Creating Data for Site Renovation

A 1.090Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

We all like to enter a clean, flat field and commence earthmoving. Those days are mostly in the past, it seems all the good land is gone. We are now building on steeper sites and moving less than high quality dirt. The other difficult site condition is when renovating an existing site. I want to cover the issues you will be presented with and how to deal with them. Over the years, we have been able to provide more and better information for contractors doing site renovations; this critical data has been a real advantage to field crews and the office as well.

Items specific to renovations
When working on an existing active site, you are presented with issues that make this type of job more interesting. Let's start at the beginning.

Existing Conditions
You will need to pay attention to the existing conditions when approaching the job. During the bid phase, there will be no time to go and do a good review. When you are awarded the job, it's time to go out and do a careful inspection of the site. Here is the process;  
• Load the existing conditions file into a data collector and bring it to the site. When localized, you are now ready to confirm the information you have been given.
• Sometimes the existing conditions file may not be current. Now is the time to make sure you have up to date information.
• If there are bore holes indicated, note their location on the site and the relevance to the new work to be done. Often times bore holes are placed close to where they need to be due to existing items that need to be removed before improvement. Do you need additional bore holes after demolition?
• Make note of the differences.

When it comes to removing current improvements before rebuilding, you must proceed with caution. When properly planned, the demolition can progress smoothly and rebuilding efficiently. One of the great advantages of a digital life is the fact you can plan the job on the screen and find the issues before they get performed in the field. Here are some tips;  
• Load the demolition file and bring it to the field to verify what is to be removed and what needs protection.
• Often times the limits of demolition need to be changed. Make a note of the differences so they can be reported before demolition begins. After you go in and start making dust, there is no room for negotiation. This is critical for parking lots. Too many times we see a five year old demolition plan for parking lot improvements. In the time between the survey and job start, the asphalt has deteriorated requiring larger removal/ replacement areas to be done.  
• Figure 2 shows new paving at the end of an existing parking lot. A couple existing spot elevations may be all that are needed to make a smooth transition from the old to the new. Verify in the field. Be sure to check the condition of the paving if a full overlay is not called out.
• When tree salvage is on the demolition list, make sure pictures become a part of the site review. Owners often times have enhanced memories of old tired landscaping. This holds true for any item that is to be salvaged and reused or returned to the owner.
• Utilities are always a wild card. Water jetting is a favorite of ours and can save you hassles when locating and updating utilities. It always seems that there are more utilities than shown, and they are in different locations than the plans indicate. I'm sure we are all used to that. This pre-demo walk around the site will go a long way to benefiting you in two areas; identifying differences that need to be addressed and phasing your work.

2D to 3D Demolition
When initially reviewing a site for demolition and rebuilding we have developed a process of 2D to 3D information gathering. Here is it goes;
• After localizing the site, verify the conditions as outlined previously.
• With the existing conditions verified, look at the saw cut and demolition lines to verify they are located well. Make proposed line changes in the field to send to the owner for review.

With the "lines on the screen" looking good, it is now time to add the third dimension to the demolition review. The reason we propose a two-step process is that rehabilitation work can get involved and quickly overwhelm you in the field during review. The thought process is to physically place the 2D plan sheets on the ground. Your experience will help you to plan the job in your head before the actual start. If you are able, paint and flags go a long way during the 2D phase of demolition planning. Now it's time to move the project to 3D;
• Verify the elevations called out in the site plan. Make a note of any differences.
• Increase the point density to make the match to the existing more accurate. You need to make a choice at this point. If there were areas where you propose more removal than the plans, you can wait to see if the change order makes it through or just shoot both areas if it is convenient.
• When doing a regular surface topo, it is possible to move quickly and know some of the shots may not be highly accurate. The pole may not be plumb, signal RMS may be poor. That may be OK for a 20 acre topo. When shooting saw cut lines we recommend the use of a bipod and taking a longer timed shot with a plumbed pole. You will be glad you took this time when laying finished surfaces.
• With this work completed, it's now time to get back into the office.

3D Rehabilitation Data Prep
With the 2D and 3D information collected in the field, we now need to build the data that represents actual conditions today. Here is how we proceed;
• Contact the owners and get any proposed changes approved or understood. The understood part is when you feel there should be more paving replacement, but their budget will not allow. They will forget the conversation when only 30% of their parking lot looks nice and they want the rest to look like what you just did. That's a good time to recall the emails or letters that mentioned this a year ago.
• With a good idea of what work is required. You can now start to combine the 2D limits of work with the 3D information to create a good model to take to the field.
• Figure 4 is the same area we reviewed on the plans in Figure 3. There were changes to the area as the work progressed from the 2D to 3D site review. The parking replacement areas were enlarged in several areas and tight topo shots were used to blend the new work into the existing.

