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{{305inprogress|Spring, 2013}}
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==Background==
==Background==
 
Hello, and welcome to our Spring 2013 [[Appropriate Technology]] project at [[Humboldt State University]] ([[HSU]]). Our team is comprised of [[User:ind2|Ivan Diankov]] and [[User:Adkato|Alex Kato]]. We will be designing and constructing an erosion control system on the slope behind the [[CCAT yurt]] house at HSU's [[Campus Center for Appropriate Technology (CCAT)]]. Erosion control and slope management come in many forms. From retaining walls to bio-engineered erosion control (BEC) techniques, there are various methods to maintain and control a hillside. The use of BEC techniques specifically provides avenues to enrich the surrounding area with more plant life and thus more stability than a traditional retaining wall.
Hello, and welcome to our Spring 2013 Appropriate Technology project at Humboldt State University (HSU). Our team is comprised of Ivan Diankov and [[User:Adkato|Alex Kato]]. We will be designing and constructing an erosion control system on the slope behind the Yurt house at HSU's Campus Center For Appropriate Technology (CCAT). Erosion control and slope management come in many forms. From retaining walls to bio-engineered erosion control (BEC) techniques, there are various methods to maintain and control a hillside. The use of BEC techniques specifically provides avenues to enrich the surrounding area with more plant life and thus more stability than would a traditional retaining wall.


==Problem Statement==
==Problem Statement==
The Campus Center for Appropriate Technology (CCAT) at Humboldt State University is a student run facility for both education and hands-on experience. On site are many examples of sustainable and appropriate building and living. The Yurt house, located on the hill adjacent to the main house, is one example at CCAT promoting a sustainable living household. Several problems have arisen from the location of the Yurt House.
The Campus Center for Appropriate Technology ([[CCAT]]) at HSU is a student run facility for both education and hands-on experience. On site are many examples of sustainable and appropriate building and living. The Yurt house, located on the hill adjacent to the main house, is one example of promoting a sustainable living household. Several problems have arisen from the location of the Yurt House.
 


# Complete access around the house perimeter is severely restricted due to the small space between the hillside and the side of the house and the large amount of vegetation that grows within and about that small space.
# Complete access around the house perimeter is severely restricted due to the small space between the hillside and the side of the house and the large amount of vegetation that grows within and about that small space.
# There is concern over possible damage to the Yurt from erosion as well as concern over how the hillside is being currently used. As of January 2013, the area behind the Yurt comprises of two large fern patches crisscrossed with footpaths.  
# There is concern over possible damage to the Yurt from erosion as well as concern over how the hillside is being currently used. As of January 2013, the area behind the Yurt comprises of two large fern patches crisscrossed with footpaths.  
<gallery>
{{gallery
Image:yurtslope1.jpg|1. Work space between Yurt wall and hillside as of Jan 2013. Not a lot of room!
|width=180
Image:yurtslope2.jpg|2. Area behind yurt, Jan 2013. White post marks edge of CCAT boundary.
|height=135
</gallery>
|lines=3
|Image:yurtslope1.jpg|Work space between Yurt wall and hillside as of Jan 2013. Not a lot of room!
|Image:yurtslope2.jpg|Area behind yurt, Jan 2013. White post marks edge of [[CCAT]] boundary.
}}


Our project is to clear a small space from the perimeter of the Yurt and to stabilize the surrounding hillside to prevent further erosion. The goal is to reinforce the hillside using bio-engineered erosion control techniques involving live stakes and branch packing.
Our project is to clear a small space from the perimeter of the Yurt and to stabilize the surrounding hillside to prevent further erosion. The goal is to reinforce the hillside using bio-engineered erosion control techniques involving live stakes and branch packing.
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==Literature Review==
==Literature Review==


===Exploring Different Bio-engineered Erosion Control (BEC) Methods:===
===Bio-engineered Erosion Control Methods===
 
