SURVEYING THE UNDERGROUND

Transcription

1 SURVEYING THE UNDERGROUND An Introduction to ASCE and the Practice of Subsurface Utility Engineering ACECMD March 28, 2018 Presented by: Art Worthman A. Morton Thomas & Associates, Inc. John Berrettini Accurate Infrastructure Data, Inc.

2 SURVEYING THE UNDERGROUND Agenda Brief History and introduction to ASCE & Subsurface Utility Engineering (SUE). Look at some technical aspects of locating UG utilities Answer questions about: SUE locating & mapping underground utilities

3 THE CHALLENGE Source: Federal Laboratory Consortium for Technology Transfer COMPLEX UTILITY LAYERS UNDERGROUND

4 TRADITIONAL METHODS TO MAP UTILITIES Records research Field survey of surface features Valves, hand boxes, meters, manholes, hydrants Perhaps locate Miss Utility marks if found in field designer ticket Fit record information to surface evidence & marks Disclaim responsibility for underground utilities per plan

5 WHAT IF RELIABLE INFORMATION IS NOT AVAILABLE? Incomplete or inaccurate data models Poorly informed designs Designs that cannot be executed or constructed as planned Construction delays Re-designs Change orders Cost increases Back charges Lawsuits Damages Insurance claims Increased operating costs Loss of profits Loss of client confidence, loss of client

6 CI/ ASCE 38-02

7 DEFINITION Subsurface Utility Engineering A branch of engineering practice that involves managing certain risks associated with: utility mapping at appropriate quality levels, utility coordination, utility relocation design and coordination, utility condition assessment, communication of utility data to concerned parties, utility relocation cost estimates, implementation of utility accommodation policies, and utility design.

8 BRIEF HISTORY OF SUE 1981 NOVA company founded to dig A/V test holes 1983 Company adds surface geophysics to the process 1984 VDOT successful use of SUE on pilot project. Big $$$ savings realized 1989 Subsurface Utility Engineering named at FHW National Highway Utility Conference 1990 s FHWA develops SUE handbook Aggressively promotes use of SUE with DOT s Defines Quality Levels of utility depiction Funds Purdue Study $4.62 savings per $1.00 spent Helps fund development of ASCE Standard 2003 CI/ ASCE published Update expected

9 38-02 KEY TERMS Designating Interpret the presence of subsurface utility through surface geophysical methods Mark its approximate horizontal position on the ground Locating Expose and record the precise vertical and horizontal location of a utility. Utility Quality Level A professional opinion of the quality and reliability of utility information.

10 38-02 QUALITY LEVELS QL D Information derived from existing records alone QL C Correlate (rubber sheet) existing utility records to surveyed utility surface features QL B Designate utilities using appropriate utility locating instruments and methods. Survey designated utilities in the project datum Results in plan view positions of utilities (no vertical info) QL A Direct survey of an exposed utility to obtain precise horizontal and vertical position at a specific point. Usually through the use of air/ vacuum excavation

11 SURVEYING THE UNDERGROUND Professional SUE providers use ASCE as their framework to meet standards of professional care SUE is distinctly different from Miss Utility Designer Tickets Care in research, field investigation from mains to mechanical room, search & trace all utilities, survey, map, correlate with records Comprehensive consideration of all utilities; known and unknown; public & private, active & abandoned QL labels inform designer about the source and reliability of utility information Test holes are excavated to validate utility designating and provide vertical component at critical points Comprehensive investigation and conformance to standard enables SUE providers to assume professional liability

12 QUESTIONS? What s next Utility Investigations: Some Theory and Practice QL B and QL A Data Collection

13 LOCATING THEORY & PRACTICE Basic introduction to common detection theory and methods Electromagnetic (EM) Pipe and Cable Detection Ground Penetrating Radar Utility Designating Quality Level B making a more accurate, more complete utility map Utility Locating (Test Holes) Quality Level A when accuracy and precision are critical and to validate mapping adds precise depth/elevation information

14 ELECTROMAGNETIC PIPE AND CABLE LOCATING DETECTING MAGNETIC FIELDS Signal: a flow of electrical current at a specific frequency on conductors such as metallic pipes, wires or cables Conductor: a linear object that electrical current can travel along (in our case a utility pipe, wire or cable) Magnetic Field: a cylindrical field that forms around a linear conductor when current is flowing along it

