Contact Grouting Slide

Microtunnel Contact Grouting

Clarksville, Tennessee

The Job

This microtunnel contact grouting project is located in Clarksville, Tennessee. It is part of a new water intake structure along the Cumberland River to improve the reliability of the city’s municipal water source.

The Challenge

Based on the overcut of about an inch, and length of the 450 foot long tunnel, the contact grouting volume was approximately 50CY. In order to efficiently place the grout against the roughly 40′ of head from the river that that the tunnel terminates in, high volume, high quality mixing was required.

The tunneling contractor reached out to CJGeo to use onsite colloidal batching to generate grout quickly, safely, and without the risks of using ready mix.

The Solution

CJGeo proposed using a 0.55 water : cement ratio slurry generated onsite with colloidal mixing for the contact grout. While there were nearby ready mix plants that could have supplied the job, mixing neat grouts in transit mixer trucks typically does not uniformly wet out the cement. This can make it very difficult to pump, and typically results in highly variable mixes. Because the grout is the same as the cement slurry used for making CJFill cellular concrete, CJGeo used a cellular concrete batch plant with the foam generator turned off.

CJGeo batched and placed 50CY of slurry over about 2.5 hours to complete the microtunnel contact grouting. Placement of the grout was through 2″ ports, and the grout displaced both the lubricating bentonite slurry, and significant amounts of water. Due to the exceptionally high mobility of colloidally mixed neat cement grout, CJGeo’s crew was able to grout the entire length of the tunnel from two ports located just in from the launch shaft.

Grout communication was confirmed through lubricating ports, visual confirmation from the casing pipe drying due to heat of hydration, and divers in the river witnessing grout at the tremied bulkhead.

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