Final Report

ENGR 103 - Spring 2016
Freshman Engineering Design Lab
“Emergency Soil Stabilizing Method”
Final Report

Date Submitted: May 30, 2016


Submitted to:
Grace Hsuan, ghsuan@coe.drexel.edu
Group Members:
Jennifer Cromley, jlc524@drexel.edu

Chris Laudando, cvl27@drexel.edu

Jessica Butterly, jab592@drexel.edu

Matthew VanTrieste, mjv54@drexel.edu

Keith Colon, krc84@drexel.edu
Abstract:
The Emergency Soil Stabilizing Method was created to prevent degradation of soil slopes that occurs too quickly for a long term solution to be immediately applied. The goal of this project was to design a method that would stabilize a degrading slope in a three step process until conditions are suitable to implement a long term solution.  The first step of the process is to construct a brick toe wall, which will quickly give more support to the slope. The second step, an intra-soil grid, is a unique structure that stabilizes the slope internally. It is biodegradable and inserted directly into the soil. The last step is to apply a surface blanket to prevent erosion. Surface blankets are commonly seen and may contain seeds to grow vegetation as a long term solution. There were two majors tasks completed - rain simulations and applied pressure tests. These tests were conducted on a constructed slope inside a plastic container. Technical challenges faced were the inability to test due to weather, (most tests needed to be conducted outside), and simulating the rain at a constant rate. The final deliverable of the Emergency Stabilizing Method are the toe wall and intra-soil grid within the test area, and the assertion of the optimal method of stabilization.

1    Introduction

1.1                Problem Overview

The idea of an emergency soil stabilizing method was motivated by the difficulties found in preventing and coping with slope degradation. The unstable nature of a degrading slope can create problematic situations for implementing a long term solution. The goal of the Emergency Soil Stabilizing Method was to find a way to quickly stabilize a slope without damaging the surrounding environment. The process is not intended to stand alone as a long term solution, but rather provide time for a long term solution to be put in place. The model of the Emergency Soil Stabilizing Method completed was a relatively low cost project. However, if it were to be implemented in full-scale the cost would be much greater. The nature of the project, being a miniaturized version, also leads to many constraints. The most prominent issue is that not all factors of true soil erosion can be included. Soil on a slope can degrade due to high winds, heavy rainfall, sustained pressure, human interaction, and a variety of other factors as well. The isolated  factors that were focused on for the Emergency Soil Stabilizing Method included rainfall and applied pressure.

1.2                Existing Solutions

1.2.1       Planting Vegetation
A long term solution to soil erosion that currently exists is the planting of vegetation along the degrading slope. The root system that the vegetation develops provides a natural structure that stabilizes the slope. Results from an experimental study show that plant root systems were vital for the conservation of soil and water on a slope experiencing soil erosion [5].  The Emergency Soil Stabilizing Method would be carried out if planting vegetation is not possible due to seasonal issues or if the slope would be beyond repair before the roots of vegetation could take place.
1.2.2       Toe Wall
Toe walls are not a new invention and have been in use for many years to stop hills from collapsing onto man-made structures. These structures are generally made from large stones stacked on each other to the appropriate height. Concrete and other materials may also be used as structural demands are changed on a situational basis. Toe walls are generally long term solutions and are, for the most part, successful. The main reason why a toe wall would fail is because of improper drainage behind the wall. Water builds up behind the wall in the soil, and the excess weight added by the water causes a mechanical failure in the wall. The most heavily affected section will subsequently fail.
1.2.3       Erosion Control Blanket
Erosion control blankets are already a widely used and effective method to halt the process of erosion. Examples of items specifically designated for erosion control exist in such diversity that one can be implemented on almost any slope, no matter the angle or contour [1]. Many are also designed with long term solutions in mind, and as such are specifically designed to protect seeds that will prevent erosion long after the seed blanket has degraded.

1.3              Project Objectives

1.3.1       Toe Wall  
One objective of this project is to create a wall that can stand for as long as it takes to install a long term solution, such as plants. A key factor in the design is creating something that can be implemented quickly while keeping strength. There must be proper drainage throughout the toe wall for it to be effective. Several efficient models of toe walls have been create and tested prior to the development of this project. 
1.3.2       Intra-soil Grid
While toe walls and surface covers are already typically employed solutions, the intra-soil grid is a more unique concept to this project. This concept was born from the limitations associated with the wall and cover. Toe walls can act as dams and surface coverings can prevent superficial erosion, but neither cannot prevent soil shifting and partial slope collapse. The intra-soil grid is meant to help stabilize the slope directly. The grid itself would be laid into the slope and would penetrate down to a reasonable depth. The depth varies depending on the model. Design goals for this aspect of the project include using biodegradable materials, creating a method of easy application, providing reasonable support with minimal use of resources, and creating a system that can accommodate for irregular surface areas. Different models were produced, such as a simple model shaped either like an egg crate, noted as Phase 1, or small plugs, noted as Phase 2, which can be seen below in Figures 1A and 1B.
 