15 DETECTING MAGNETIC FIELDS

16 APPLYING THE SIGNAL DIRECT CONNECT, CLAMP INDUCTION AND SURFACE INDUCTION

17 LIMITATIONS: EM PIPE AND CABLE LOCATING Depth of bury Shallow stronger field, easily detected Deep weaker field, more difficult to detect Physical access to utility surface induction may be the only option for applying signal Utility type and material The easiest utilities to detect are conductive cables and pipes with minimal restrictions to current travel. Conductor congestion both above and below ground causes signal bleed to adjacent conductors making it difficult to interpret the multitude of magnetic fields. Rebar in pavement and prove

18 MODERN GPR UNITS

19 BASIC GPR PRINCIPALS Electromagnetic pulses of energy are emitted from transmitting antenna downward through the ground The pulses reflect back from objects that contrast with the surrounding soils The reflections are detected by the receiving antenna and processed through circuitry and software to produce an image of the reflections

20 CLASSIC GPR DATA A SINGLE SCAN (CROSS SECTION)

21 EM VS GPR COMPARISON EM Pipe and Cable Locators Works in wide variety of soils Utilities need to be conductive (or snaked with conductive rodder) Small diameter utilities detected Useful for linear utilities pipes and cables/ wires Lower cost to detect most utilities (90% to 100% effective) Ground Penetrating Radar Wet or conductive soils limit or prevent use (MD soils vary) Non-conductive utilities can be detected in good soils Small diameter utilities hard to detect Useful for tanks, drums, vaults, larger pipes / cables Higher cost to detect few utilities (0% to 40% effective locally)

22 DESIGNATING QL B MAPPING EMPLOYED AT 0% TO 30% DESIGN Records Research (utilities known to exist) Geophisical Field Investigation Pipe & Cable Locators Ground Penetrating Radar APWA-ULCC Field Marking (Red electric, blue-water, etc.) Field Sketch and Survey & Map Documented Results Represent Professional Opinion Most Reliable Non-excavated Utility Location Can Include Private, Public, Abandoned Utilities

23 UTILITY DESIGNATION: FIELD INVESTIGATION W/ MARKINGS PLACED

24 FIELD NOTES/ SKETCH SURVEY & CAD PROCESSING

25 FIELD/ OFFICE COLLABORATION QA/ QC throughout Debrief field crews for unique site issues and problems Compare and correlate surveyed results to field sketches and utility records Assign QL to utility depictions (QL-B is the goal with QL-C or D as needed Provide mapping in AutoCAD or MicroStation

26 SUE LEGEND & NOTES

27 LOCATING QL A TEST HOLES EMPLOYED AT 60% TO 90% DESIGN Engineer determines TH locations considering progress design and QL B data Notify the Miss Utility notification center. Plan traffic control. Apply for an excavation permit (public ROW) Coordinate with utility inspectors Schedule the test hole rig, crew and surveyors. Compile results and report to designers

28 AIR / VACUUM EXCAVATION What does it look like? Short Video.

29 TEST HOLE OPERATIONS SET MARKER, MEASURE AND DOCUMENT BACKFILL, COMPACT AND RESTORE HORIZONTAL AND VERTICAL POSITION

30 WHY AIR/ VACUUM EXCAVATION? COMPARED TO MECHANICAL/ BACKHOE ETC. Less impact to utilities Safer than mechanical digging Safer than hand digging Less impact to property and the public Small hole test hole not test pit Small work footprint Neat work area (soils contained) Short duration occupancy (9 to 3 restrictions) Low cost (particularly in paved roadways)

31 HOW ACCURATE IS QL B? THIS EXAMPLE IS 0.4 FEET AND FAIRLY TYPICAL ACTUAL POSITION OF WATER LINE DESIGNATED POSITION OF WATER LINE IS APPROX. 0.4 FROM ACTUAL POSITION

32 SUE REPRESENTATION Possible Engineer s Note on Plans Subsurface utilities are depicted in accordance with ASCE based on professional designating services provided by on August 5, Contractors shall validate subsurface utility data to their own satisfaction. Show Quality Level definitions in drawing legends. Use labeling conventions in plan view. These steps help distinguish paint on the ground from professional services rendered Design excellence is built on quality base data

33 COST VS. RISK HOW MUCH SUE IS ENOUGH? Project progression Conceptual to Bid Docs QL D.... C.. B.. A..

34 QUESTIONS? FHWA - ASCE - COMMON GROUND ALLIANCE