Engineering
The Engineering Department is responsible for 452.98 miles of county roads (324.80 CSAH roads, 103.86 county roads, & 24.32 muncipal roads), 255 bridges (103 county bridges and 152 township bridges located on 790.31 miles of township roads), and pedestrian/bicycle routes. Engineers provide efficient planning, design, construction and maintenance for roads, bridges, and trails. Engineers are also responsible for the complete management, direction, coordination and budgeting of these modes of transportation. The Department seeks and implements Federal, State and Local funding assistance for eligible projects and pursues cooperative projects with other governmental units. Partnering with contractors, utility companies, governmental units and other project participants is also necessary to ensure an efficient construction schedule is reached. Financial details regarding all construction plans are reported annually by our Public Works Accountant.
Bridge Safety Inspection
Minnesota statutes require that all bridges in the state be inspected by certified personnel at least every two years to ensure that they are safe, able to carry traffic loads and are kept in good condition. Annually, 255 bridges and large culverts are inspected and documented. Documentation includes details on the condition of all the components that make up each structure: abutments, wings, beams, deck, railings, etc. An annual inspection monitors the condition of these items and note any changes that warrant cleaning, minor or major repairs, reduction of load limits, or closure of the bridge and roadway. This also includes inspections on large culverts or groups of culverts.
Bridge Construction
Because of the potential peril that could result from constructing a faulty bridge or overlooking needed repairs to an old bridge, engineering personnel must undergo extensive training to be certified. The engineering staff must understand and apply the following concepts:
- timber bridges, concrete bridges, and combination
- box and arch culverts
- substructure construction
- spread footings
- pile foundations
- forms and falsework
- prestress concrete beams
- deck expansion joints
- deck overlays
- slope protection
Bituminous Quality Management and Bituminous Street
(“bituminous” in lay terminology is “blacktop”)
- Before bituminous construction begins it is the responsibility of the engineering staff to calibrate the plant’s cold feed belts for proper mixture proportions. He/she must make changes as needed to insure the final bituminous product meets specifications before leaving the plant and incorporating into the road.
- A test shack must be set up. This is where inspectors keep records and perform tests.
- Areas tested and inspected are:
- gradations on all materials incorporated into the bituminous mix including: coarse aggregate, fine aggregate, crushed concrete and recycled asphalt pavement
- nuclear density tests for required density specifications
- oil extraction test for assurance of proper asphalt cement
- air voids tests
- rice test for maximum densities
- marshall stability tests for bulk densities
- gravity tests
- control strip densities to determine optimum rolling patterns
- shale tests
- quality management testing
- yield calculations to insure proper mat thickness and tonnage
- sampling AC oil for quality assurance
- Bituminous street inspection involves three primary concerns: final appearance, ride quality and durability of the bituminous mat.
- Collect and send samples to MnDOT for verification testing.
- Communicate the on-site and MnDOT test results to the contractor.
Concrete field and Concrete plant
- Construction involving concrete must conform to MNDOT specifications for aggregate requirements, mix designs, gradations, admixtures and transporting. Concrete must be made in certified ready mix plants.
- Areas tested and inspected include:
- gradations on coarse and fine aggregate to check for proportions and type
- moisture tests on coarse and fine aggregate to check that water volume is included in the concrete according to the trial mix
- air entrainment tests to check air content
- slump tests on concrete to insure proper consistency of mix
- concrete cylinders which typically will be broke at 7, 14, and 28 days to determine compressive strength
- admixtures for quality and proportion in the trial mix; examples of typical admixtures are accelerators, retarders, water reducers, and flyash
- curing agents to observe whether the application is being done in a timely manner
- cement-voids ratios and Warren’s Modulus
- hydration involving water, temperature and time
- strength of concrete in paving and tensile
- Technicians must be knowledgeable in the different types of materials such as:
- cement (example: Portland cement)
- flyash
- water
- air-entraining
- corrosive inhibitors
- Concrete according to the American Concrete Institute (ACI) Areas to be inspected and involve responsible decisions include:
- statistical formulations for quality assurance
- material consistency
- how materials are handled
- concrete mixtures
- batching
- curing
- form removal
- pavement slabs including bridge decks, pre-cast and pre-stressed concrete
Aggregate Production
Inspectors check that the contractors’ equipment has compacted the base material effectively. Sometimes it is necessary for base material to be stockpiled prior to spreading. This process will help avoid segregation. The inspector must keep detailed records of hours, location, lift thickness, test results, quantity and yield. Tests that need to be conducted to insure optimum conditions for compaction include:
- gradations on composite aggregate sample
- proctor tests for relative moisture densities
- sand cone densities
- aggregate quality tests
- soil and aggregate moisture tests
- percent crushing tests
- spall tests
- quality compaction tests
- soil type tests for determination of sand, silt, and clay content
- soil boring tests
Surveys
Surveying is often conducted in hazardous environments. Preliminary road and bridge survey operations are performed in the midst of traffic so caution must be exercised. The work zone must be delineated with proper signage since some or all of the crew are working in the traffic lanes. The crew leader must communicate each operation with hand signals or portable radios due to excessive noise or distance from crew members. Often a decision is required as to whether this particular operation can be performed safely due to some variable such as visibility. The crew leader then determines a course of action, such as getting a flag person or changing operations altogether.
