Ground Freezing Archives - Moretrench

TBM Tunnels

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Mixed Face Conditions
Mixed face conditions for a hard rock tunnel boring machine (TBM) can be alleviated by creating a frozen mass that encompasses the runner face, presenting a homogenous, strengthened zone to allow tunneling to proceed safely.

Safe Havens
Mass ground freezing of a designated area along the tunnel alignment allows for a ‘safe haven’ for the tunnel boring machine to undergo inspection and cutter head changes. The freeze pipes within the alignment may be constructed with aluminum, or heated and pulled as the TMB enters the frozen mass to avoid damage to the TBM.

Launch and Retrieval Blocks
When ground freezing is the method used for groundwater control and support of excavation for deep shafts, the freeze can be extended via additional freeze pipes to create a targeted stabilized mass for cutting of the eye for TBM launch or retrieval.

Other Applications

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Additional candidates for ground freezing include:

  • Circular or elliptical, open excavations, such as might be required for pump stations and other large structures.
  • Containment of contamination.  Installation of a frozen perimeter zone around the contaminated soils allows excavation and removal without permanently impacting the surrounding groundwater regime.
  • Fast acting liquid nitrogen can be used to stabilize loose or disturbed soils above a mired or damaged TBM for retrieval or repair.

Open Face Tunnels

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Vertical and Horizontal Arches
Ground freezing can be utilized to assure stability of sequentially excavated (SEM) or hand mined tunnels.  The freeze pipes may be installed vertically or near vertically from the surface, or they may be installed horizontally from access shafts to create a frozen envelope parallel to the tunnel alignment.  With either freeze pipe orientation, a full face freeze may be an advantageous option, depending on the excavation method, so the excavation sees homogeneous conditions.

Cross Passages and Connector Tunnels
Ground freezing can be utilized to facilitate connections between structures such as a cross passage between twin tunnels or a mined connection between deep structures. The frozen ground will conform to adjoining subsurface installations or obstructions, if necessary, to provide a composite cut-off structure.

 

Shafts

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Groundwater cut-off in conjunction with excavation support for the sinking of vertical shafts was the earliest application of ground freezing and remains the most common.  For deep mines, no better method of sinking shafts through deep, water-bearing ground has yet been established.  However, over the past 20 years, ground freezing has become a versatile tool for both soft ground and hard rock excavation and tunneling.

There are several advantages of ground freezing unique to the construction of vertical shafts.  The freeze can be implemented perfectly through the soil/rock interface, which is often the most difficult geology in which to create a groundwater cut-off by other methods.  Proper instrumentation can provide assurance of the integrity of the full depth freeze prior to excavation.

Overview

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Artificial ground freezing for groundwater control and excavation support has been practiced in construction for more than a century. The technique is cost-effective in a relatively well-defined niche where both support of excavation and groundwater cut-off are required, and it is performed at significant depth or in difficult, disturbed, or sensitive ground. Moretrench has been the North American industry leader in this highly specialized technology since 1976. Read more.

For further information on ground freezing, please visit groundfreezing.com.