Portuguese 
English 
Spanish 
4 min of reading 
0 comments 
Engineering Teams Freeze The Subsoil In Urban Areas Like Boston, Using 2,000 Pipes And Continuous Refrigeration To Block Water, Give Strength To The Ground, And Enable Tunnels In Unstable Soil
The technique of freezing the ground to excavate tunnels seems simple in concept but is highly precise in execution. It is used when the terrain has so much water and loose material that any opening becomes a real risk of collapse.
Instead of trying to drain everything, engineers change the behavior of the subsoil. By removing heat from the ground, the water between the grains freezes, creating a rigid mass and reducing the flow of water into the excavation.
Why Frozen Soil Becomes A Solid And Almost Impermeable Barrier
The central point lies in the water present in the soil pores. When it freezes, it forms ice that acts as a kind of natural glue, joining particles and increasing the strength of the ground.
-
Smaller than a grain of salt and invisible to the naked eye, scientists have created robots measuring 200 micrometers that swim, sense temperature, make decisions, and usher in a new scale of autonomous machines within the human body.
-
Scientists discover that microbes trapped 1 kilometer beneath the ocean floor can come back to life when earthquakes open fractures, push fluids upward, and reactivate organisms after millions of years.
-
Buried for centuries in the North Sea, it has now surprised archaeologists: a 2,000-year-old anchor appears almost intact beneath the sand.
-
Just 6 light-years from Earth, the closest solitary star to the Solar System has revealed, after 20 years of observations, a super-Earth that completes an orbit every 233 days and faces temperatures of -170°C beyond the habitable zone.
This effect changes the game in saturated soils, with loose sand, mud, fills, and irregular mixtures. The combination of soil and ice gains enough stability to maintain its shape during the work, which reduces the risk of collapse.
Another advantage is the reduction of water flow. Freezing creates a barrier that helps control seepage and hydraulic pressure, something that often hampers excavations in areas with a high water table.
How The Project Freezes The Subsoil With Pipes, Brine, And Continuous Operation
The process begins with drilling around the section of the tunnel, well, or gallery. Into these holes, freezing pipes are inserted, positioned so that the cold zones meet and form a continuous ring of frozen soil.
A refrigeration plant circulates a chilled fluid inside these pipes, typically brine. In typical projects, the operation works with temperatures equivalent to -30 to -40 °C, enough time for the ice to spread and seal any weak points.
When the frozen wall reaches the desired thickness and temperature, excavation begins with the subsoil already stabilized. Refrigeration remains on while the work progresses, keeping the frozen “shield” active.
When Liquid Nitrogen Enters And How Monitoring Prevents Critical Failures
In situations that require speed, liquid nitrogen may be used, operating near -196 °C and freezing the ground much faster. This tends to raise costs and complexity but solves scenarios where time is the decisive factor.
According to TU Delft OCW, an academic platform for open courses from the university, the success of freezing depends on continuous thermal monitoring and control of underground water flow, which can carry away the cold and prevent the full sealing of the barrier.
Sensors in the ground confirm whether the ice has sealed without fail and if there is no warmer zone capable of becoming a water entry point. This monitoring also reduces the risk of deformations that can affect nearby structures.
What Can Go Wrong And Why Thawing Also Needs To Be Planned
Freezing the soil is not just about “hardening” it. The expansion of ice can cause displacements, and this requires care in urban areas with nearby pipelines, foundations, and roads.
Another critical point comes afterward. When the system is turned off, the soil thaws and may lose some of the behavior acquired during the frozen phase, which can lead to settlement if the project does not account for this transition.
Therefore, freezing is often adopted as a temporary solution in critical sections where other techniques may be riskier or unfeasible. The idea is to stabilize the moment of excavation and then return the ground to a more natural condition.
The Boston Case Shows The Scale With Thousands Of Pipes And Months Of Operation
In Boston, freezing the soil has gained prominence for facing challenging urban soil conditions, with water presence and irregular materials. The solution required a central plant and continuous circulation of the chilled fluid.
The notable figure is the scale. There were over 2,000 pipes installed, and the operation remained active for months to support critical stages of the underground advance.
This type of application demonstrates why the technique is treated as a high-control alternative in extreme scenarios. It creates a safe window for excavation where, without stabilization, the ground simply would give way.
The soil freezing technique remains one of the most effective tools when the subsoil does not provide enough stability to safely open tunnels. It reduces seepage, increases strength, and provides predictability to the advance.
In the end, the practical impact is direct: underground works become possible in locations previously considered unviable, with greater risk control in urban areas and in water-saturated soils.
-
-
2 pessoas reagiram a isso.