Ingredients

Preparation hall

The preparation hall provides room and technical facilities for assembling the test set-up, preparing and building the soil model and installing the instrumentation. All the facilities have been built to be close to the centrifuge chamber and the control room so that when the testing equipment and the model are ready they can be directly placed in the container. There, connections can be made to hydraulic and electrical channels.

Test set-up

With years, several test set-ups have been built in the workshop of GeoDelft to perform experiments in the centrifuge. Areas of applications vary from geotechnical problems in the fields of foundation, tunnelling, anchoring to, lately, environmental problems related to the transport of DNAPL, see the the list of papers. Usually, GeoDelft is commissioned to study specific problems, which implies the need to build a special test set-up.

Soil Model preparation

Model soils of sand and/or of clay are generally used. Often, commercially available sand and clay are used. This presents the main advantage of controlled soil characteristics and should guarantee reproducibility of the tests performed. Therefore, reproducibility of model tests lays mainly on the model preparation techniques.

Soil preparation techniques have been developed and their results have been published. Efforts have been spent not only to control the preparation but also to characterise the models. These can be prepared with a chosen density varying from loose to completely dense. Moreover, it is possible to prepare fully saturated as well as partly saturated models. For fully-saturated sand models, the method consists of pouring sand grains into de-aired water while tamping under water or using shock waves. In-flight preparation of sand models is possible using a sand hopper. Layers or marks of coloured sand can also be used to show deformation patterns in the model.

Clay models can be prepared as slurry or pre-consolidated under simulated hydraustatic pressure profile. The consolidation is monitored through pore pressure gauges and displacement transducers. They can be reconsolidated under centrifuge conditions before testing. Normally, preparation and characterisation of models in clay or sand are performed according to routine procedures.

Instrumentation
At GeoDelft, various sensors are available. Some of them are presented in the table hereafter.
Most commonly used sensors:

Sensors:	Parameter measured:	Brand; Type; Range; Accuracy full-scale:
Pore pressure transducer	Pore pressure	Druck; PDCR 81; sereval ranges; < 0.2 %
Total stress transducer	Total pressure	Kulite; IPT-14A-750-11; 14 bar; <0.5 %.
Displacement transducer	Displacement	Sensorix; SX12R020, ± 10mm; 0.02 mm
Load cell	Force	HBM; several types; 5-100 kN; < 0.2 %
Accelerometer	Acceleration	Sunstrand, several types; 20-g.