Invert struts are used to support tunnels in which ground condition?

Invert struts are used to support tunnels in which ground condition?

• A. Squeezing ground conditions
• B. Soft soils with high moisture
• C. Non-squeezing stable rock
• D. Dry, massive bedrock

Answer: (D)

Invert struts act as temporary braces at the tunnel invert, transferring load from the bottom of the lining into the surrounding ground and keeping the invert in the proper level and geometry during construction. This works best when the ground is stiff and can carry thrust without large deformation. In a dry, massive bedrock setting, the rock mass has high strength and very little moisture, so it resists squeezing and excessive movement. The stability needed for the invert to stay in place while the lining is installed comes mainly from the rock’s capacity, and the struts provide controlled support to prevent any sag or misalignment of the invert during excavation. In softer or more water-saturated ground, or in squeezing conditions, the same bracing would face greater movement and may not perform as reliably. Hence, in the dry, massive bedrock scenario, invert struts are the appropriate support choice.

Invert struts act as temporary braces at the tunnel invert, transferring load from the bottom of the lining into the surrounding ground and keeping the invert in the proper level and geometry during construction. This works best when the ground is stiff and can carry thrust without large deformation. In a dry, massive bedrock setting, the rock mass has high strength and very little moisture, so it resists squeezing and excessive movement. The stability needed for the invert to stay in place while the lining is installed comes mainly from the rock’s capacity, and the struts provide controlled support to prevent any sag or misalignment of the invert during excavation. In softer or more water-saturated ground, or in squeezing conditions, the same bracing would face greater movement and may not perform as reliably. Hence, in the dry, massive bedrock scenario, invert struts are the appropriate support choice.