Strona 2_redak - Instytut Agrofizyki im. Bohdana Dobrzańskiego ...

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6. Vertical consolidation reference pressure, σ r , was released to zero;
7. Vertical pressure, σ z1 , was applied for a period of static holding;
8. Sample was sheared under pressure, σ z1 , until the end of the prescribed
shear path;
9. Steps (4) to (8) were repeated for vertical pressures of σ z2 and σ z3 , and
thus three points on the yield locus were obtained.
The Jenike method allows the determination of: cohesion c, angle of internal friction
φ and effective angle of internal friction δ (see ϕ =ϕ i and δ =ϕ l in fig. 7.2).
Eurocode 1 [50] recommends using a simplified Jenike method (including
consolidation and shearing of the sample) for the determination of strength
parameters (fig. 7.2). The shear cell diameter D should be at last 20 times the maximum
particle size and not less than 40 times the mean particle size. The height H
should be between 0.3 and 0.4 D. The maximum particle size is limited to ensure that
interaction of material with the cell wall will not influence the measured property.
The sample should be poured into the test cell, without vibration or other compacting
forces, and the consolidation stress σ r applied. A top plate should be rotated clockwise
and anticlockwise about the vertical axis several times through an angle of at least 10
degrees to consolidate the sample.
The Eurocode 1 shearing procedure is as follows:
1. The reference stress σ r should be approximately equal to the vertical stress in
the stored material.
2. Shearing of the sample should be carried out at a constant rate of approximately
0.04 mm min -1 .
3. To calculate strength parameters of granular material maximum shear
strength τ should be used that developed at or before the horizontal
displacement had reached the value of ∆L = 0.06D.
4. At least two tests should be carried out as defined in (5) and (6) below.
5. The first sample should be sheared under a normal load causing the reference
stress σ r to obtain the failure shear stress τ a .
6. The second sample should first be preloaded under a normal load causing
the stress σ r and just brought to shear failure as for the first sample.
Shearing should be stopped and the applied shear load reduced to zero.
The normal load on the second sample should than be reduced to a value
causing approximately half the consolidation stress (σ b = σ r /2) and sheared
again to obtain the failure shear stress τ b .