GDS Hardin RCA Hollow Cylinder Sample Set

Kit components

The HCA sample set for the Hardin RCA includes the following:

A - Inner membrane guide rod

B(2x) - Inner membrane slim side guides

C(2x) Inner membrane wide side guides

D - Inner membrane top seal

E - Lower topcap

F - Base pedestal

G - Upper topcap for inner membrane seal

H(2x) - Inner membrane base seal

I(2x) - Porous disks

O-rings

The HCA sample set for the Hardin RCA includes the following o-rings:

1 - Fitting seal on topcaps

2 - Inner membrane seal for pedestal

3 - Inner membrane seal for top cap

4 - Seal between the two topcaps

5 - Outer membrane seal on pedestal and top cap

Basic cohesion specimen preparation

• The sample is placed in a split-mould to trim the ends of the sample and then positioned in the purpose-built soil lathe. Filter paper rings can be placed on the ends of the sample to enable easy removal from the soil lathe after trimming.

• A wire saw (with piano wire) running against the two guide rods of the soil lathe is used to trim out a cylindrical specimen with outside diameter of 70mm. These guide bars can also be adjusted to enable the cutting of a sample with a 100mm outer diameter.

• A single layer of cling film can be wrapped around the sample to prevent drying of the sample and to ensure easy removal of the split-mould.

• The 3-part split-mould can be placed around the sample to maintain the geometry of the sample while trimming the inside diameter of the sample.

• An adjustable wood drill is used to drill a small diameter hole through the sample from its bottom end or even from the top end. Coring from below is recommended as it allows for the material to naturally fall away. The cutting diameter of the drill was gradually increased to trim the hole to the correct dimension, namely 30mm in diameter.

• The outer and inner diameters, height, and mass of the specimen are recorded.

Bottom pedestal and top cap preparation

• Firstly the inner edge of the base pedestal (F) should be covered with a thin layer of silicone-based lubricant where the inner membrane would be placed.
• Centrally position the lower membrane holder (H) on the bottom surface of the base pedestal.
• Assemble the upper membrane holder and o-ring (2) and insert into the end of the inner membrane.

• Now insert the upper membrane holder, o-ring, and inner membrane into the base pedestal, ensuring that the membrane is located in its final position between the o-ring and the lower membrane holder.
• Four screws are used to bolt the upper membrane holder, through the lower membrane holder onto the base pedestal, thereby compressing the o-ring and ensuring a tight seal between the inner membrane and base pedestal.
• Fasten the saturated porous disk (I) onto the base pedestal with six nickel-plated brass screws.

• Assemble the inner core, begin with screwing the inner membrane guide rod (A) into the central hole, an allen key can be used to fully screw this in.

• Begin sliding the slim (B) and wide (C) inner guides into the membrane to create a solid inner core. The slim side guides should be positioned in line with the two wedges on the guide rod.

• Once all the inner metalwork has been positioned, the top seal (D) and accompanying o-ring (1) can be placed on top.

• Now the solid inner core formwork has been created, the cored sample can be placed.

• The 3-part former can also be used to help create a noncohesive sample or support and prevent any damage from occurring to a softer cohesive sample.

• The top cap (E) can be placed above the sample. O-ring 3 is used to seal the inner membrane and o-ring 5 to seal the top and bottom of the outer membrane

• Creating a vacuum at this stage for extra stiffness can be useful to prevent the sample from being disturbed.

• The 3-part sample former can be taken apart or kept on to support the sample until mounted in the Hardin RCA.

• Once the top cap has been placed and both inner and outer membranes sealed, the inner core can be removed to allow the upper top cap to be secured

• An allen key can be used to remove the inner guide rod, when removing this rod it may also bring the slim side pieces with it.

• A tweezer can be used to remove the remaining metalwork.

• Once all the inner metalwork has been removed, the upper top cap (G) along with its o-ring (4) can be placed on top.

• Alternatively, if a very soft sample is being tested, the 3-part sample former can remain secured to provide radial support and the upper top cap can be pre-mounted to the RCA rotor arm to prevent any disruption to the sample due to its weight. Additionally, a vacuum can be applied through the pedestal to create a positive effective stress, providing the sample with extra support.

The end result will look similar to the image below.