   
            Figure 1A: Grid Phase 1.                 Figure 1B: Grid Phase 2.
From these simple designs a more complex model was developed, which was designed to not only provide support, but also catch eroding soil. The model used for tests included hot glue for stability, but this material would not be used in a final product. This unit acts more as a stake, and may be more tedious to install then other models, but potentially provides greater aide. This can be seen in Figure 2                      

                            
                 
                   Figure 2: Grid Phase 3.                                   
1.3.3       Surface Cover
Surface coverings are already manufactured and widely used. Because of this, it was determined that the most effective and efficient way to implement a surface covering was to use one that already exists. A combination of modern seeding techniques and an existing type of biodegradable erosion control blankets, which can be implemented as the seeds are planted, will provide the desired effect while eliminating the need for any extraneous research and manufacturing.

2    Technical Activities

2.1                Rain Simulation
One of the main factors being tested in this project was soil erosion due to rainfall. There were many designs initially considered to simulate rain. The design for rain simulation continuously changed throughout testing. The first method tested used window screening. The item purchased could be pulled for extension but for the purposes of the project was left as a double screen. The screen can be seen in Figure 3.

Figure 3: Screen used for rain simulation.
Various materials were put between the two layers of screening for testing. The first test was carried out with cheese cloth and the second with weed block. The cheese cloth absorbed the water instead of allowing it to pass through, but the weed block seemed to distribute the water more evenly. It was porous enough to allow the passage of water, but not so thin that the water would pass through as a single stream.
However, testing at later time showed faults in the method of rain simulation with weed block between the layers of screen. If too much water was poured at once, it would pool on the surface of the screen rather than pass through. The next method consisted of just the screen at approximately 32-in from the bottom of the control environment, with the water being poured approximately 16-in from the top of the screen. This method was tested on the soil slope. The only change that was visible to the human eye was a more rounded slope edge as opposed to the angled slope initially built. However calculations proved that the slope angle deteriorated by approximately two degrees. 
This method was later refined from the pouring of water directly onto the screen to pouring the water into a cup with a small hole in the bottom. This cup allowed for a more constant rate of rainfall if the water inside was kept at the same volume. The goal for the simulation was to not exceed an approximate rain fall of two inches per hour, as this is deemed a “violent” storm.  The cup method was tested by carrying out a simulation for nine minutes and ten seconds. A small graduated cylinder was placed in the bottom of the control environment to measure the volume. The amount of rainfall after this time period was 1.5-in, which led to an hourly projection of 9.8-in per hour. The size of the cup and the hole were then reduced.
This rain simulation method was then used as a baseline test for the three phases of grid structures. The measurements and calculations for this testing can be viewed in the Appendix.
2.2                Applied Pressure
Various applied pressure tests were done on the slope of the soil. There was initially one large 12-lb brick placed on the smooth top of the slope. The brick was then cut into two for a better fit on the slope. In these simulations it was desired that the slope would fail. The failure of the slope would be the baseline that the Emergency Soil Stabilizing method could be compared to. Figure 4 shows the set up of the applied pressure test.



Figure 4: Applied pressure testing.
This pressure testing was done on the control slope and the three phases of grid structures. The slope did not fail under any of these tests. However, changes did occur. The measurements and calculations for these tests can be viewed in the Appendix.

2.3                Project Timeline

Throughout the progression of the project, the Emergency Stabilizing Method has followed the initial schedule made in the project proposal with only minor changes. The project had a few delays due to testing and insufficient data. One major factor that caused the control testing to be longer than planned was simulating rain, as all of the original ideas did not achieve the desired results. Once the simulation was effective, the project continued with ease. Another issue was the weather because testing can not be performed effectively inside without creating a mess. The general project timeline can be seen in Table 1.
Table 1: Project Timeline
                 

