Detailed plans—and following them—are key to grouting success.
By Gary Shawver, MGWC
I’ve covered grouting with both high solids bentonite grouts as well as neat cement in my last few columns. I’ve outlined how each has their place and should be used based on formations drilled through, the depth the grout is to be pumped to, as well as the size of tremie and annulus the grout is to be pumped in.
All grouts have their limitations as well as benefits. For example, bentonite grouts have a limitation on the length of time they can be pumped. Our firm has always considered this when determining which type of grout we will use on a particular job—unless the job has a written specification for a particular type of grout from the engineer.
Our deepest grouting job was a 10-inch well with 1500 feet of 10-inch casing to be grouted in a 15-inch-diameter hole. On a job like that, we had a protocol we followed and we followed it closely to minimize the potential of grout failure.
Know the Protocol
For us, we first employed two high-pressure duplex piston pumps, one of which is designed specifically for high pressure grouting. The primary grout pump is a 5 × 10 and the second is a 7½ × 10. The second pump is a pump we use when fluid drilling to deeper depths, but the configuration of the pump is set so it can sustain higher pressures while giving up gallons per minute.
The two pumps are tied together using a series of high pressure hose and valves so if one pump goes down, the other can start immediately with minimal interruption in the grout flow.
Second, we prefer to use a “Braden head” setup to pump the grout. It’s a device we fabricate that attaches to the top of the casing string. The Braden head consists of a domed head to handle the pressure. A series of ports and valves are built into the head to facilitate pumping the grout. In the top of the head is a “wiper plug” that is pumped down the casing string after the grout is pumped. The wiper plug is forced down the hole with water after all the neat cement has been pumped.
The third thing we do in our protocol is use a grout shoe on the bottom of the casing string to facilitate placement of the grout. The grout shoe also has a domed bottom to help prevent the casing string being forced up the borehole due to the flow and pressure of the grout being pumped. Domed bottoms on grout shoes minimize this problem. The shoe also has a drillable check valve installed in the shoe to prevent the cement from backflowing once it is pumped.
Fourth, we use a cement additive that enhances the pumpability and filtrate control of the cement as well as lessening the viscosity of the cement grout. This product has proved invaluable on deep-cement grouting projects. The extra time it affords during the grout installation is a huge plus as well as the filtrate control. If you have ever had a flash set of cement, you will understand the important value of this additive.
These four protocols are not the only ones we use, but they are some of the most important. There are many other details we employ to ensure our grouting is successful and I enumerate some of them as follows.
Detail Is Key
On a deep well grouting using neat cement grout, we do a calculation on the anticipated pressure the grout pump will develop. This is based on the depth the grout will be pumped to. We calculate this in advance so we can monitor the pressure while grouting to make sure we are not running into excess pressures. One person on site is responsible for continually monitoring the pressure and we record these pressures periodically through the grouting process.
We also calculate the water needed to pump behind the wiper plug so we know when enough water has been pumped and to get the wiper plug as close to the grout shoe as we can without bottoming it out. We don’t want to take a chance and bottom the plug out on the grout shoe when we’re pumping 500 psi or higher, so we stop the plug before it bottoms out. Water volume is monitored through a water meter.
Also during the grouting process we agitate the casing string while pumping, especially during the first half of the grouting process, and if possible, longer. We agitate the casing to prevent channeling of the grout.
On most of the projects we do, we pump a light bentonite slurry prior to grouting to determine if we can get circulation for air-drilled holes. On fluid-drilled holes, we thin the fluid down to a lower viscosity with clean fluid prior to grouting.
However, understand all solids in the fluids can settle in the annulus. Agitating the casing helps break up the fluid and potentially stop any differential sticking of the casing—thus preventing any channeling of the grout up one side of the annulus.
The agitation of the casing is typically done with the rig winch. Be sure to do the calculations to see if your winch can handle the weight of both the casing and cement.
As the cement is being pumped, finally is out of the bottom of the casing, and working its way up the annulus, the casing will become lighter as the buoyancy of the cement will lighten the load on the winch.
Wrapping It Up
We employ a minimum of four people on grouting projects like this. On very deep projects, we like to use up to six people. Every person is assigned a task or tasks to perform while the grouting is in process. Before the grouting takes place, a brief meeting is held to be sure everyone knows their job and “who backs up whom” if there is a problem. Detailed records of the grouting are kept and submitted as part of the record upon completion.
Deep-well cement grout jobs can be gratifying when the plan comes together, but I can assure you they can be disheartening when problems arise. Plan with detail, educate yourself to the potential problems, and do not take shortcuts. Shortcuts will typically lead to an eventual failure.
An old adage is appropriate for these types of grout jobs: “If you fail to plan, you will plan to fail.”
Gary Shawver, MGWC, is president of Shawver Well Co. Inc. in Fredericksburg, Iowa. He has been in the water well industry for 40 years and is a Master Groundwater Contractor. He has served as president of the Iowa Water Well Association, the Iowa Groundwater Association, and most recently served on the NGWA Board of Directors. Shawver is semi-retired, having sold his business to his employees. He contributes to NGWA’s member e-publication and can be reached at firstname.lastname@example.org.