Haul Road Design - Handling Constraints

When designing a haul road, you will inevitably have constraints and design criteria to work with, and those can be testing to get a design to work. In the video below I explore the options that you have to work with when modeling a haul road and how to use the corridor modeling tools to manipulate the model in different ways t get the result you need.

In the example I have been discussing with a user, they have the following scenario

  • The haul road starts at say elevation 100’ which is the water level of a lake to which they have to haul the material from a quarry above them on the hillside.
  • The hillside is pretty steep coming out of the lake so they have to design the haul road across the hillside to get the long slope of the haul to be less than 15% maximum.
  • They are going to build a large pad at elevation 130’ for rock crushing equipment to crush the rock being quarried out in areas above the pad.
  • They are going to build a couple of quarry areas in the hillside to extract the rock that they need for the project, the rock will be hauled to the crusher, crushed and stockpiles and then hauled and loaded onto barges that will take the material across the lake to the project.

In addition

  • The haul road design calls for a 25’ width haul road at 0% cross slope with 2:1 max side slopes to tie to existing ground
  • The max slope longitudinally for the haul road is 15%
  • The sideslopes cannot cross existing right of way boundaries that form the limits of where they can quarry and extract the material.
  • The desired location for the pad puts the end of the pad at which they want to connect the haul road quite close to the ROW boundary and the elevation delta between the pad and the existing in that area is such that long 2:1 sideslopes are needed to tie to ground making it difficult to fit a bend in the haul road to give the length of haul road required to keep the slope less than 15%

So what tools do you have at your disposal to make all of this work?

Key Things To Remember

  • When you have a sideslope of 2:1 you have a max of 2x the elevation delta between the pad and existing to work with in terms of horizontal distance to the toe of slope i.e. with the pad at 130 and the existing at the lake at 100 you have a 30’ delta so you have a max of 2x 30’ horizontally to hit existing from the pad / haul road and that assumes that the existing ground is less steep than 2:1 i.e. if Existing has a slope of 1:1 a 2:1 side slope is never going to hit existing. At existing slope of 2:1 the sideslope is also not going to hit because it runs parallel to existing, the side slope has to be steeper than existing for it to tie to existing.
  • The 60’ is your max offset from the ROW line if the ROW is at elevation 100. As the ROW increases elevation then your elevation delta decreases such that at ROW elevation of 130 you can come off your pad or haul road elevation horizontally to hit the ROW with a zero length side slope. You can use eg Slope Designer to model a 2:1 sideslope from the ROW line to elevation 130 to see where the Edge of pavement limit is for your haul road and then design inside that for your haul road.
  • If you put a bend in the haul road of a specified arc radius, remember that from your edge of pavement arc you will have a max of 0.5x Radius at a slope of 2:1 before the slopes on one side of the arc will cross over the slopes from the other side of the arc. So for a Radius of 50’ at centerline, on the inside of the curve you will have a 37.5 radius, and at a 2:1 slope that will give you a maximum of 37.5*.5 i.e. 18.75’ of elevation delta between the Edge of pave and existing ground before the slopes will cross over each other i.e. a 20’ elevation delta will not work so through the curve your EP profile needs to remain less than 18.75’ above or below existing.

What things can you change?

  • You can change the radius of arcs
  • You can change the profile of the vertical alignment (raise / lower, add vertical curves etc.
  • You can change the position / path of the road - start point, end point, PI points to get a better shape and provide room for side slopes
  • You can raise / lower the target pad which can change the slope needed and the sideslope lengths required
  • You can increase or decrease sideslopes if you have design OK to do so
  • You can add in Retaining Walls to account for elevation deltas that do not allow for a 2:1 slope to work i.e. if you have a 30’ elevation delta and only have 50’ for your sideslope then you can do 50’ at 2:1 which accounts for 25’ of the slope and for the remaining 5’ you can use a retaining wall if the design allows - in this scenario you can either move the edge of pave at least 10’ to give yourself the required 60’ or you can change the sidelsope to a steeper slope or you can use a retaining wall, or you can lower the road to reduce the elevation delta that you are working with - those are the options to make it work.

Methods to Use

  • When you define your alignment use a curvilinear line not a chorded line - the straight segments will have angle breaks in between them and because they are non tangential that will cause issues with your corridor design - tangential elements work best i.e. Straight - Arc - Straight etc.
  • When you define your alignment it will be easier to manipulate if you create your HAL using the PI method and inscribe curves at the PIs - you can then edit the location of the PIs or the Radius of any arc element and the PC / PT points will be recomputed for you automatically.
  • When you design your profile, create a Ground profile along your alignment so you can see how the ground profile is working along the current alignment - if you change the alignment the ground profile will update automatically.
  • You may also want to create a large planar surface for your Pad that extends over the entire area of the haul road and do that using a rectangle and set the rectangle at elevation 130 - this way you can also see where your pad elevation is that you have to tie into at the end of the haul road.
  • Define your vertical alignment - remember the VAL is independent of your HAL and it does not dynamically change when you modify your alignment, you will need to change the end stations of the VAL and update any Grade Breaks or Vertical curves that you have in the VAL after each edit of the HAL.
  • Create your alignment at the most important location - this can be at centerline, but in some cases you may want to design the Left edge of the pavement or the right edge of the pavement with your alignment because that is where your sideslope is going to come of, and that may in this case be the hardest thing to calculate.
  • Create your corridor by adding shapes at offsets and slopes from the alignment i.e. 12.5’ at 0% for your road edges and then a 2:1 side slope to Existing Ground in Cut or Fill.

Note - when you define your sideslopes to existing, the sideslopes may cross over each other before they tie to existing in the area between the two sides of your planned horseshoe bend

In these areas you can try connecting your road edges together into a single surface (you cannot do that in a corridor model directly (because they are the same road edge) however because the two sideslopes crossed over each other it is likely that the slope between the road edges will be greater than 2:1 - so again you are faced with how to solve the problem - your options inculde

  • Lower the road / raise the road
  • Move the road nodes to give more space in between the road edges
  • Increase / decrease the road radius (this will also move the road which will cause different issues elsewhere
  • Add in a retaining wall to take out some of the elevation delta
  • Increase the side slopes

Remember that every design decision has an impact on something else - it may increase / decrease your Cut / Fill quantity giving you an excess or a deficit to handle, it may push your sideslopes Out or In and may push them over your Right of Way line, it may change your road profile slope so that it exceeds your design limits and so on. The software will not “Design It For You”, you need to make the decisions and change the design to determine the effect on the design in terms of quantities and meeting all the criteria - it is an iterative process to create something that works and what works may not provide a balance of materials - then you need to look at increasing or decreasing the size of your Pad to take more or less material to create your balance etc. If the material you are cutting for the infrastructure (Roads and Pads) is usable for your project as a Fill, then having an excess may or may not be an issue depending on the balance needs of the project and you can use the mass excavation for your roads and pads as a part of the quarrying operation to generate the initial material for the project.

Video shows you how