First of all, I would like…

First of all, I would like to thank you for the hard work and significant effort that you have put into developing the specification.

As you know it is our objective to work with the Ministry to introduce a milling procedure with this specification that will provide a high quality roadway with a minimum amount of milling and padding while ensuring safety and the comfort of transportation.

Our comments on the specification are provided with this objective in mind.

In this regard, we believe that it is very important to require a high level of accuracy in the initial surveys and the final measurements between the DDM and the final milled surface.

A high level of accuracy at each step in the process is required to ensure that there is not a compounding of the decrease in the level of accuracy through the process that leads to an undesired result.

We also believe that it is important to stipulate the Quality Control (QC) and Quality Assurance (QA) requirements clearly so that contractors understand the complete role and how their work will be evaluated.

Since Quality Control is done by the contractor for their own benefit the randomness of the process and the number of checks and reside with the contractor.

Since Quality Assurance is the basis of acceptance, the process must be more prescriptive. It must detail the number of test measurements, possibly per km and the locations must be selected in a random way to avoid any bias.

Following are my comments based on the above objectives.

510.04.02.01 f) Certification that the DDM meets the requirements of the Contract Documents, including cross fall.
- To the best of our knowledge, the contracts only stipulates an absolute cross fall and superelevation.
- We suggest that a tolerance for each be stipulated because all would agree that an absolute 2% cross fall or 8% superelevation cannot be exactly satisfied in every instance.
- We suggest a tolerance of +/- 0.3%.
- This would ensure that all boundary constraints such as residual asphalt thickness, drainage and appurtenance matching (curbs, catch basins etc.) could be achieved.
- this tolerance could be in this spec or elsewhere in the contract documents and drawings.

510.07.06.04.02 Operational Constraints
- The second paragraph we believe is intended to describe the crossfall at each station and not the smooth transition between stations that will be often required. Some clarification can be achieved with the following wording.
-The surface remaining after removal shall have a constant and continuous crossfall at each station with a smooth transition where crosstall transitions are required between stations.

510.07.06.04.03 Road Surface Survey
- This is a critical step that significantly affects the overall outcome of the DDM and the final surface achieved after milling
- The relationship between the survey registration points and the existing geodetic control monuments is appropriate at 4 mm in the vertical direction.
- The relationship between the adjacent registration points must be to a higher level of accuracy to ensure that an 8 mm error does not arise between adjacent registration points
- A+/- 2mm difference between adjacent registration points with a +/- 8mm difference per km between registration points is necessary. This can will be achieved/checked by running a closed leveling travers.

510.07.06.04.04 Digital modelling
-The standard deviation of the calculated elevation difference for all the points at each cross section location shall not exceed 8mm.
- In general the tolerance is usually 2.5 times the standard deviation https://en.wikipedia.org/wiki/68%E2%80%9395%E2%80%9399.7_rule).
- This standard deviation is equal to a tolerance of +/- 20mm at a 98% confidence (and +/- 24mm at a 99% confidence)
- This tolerance can result in a 20mm elevation difference between the centre line and the edge of pavement which translates into a 0.6 % cross fall error that will not meet the desired outcome but will satisfy this specification requirement. See diagram below.
- we recommend that the standard deviation be at 3 mm which has been demonstrated to be achievable and provides the desired outcome
- the tolerance will become 7.5 mm at the limit and the cross fall error will be reduced by more than half
- this was our original suggestion at the first drafting of the spec
- There must be a precise definition of the location of the control cross-section. This cross-section should also be approximated at the midpoint of the distance between survey registration points (where the maximum errors is assumption),

510.07.06.04.05 Automated Machine Guidance

This specification is new and when fully implemented after beta testing on several projects, contractors will be able to replace their millings fleets with equipment that can fully achieve the objectives and goals of this specification. In the mean time the specification should allow milling machines that use only local ground referencing systems.

Similarly, some manual intervention will be required on some milling machines that can still use the 3D model to achieve the precision milling. Until existing fleets can be replaced, the specification should just rely on the stipulated requirement to achieve a milling tolerance of +/- 5mm from the DDM.

This section stipulates that “The Contract Administrator will carry out total station measurements of the milled surface to verify that the +/- 5mm tolerance from the DDM tolerance is met".

The location and number of measurements to be take are not specified. We recommend that the number of either individual shots or total cross sections be stipulated per kilometre. We also suggest that the location be selected on a random basis to eliminate any bias in the selection of the locations. This approach should reduce, if not eliminate any disputes between the CA and the contractor.