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

Stem Wall Backfilling With Cellular Concrete

The Job

This work was associated with the construction of a new academic building at a school in Lynchburg, Virginia.

The Challenge

Due to a sloped site, there was up to an 8′ difference in elevation between the existing ground and the desired finish floor elevation. Various options for filling the CMU stem walls included soil, aggregates and EPS foam blocks. EPS foam blocks were chosen to reduce loads on the footings, which would have required deep foundations in the case of soil or aggregate backfilling.

Due to the extensive sub-slab plumbing, the design called for EPS blocks cut to fit the curved walls & uneven ground profile, and then backfilled with 18″ of stone dust, to allow for the plumbers to dig and install the plumbing.

The Solution

CJGeo proposed installing 23lb/cuft cellular concrete to speed up the installation, reduce supply chain risks, and reduce the loads applied to the foundations and underlying soil.

CJGeo placed 1914CY of cellular concrete over three days onsite. All material was walkable within 12 hours, and the project saved approximately 3 weeks relative to the original design’s timeframe.

The cellular concrete was brought all the way to the bottom of the 6″ stone layer below the slab, and the plumbers were then able to excavate through the cellular concrete with a mini excavator and hand tools to install the plumbing, and the trenches were backfilled with 57 stone.

The total load using cellular concrete was reduced by approximately 120lbs/sqft relative to the EPS/stone dust backfill design.

Precast Lagging Wall Lateral Load Reduction

The Job

This work as associated with the replacement of Scaife Hall, at Carnegie Mellon University, in Pittsuburgh, Pennsylvania.

The Challenge

The H-pile and precast lagging wall was situated at the top of a steep slope, which had a Class I railroad at the base. Because of site constraints, an HDPE stormwater detention structure was situated within the fill area, along with extensive stormwater pipes and manholes.

In order to optimize the drilled shafts for the H-piles by reducing the lateral loads, the designer sought a lightweight, permeable backfill material that would not apply lateral loads once in place.

The Solution

CJGeo proposed 20lb/cuft permeable cellular concrete to minimize lateral loading on the wall during construction, buoyancy of of the stormwater system components, and ensure a free draining material.

Because the material is permeable (modified ASTM D-2434 2.0cm/sec), it is freely draining and reduces hydrostatic loads on adjacent structures.

620 cubic yards of lightweight backfill were placed over two mobilizations.

HRSD 24″ Forcemain Abandonment

The Job

HRSD’s Virginia Beach Boulevard Forcemain Replacement project installed more than a mile of new pipe to replace an aging 24″ force main.

As part of decommissioning the original force main, it needed to be filled completely with grout.

The Challenge

Due to extensive widening of the roadway, the pipe was originally constructed alongside, extensive commercial and residential development, the number of access points needed to be as few as possible. This was driven by extensive structures over/adjacent to the old pipe, and a desire to reduce disruptions to adjacent stakeholders, and the risk of any utility strikes during access pit excavation.

The Solution

CJGeo grouted more than 7,000LF of the 24″ pipe over a period of four working days onsite. The pipe was completely filled, which was verified by uniform material venting from the far end of each run. Run lengths ranged from 450LF to more than 2000LF.

DeRuyter Reservoir Outfall Abandonment

The Job

The DeRuyter Reservoir, in DeRuyter, New York, is a 557 reservoir originally developed as part of the Erie Canal system.

As part of a dam upgrade project, the three parallel 22″ diameter, 300LF outfall pipes needed to be abandoned, along with a stone box culvert downstream of the valve chamber the pipes terminated into.

The Challenge

Each of the three pipes had been previously blindly flanged by divers. Therefore, the only access was from the downstream end within the valve chamber. In order to vent the air displaced by the abandonment grout, vent or placement points needed to be installed just behind the upstream blind flanges, which were approximately 40′ below the water surface.

The Solution

CJGeo worked with the general contractor to design an internal venting system utilizing sacrificial placement pipes installed from the valve chamber. After each of the sacrificial grout pipes was installed, the downstream terminations were bulkheaded, with vent stubs.

CJGeo mobilized a cellular grouting crew, who placed 30lb/cuft cellular concrete through each of the sacrificial grout pipes, until grout returned to the bulkhead vents, confirming fill. The work was completed over two days an onsite-the first day for the abandonment pipes and first lift in the box culvert, and the second day for a top-off pour on the box culvert.

250000 Gallon Oil Tank Abandonment

The Job

As part of decommissioning an underground oil tank at an institutional facility in Washington, DC, it needed to be filled with excavatable material that was lighter than the roughly 55lb/cuft heating oil it was designed to hold.

The tank is located in a small empty lot, which is slated for redevelopment in approximately three years.

The Challenge

To be officially considered decommissioned, the tank had to be completely filled. It is slated for removal as part of the redevelopment process of the area (it sits within a future basement excavation) so the fill material had to be excavatable.

The Solution

CJGeo proposed 20lb/cuft cellular concrete for the abandonment grouting. This afforded plenty of factors of safety to reduce the likelihood of settlement induced by filling the tank and maximized excavatability.

CJGeo placed the fill material over a period of two days onsite. Because cellular grout is highly mobile, no entry was required during the placement of the fill material, which designed a significant amount of risk out of the process.