The sequence of operations for a typical road survey usually is as follows:
- Locate and perpetuate section corners
- Run centerline stationing at 100 foot intervals between these section corners
- Carry datum elevations along project to termini establishing “elevation checkpoints”
- Map all topography adjacent to road
- Perform a cross section of the existing ground at right angles to the road centerline for earthwork computations
This data is recorded in a field book or electronic data collector to and later entered into a computer. The survey crew leader is also responsible for establishing control stakes for the contracting agency to build the road or bridge to the required specifications. This usually involves setting horizontal and vertical control stakes to establish where the road or structure will be placed. This also includes stakes for curb and gutter, storm and sanitary sewers, county and judicial ditches and bituminous offset. Correct positioning is crucial since an error could cost thousands of dollars, delay completion, or lead to a lawsuit. Due to the relatively short construction season in Minnesota, it is often necessary to work in adverse weather conditions to complete the surveying process. Speed, accuracy, thoroughness and the ability to make sound and safe job decisions are paramount to performing this duty effectively.
Total Station & GPS:
This instrument is used to accurately turn angles and measure horizontal distances. The smallest error in operating this instrument could result in the misalignment of a road or the wrong placement of reference point on a bridge substructure which could cost many thousands of dollars to correct. Because tight accuracy tolerances are now required to meet coordinate data being generated by global positioning systems (GPS), sophisticated instrumentation is required. Engineering personnel also uses the total station to aid in the re-establishment of section corners after construction projects have disturbed them. These corners have been precisely placed through GPS at a substantial cost to the agency and must be replaced for future use. Majority of surveys performed at Faribault County is now done with the use of GPS.
Data collectors:
It is used in conjunction with the total station & GPS for traversing, topographic and cross sectional data, taking out working points and setting alignments of bridges and roads.
Levels:
A surveyor must be proficient in the use of automatic levels and hand levels. These are used routinely in the establishment of vertical control for calculating elevation. The ability to read both English and metric leveling rods accurately is important. A misreading can cost a crew a whole day’s work or the possibility of setting an important point wrong. A hand level is utilized where the terrain is inaccessible with an automatic level and by inspectors to perform quick checks on a grading operation.
Lasers:
This apparatus calculates and establishes correct grades for ditch drainage, sanitary and storm sewers, and tiles.
Designs:
A thorough understanding of engineering principles and pertinent mathematical formulas are imperative to achieve a well designed plan. A solid foundation in usage of the engineering and computer aided drafting software is also essential for the designer. Care must be given to insure that proper governmental regulations are followed to avoid litigation. Whenever possible the designer should try to preserve the aesthetics of each property while still meeting the specifications.
Grading & Base
- An inspector must first conduct a document review which examines specific construction details, sources of materials, limits of excavation, depth of topsoil, compaction and moisture requirements, preparation of sub-foundation, culverts, fill and overload.
- During construction an inspector should be aware of haul roads used and dust control on or off the limits of the project. To correctly interpret the specifications for clearing and grubbing trees you must be aware of erosion control and slated times that seeding, sodding, mulching or other turf establishment should begin. When contemplating disposal of debris the inspector is also mindful of environmental concerns.
- During primary excavations an inspector must be aware of the actual common excavation, rock, muck and subgrade excavation.
- Culvert installation inspection is another important phase of construction inspection. An inspector needs to check for any major defects of materials that could reduce the strength of the pipe. Also he must ensure proper location, elevation, placement, connections and compaction of trench materials.
- A final inspection is done on all installations checking for damage, cleanliness and correct quantities.
Communicate with interested parties
Because a project involves many people, it is essential that the engineering staff have excellent communication skills. In many ways he/she is the “gatekeeper of information” gathering and disseminating information amongst interested parities. The engineering staff helps the engineer in hold pre-construction meetings and right-of-way hearings. Besides communicating information about construction projects, the engineering staff must field many questions from the public on road conditions, drainage issues, and county reimbursement to name a few. A listing of the groups of people involved include:
Internal:
- The engineer
- The engineering and maintenance staff
- County commissioners upon their request or the request of the engineer
External:
- Contractors
- Governmental officials: Minnesota Department of Transportation (MNDOT), Minnesota Pollution Control Agency (MPCA), Minnesota Department of Natural Resources (MNDNR), Minnesota Historical Society, Army Corps of Engineers (COE), Occupational Safety and Hazard Administration (OSHA), District State Aid Engineer (DSAE)
- Land owners
- Utility companies
- Railroad representatives
- Post office personnel
- Sales representatives and suppliers
Other Duties done by Engineering:
- Right-of-Way acquisition
- Contract Administration
- Project Scheduling & Management
- Inspection of Projects