Mining & Minerals

By applying unique solutions to increase the safety and longevity of our environment.

25MGD Sinkhole Leak Grouting

The Job

An underground minerals mine started to lose up to 8VF per day of mine due to water infiltration. Investigation of an adjacent stream uncovered multiple sinkholes which had opened up where the stream crossed a fault. Two sinkholes were adjacent to bridge abutments of a public road, which served as the sole access for multiple homes and farms.

The Challenge

Mine personnel started to self-perform chemical grout in some of the sinkholes. Due to the slow rate of grout installation relative to the water flow, the self-performed grouting was unsuccessful.

Due to endangered fish habitats within the stream, cementitious grouts weren’t allowed, and any chemical grouts needed to be certified for potable water use.

The Solution

CJGeo mobilized two polyurethane grouting crews in the third week of the Covid-19 pandemic to the site. To facilitate safe access to the site, all grouting was performed from aerial platforms reaching out over the work area.

During the grouting process, multiple additional sinkholes opened up; CJGeo would seal one sinkhole, and an adjacent soil filled feature would blow out. Super sacs of aggregate were dropped in the sinkhole throats to fill the bulk of voids, and then polyurethane grouting was performed below the super sacs.

Using nearly 50,000 pounds of CJGrout 35NHV61, CJGeo was able to slow the leaks to the point where no additional sinkholes formed, and the mine’s pumps were able to dewater the facility.

Coal Pier Sinkhole Grouting

The Job

With an annual throughput capacity of 48 million tons, Norfolk Southern’s Pier 6 at Lamberts Point in Norfolk, Virginia is one of the largest coal trans-loading facilities in the world. As an around-the-clock facility built around precision logistics, there’s little tolerance for disruption or downtime.

The Challenge

When two sinkholes opened up at the end of Pier 6 adjacent to the bulkhead, railroad personnel reached out to an onsite maintenance contractor. Steel plates were installed to provide temporary protection while a long-term solution could be implemented.

The Solution

CJGeo performed DCP testing at the site in order to quantify the depth of voids below the pavement adjacent to the sinkholes. The DCP testing showed that in addition to large voids visible from the sinkholes immediately below the pavement, there were large pockets of voids down to 15’ below the surface. 

CJGeo crews then used CJGrout 35NHV61, a hydro insensitive, NSF-certified geotechnical polyurethane to fill all voids and restore stability to the area. The grouting work took five hours onsite to install 3400 pounds of material, with zero disruption to operations.

Acid Drainage Grouting

The Job

A 72″ CMP stream diversion pipe under a coal stockpile at a coal mine in West Virginia was experiencing acidic water infiltration. This was causing bypassed stream water to become acidic, so regulators required all of the stream flow to be pumped to treatment ponds and treated. This was expensive, and the flow volume was greater than the design capacity of the treatment system.

The Challenge

Access was quite challenging; the pipe was either 700LF or 1300LF from the nearest access points to the farthest grouting location. Additionally, the infiltrating water was pH 2.

The Solution

CJGeo recommended a hydrophobic prepolymer chemical grout with an extensive performance history in high acidity environments. CJGeo crews sealed a combination of 20 joint leaks and point infiltration sources using the prepolymer chemical grout.

To address acidic water migrating through the stone dust backfill outside of the pipe, CJGeo crews then grouted an in-situ cutoff wall in the trench just downstream of the lowest leak using permeation grouting. The mine operator installed two dewatering wells immediately upstream of the cutoff wall to intercept and pump out the acidic drainage, to keep it isolated from the stream water.

Tub Crossing Repair

The Job

The sandy soils of South Jersey are great for growing produce and mining pure silica sand. While most of the produce is shipped by truck, a lot of the silica is shipped by rail. The rails inevitably cross the roads, and many of the crossings are at grade.

The Challenge

A short-line railroad was experiencing significant settlement and pumping of multiple precast modular crossings in the Vineland & Millville areas. Each crossing saw significant truck traffic, primarily from aggregate mining, and also significant heavy haul rail traffic from transporting sand.

The Solution

Working with a rail maintenance contractor, CJGeo performed polyurethane grouting on a total of four precast tub crossings in the area. Each was done in a single day, with the immediate resumption of automobile traffic, and rail traffic. Supplemental bolting was performed to address the deterioration of the panels that had resulted from the extensive movement of the panels.

Industrial Driveway Crossing Repair

The Job

MARC’s Brunswick Line’s Frederick extension passes through multiple industrial sites & driveways. This particular crossing served as the driveway of a ready mix concrete operation, so saw extensive high dynamic loading in a wet environment.

The Challenge

The repair had to be performed without disrupting either rail or industrial traffic. There was a four-hour window between the last morning train and the first evening train for performing the repair to the eight modular tub crossing panels. The settlement was up to two inches, with extensive spalling.

The Solution

CJGeo’s crew installed supplemental bolts due to replace the OEM center panel anchors, and then grouted the crossing in the mid-day window, without disruption to any stakeholder.

Mine Shaft Abandonment


The inverted pyramid concrete cap on a Civil War-era coal mine shaft collapsed catastrophically. The mine shaft was located in the middle of a suburban golf course in Richmond, Virginia. The collapse was due to the deterioration of timbers lining the shaft through soft sandy soils. The soft sandy soils extended approximately 25VF down to rock. As the timbers deteriorated with time, they lost the ability to support the cap.


The tunnel shaft was completely full of water, which was approximately 60 degrees. The area around the cap was very unstable and did not facilitate top-down access over the mine shaft.


The repair was designed around drilling well casing at an angle to intercept the mine shaft at various elevations between the bottom of the cap and socketed down into the underlying rock. 3.5PCF hydro insensitive polyurethane grout was chosen for its ability to provide the necessary structural support to the cap.

CJGeo performed pre-mobilization testing at our facility in collaboration with the design engineer to ensure that the grout would perform as desired. CJGeo placed polyurethane grout through approximately 15 different injection points, grouting from the top down. The end result was a plug extending at least 5′ into the shaft through rock, ensuring that the shaft through soft soils was completely stabilized.