Task
1
2
3
4
5
6
7
8
9
10
Initial Planning
x
x








Getting the Materials

x
x







Control Testing


x
x
x





Toe Wall





x
x



Rain Simulation Design and Testing



x
x
x
x
x
x

Grid Structure





x
x
x
x

Testing in Combination







x
x

Final Report Drafting





x
x
x
x
x

2.4                Project Budget

The budget was relatively low due to the amount of research and testing being conducted compared to the complete fabrication of a product. Expenses stemmed from four main components: the control environment, toe wall, intra-soil grid, and the seed blanket for the surface. Various materials such as the soil used, small garden shovels, Styrofoam cups, etc. were obtained through resources already available and therefore had no impact on the budget. The total cost to carry out the Emergency Soil Stabilizing Method was $124.11. Table 2 outlines the products purchased, their cost, and a brief description of their use.
                                                         Table 2: Project Budget
Item
Quantity
Cost
Brief Description of Use
Home Depot Bucket
2
$5.97
Collect water used in testing and carry materials
Rumblestone
2
$3.76
Weight for the top of the slope
Gloves
1
$3.98
Creating soil slope without getting dirty
Paint Rags
1
$3.97
Intial idea to simulate rain
Weedblock
1
$5.00
Line the bin to add more friction and makes the water go through the slope
24” Window Screen
1
$7.68
Water is poured through to simulate rain
Jiffy Strips Pots
(grid)
2
$5.56
Material for grid structure
Jiffy Strips Pots (round)
2
$4.56
Material for grid structure
Bounty Paper Towels
1
$1.00
Clean up the water
Plastic Latch Box
2
$15.94
Hold the slope and testing is conducting inside of it
Brick (thin)
3
$1.95
Toe wall
Paver Saw Rental
1
$64.74
Cut bricks into specific shapes for construction of toe wall
Total Cost

$124.11

3     Results

The initial goal of this project was to test a toe wall, surface blanket, and intra-soil grid together under the condition of heavy rain and pressure. Due to limitations on time, the testing with the surface cover and toe wall was not achieved. The decision to cut these from testing, but not the methodology, was validated by the significant amount of outside testing and data that predates the start of this project. Both toe walls and surface blankets are standard methods used in the field for stabilization. Furthermore, as research continued it was found that an optimal toe wall design was not achievable with the resources and materials acquired.
The goals of the project were restructured, and the main product to be tested became different samples of the intra-soil grid. Three versions of the grid design were tested. The three structures were tested under pressure and rain conditions to see how the change in slope angle differed between grid design and the control test. The grids were also tested to see what change there was in the slope during their application process. The angle was chosen as the test variable due to its ability to capture the relationship between the length, height and slope of the soil structure. It would have been ideal to have at least three test trials for each scenario, but as the project evolved and different test methods were implemented only 1 trial of each test was possible.
In the control test for pressure the angle change was 4.3%. Grid 1 and 3 had changes around 6 %, which were deemed too small of differences and making viability in terms of pressure inconclusive for these models. For Grid 2 there was an 18% change, thus grid 2 weakened to the slope to degradation from pressure.
For the rain simulation the control test yielded on 8.74% change. The data was again inconclusive in terms of Grid 1, but showed some promise for Grid 2, which had 4.5% change. The best results were yield from Grid 3 in which there was only 3.01% change in the angle.
The final set of data showed that the slope angle was changed by 8.4% by Grid 1, 19.8% by Grid 2 and 3.75% by Grid 3. The overall analysis of the data indicates that Grid 2 is overall damaging to the slope structure, and Grid 3 has the most promise out of all the models. Though Grid 3 yield the best results, the design would need refinement and more thorough testing before implementation.

4     Discussion

Part of the focus of this project was that the design could be implemented at full-scale. For obvious reasons the materials used in small scale tests could not be used on a full-scale system, so research was done to determine what materials could be used. It was found that bamboo is the only biodegradable material strong enough to make the intra-soil grid. Bamboo plates, which would be similar to the walls of the grid, are already manufactured [2]. Biodegradable stakes, some of which are as strong as or stronger than metal stakes of the same size, can be used to hold the grid in place [3]. As previously stated, existing erosion control blankets and seeding methods would be used for the seed blanket. Erosion control blankets already come in amounts large enough to be used in a full-scale implementation.
Given more time, this project could have been improved through more extensive testing. Different materials for the toe wall and intra-soil grid could have been tested at the small scale to allow further analysis on how this project could be scaled up in size. These results could also be paired with the cost of these materials to maximize the cost effectiveness of the final product. Different designs of the wall and bridge could also have been planned and tested to ensure that the design’s effectiveness is maximized.
There were few possible errors in this project. Errors in calculation, measurement, and estimation are the most likely to have occurred. Any experimental errors would have been obvious in the results of the experiment, and as such they would have been corrected at the time.
Various concepts and practical skills were learned through the process of developing this project. The theoretical concepts surrounding the effectiveness of retaining walls, as well as their application, were demonstrated. Concepts involving rain rate and its erosive effect on the dimensions of a slope were also an integral part of experimentation.

