Week 9 Lab Goals

The goals for the lab today is test using the water and the grid, and to start making the presentation for next week and have that finished by the end of the week due to majority of the group heading home for the weekend.

Intrasoil Grid Phase 2

As the initial design for the grid was being created, the leftover material proved useful for a second kind of grid. This grid is disconnected and instead of supplying an outline of a structure, the pieces enclose the soil. A picture can be seen below:

The same measurements were taken as in phase 1. The angle decreased only by .8% upon applying immediate pressure. After 30 minutes, the angle decreased by another 18%. So far, the grid structures may actually be weakening the slope instead of helping. There are a few more that need to be tested. Grid structures 1 & 2 also need to be tested under rain simulation.

Intrasoil Grid Phase 1

This weekend, a few of the grid designs were tested under applied pressure. The first tested was our very initial design, simply structural squares. A photo can be seen below:

The first test resulted in failure after less than a minute due to the container being bumped. The next test was successful and ran for 30 minutes with the bricks used as applied pressure. Measurements were taken before applying pressure, immediately after, and after the 30 minute time interval. The angle from the first stage to second had a 6.22% increase. This may be due to the compression of the soil as the bricks were laid or from sliding of the soil. The change between immediately after and after 30 minutes was a 6.27% decrease. 

A decrease shows that the soil eroded. This may have to take into the account the change in slope as a result of putting the grid in place. Testing on these changes have been done and will be added to the blog in coming posts. This angle decrease is a larger percent from that of the toe wall. Multiple structures of the grid will be tested in the coming week. 

First Toe Wall Test

Tonight the first testing of a toe wall was done. Below is a picture of the set up once the bricks were removed from the soil.

Measurements were taken before the bricks were placed, immediately after the bricks were placed, and 30 minutes after the bricks were placed. Before pressure was applied, the angle was approximately 32.26 degrees. As the pressure was applied there was visual degradation. Some of the soil compressed while a lot of it slid down the slope. The angle changed 11.45% between these two stages. After 30 minutes the new angle was 27.93 degrees. This was only a 2.21% decrease from immediately after the bricks were placed. While there was still soil degradation, this test of the toe wall showed less change than the pressure applied without a barrier. 

It is important to note that at approximately seven minutes in one of the bricks being used for applied pressure fell from the slope. It was replaced so that the simulation could continue. This may have also been a cause of error in this test. However, it can be viewed as success because it may have fallen from a gradual loss of soil from beneath it. We want an unstable slope to begin with so we can test our methods to see if they prevent/slow degradation. 

Results from New Pressure Test Design

The results from the new pressure test design were consistent with degradation of soil, as the slope angle decreased by 3.83%. The measurements from the height, slope, and bottom did not change as expected. The slope actually decreased instead of increasing, the bottom increased very slightly, and the height remained almost exactly the same. We think the change in angle came from a compression of the soil rather than the soil sliding but both are issues within soil erosion. The measurements were taken from immediately after bricks were placed and after 30 minutes of them being on top of the soil.

This new style of testing can have improvements in the future, such as where to place the bricks. If we decide to continue using the new design of slope, it will be carried on through toe wall and rain simulation testing.

New Pressure Test Design

In previous trials a small ledge was made at the top of the slope to create a place to place bricks, like so:

This structure is actually very stable and shows little changes, so the group decided to try another form of test test slope:

Not only is there more immediate change, bu the measurements are slightly easier, though there are more. The bricks are placed on the slop and allowed to shift the soil downward. measurements are taken before the placement, immediately after the placement and 30 mins after placement. This test is still in the trial stage, so moving forward it may or may not be the standard. 

Current Research

The strength of the wall varies depending on factors such as the materials used, the design of the wall and the type of soil behind the wall. However, one factor remains constant between all walls, water pressure behind the wall. This factor can make or break most walls. The toe wall's defense is proper irrigation.Without this system, the wall is bound to have a short lifespan.