====Branch Packing====
====Branch Packing====
Branch packing is a technique that introduces roots into small sloped areas. The layering of branches traps sediment flow and the growth of a root network solidifies the earth into a connected mass.
Branch packing is a technique that introduces roots into small sloped areas. The layering of branches traps sediment flow and the growth of a root network solidifies the earth into a connected mass.
A layer of crisscrossed live branches (0.5in-2.0in diameter) covers the surface. Live stakes are placed at intervals (2ft-3ft) throughout the area. A cover layer of soil no greater than 12in is applied and compacted. <ref name="Soil">Eubanks, C.. "Soil Bioengineering Techniques." A soil bioengineering guide for streambank and lakeshore stabilization. San Dimas, CA (444 E. Bointa Ave., San Dimas 91773): U.S. Dept. of Agriculture, Forest Service, Technology and Development Program, 2002. 75 - 131. Print.</ref>
A layer of crisscrossed live branches (0.5in-2.0in diameter) covers the surface. Live stakes are placed at intervals (2ft-3ft) throughout the area. A cover layer of soil no greater than 12in is applied and compacted. <ref name="Branch">Eubanks, C.. "Soil Bioengineering Techniques." A soil bioengineering guide for streambank and lakeshore stabilization. San Dimas, CA (444 E. Bointa Ave., San Dimas 91773): U.S. Dept. of Agriculture, Forest Service, Technology and Development Program, 2002. 75 - 131. Print.</ref>


====Live Stakes====
====Live Stakes====
 
Live stakes are a natural and locally sourced tool for erosion control. Stakes 2-3ft in length and 1-2in in diameter are prepared and then tamped into the ground somewhere between 1 ½ - 3 ft. Stakes stabilize a slope by absorbing water from the soil and by providing addition root structure. By choosing a shrub or tree species that roots quickly, a slope can benefit from live staking within a season. For excessively wet environments, live staking alone is not sufficient for slope reinforcement. <ref name="Stake">Gray, Donald H., and Robbin B. Sotir. "Brushlayering." Biotechnical and soil bioengineering slope stabilization: a practical guide for erosion control. New York: John Wiley & Sons, 1996. 231. Print.</ref>
Live stakes are a natural and locally sourced tool for erosion control. Stakes 2-3ft in length and 1-2in in diameter are prepared and then tamped into the ground 1 ½ -3ft. Stakes stabilize a slope by absorbing water from the soil and by providing addition root structure. By choosing a shrub or tree species that roots quickly, a slope can benefit from live staking within a season. For excessively wet environments, live staking alone is not sufficient for slope reinforcement. <ref name="Stakes">Gray, Donald H., and Robbin B. Sotir. "Brushlayering." Biotechnical and soil bioengineering slope stabilization: a practical guide for erosion control. New York: John Wiley & Sons, 1996. 231. Print.</ref>


====Live Fascines====
====Live Fascines====
 
Live fascines are bundles of live branches that are places at the bottom of a slope or at the line of a river bank. The perpendicular growth of the roots provides structural support at the base of a slope and can act as a sediment catchment system. Fascine bundles can also be constructed  with dead branches to help control sediment and water flow. Fascine bundles are prepared as 6-8in diameter bundles that are fastened with twine. They are installed in shallow trenches that follow the contour of the slope. In our original ideas for this project, we envisioned using fascine bundles to line the bottom of the slope. Our final project did not incorporate them into the design. This was due to lack of materials and necessity. <ref name="Branch"/>
Live fascines are bundles of live branches that are places at the bottom of a slope or at the line of a river bank. The perpendicular growth of the roots provides structural support at the base of a slope and can act as a sediment catchment system. Fascine bundles can also be constructed  with dead branches to help control sediment and water flow. Fascine bundles are prepared as 6-8in diameter bundles that are fastened with twine. They are installed in shallow trenches that follow the contour of the slope. In our original ideas for this project, we envisioned using fascine bundles to line the bottom of the slope. Our final project did not incorporate them into the design. This was due to lack of materials and necessity. <ref name="Soil"/>


===Other Retaining Systems===
===Other Retaining Systems===
====Log Retaining Wall====
====Log Retaining Wall====
 
Logs are a popular material to use for retaining walls. Their intrinsic strength and durability make them appropriate resources for retaining large amounts of earth. Their natural aesthetic can add visual appeal to the landscape. An existing vertical log retaining wall at [[CCAT]] served as inspiration for our wall.<ref name="Log">"Patios and Courtyards." The complete backyard book. New ed. Sydney, NSW: Murdoch, 2002. 99. Print. </ref>
Logs are a popular material to use for retaining walls. Their intrinsic strength and durability make them appropriate resources for retaining up to large amounts of earth. Their natural aesthetic can add visual appeal to the landscape. An existing vertical log retaining wall at CCAT served as inspiration for our wall.<ref name="Timber">"Patios and Courtyards." The complete backyard book. New ed. Sydney, NSW: Murdoch, 2002. 99. Print. </ref>