When dealing with a mill and overlay in a parking lot, things get more complicated. When everything works right, milling and filling are at a minimum and the lot drains well when the paving is finished. In order to do this, you will need a well-made existing ground model and closely watch the demo and replacement values. Let me explain.

There will be thicknesses that need to be met during the rehab of paving. There may be minimum milling, maximum secondary fill asphalt and minimum thickness for the finished mat. Due to the differences in takeoff software, the answers to these questions are achieved using varying methods. Here is the process to making the pieces work;
• Everything is taken as a depth below finished surface. The critical thing to remember is the finished product needs to look good and drain well. Make a good looking model that incorporates the features to remain. These can include intact recent paving, curbs and sidewalks.
• Make a surface of the existing conditions. Lower the surface to the required milling depth.
• Perform a takeoff of the two surfaces and look for areas of too much or too little finish asphalt. A third surface can be made with the thin areas milled more and the thick areas partially filled with cheaper fill asphalt. This will result in a good finish and cost savings.

This may seem like a lot of work. It is far easier to perform this in the office than the field where it gets a lot more expensive to find out what things really look like.

Regarding Accuracy
We know that GPS is a great tool for the work mentioned previously. You can take some great topo shots and grade the parking lot with GPS. Some of our clients have purchased a robotic total station for doing detailed work like this. There are plusses and minuses associated with using a robot, the biggest being the one to one relationship of the robot to a machine or rover. GPS excels here with the one to many associations.

When considering the use of a robot, it is also wise to consider automating your paving operation as well. I don't mean to complicate things or spend your money but these tools are priced competitively and can make a big difference in your arsenal.

In a nod to old school grading, I hope you have not turned the 2D laser grading equipment into a door stop yet. For rehabilitation jobs they really shine, here are some ideas;
• When the plans call out for matching existing pavement with no possibility of cutting out a larger area, going 2D against the existing paving will get you a good match.
• Use the laser to cut subgrade against the existing paving. Set the cross slope across the blade to insure you leave base rock to cut.
• Here is where you need to make a decision. You can take shots along the new subgrade and go to the office and warp them into the model of the rest of the parking lot or...
• Switch to 3D and grade a blade or two width from the saw cut line. The distance depends on the elevation and slope differences in these areas. When you have the base at the saw cut and the base in the lot close to the saw cut, you can blend them by hand.
• It makes good sense at this time to have a grade checker with GPS on site to verify the slopes to the saw cut and verify drainage.

In any rehabilitation job, there will be utilities to move and add to the project. As with the grading and paving file, there are things you can do to make sure the utility work goes smoothly. There is no real need to talk about utilities in the middle of a replacement area. I would like to address the new run of pipe across an existing street. Never easy to do and seldom looks as good as we want. Figure 5 shows a new storm drain that needs to be added to a job. The road was reworked down station and this area now needs a drain.
• The best way to verify the conditions is to pothole along the route and find all the surprises first. This crossing is an old street at a major university; there were a lot of sub-surface utilities that needed to be protected.
• With the information of what crossings had to be dealt with the job was split in half down the centerline of the street. The affected utilities were present at their portion of the work, reducing the circus only to the players involved.
• The pre-cast manhole needed to be changed to suit conditions on site. Much easier to find before commencing work.
• The information acquired by the contractor is shared with the engineer and surveyor in order to streamline work progress.

Other advantages
To this point I have discussed the details of the aspects that make up a rehabilitation project. To tie things up in a neat package, let's look at what advantages technology gives you;
• The whole picture. You can look at what the current conditions are and how they will look when done. This can help with everything from phasing to where to place the trees for replanting.
• Before you begin work you are able to identify and intelligently talk about problem areas before starting work.
• Precision surfaces lead to detailed quantities and verification that removals and replacements are within specification.
• Safety. Rehabilitation sites are busy with people other than you, that is why they are expanding. Looking at a map of the site and coordinating traffic patterns in the office will go a long way to a smooth running job.

Marco Cecala is the owner of Take-off Professionals in Arizona and is a nationallyknown expert and teacher of CAD, automated surveying and machine guidance.

A 1.090Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

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