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The Delft Sand, Clay & Rock Cutting Model, 2019a

The Delft Sand, Clay & Rock Cutting Model, 2019a

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Exercises.<br />

F: Determine the pore pressure at the centre of the shear plane using the parallel resistor method for a<br />

cutting velocity of 0.5 m/sec.<br />

First the 4 lengths have to be determined:<br />

hb<br />

s1 Lmax<br />

L <br />

0.486<br />

2 2<br />

<br />

<br />

sin<br />

2<br />

3<br />

<br />

s 0.8 L 0.163<br />

<br />

s 0.8 L 0.327<br />

<br />

<br />

i<br />

<br />

4 max i<br />

0.5 0.4<br />

h 2 ki<br />

<br />

<br />

hb<br />

kmax<br />

<br />

s L L 0.9 h 1.85 0.636<br />

Secondly the total resistance has to be determined:<br />

1 s1 s2 s3<br />

s4<br />

<br />

Rt<br />

439<br />

Rt kmax kmax ki ki<br />

<br />

<br />

p g v sin R 120.8 (kPa)<br />

w c t<br />

Below which water depth will we have cavitation at this point?<br />

An absolute pressure of 120.8 kPa is reached at a water depth of 2.07 m, so the point on the shear plane considered<br />

will cavitated for water depths below 2.07 m.<br />

Pore Pressures on the Blade & the Shear Plane<br />

200<br />

180<br />

160<br />

Pore Pressure p 1 & p 2 (kPa)<br />

140<br />

120<br />

100<br />

80<br />

60<br />

p1<br />

p2<br />

40<br />

20<br />

B-C<br />

0<br />

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100<br />

Percentage of Blade & Shear Plane (%)<br />

A<br />

© S.A.M.<br />

Figure 16-3: <strong>The</strong> pore pressures on blade and shear plane.<br />

Copyright © Dr.ir. S.A. Miedema TOC Page 413 of 454

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