==Project Evaluation Criteria==
==Project Evaluation Criteria==
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! Completion
! Completion
|-
|-
| Meet with CCAT to Finalize Design
| Meet with [[CCAT]] to Finalize Design
| February 25
| February 25
| March 2
| March 2
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| March 2
| March 2
|-
|-
| Building Materials (as approved by CCAT)
| Building Materials (as approved by [[CCAT]])
| Tentative  
| Tentative  
| Tentative
| Tentative
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|}
|}


==Retaining Wall Basics/Background under construction==  
==Design==
A well –built retaining wall should be firm, solid, and durable.  A poorly built wall will lean, separate, and topple.  A retaining wall need only retain a wedge of soil that lies in front of the plane of failure – the maximum slope beyond which the soil won’t stay put on its own.  The undisturbed soil behind the failure plane has been naturally compacted for thousands of years, and if undisturbed, will stay where it is by itself for thousands more.
A well-built retaining wall will take into consideration three things:


# The bottom layer of the retaining wall should be buried one tenth of the height of the wall. This will prevent the soil behind it from pushing the bottom of the retaining wall out.
===Preparation===
# The building material should be layered and stepped back with each layer. This enables the building material to use gravity to push back on the backfillA perfectly vertical retaining wall will often topple as soon as it starts to lean.
====Fern Relocation====
# The base of the retaining wall should be highly compacted to ensure foundation stability.
The first step in our project was to relocate the existing vegetation.  Our site was covered in large fern patches that needed to be removed before any work could be done. These fern patches also contributed to the restricted access around the Yurt, so their removal was necessary for Yurt maintenance. We used shovels and pickaxes to remove the ferns. Once removed, we planned to relocate them beyond the [[CCAT]] property line. [[HSU]] Plant Operations expressed their desire to make the foot trails behind [[CCAT]] more narrow and discreetThus, we planned to relocate some of these ferns along the trail.


====Concerns====
====Live Stake Preparation====
The major concerns with building our retaining wall have to do with the natural elements of Humboldt County; rain and seismic activity.
Live stakes are crucial for our soil erosion control system.  They are also very expensive.  The alder trees that line the [[CCAT]] property border are a perfect resource for our live stakes, as there are many large branches crowning their tops.  We plan to cut these branches using a large ladder and an extendable tree pruner.  Each branch will be stripped of its offshoots, and cut down to size.  We will need about 50 stakes that are 2 – 3 ft. long and ½ - 1 in. in diameter.  Each stake needs to have a flat and a pointy tip.  These cuts will be made using a table saw.  All small branches, offshoots, and other alder leftovers will be used for branch packing.  Finally, all stakes will be preserved in a bucket of water for at least 24 hours prior to use.<ref name="Stake"/>


# Because damp soil weighs more than dry soil, proper drainage is extremely important for our success.
====Slope Grading and Shaping====
# Although our wall is small, it should be over engineered in case of earthquakes.
After the site has been cleared of plant material, the slope will need to be graded. One of the objectives of the project is to ease concern over soil erosion therefore lessening the slope steepness will contribute to that goal. We plan to remove soil from the slope starting from the back of the site and working toward the Yurt and relocate it off site. In addition, the slope will be pushed back about a foot from the Yurt. We will do this by shoveling the earth away from the Yurt and relocating it off site. <ref name="Branch"/>


===Installation===
====Installing the Live Stakes and Branch Packing====
In order to implement the branches for the branch packing system, we will remove up to 1 ½ ft of soil from the slope. Once the soil is removed, we will install the live stakes. The stakes will be spaced in a 2 ½ ft square grid and tamped into the soil to a depth of 2ft. Once all of the stakes have been put into place we will lay the live branches into position. The live branches will be laid in a crisscross pattern across the site, in between the stakes. Once a layer of branches is in place will be fill the site back with the 1 ½ ft of soil we initially removed. This soil will then be compacted and wet. An additional layer of live branches may be laid down and covered, but this depends on the amount of material we can gather. If any extra live branches are left over, it is an idea to make live fascine bundles. These bundles will then be placed in a shallow trench that lines the bottom of the slope.
==Construction==
===Preparation===
====Fern Relocation====
The two large fern patches contained about a dozen large ferns and several small ones.  Shovels were used to dig around the ferns and expose their roots.  Pickaxes were then used to gently hack away at the ball of roots and free them from the soil.  As each fern was pulled out of the ground, a new hole was dug nearby to accommodate it.  This task proved much harder than anticipated. 
{{gallery
|width=180
|height=135
|lines=1
|Image:fern1.jpg|First patch of ferns.
|Image:fern2.jpg|Second patch of ferns.
}}