"Built right, he says, a retaining wall can outlast most people. But like any structure, their lifespan depends on how they're built. A wall built of railroad ties isn't likely to last as long as one made of concrete blocks, but even a concrete block wall can fail early. A lot of factors play into lifespan including: the soil type behind the wall, drainage around the wall, the material the wall is made of, and how strong the wall's foundation is.

"There's a lot of different ways to design [walls]," he says. "Ensuring that there's low water and water pressure behind [the wall] is critical.""

Walls Come Tumbling Down, J. Adrian Stanley, (Article found Here)

Rain Control Test

Last week, 3 tests were preformed, 2 pressure and 1 rain test. Unfortunately measurement errors made during the pressure tests that made the data unusable. The rain test data, however, was viable. The test preformed without pressure or an upper shelf on the slope. The rate of rain was 1.5 inches per hour and the slope was subjected to the rain simulation for 30 minutes. Measurements showed that that the angle of the left slope decreased by 8.8% and the right side angle of the slope by 9.4%. Qualitative investigation showed that there was erosion, but on very small, and near impossible to measure scale. This team has the ability to perform a test that will simulate approximately 6.5 inch/hour rain. this simulation may be subjected to the slope.  

Week 8 Lab

The goal for the lab today is to test the toe wall and grid system under pressure to see if there is a difference from the control data.

First Successful Applied Load Test

This week in lab we were able to get results from our applied load testing. After 30 minutes, there was no visible change but the calculations prove shifting took place. Initially, the angle was calculated to be 35.8 degrees. The calculated angle after applying the bricks was 32.5 degrees. A decrease in angle is consistent with soil degradation because the slope becomes gradually flatter.

Week 7 Lab

For today's lab, we are testing the rain simulator again to get a slower rate and to make a slope that will collapse under the pressure of the weight

Applied Load Test 2

During Week 6 lab we performed another applied load test. This time, the soil was dry and a new slope was built. The measurements for the initial slope are shown in the picture:

After 30 minutes of applied pressure, the calculations gave an angle greater than the initial angle.

This is inconsistent with predicted soil erosion. There could have been errors in measurements that caused this inconsistency. For improvements, we can make the initial slope steeper. We will continue to test. Our hope is to find a slope that will fail so that we can implement our solutions to stabilize it.

Week 6 Lab goals

The main goal of the lab today is to get the rain rate down and getting the consistency of it. We are also testing the slope under pressure to see how it reacts under pressure

Group Meeting on May 2nd

Meeting goals for tonight are to figure out why some images are not showing up on the site, finish the blog for the blog check, final report drafting and when and where to test next.

Drying the Soil

As mentioned previously, the testing needs to be done while the soil is drier. It does not need to be entirely dried out, as in nature it is possible for a rainstorm to occur before the soil has dried from previous precipitation, but the soil should be around the natural state in which we obtained it. (The soil from southern New Jersey should be very dry, while the soil from Pennsylvania woods is naturally dense). Due to our time constraints we decided to speed the process by using a hair dryer to take moisture out of the soil. With this in mind our next rain simulation will only be done when absolutely necessary.

Blow Drying the Soil:
We took 2-3 "garden-shovel-fulls" at a time in a separate plastic container. We placed the lid over half of the box and used flexible cardboard to keep soil from escaping out the back and the remainder of the top of the box.

Here are some before and after pictures of the soil.

Applied Load Test

This weekend the team decided to conduct a test with only a load applied to the slope (no other factors tested). The slope was built at approximately a 45 degree angle, steeper than built before. At this point in the project, we want the slope to fail so that we can test our solutions to fix that same kind of slope. We placed two bricks on the top of the slope which created a load of approximately 98 N. After watching for 30 minutes, there was no change or collapse in the slope.

The problem with this test was that the soil was still wet from our previous rain simulation. The moisture in the soil caused it to be very closely packed which would prevent it from failure under our tests. The next applied load test will be conducted when the soil is dried out.

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.