GEONOR - Geotechnical - Structural

GEOTECHNICAL LABORATORY TESTING

DIRECT SIMPLE SHEAR APPARATUS & FALL CONE APPARATUS

DSS MANUFACTURING TEMPORARILY SUSPENDED

DIRECT SIMPLE SHEAR APPARATUS

Direct Simple Shear Apparatus Specifications

APPLICATION

The Direct Simple Shear Apparatus (DSS) is designed for testing soil specimens with conditions of simple shear and plane strain throughout out the specimen. These conditions are representative for a number of field problems (e.g., horizontal portions of failure planes), that cannot be obtained with other standard laboratory testing methods. The apparatus is designed for drained or undrained (constant volume) shear tests on undisturbed or reconstituted specimens of clay, silt or sand. Deformation-controlled monotonic or load-controlled cyclic shear tests can be performed.

PRINCIPLE

The soil specimen is mounted inside a rubber membrane of circular cross section and reinforced by a spiral wire winding. This membrane prevents radial deformation of the specimen, but allows vertical deformation during consolidation (K0 conditions) and shear deformation during simple shear with very little resistance. With this membrane, constant volume conditions during shear are attained by simply keeping the height of the specimen constant. The change in stress (load/area) required to keep the specimen volume constant is equal to the pore pressure measured in an undrained test.

The standard DSS apparatus consists of a direct simple shear device with vertical and horizontal motors, load cell and a control unit for:
Consolidation load, constant load or height during shear for the vertical motor
Shear direction rate and direction for the horizontal motor.
Electro-Pneumatic control for the cyclic loading generator cylinder.

The original Geonor h-12 DSS apparatus was developed by Landva and Bjerrum in the mid 1960’s, and has been used extensively at The Norwegian Geotechnical Institute (NGI) and by others through the world.

The wire reinforced membranes and soil specimen trimming apparatus are still the same as for the h-12 DSS device. As before, piezoelectric bender elements for determining Gmax of the soil specimen can be supplied as an option. (Please contact us for more information.)

REFERENCES

-Direct simple shear tests on a Norwegian quick clay - L. Bjerrum and A. Landva, 1966, Norwegian Geotechnical Institute, Publication No. 70.
-Comparison of truly undrained and constant volume direct simple shear tests - R. Dyvik, T. Berre, S. Lacasse and B. Raadim, 1987, Norwegian Geotechnical Institute, Publication No. 170.

FALL CONE APPARATUS

APPLICATION

The Fall Cone Apparatus, first introduced in 1915, provides a rapid, simple and accurate method for determining empirically the undrained shear strength, the shear strength of remolded samples and thus the sensitivity of clays. The equipment is also used for determination of liquid WL (or fineness number WF ). Four cones of different weights and apex angles are provided.

PRINCIPLE

The shear strength of a soil is (s) is proportional to the weight of the cone (Q) and inversely proportional to the square of the penetration (h) of the cone into the sample: s=K·Q/h² (Hansbo, S (1957): A new approach to the determination of the shear strength of clay by the fall cone test. Swedish Geot. Inst. Pub. No. 14, Stockholm). The proportional constant K depends primarily on the angle of the cone and sensitivity of the clay.

The shear strength is measured by placing the sample underneath the cone holder, with the tip of cone touching the sample. After releasing the cone from the magnet holder and measuring the depth of penetration, the shear strength of the undisturbed or of the remolded sample is given in tables accompanying the apparatus.

DETERMINATION OF THE LIQUID LIMIT

The standard cone used to determine the liquid limit WL (see diagram) has a weight of 60 g and an angle of 60° (part no: 200400). The upper limit of plasticity corresponding to the liquid is defined as the moisture content at which the cone impression is 10 mm (Karlsson, R. (1961): Suggesting improvements in the liquid limits test, with reference to flow properties of remolded clays. 5th Ont. Conf. On Soil Mech, and Found. Eng., Vol 1. p. 171, Paris).

DETERMINATION OF THE SENSITIVITY

The undrained shear strength of an undisturbed sample is first measured. Thereafter, the sample is completely remolded and the new shear strength is measured with the same water content. The ratio of the undisturbed to remolded shear strength is defined as the sensitivity (S)