===Designing interpretive materials===


# Live Alder Stakes
We asked [[CCAT]] for some volunteers on a Friday.  [[CCAT]] volunteers drastically reduced the time it took to relocate our ferns.  However, even with the extra workers, this first phase of construction took several weeks. 
# Branches (?)
# Logs (4' - 6' long)
# Flowers


==Design:==
{{gallery
|width=180
|height=135
|lines=2
|Image:fern3.jpg|Ivan, Alex, and the volunteers at CCAT.
}}


===Preparation===
It is important to note that a lot of care was taken to preserve the ferns and incorporate them into our system.  Half of the ferns replanted were used to shape the foot trails on the edge of the [[CCAT]] property line.  The other half were used to fill void space in the surrounding hillside.


====Fern Removal====
{{gallery
|width=180
|height=135
|lines=2
|Image:trail.jpg|The footpath behind the Yurt.
}}


The first step in our project is to relocate the existing vegetationOur site is covered in large fern patches that need to be removed before any work can be done. These fern patches also contribute to the restricted access around the Yurt, so their removal is necessary for Yurt maintenance. We plan to use shovels and pickaxes to remove the ferns. Once removed, we plan to relocate them beyond the CCAT property line. HSU Plant Operations expressed their desire to make the foot trails behind CCAT more narrow and discreetThus, we plan to relocate some of these ferns along the trail.
We also thought it would be super eco groovy to incorporate some of the ferns into our branch packing part of our soil erosion controlTwo whole ferns were saved and, later, stripped of their branches. The branches were incorporated into our branch packing to decrease top soil erosionThe remaining root masses were replanted around the area


====Slope Regrading and Shaping====
====Live Alder Stakes====
Harvesting our live alder stakes was done concurrently with the fern relocation.  A large aluminum ladder was secured to an alder by a piece of rope. A large extendable tree pruner (12 ft. reach) was used for the cutting of the branches.  In addition to its cutting tip, our tree pruner has a large saw blade at the tip.  This blade was covered up with newspaper and taped up to prevent any injury.  The cutting phase was extremely dangerous, and a lot of care was taken to prevent injury.  The felled branches were taken to a processing area where they were stripped of their offshoots, and cut down to size with a table saw.  Each felled branch yielded 2 - 3 finished stakes and plenty of smaller branches and offshoots.  A 44 gallon trash can was filled with water and used to soak about 60 stakes, pointy tip down.  All smaller branches, offshoots, and other alder leftovers were set aside and treated with water every other day until used for branch packing.


After the site has been cleared of plant material, the slope will need to be regraded. One of the objectives of the project is to ease concern over soil erosion therefore lessening the slope steepness will contribute to that goal. We plan to remove soil from the slope starting from the back of the site and working toward the Yurt and relocate it off site. In addition, the slope will be pushed back a short distance (1 ft) from the Yurt. We will do this by shoveling the earth away from the Yurt and relocating it off site.
{{gallery
|width=180
|height=135
|lines=1
|Image:stake1.jpg|Ivan cutting alder branch.
}}


====Live Stake Preparation====
====Hillside Excavation====
Some last minute changes by the client required us to make the Yurt all around accessible, according to the Americans with Disabilities Act (ADA).  The desire was a five foot clearance between the Yurt and the hillside.  Thus, an actual retaining wall structure, and not just a soil retaining system, was required.  This was a very challenging change to our design, and excavation began immediately.  An area around the Yurt was excavated to about 5 feet wide and almost 6 feet deep.  The area was heavily rooted and required the use of Pulaski.  Pickaxes and shovels were also heavily used.  About a week later, the ADA idea got scrapped by our client.


