Chapter 4- Bench Checks1 Chapter 4 Bench Checks Chapter 4- Bench Checks2 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 Checks3 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 Checks4 Preparation and Documentation Manual 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 Checks5 Plans with BMs. Set up Field Book. Peg Test Level. Chapter 4- Bench Checks6 Peg Test Chapter 4- Bench Checks7 8 9 B.M.B.S. + H.I.F.S - ELEV.B.M. ELEV. B.M. # = TP # = Chapter 4- Bench Checks10 B.M.B.S. + H.I.F.S. - ELEV.B.M. ELEV. TP # = = TP # = = BM # = = Chapter 4- Bench Checks11 B.M.B.S. + H.I.F.S - ELEV.B.M. ELEV. BM # = = TP # = = TP # = = BM # = Chapter 4- Bench Checks12 B.M.Elev.B.M. Elev. BM # BM # Rt Brass Disk In Headwall BM # BM # Rt Conc. Monument with Disk BM # BM # Lt Conc. Monument with disk Chapter 4- Bench Checks13 What if one of the BMs did not check in tolerance? What if you cant find a BM that is listed on the plans? What is a TBM? FLA. DEPT. OF TRANSPORTATION B M SURVEY MARKER PLEASE DO NOT DISTURB Chapter 4- Bench Checks14 Sample Exercise # 2 BENCH MARK LOOP RUN Date Temp: Sunny 85 Level: J. Depp Rod: P. Brosnen Notes : R. Crowe BM ELEV BM #1 R.R. spike 20 Lt Sta BM #2 Disk 35 Rt Sta BM #3 R.R. spike 25 Lt Sta BM #4 Nail in pine tree 50 Rt. Sta Chapter 4- Bench Checks15 Sample Exercise # 2 BENCH MARK RUN Continued BM # 1Elevation Reading 5.25 T.P.#1- Reading Reading 9.67 T.P.#2- Reading Reading BM #2- Reading Reading 4.61 T.P.#3 - Reading Reading 5.21 T.P.#4 - Reading Reading 9.11 BM #3 -Reading Reading T.P# 5- Reading Reading 9.10 T.P#6 - Reading Reading 8.63 BM #4 - Reading 5.02 Chapter 4- Bench Checks16 Sample Exercise # 2 BENCH MARK RUN Continued Document the above readings, BMs 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 Checks17 ANY QUESTIONS ?