4.52
4.22 = 4.22
3.92
12.66
Chapter 4- Bench Checks
43.64
9
B.M.
TP #1
TP #2
B.S.
+
4.70
4.40 = 4.40
4.10
13.20
5.72
5.44 = 5.43
5.14
16.30
6.43
BM #21 6.07 = 6.07
5.71
18.21
H.I.
48.04
49.27
50.81
F.S.
4.52
4.22 = 4.22
3.92
12.66
4.50
4.20 = 4.20
3.90
12.60
4.82
4.53 = 4.53
4.23
13.58
Chapter 4- Bench Checks
ELEV.
B.M.
ELEV.
43.64
43.84
44.74
44.75
10
B.M.
BM #21
TP #3
TP #4
BM #22
B.S.
+
6.43
6.07 = 6.07
5.71
18.21
2.43
2.14 = 2.14
1.85
6.42
4.69
4.39 = 4.39
4.09
13.17
H.I.
50.81
51.09
49.13
F.S
4.82
4.53 = 4.53
4.23
13.58
2.17
1.86 = 1.86
1.56
5.59
6.72
6.35 = 6.35
5.98
19.05
5.59
5.30 = 5.30
5.00
15.89
Chapter 4- Bench Checks
ELEV.
44.74
B.M.
ELEV.
44.75
48.95
44.74
43.83
43.85
11
B.M.
BM #20
Elev.
B.M.
Elev.
42.48
BM #21 44.74 44.75
BM #22 43.83 43.85
BM #20
98.0’ Rt.
305+18
BM #21
110.0’ Rt.
315+20
BM #22
115.0’ Lt.
325+00
Chapter 4- Bench Checks
Brass Disk In
Headwall
Conc.
Monument
with Disk
Conc.
Monument
with disk
12
• What if one of the
BMs did not check
in tolerance?
FLA. DEPT. OF
TRANSPORTATION
B M
SURVEY MARKER
PLEASE
• What if you can’t
find a BM that is
listed on the plans?
DO NOT DISTURB
• What is a TBM?
Chapter 4- Bench Checks
13
• Sample Exercise # 2
• BENCH MARK LOOP RUN
BM #1 R.R. spike 20’ Lt Sta. 10+00
BM #2 Disk 35’ Rt Sta. 15+00
BM #3 R.R. spike 25’ Lt Sta. 20+00
BM #4 Nail in pine tree 50’ Rt.
Sta. 25+00
BM ELEV.
101.21
121.57
119.56
125.56
Date 7-12-05
Temp: Sunny 85º
Level : J. Depp
Rod
: P. Brosnen
Notes
: R. Crowe
Chapter 4- Bench Checks
14
• Sample Exercise # 2
• BENCH MARK RUN …Continued……
BM # 1 Elevation
Reading
T.P.#1
T.P.#2
BM #2
T.P.#3
T.P.#4
BM #3
101.21
5.25
T.P# 5
T.P#6
- Reading 3.21
+Reading 9.67
- Reading 1.56
+ Reading 12.51
- Reading 2.31
+ Reading 4.61
- Reading 8.17
+ Reading 5.21
- Reading 8.98
+ Reading 9.11
-Reading 3.78
+ Reading 10.15
BM #4
- Reading
+ Reading
- Reading
+ Reading
- Reading
Chapter 4- Bench Checks
6.76
9.10
10.11
8.63
5.02
15
• Sample Exercise # 2
• BENCH MARK RUN …Continued……
Document the above readings, BM’s and TPs,
and calculate the elevations and document as
should be documented in a field book. Run the
third order of accuracy, distance is 1500’
Chapter 4- Bench Checks
16
ANY
QUESTIONS ?
Chapter 4- Bench Checks
17