The alder trees that line the CCAT property border will be perfect resources for our live stakes. There are multiple large branches that are, with the aid of an extendable tree pruner, within cutting distance. We plan to cut large branches from these trees, strip them of the outshooting branches, and cut them to size (2-3ft). The smaller branches that are stripped off will be saved to use for the branch packing. Once the stakes are cut to size, we will cut one end into a pointed tip using a table saw. Once the stake preparation is complete, the stakes will be preserved in a water filled bucket for at least 24 hours prior to use.
{{gallery
|width=180
|height=135
|lines=1
|Image:ada1.jpg|ADA clearance.  
}}


===Installation===
===Installation===
====Installing the Live Stakes and Branch Packing====


In order to implement the branches for the branch packing system, we will remove up to 1 ½ ft of soil from the slope. Once the soil is removed, we will install the live stakes. The stakes will be spaced in a 2 ½ ft square grid and tamped into the soil to a depth of 2ft. Once all of the stakes have been put into place we will lay the live branches into position. The live branches will be laid in a crisscross pattern across the site, in between the stakes. Once a layer of branches is in place will be fill the site back with the 1 ½ ft of soil we initially removed. This soil will then be compacted and wet. An additional layer of live branches may be laid down and covered, but this depends on the amount of material we can gather. If any extra live branches are left over, it is an idea to make live fascine bundles. These bundles will then be placed in a shallow trench that lines the bottom of the slope.
====Retaining Wall====
Excavating a large amount of hillside behind the Yurt left us with no real option but to continue with the construction of a retaining wall structure. The decision to erect a vertical, rather than horizontal, log wall was heavily influenced by our available resources in the area. Piles of decent sized logs littered the hillside behind our work site and would be ideal for vertical building. Also, the height and intensity of the wall made it unrealistic to consider contour wattling.


== Construction ==
We selected our logs based on strength and desired length for the different sections of our wall.  The center pieces have to provide the most structural support so we chose the largest and sturdiest of the logs.  We started building at the center and worked our way out.  The side of the hill was carved out to accommodate the log’s dimensions, and a 1 ½ - 2 ft. trench was dug at the bottom of the wall.  We fit each log into the trench and tinkered until everything was snug against the wall, before filling with dirt.  A tamper was then used to tamp each log into place.  Lastly, the logs and the soil around them were tamped, watered, and tamped again.


===Fern Relocation===
{{gallery
The two large fern patches contained about a dozen large ferns and several small ones.  Shovels were used to dig around the ferns and expose their roots. Pickaxes were then used to gently hack away at the ball of roots and free them from the soil.  As each fern was pulled out of the ground, a new hole was dug nearby to accommodate it. This task proved much harder than anticipated. It also seemed to be taking forever, so we asked CCAT for some volunteers on a Friday. CCAT volunteers drastically reduced the time it took to relocate our ferns. However, even with the extra workers, this first phase of construction took several weeks.  It is important to note that a lot of care was taken to preserve the ferns and reduce their stress.  Half of the ferns replanted were used to shape the foot trails on the edge of the CCAT property line.  The other half were used to fill void space in the surrounding hillside.
|width=180
|height=135
|lines=2
|Image:wall1.jpg|Finished retaining wall, left side.
|Image:wall2.jpg|Finished retaining wall, right side.
|Image:wall12.jpg|Finished retaining wall, up close.
}}


We also thought it would be super eco groovy to incorporate some of the ferns into our soil erosion control.  Two whole ferns were saved, and later, stripped of their branchesThe branches were incorporated into our branch packing to decrease top soil erosion.  The remaining root masses were replanted around the area
====Slope Grading and Shaping====
The log retaining wall negated the initial design requirement of grading the slope.  Instead, grading was incorporated into our live stake installation, and began after most of the log retaining wall was installedWe used shovels to dig about  1 ½ ft. deep into our soil erosion grid.  The recovered soil was relocated close by for later use.  We started digging near the back of the grid, and moved toward the retaining wall.  This helped naturally back fill soil behind our logs and helped better secure them into the ground. 