The 1200CY placement was performed over two days onsite.

Retaining Wall Lightweight Backfill

The Job

Sanitary sewer right of ways straddling lot lines can be particularly troublesome if a problem occurs with a line and trenchless repairs aren’t possible. This was the case on an 8″ gravity line in Arlington, Virginia. Extensive structural damage to the line caused repeated backups and raised stability concerns for multiple retaining walls which had been constructed over the line.

The walls ranged from four to eight feet tall and were a mix of concrete and natural stone.

The Challenge

Timber-shored, hand-excavated work was done on the high side of the wall to expose and replace the affected lines. Because of stability concerns with the walls, the geotechnical engineer specified material no heavier than 25lbs/cuft.

The only access was pumping material from the street, down a decorative flagstone pathway between two homes, and into the excavated pits.

The Solution

CJGeo proposed 25lb/cuft wet cast density permeable cellular concrete for the backfill material. Because there is no aggregate, it can easily be pumped through small-diameter lines at low pressure, which addressed the accessibility concerns.

Because the material is permeable (modified ASTM D-2434 2.0cm/sec), it is free draining and reduces hydrostatic loads on adjacent structures.

CJGeo mobilized twice for the phased project and backfilled each of the pits in a single lift.

Fire Station Floor Lifting

The Job

The concrete slab on the grade floor inside of a fire station on the North Neck of Virginia settled up to two inches. As part of the investigation into the cause, an engineer discovered voids up to 8″ below the slab and multiple broken sanitary sewer pipes below the floor.

The affected areas included a dayroom, kitchen & meeting hall.

The Challenge

In order to minimize disruption to the fire station’s operations, the proposed repair had to be quick, clean, and minimize uncertainty associated with the plumbing repair slab cuts.

The Solution

CJGeo performed ground improvement grouting of the underlying soils to 5′ below-grade utilizing plural component polyurethane compaction grouting. Shallow voids were filled using plural component polyurethane, which was also used for settlement correction.

Because polyurethane grouts cure very quickly, the floor was repaired the day before the plumbing work was scheduled. This allowed the plumbers a stable work surface and eliminated the risk of stuck saws or sudden collapse of the floor during floor sawing for plumbing access.

Pre & post-grouting DCP testing was done to verify grout travel.

NY Thruway HDD Annular Space Grouting

The Job

As part of distribution improvements, National Grid’s contractor bored 830LF through rock using HDD. The bore was 30″, with a 16″ HDPE casing, carrying three, 4″ HDPE conduits.

As part of the installation, the NY Thruway Authority required the casing to be back-grouted, and the casing pipe’s annular space grout filled.

The Challenge

The proposed back-grout had to be pumpable 830LF at very low pressure, dense enough to displace the 10PPG drilling mud and provide sufficient strength to meet Thruway requirements. The proposed annular space grout had to be pumpable 830LF at very low pressure, light enough to not apply excessive pressure on the conduit pipes, and also provide sufficient strength to meet Thruway requirements.

The Solution

CJGeo proposed two different grout mixes to meet the project requirements. 85lb/cuft casing background for the displacement of the 10PPG (75lb/cuft) drilling mud, and 25lb/cuft annular space grout within the casing.

CJGeo’s crew mobilized to the site, and successfully performed the back-grouting and annular space grouting in a single day.

8″ Toe Drain Abandonment

The Job

Lake Whetstone is an approximately 30-acre manmade impoundment located in Montgomery Village, Maryland. It is utilized for stormwater runoff control, and also recreation, with an approximately 1000LF earthen dam.

As part of a retrofit program of the embankment, two 8″, perforated CMP toe drain pipes need to be grouted for a minimum of 100LF, underactive flow.

The Challenge

Each of the two, 100′ long pipes needed to be grouted full, but could only be accessed from the downstream end of the pipes. One pipe had nominal flow, and the second pipe had approximately 10GPM and discharged through an end wall structure at the stilling basin.

The Solution

The project designer, Gannett Fleming, specified NSF Section 61 certified grout (potable water contact) for the abandonment grout. Due to the “one-shot” nature of the project, above-ground mockups, including sacrificial pipe installation, chemical grout cup testing, yield analysis, and visual inspection, were all required prior to the start of grouting.

CJGeo performed the onsite mockup testing and analysis, and then grouted the two pipes in place successfully over a period of two days onsite.

5520CY Tank Abandonment

The Job

As part of a water treatment plant rehabilitation project in Stamford, Connecticut, a 25,000sqft underground tank needed to be abandoned, and the concrete roof removed.

The geotechnical engineer required an average fill density of less than 60lbs/cuft to avoid settlement.

The Challenge

The lightweight fill material had to provide sufficient support for approximately 4′ of compacted fill material, and a delivery truck loading dock, and future building.

The Solution

CJGeo proposed 25lb/cuft permeable cellular concrete with an approximately 10ksf compressive strength to fill the structure.

CJGeo placed the 25lb/cuft cellular concrete in daily pours up to 980CY, in single lifts up to 36 inches thick. The roof demolition debris dropped onto the top of the cellular concrete and was then buried with fill material.

The total project volume was approximately 5520CY.

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