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)