====Live Stakes====
The installation of our live stakes was done after the ‘grading’ of our slope.  The alder stakes were positioned 2 ½ ft. from each other in each direction.  A long heavy metal pole, called a digging stick, was used to poke holes in the soil a little over a foot deep.  The stakes were inserted pointy tip first, and tamped down with a rubber mallet.  Only 40 out of our 60 stakes were used, which gave us the opportunity to be a little selective.  The remaining stakes were incorporated into the retaining wall structure or into the branch packing system.  The larger stakes were used to fill some of the gaps between the logs in the wall.  This will prevent soil erosion through the cracks while providing proper drainage for the wall.  The smaller stakes were used in the final layer of branch packing


===Live Alder Stakes===
====Branch Packing====
Live stakes are crucial for our soil erosion control system, but are also very expensiveA survey of the surrounding area revealed a dozen mature alder trees, with a score of decent sized branches crowning each treeWe decided it would be much cheaper to source live stakes from the surrounding alder trees, rather than purchasing them from a local vendorWe used some rope to secure an old 20 foot aluminum ladder to each tree.
The installation of our branch packing system was done right after stake installationAll of the smaller branches, offshoots, and other alder leftovers were laid down in crisscross patterns across the site and covered with a layer of soilAnother layer of fern branches was laid out in crisscross patterns and finally filled with the remaining soilThe soil was lightly compacted and saturated with water.
 
{{gallery
|width=180
|height=135
|lines=2
|Image:brush1.jpg|Layers of branches and brush.
}}


===Hillside Excavation===
====Finishing Touches====
about the digging
The soil retention system was almost complete, but we felt there were still a few things that needed to be worked on.  A lot of watering was done to help promote the rooting of our alder stakes and help to further secure the logs in the ground.  The soil around the logs sank further in with each watering.  We continued to water and tamp around the wall until no changes were observed.  Last of all, we decided to use a chainsaw to shave a little bit off the tops of some of the logs to create a nice tier down the wall.


===Retaining Wall===
====Finalized Product====
about the logs
January 2013
{{gallery
|width=180
|height=135
|lines=0
|Image:finish8.jpg|
|Image:finish7.jpg|
|Image:finish5.jpg|
|Image:finish6.jpg|
|Image:yurtslope2.jpg|
}}


<gallery>
May 2013
Image:Retainwall-brick1.jpg|Offset between the bricks
{{gallery
Image:Retainwall-brick2.jpg|General View
|width=180
</gallery>
|height=135
|lines=0
|Image:Wall12.jpg|
|Image:Wall1.jpg|
|Image:Wall2.jpg|
|Image:finish10.jpg|
|Image:finish1.jpg|
}}


===Soil Erosion Control===
{{#widget:YouTube|id=uF5YB4orxtw}}
about the alder stakes


==Update October 2014==
Most of the retaining wall is working well; however, the edges of the wall are letting some of the soil into the path area. The soil that is falling from the retaining wall is currently not enough to warrant immediate action, but the heavy rain fall of this environment could cause problems eventually and the retaining wall would do well to be improved or rehabilitated sometime soon. Additionally a number of the logs used in the retaining wall appear to be rotting, the rain and high humidity of the environment that the wall is in would allow for degradation of the wood faster than that of a dry environment, still logs appear to be the best material for the job, they may require more maintenance than other materials but they are the most available materials for the best price. It should be stressed that the wall is holding back just about all the soil at this time and the improvements or rehabilitation of the wall would be good future projects. A good number of the Live stakes appeared to be standing and in satisfactory condition.


<gallery>
<gallery>
Image:Retainwall-wattling1.jpg|Contour Wattling - First sitck is wedged between the ground and the rebar.
Image:Wall1-2014.jpg|Retaining Wall October 2014
Image:Retainwall-wattling2.jpg|General View
Image:Wall2-2014.jpg|Close up of the Wall
</gallery>
</gallery>
===Finalized Product===
[[Image:Retainwall-all1.jpg|thumb|Overall view of the finished project]]
chainsawing, tamping, backfill, flowers, watering


==References==
==References==
Line 226: Line 278:


[[Category:Engr305 Appropriate Technology]]
[[Category:Engr305 Appropriate Technology]]
[[Category:Projects]]

Revision as of 01:37, 20 October 2014

Background

Hello, and welcome to our Spring 2013 Appropriate Technology project at Humboldt State University (HSU). Our team is comprised of Ivan Diankov and Alex Kato. We will be designing and constructing an erosion control system on the slope behind the CCAT yurt house at HSU's Campus Center for Appropriate Technology (CCAT). Erosion control and slope management come in many forms. From retaining walls to bio-engineered erosion control (BEC) techniques, there are various methods to maintain and control a hillside. The use of BEC techniques specifically provides avenues to enrich the surrounding area with more plant life and thus more stability than a traditional retaining wall.

