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University of Pretoria: Geotechnical Centrifuge

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Introduction

Geotechnical centrifuges facilitate the modeling of complex processes in the soil. Reliable data acquisition is as important as the centrifuge itself.

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Reliable Results at 150G Using QuantumX for Data Acquisition in a Geotechnical Centrifuge

Safe ground under our feet -- this is what we all want. However, soilis composed of many different components, and the highly dynamic processes that can occur within the soil can destabilize buildings and infrastructure facilities in a very dangerous way. Geotechnical centrifuges facilitate realistic modeling of the complex relationships of stress and strain processes under load in the soil. However, reliably measured data acquisition is just as important as the centrifuge itself.

For this reason, engineers at Pretoria University trust HBK's QuantumX data acquisition system in combination with their state-of-the-art geotechnical centrifuge. Building the ultra-modern "Gautrain" railroad line linking the South African metropolises of Pretoria and Johannesburg, engineers faced a big problem. In the south of Pretoria, the train's route was to cross a karst landscape characterized by dolomite bedrock prone to the formation of sinkholes. To safely build a viaduct on this subsoil, complex full-scale surcharge experiments had to be carried out involving the assembly of over 1,000 heavy concrete blocks weighing ten tons each in order to explore the stiffness of the ground above potential sinkholes.

Geotechnical Centrifuge

Since the results of the full scale tests were highly variable, the behavior of the concrete block surcharge stacks was explored more in detail in the Centrifuge Laboratory at Pretoria University, which officially opened in June 2012.

The laboratory is among the most advanced technical institutes in this field worldwide, and has outstanding technical highlights to offer. The centrifuge, manufactured by the French company Actidyn, can accelerate a mass weighing up to one ton to 150 times Earth's gravity (150G). This extremely high acceleration is needed to simulate as realistically as possible the complex stresses and strains occurring in the soil.

_{The Geotechnical Centrifuge at the University of Pretoria}

Data from Many Transducers and Sensors

Such complex experiments also require continuous acquisition of many different parameters and measurement quantities. In addition to cameras used for particle image velocimetry, actuators and different sensors have been integrated with the centrifuge for measuring:

Displacement using LVDTs, potentiometers, and laser displacement sensors and scanners
Pressure using hydraulic pressure transducers measuring soil pressure
Force/Weight using strain-gauge technology-based load cells
Temperature

HBK's QuantumX DAQ system is used for data acquisition. QuantumX shows particular advantages when many different measurement quantities need to be acquired -- even when different transducer technologies are involved. More than any other data acquisition system, QuantumX offers outstanding versatility and flexibility. Advanced Plug & Measure allows transducers based on different technologies to be easily connected to the QuantumX modules. You can start measuring immediately. The measurement data acquisition system does not require any complex settings or configuration. The following QuantumX modules guarantee reliable measurement in the geotechnical centrifuge:

A QuantumX CX22 data recorder for data storage directly on the centrifuge
QuantumX MX840A (8 channels) and MX440A (4 channels) universal amplifiers for smooth, fast, and reliable acquisition of differing measured quantities
A QuantumX MX878 signal generator

Ethernet and fiber optic cables with 1 GB throughput are used for data transmission.

Advantages of Experiments Using Centrifuges

This test setup that offers many advantages to engineers of Pretoria University allows modeling of complex 3D problems using simple means. Engineers can precisely observe actual physical events and mechanical processes, while at the same time benefiting from reliable data acquisition equipment from HBK.

Advantages with HBK

Reliable data acquisition for complex measurements
Support of inumerous transducer technologies in one device and systems.

About University of Pretoria

The University of Pretoria (UP) is a seven-campus public university with its largest campus in the heart of Hatfield, the picturesque diplomatic hub of South Africa’s capital city. We’re proud to stand among the world’s leading research universities.

Geotechnical Centrifuge Laboratory at the University of Pretoria

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