General Description

There is an increasing tendency in the field of Civil Enginnering to built earth dams, embankments and dykes of great height.

To protect and stabilise these works, shoulders incorporate granular materials with large particles, whose intrinsic angle of friction plays a fundamental role in the economic and safety aspects of the design. This parameter depends basically on the granulometry, type of material and confining pressure. Therefore it is of great interest to use a device which permits its determination in a way which closely approaches the in situ conditions, i.e.: the particles size and confining pressure, without the need to stablish parallel granulometries of smaller size compatible with conventional equipments.

The direct shear equipment with 1m x 1m box developed by the Laboratorio de Geotecnia of CEDEX permits the testing of granular materials up to 20cm (equivalent diameter), keeping the superimposed vertical load constant up to a value of 100 t by means of an electronic feedback system that acts on a servovalve that regulates the flow of the oil to and from the load cylinder.

Similarly, the horizontal load has a range up to 100 t and the displacement velocity is servocontrolled maintaining constant this magnitude independent of the load necessary to produce failure in the material. The test is monitored from a remote safe control room.

With this equipment test can be made with materials at different degrees of compactness, from simply poured to compacted by mechanical vibrator. Also, it has the necessary components to perform pull out test of geotextiles, placing them in different types of soil to form samples of up to 1 m2 that can be subjected to a maximum traction of 25 t.