5         References
[1] “A.M. Leonard Tools for the Horticultural Industry since 1885.,” Straw-Coconut Erosion Control Standard Blanket, 8ft x 113ft Roll. [Online]. Available at: http://www.amleo.com/straw-coconut-erosion-control-standard-blanket-8ft-x-113ft-roll/p/sc3000/. [Accessed: 09-May-2016].
[2] “Bambu 063200 9’ Disposable Square Bamboo Plate - 25 / Pack,” WebstaurantStore. [Online]. Available at: http://www.webstaurantstore.com/bambu-063200-9-disposable-square-bamboo-plate-25-pack/999063200.html. [Accessed: 09-May-2016].
[3] “Biodegradable Ground Stakes – 500 per Box,” ARBICO Organics. [Online]. Available at: http://www.arbico-organics.com/product/biodegradable-ground-stakes/garden-tools-supplies. [Accessed: 09-May-2016].
[4] “Walls come tumbling down,” Colorado Springs Independent. [Online]. Available at: http://www.csindy.com/coloradosprings/springs-retaining-walls-fail-without-maintenance-inspections-and-permits/content?oid=3133800]. [Accessed: 09-May-2016].
[5] X. Zhang, G. Q. Yu, Z. B. Li, and P. Li, “Experimental Study on Slope Runoff, Erosion and Sediment under Different Vegetation Types,” Water Resour Manage Water Resources Management, vol. 28, no. 9, pp. 2415–2433, 2014 [Accessed: 09-May-2016].







6          Appendix
Table Set 1.1:  Pressure Control Test
Ave. Height (cm)
Ave. Length (cm)
Ave. Slope (cm)
Angle ⁰
Pre-Pressure
15.3
23.5
28.93
33.56
Immediately Post Pressure
10.7
14.15
18.13
37.32
30 mins Post Pressure
10.6
14.65
17.83
35.71
Change



4.31%

Table Set 1.2: Pressure with Grid 1
Ave. Height (cm)
Ave. Length (cm)
Ave. Slope (cm)
Angle ⁰
Pre-Pressure
10.5
19.55
24.3
29.11
Immediately Post Pressure
10.67
18.8
23.3
30.92
30 mins Post Pressure
10.5
20
23.9
28.98
Change



6.27%

Table Set 1.3: Pressure with Grid 2
Ave. Height (cm)
Ave. Length (cm)
Ave. Slope (cm)
Angle ⁰
Pre-Pressure
12.25
18.5
21.67
32.33
Immediately Post Pressure
12.15
18.45
21.2
32.59
30 mins Post Pressure
10.85
19.75
21.17
26.72
Change



18%



Table Set 2.1: Rain Simulation Control
Ave. Height (cm)
Ave. Length (cm)
Ave. Slope (cm)
Angle ⁰
Pre-Rain
14.25
23
27.8
32.26
Post-Rain
13.6
24.3
28.1
29.44
Change



8.74%

Table Set 2.2: Rain Simulation with Grid 1
Ave. Height (cm)
Ave. Length (cm)
Ave. Slope (cm)
Angle ⁰
Pre-Rain
13.9
25.1
28.2
27.63
Post-Rain
13.3
25.4
26.8
25.33
Change



8.3%

Table Set 2.3:  Rain Simulation with Grid 2
Ave. Height (cm)
Ave. Length (cm)
Ave. Slope (cm)
Angle ⁰
Pre-Rain
12.25
22.15
29.25
31.49
Post-Rain
12.25
23.85
31
30.06
Change



4.5%

Table Set: 2.4:  Rain Simulation with Grid 3
Ave. Height (cm)
Ave. Length (cm)
Ave. Slope (cm)
Angle ⁰
Pre-Rain
11.25
18.8
29.65
34.6
Post-Rain
11
19.55
29.4
33.22
Change



3.01%

Table Set 3.1: Grid 1 Application Movement
Ave. Height (cm)
Ave. Length (cm)
Ave. Slope (cm)
Angle ⁰
Pre-Grid
11.15
21.75
28
27.878
Post-Grid
11.35
21.95
29.13
30.44
Change



8.4%

Table Set 3.2: Grid 2 Application Movement
Ave. Height (cm)
Ave. Length (cm)
Ave. Slope (cm)
Angle ⁰
Pre-Grid
12.2
22.1
27.2
25.49
Post-Grid
12.06
22.2
28.03
30.544
Change



19.8%

Table Set 3.3: Grid 3 Application Movement
Ave. Height (cm)
Ave. Length (cm)
Ave. Slope (cm)
Angle ⁰
Pre-Grid
11.25
23.2
29.95
29.05
Post-Grid
12.05
23.6
31.05
30.14
Change



3.75%

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