sensors

VW Shotcrete Stress Cell

Radial and tangential stress cell designed for monitoring stress in shotcrete tunnel linings.

Range
2, 5, 10, 20 MPa
Accuracy
±0.1% F.S.
Resolution
0.025% F.S.

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Overview

Radial and tangential stress cell designed for monitoring stress in shotcrete tunnel linings.

The Geolook Vibrating Wire Shotcrete Stress Cell is specifically engineered to measure the development of radial and tangential stresses within shotcrete (sprayed concrete) linings in tunnels and underground excavations. Unlike standard pressure cells, this unit features a specialized 'pinch tube' for repressurization. As shotcrete cures, it shrinks, potentially pulling away from the sensor face and causing data loss. The pinch tube allows the operator to re-inflate the cell after curing, ensuring perfect contact with the surrounding concrete for accurate stress transfer.

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Benefits & Features

  • Includes re-pressurization tube (pinch tube)
  • Compensates for shotcrete shrinkage
  • High stiffness to match concrete modulus
  • Vibrating Wire technology for long cable runs
  • Rugged stainless steel construction
  • Available in Radial (flat) and Tangential (curved) geometries
  • Integral thermistor

Detailed Description

Radial vs. Tangential Cells

A complete monitoring station typically uses both types:

  • Radial Cells: Rectangular cells installed flat against the rock face before spraying. They measure the pressure the rock mass exerts onto the lining.
  • Tangential Cells: Elliptical or circular cells installed perpendicular to the rock face (standing on edge). They measure the 'hoop stress' or compression forces squeezing the tunnel ring.

The Shrinkage Problem & Solution

As shotcrete hydrates, it shrinks. This creates a tiny gap between the concrete and the sensor, causing the pressure reading to drop to zero even if the tunnel is under load.

The G73-V660 solves this with a built-in repressurization tube. After the concrete sets (typically 24-48 hours), a crimping tool is used to squeeze this tube, forcing hydraulic fluid into the cell pad. This expands the cell slightly to bridge the gap and restore active pressure monitoring.

Why Monitoring Matters

In modern tunneling (NATM/SEM), the shotcrete lining is a structural element, not just a covering. Knowing the exact stress levels allows engineers to optimize the lining thickness—saving millions in concrete costs—while guaranteeing safety by detecting overload conditions before visible cracking occurs.

Available Models

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Specifications

Range
2, 5, 10, 20 MPa
Accuracy
±0.1% F.S.
Resolution
0.025% F.S.
Dimensions
100 x 200 mm (Tangential)
Material
Stainless Steel
Over-range
150% F.S.
Temperature Range
-20°C to +80°C