Chapter 4 Bench Checks

1. Chapter 4Bench Checks Chapter 4- Bench Checks

2. 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

3. 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

4. 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

5. Plans with BMs. • Set up Field Book. • Peg Test Level. Chapter 4- Bench Checks

6. Peg Test Chapter 4- Bench Checks

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13. FLA. DEPT. OF TRANSPORTATION B M SURVEY MARKER PLEASE DO NOT DISTURB • What if one of the BMs did not check in tolerance? • What if you can’t find a BM that is listed on the plans? • What is a TBM? Chapter 4- Bench Checks

14. 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

15. Sample Exercise # 2 • BENCH MARK RUN …Continued…… BM # 1 Elevation 101.21 Reading 5.25 T.P.#1 - Reading 3.21 +Reading 9.67 T.P.#2 - Reading 1.56 + Reading 12.51 BM #2 - Reading 2.31 + Reading 4.61 T.P.#3 - Reading 8.17 + Reading 5.21 T.P.#4 - Reading 8.98 + Reading 9.11 BM #3 -Reading 3.78 + Reading 10.15 T.P# 5 - Reading 6.76 + Reading 9.10 T.P#6 - Reading 10.11 + Reading 8.63 BM #4 - Reading 5.02 Chapter 4- Bench Checks

16. 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

17. Date: 7/12/05 3 Bench Loop Run Temp: Sunny 85º Level: J. Depp + Sta. H.I. - Elev. BM Elev. Rod: P. Brosnen Notes: R. Crowe BM #1 5.25 106.46 101.21 RR spike 20’ Lt. Sta. 10+00 T.P. #1 9.67 112.92 3.21 103.25 T.P. #2 12.51 123.87 1.56 111.36 126.17 BM #2 4.61 2.31 121.56 121.57 Disk 35’ Rt. Sta. 15+00 T.P. #3 5.21 123.21 8.17 118.00 T.P. #4 9.11 123.34 8.98 114.23 BM #3 10.15 129.71 3.78 119.56 119.56 RR spike 25’ Lt. Sta. 20+00 132.05 T.P.#5 9.10 6.76 122.95 T.P. #6 8.63 130.57 10.11 121.94 5.02 BM #4 125.55 125.56 Nail in pine tree 50’ Rt. Sta. 25+00 .05 x Sq. Root of M (M= Miles) 1500/5280 = 0.2840909 .05 x .5330017 = 0.02669

18. ANY QUESTIONS ? Chapter 4- Bench Checks