Sample Assembly for the DSS with Confining Pressure
The dynamic simple shear with confining pressure system is supplied with sample preparation accessories to enable the user to prepare undisturbed and remoulded test specimens. The system has been designed so that the sample preparation can be conducted outside of the cell of the simple shear system to ease the sample preparation process. It is also possible to prepare the sample inside the apparatus.
1 Confining Pressure
1.1 Initial setup
The following is required to prepare a sample:
1. Setup the base pedestal on a flat stable surface. Or if the sample is to be prepared in the simple shear cell secure the base pedestal into the cell with the 4 screws highlighted in Figure 24.
1. Place one of the porous discs into the base pedestal.
1. Next take the membrane and cut it to the required length. For 100mm diameter samples 110mm to 120mm; for 70mm diameter samples 80mm to 90mm in length.
1. Take the cut membrane and place it over the base pedestal and then using the ‘O’ Ring tool place two of the ‘O’ Rings over the membrane sealing it to the base pedestal (see Figure 5)
1. Now place the two halves of the sample former together & using the ‘C’ clamp lock the two halves together
1. Now place the sample former over the base pedestal so that the membrane sticks up through the former (see Figure 7).
1. Stretch the excess membrane over the top of the sample former.
1. Attach the suction device to the sample former and apply suction to stretch the membrane.
1. Make sure that the membrane has been stretched tight against the sides of the sample former.
1.2 Preparing a Remoulded Specimen
The process described below is designed to produce a specimen to a specific density.
1. First calculate the volume of the specimen. This can easily be done by entering the dimensions of the sample into the specimen details form in Clisp Studio. In this case enter the sample height and sample diameter, and the initial volume will be calculated
1. To calculate the required weight of material to achieve the required density use the following equation:
Weight of material (g) = volume of sample (cm3) * density required (Mg/m3)
In the following example, a density of 1.34Mg/m3 is required for a sample volume of 298.451cm3.
298.451 * 1.34 = 400g
1. Place a bag or container into which you will weigh your sample onto a balance and tare the weight.
1. Next weigh out the required amount of material into your container, in this example 400g is weighed out.
1. Next place the extension ring on top of the sample former as per Figure 14.
1. Now carefully fill the sample former with the weighed sample.
1. Now place the weighted platen on top the material in the sample former. The weighted platen should be moved down until it touches the extension ring to form a sample of the correct height and density (see figure 17). This can be done either by pressing down on the weighted platen or using a vibrating plate (note: this is not supplied with your sample preparation accessories) to vibrate the assembly so that the sample will consolidate and the weighted platen will slowly move down giving a sample of the correct height.
1. Carefully remove the weighted platen and extension ring. Place the second porous disc on top of the prepared sample.
1. Now carefully place the top cap onto the porous disc. Remember the two drainage lead connectors must line up.
1. Carefully roll up the membrane over the top cap.
1. Fit two ‘O’ Rings over the ‘O’ Ring tool. Carefully place the two ’O’ Rings onto the top cap, sealing the membrane. The ‘O’ Rings should slot into the grooves on the top cap.
1. If the sample was prepared outside the cell, then the sample needs to be carefully transferred to the cell and the base platen fixed into place using the 4 screws shown in Figure 24.
1. The drainage leads (Back Pressure and PWP) should be flushed before fitting to remove any air from the lines.
1.3 Preparing an Undisturbed Specimen
1. Follow the instructions in section 1.1 - Initial setup.
2. A sample cutter is provided to cut an undisturbed specimen. This could be cut from a block of soil or other undisturbed sample. The sample should be trimmed and levelled in the cutter.
1. The mould and specimen should be weighed so that a density can be calculated. Place the cutter onto the top of the sample former.
1. The sample then needs to be pushed from the cutter into the sample former. This can be partially done using the weighted platen or using a wooden dolly (note this is not supplied with your accessories).
1. Once the specimen is in the former, place a porous disc of the correct size on top of the specimen.
1. Place the top cap onto the porous disc, making sure that the drainage line connection on the top cap is in line with drainage line connection on the base pedestal (see Figure 29).
1. Roll up the membrane over the top cap.
1. Using the ‘O’ Ring tool place two ‘O’ Rings over the top cap to seal the membrane, the ‘O’ Rings should sit in the grooves of the top cap.
1. Remove the ‘C’ clamp and sample former, and then roll down the excess membrane.
1. If the sample was prepared outside the cell, then the sample needs to be carefully transferred to the cell and the base platen fix into place using the 4 screws shown in figure 24. Before fitting the drainage leads (back pressure and PWP) these should be flushed to remove any air from the lines.
Confining Ring Setup
A confining pressure DSS can be used with a traditional stacked ring confining system. The assembly of this optional assembly is described below.
2.1 Initial setup
The following items are required to prepare a sample:
Place the base pedestal on a flat stable surface.
Place the cut 70 mm membrane over the base pedestal. (see section 1.1 step 3 for cutting instructions)
Using the ‘O’ Ring tool, place 2 of the 70mm ‘O’ Rings over the base pedestal, so that the membrane is sealed against the pedestal.
Now place the metal split base ring over the membrane and pedestal. This ring is held together using a 70mm ‘O’ ring.
Place the two halves of the sample former together and secure them using the ‘C’ clamp.
Place the former over the membrane, the inside of the former where it is widest (Figure 39) is placed up, so the narrowest part of the former covers the metal split base ring, so the former rests on the base pedestal as shown in figure 40.
The Teflon coated confining ring stack is made up of 12 standard rings and 2 thicker rings. Take the ring stack and arrange them so that the thicker rings are at the top and bottom of the pile.
The confining ring stack should then be carefully place into the sampler former; the membrane will come out through the centre of the ring stack.
Stretch the excess membrane over the sample former and then place the thick extension ring over the top.
Place the suction device onto the sample former so that the membrane can be stretched if required.
Weigh out the material accurately to achieve the required density for the volume of the sample inside the stack of rings. Details of this can be found in this document in section 1.2 steps 1 to 4.
Once weighed out, carefully place the material into the cavity.
Then place the weighted platen onto the sample. The weighted platen needs to be moved down so that it touches the extension ring, this way the material used will be compacted to the correct height. This can be done using a vibrating plate (not supplied) or gentle force applied from above.
Remove the platen and extension ring and carefully place the grooved top cap onto the sample.
1. When placing the top cap on, make sure the connectors for the drainage lines on the top cap for Back Pressure and on the base pedestal to measure Pore Water Pressure line up (see Figure 48).
1. Roll up the excess membrane and over the top cap and then release the ‘C’ clamp. Now carefully remove the sample former.
1. Now using the ‘O’ Ring tool place two 70mm ‘O’ Rings over the top cap sealing the membrane; then roll over the excess membrane.
1. If the sample was prepared outside the cell, then the sample needs to be carefully transferred to the cell and the base platen fixed into place using the 4 screws shown in Figure 24. The drainage leads (Back Pressure and PWP) should be flushed before fitting to remove any air from the lines.
1. Follow the initial setup for a remoulded specimen in section 2.1 until you reach step 8. Note that the extension ring is not required. Then place the suction device onto the sample former.
1. The undisturbed specimen should be prepared in the provided sample cutter and weighed to determine density. The cutter should be placed onto the top of the stacked rings with care being taken not to damage the membrane (see Figure 51).
1. The sample should then be pushed out of the cutter into the simple shear assembly using a dolly; the membrane may need to be stretched using the suction device to enable the sample to be pushed in smoothly.
1. Once the sample is located in place, the instructions in section 2.2 steps 4 to 7 must be followed to complete the assembly of the sample.