Concluding remarks

The formation sample was initially intended to be a concrete mixture made directly in the sample container cylinder. This method utilizes the steel tube to provide some tensile strength to sample. This negates the need to add any internal structure but it creates other problems that are difficult to solve. The first issue is that it requires the sample container cylinder to be removed to add a sample. To make the clearance necessary to remove the sample containment cylinder, the drill shaft must first be removed. This requires

additional work and steps that could be avoided. Another major issue with this method is

taking into account the scenario where the concrete sample would have to be replaced. In order to remove the sample containment cylinder, the bolts at the bottom of the sample container must be accessed. This could be solved by making these mounting holes threaded. However, the sample containment cylinder was one of the components manufactured before and thus threaded holes could not be made that would fit with the load cell. With the current design of the load cell being bolted onto the bottom, removing the cylinder would require removing all of the concrete before the bolts could be

accessed. This adds another design problem as to what methods could be used to remove the concrete and how effective it would be. It turns out to be a very difficult design problem to remove all formation sample and to be able to effectively remove all of it with a wide range of material properties based on what the composition of the is.

Another issue is the amount of material that would be wasted by utilizing the entire length sample containment cylinder. It should be noted that the stroke of the hydraulic cylinder is only 36” and the sample container cylinder is 48”. After accounting for the position of the sample carriage before the bit touches the concrete, there is only about 20” of stroke left for drilling. This shorter effective stroke and the sample removal problems led to the design of a shorter concrete sample that could be made on its own and inserted into the sample container cylinder.

It is known that concrete does not have a lot of tensile strength so it is important to reinforce the concrete sample so that it does not break under the load of drilling. This is a disadvantage of a short sample that is made separate from the containment cylinder since a feature must be added into the design of the sample. In this case, the concrete sample was designed to be reinforced with a rebar skeleton as shown in Figure 2.17.

This rebar reinforcement gives the sample needed tensile and hoop strength while drilling.

Figure 2.17: Rebar and cup layout of the formation sample mold

Since this concrete sample would be inserted into the existing sample cylinder, there was a need for a mechanism to hold the sample into place. As a holding mechanism for the sample, two rows of three holding screw mounts were added to the cylinder. These would be used to mount set screws to hold that formation sample. To increase the effectiveness of these holding screws, cups were incorporated into the mold of the concrete sample to distribute the force of the holding screws so that the concrete would

not break at the holding points. This rebar and cup skeleton was made using tie wire and put into a 22” section of a 12” diameter concrete mold cylinder and filled with a concrete mixture as shown in Figure 2.18. The cups were protected from concrete leakage by inserting wax coated screws directly into the cups before the concrete was poured into the mold. The formation sample made for the initial testing stages is shown in Figure 2.19 as an example of how a finished formation sample looks like.

Figure 2.18: Formation sample mold

Figure 2.19: Finished formation sample used for initial testing

This concrete sample, depending on exact composition, weighs a little less than 200 lbf while the steel sample cylinder weighs about 330 lbf. This requires less need for

equipment and can be set into place with only a few people. It also creates a much better solution in loading the sample cylinder by not requiring the shaft to be removed.

The recommended method to insert and remove sample cylinders is to unthread the mud drain assembly and slide it to the back end of the shaft and remove the bit. Then remove the hydraulic cylinder pin and pull the carriage back by directing the cylinder above the back support beam as shown in Figure 2.20. This creates enough clearance to lift the formation sample up between the shaft and the cylinder and then slide it into place. This is easily performed with five people, having set the cylinder on two lifting rods. Four can lift while the fifth person slides the sample in once the sample is lifted to the correct height.

Figure 2.20: CAD Model showing the repositioning of the hydraulic cylinder and the drain assembly for sample loading