Possible Toe Wall Structures

During lab this week we brainstormed ideas for the toe wall, taking into account that the wall may need than just a single layer of bricks in terms of thickness and height.

Full-Scale Grid Materials

In our initial tests of the intra-soil grid we plan to use small, biodegradable planters and pots as materials. However, because of the obvious difference in size between our small scale-models and a full-scale implementation of this grid, we researched different materials that could be used on a full-size grid. We discovered that bamboo is both biodegradable and strong enough for our purposes. Bamboo plates (these for example: http://www.webstaurantstore.com/bambu-063200-9-disposable-square-bamboo-plate-25-pack/999063200.html), which would be structurally similar to the walls of a grid, are already on the market. The grid would be held in place by biodegradable stakes, such as the ones sold here: http://www.arbico-organics.com/product/biodegradable-ground-stakes/garden-tools-supplies. 

Goals for Week 5 Lab

The goals for the lab this week is to start to design the intra soil grid system, work on the toe wall design with the materials we have and to plan out the rest of the week for meeting up.

Rain Simulation Improvements and First Simulation

This week we tried to focus on improving the rain simulation because it is one of the most important aspects of the project. It is the main factor we are considering in our study of soil erosion, therefore it is necessary for our tests to be completed. The team may have to make a trip for more materials, but this weekend we worked with the materials we have already purchased.

The first new material tested was an old t-shirt. First, we tried the t-shirt over the double layered screen but observed that the t-shirt absorbed the water instead of allowing the water to travel through it in a randomized pattern. Our next test was with one layer of the t-shirt, however this was still not an accurate simulation.

The next method we tried was the double layered screen by itself. We had tried this before but wanted to retest it because the materials were with us at the time. We discovered that if the screen was raised above the surface of the bin and the water was poured from a height above the screen, the water was more droplet like and random close to that of rain. We concluded that the height gave the water the droplet like effect while the screen having two layers made it more random. The following video is shown with the screen approximately 32 inches from the surface of the bucket and the water being poured from approximately 16 inches from the screen.

We are still open for testing new ways but after discovering this method was close to ideal we decided to simulate it on our test slope. The test slope has none of the proposed methods to slow soil erosion in place. Initially the length of the slope was 7.25 inches, the bottom leg was 6.50 inches, and the height was 4 inches. The average angle calculated was 30.46 degrees. After the rain simulation the slope length was 7.50 inches, the bottom leg was 6.75 inches and the height was 3.75 inches. These gave an average calculated angle of 28.30 degrees. These minor changes were not visible at first glance of the slope, but they coincide with the effects of soil erosion. The only visible change we saw initially was that the top edge of the slope appeared to be more round than edge-like from before. The following video gives a closer look than what we observed during testing. While watching if you focus on the edge of the slope the soil can be seen sliding down from the "rain."

This method of rain simulation is not finalized but the test was done to see what improvements can be made. Our next tasks are to make the rain fall consistent and determine the proper rate of rainfall.

Building the Test Slope

The idea of the test slope is to find a "control value." The initial angle of the slope will be measured. Then, a load will be applied and the rain simulation will be run. After this, the new angle will be measured to see how much soil "erodes" with none of our proposed methods in place yet. 

So far, two slopes have been built and tested with an applied load but not yet with the rain simulator, as we are in the process of finalizing this design. (It has been an ongoing task to optimize its performance). 

Slope 1

The first slope created can be seen in the picture below. 

After taking measurements of the slope length, the height of the soil, and the bottom leg an average angle of 42.89 degrees was found. After applying a load, none of the soil moved. We observed that we may have packed the slope more tightly than would naturally occur in nature. It is also important to note that in a natural environment a slope would be free on the edges. 

Slope 2

We packed the soil in the second slope more loosely than that of the first. 

We took the same measurements and redid our calculations. This time the slope angle was calculated to also be around 40 degrees, it was 42.40. This was not done intentionally. However after applying the same weight, noting happened to the slope.

Improvements to be Made

• Finalize the rain simulation technique to also use in testing.
• Line the two remaining sides of the plastic container to cause less sliding.
• Line the container with a material with greater friction.
• Test using different soil types - ones that may be dryer or pack loosely because these are the types of soil that erode more easily.

Rate of Rain Fall Test Proposition

We need to be able to simulate a set amount of rain fall for each test for consistency of data. A good range for our purposes should be between 1 and 2 inches/hour, but closer to 1 in/h would be better. 2 inch is the cusp of severe rain. To measure this I propose that we take a small beaker/test tube and place it in our rain test box. We run the rain simulation for 10 mins and measure the depth of the rain in the beaker. Then that value is multiplied by 6 (there are 6 intervals of 10 mins in 1 hour) which should give us the rainfall/hour. We should then run the test again to make sure that the data can be replicated.  

Goal of Week 4 Lab

For today's lab, we decided to focus on the planning aspects of the project and make sure that everything can work together and we have all the pieces. It'll also allow us more time to test the project and each aspect rather than wait for one to finish testing to start the next piece.