Chapter 10 — Instrumentation for Ground Improvement & Temperature¶
10.1 Introduction¶
Ground improvement changes the properties of the ground in place — by grouting, densification, or drainage — to make it suitable for construction. Instrumentation confirms that the improvement has achieved its purpose and that the surrounding ground is not adversely affected. This chapter also covers temperature measurement, which is both a ground-improvement monitoring parameter (for example, ground freezing) and a correction input for other instruments.
10.2 Monitoring grouting¶
General role. Grouting fills voids and fractures and densifies or strengthens the ground. Instrumentation monitors the spread of grout, the resulting ground movement, and the effect on adjacent structures.
Principal geotechnical questions:
- Where has the grout gone, and how far has it spread?
- Has the grouting caused heave or movement of adjacent structures?
- Have the intended improvements in permeability or stiffness been achieved?
Suitable instruments (Table 10-1) typically include: piezometers (pore pressure response), inclinometers and settlement/heave points (ground movement), pressure instruments (injection pressure), and permeability tests.
10.3 Temperature measurement¶
Temperature is measured to:
- monitor ground freezing and other thermal ground-improvement techniques;
- confirm the setting/hydration of grout or concrete; and
- provide thermal corrections for vibrating-wire and strain instruments.
Instruments (Table 10-2) include thermistors, RTDs, thermocouples, and vibrating-wire temperature sensors, compared on range, accuracy, and ease of logging. Choose based on the required range and the ability to share the datalogger with the primary instruments.
10.4 Key takeaways¶
- Instrumentation confirms that ground improvement achieved its purpose and did no harm to adjacent ground.
- Grouting is monitored with piezometers, movement instruments, and injection pressures.
- Temperature is both a monitoring parameter (ground freezing) and a correction input for other instruments.
- Record temperature wherever thermal effects could bias strain or deformation.