Source: YouTube - University of Rhode Island & NPS
Preserving the accuracy of your work in the field is as important as it is difficult. Whether it's measuring slight changes in elevation or any other metric that demands consistency and preciseness over time, sectional rod monuments have become an invaluable tool for their reliability even in rugged environments.
When precise vertical measurements are needed, Berntsen’s Top Security sleeved rod monuments use a grease-filled plastic sleeve to isolate the rod from even the slightest movements in the surrounding soil. Sand backfills and a stainless steel datum point also provide a greater level of protection and accuracy.
When even the smallest change in position can affect a measurement, proper installation of these monuments is crucial. Let’s quickly look at the anatomy of a sleeved sectional rod monument and dive into installation step-by-step.
Components of a sleeved sectional rod monument
Berntsen's Top Security™ Sleeve 3-Dimensional Rod Monument System is specifically designed for high-precision geodetic and GPS surveying. Its patented design helps protect against excessive movements in the control monument.
Extendible rods, when driven to refusal, provide excellent vertical stability while the unique Y-shaped design of the Top Security Sleeve adds a second and third dimension to provide the most stable 3-D survey monument available.
How to install a sectional rod monument
The following video, created by the University of Rhode Island Environmental Data Center for the Northeast Region of the National Park Service, provides an excellent guide to installing Berntsen’s Top Security Sectional Rod Monuments.
We’ve broken down the steps explained in the video into a simple step-by-step guide below:
1. Prepare the digging site
Before breaking ground, make sure the area is clear of underground utility lines.
2. Dig the hole
Using a spade and shovel, dig a hole 12-14” wide and 42-45” deep.
3. Prepare the security sleeve
The security sleeve is designed to protect against topsoil movement that can result from water saturation and the effects of freezing and thawing.
- Glue the end caps onto the ends of the sleeve using multi-purpose PVC cement.
- Pump a complete cartridge of food-grade grease into the sleeve using a standard grease gun.
- Using the plywood as a base, keep the sleeve vertical as you apply the grease, occasionally tapping the sleeve onto the base to make sure it’s distributed evenly throughout the inside of the sleeve.
4. Prepare the rod sections
Threaded inserts are used to connect each rod section together. Use LOCTITE Thread Locker Red 271 to coat each side of the insert being connected. Tighten these connections using vice grips.
5. Drive the rod into the ground
There are a few steps involved in driving the rods into the ground:
- Attach a drive point to the end of the rod, sealed with LOCTITE Thread Locker.
- Once connected, carefully align the rod in the center of the hole and lower the supporting plywood over the top. This helps support the position of the rod as it’s driven in.
- Thread the hardened steel drive pin to the top of the rod.
- Position the manual drive adapter over the top of the drive pin and hammer the drive pin until manual driving is no longer productive.
- Attach a power drive adapter to the chuck of a gas-powered jackhammer and place it over the drive pin.
- Continue driving the rod into the ground until the top of the rod is 5 inches below the hole or until refusal is reached.
6. Make sure you’ve reached true refusal
As a rule of thumb, substantial resistance is reached when it takes one minute to drive the rod one foot with a 55-pound jack hammer. If refusal is reached before the rod is fully underground, cut the rod to the appropriate length using a reciprocating saw and smooth the edges with a power grinder. Again, the top of the rod should be about 5 inches below the hole.
7. Install the datum point and security sleeve
- Mix an epoxy and apply it to the threading on the datum point and the portion of the datum insert which will be screwed into the rod. Tighten it to the end of the rod with vice grips.
- Slide the greased security sleeve over the datum point and rod.
8. Install the PVC collar around the security sleeve
- Place 2-foot long PVC collar around the rod and sleeve within the hole.
- Backfill the hole with clean play sand both inside and around the PVC collar.
- Fill the remaining space outside of the PVC collar with wet concrete to permanently hold it in place.
9. Attach the access cover
- Apply a UV-resistant industrial strength adhesive to the base of the access cover and insert it into the PVC section.
- Check to ensure no glue or concrete is preventing the lid from opening.
Looking for more information about Berntsen’s exclusive line of Top Security Rod Monuments? Click here to learn more and watch an interactive monument installation video. Browse our product page to see Berntsen’s full line of survey monuments and markers or request a catalog.