Problem Statement

The Campus Center for Appropriate Technology (CCAT) at HSU is a student run facility for both education and hands-on experience. On site are many examples of sustainable and appropriate building and living. The Yurt house, located on the hill adjacent to the main house, is one example of promoting a sustainable living household. Several problems have arisen from the location of the Yurt House.

  1. Complete access around the house perimeter is severely restricted due to the small space between the hillside and the side of the house and the large amount of vegetation that grows within and about that small space.
  2. There is concern over possible damage to the Yurt from erosion as well as concern over how the hillside is being currently used. As of January 2013, the area behind the Yurt comprises of two large fern patches crisscrossed with footpaths.

Our project is to clear a small space from the perimeter of the Yurt and to stabilize the surrounding hillside to prevent further erosion. The goal is to reinforce the hillside using bio-engineered erosion control techniques involving live stakes and branch packing.

Literature Review

Bio-engineered Erosion Control Methods

Branch Packing

Branch packing is a technique that introduces roots into small sloped areas. The layering of branches traps sediment flow and the growth of a root network solidifies the earth into a connected mass. A layer of crisscrossed live branches (0.5in-2.0in diameter) covers the surface. Live stakes are placed at intervals (2ft-3ft) throughout the area. A cover layer of soil no greater than 12in is applied and compacted. [1]

Live Stakes

Live stakes are a natural and locally sourced tool for erosion control. Stakes 2-3ft in length and 1-2in in diameter are prepared and then tamped into the ground somewhere between 1 ½ - 3 ft. Stakes stabilize a slope by absorbing water from the soil and by providing addition root structure. By choosing a shrub or tree species that roots quickly, a slope can benefit from live staking within a season. For excessively wet environments, live staking alone is not sufficient for slope reinforcement. [2]

Live Fascines

Live fascines are bundles of live branches that are places at the bottom of a slope or at the line of a river bank. The perpendicular growth of the roots provides structural support at the base of a slope and can act as a sediment catchment system. Fascine bundles can also be constructed with dead branches to help control sediment and water flow. Fascine bundles are prepared as 6-8in diameter bundles that are fastened with twine. They are installed in shallow trenches that follow the contour of the slope. In our original ideas for this project, we envisioned using fascine bundles to line the bottom of the slope. Our final project did not incorporate them into the design. This was due to lack of materials and necessity. [1]

Other Retaining Systems

Log Retaining Wall

Logs are a popular material to use for retaining walls. Their intrinsic strength and durability make them appropriate resources for retaining large amounts of earth. Their natural aesthetic can add visual appeal to the landscape. An existing vertical log retaining wall at CCAT served as inspiration for our wall.[3]

Project Evaluation Criteria

The following Criteria will be used to assess the success of this project. These criteria were chosen based on the suggestions of the project coordinator as well as the diligent students who are working on the retaining wall. The scale (1-10) represents the importance level of meeting the constraint of each listed criteria.

Criteria Constraints Weight
(1-10)
Safety & Placement Over engineered for strength and durability
10
Eco Groovy Efficient use of recyclables and waste materials
10
Budget Must not exceed our budget of $300.00
9
Aesthetics Must be pleasing to the eye and look professional
8
Educational Aspect Must include an educational piece for community (something to explain or highlight the construction of the retaining wall)
7

Tentative Time Line

A proposed work schedule detailing the progress of this project. An unexpected change to the design has modified and extended our timeline.

Project Started Completion
Meet with CCAT to Finalize Design February 25 March 2
Sourcing of Materials February 23 March 2
Building Materials (as approved by CCAT) Tentative Tentative
Relocation of Vegetation March 2 March 12
Beginning Excavation March 12 March 23
Soil Erosion March 23 April 23
Testing and Error Correction Apr 23 May 4
Design Change by Client Apr 19 Apr 21
New Excavation Apr 19 Apr 26
Collection & Assembly of Logs Apr 26 Apr 29
Soil Erosion Control (live stakes) Apr 29 Apr 30
Tamping and Back-fill Apr 30 May 1
Chainsaw Apr 1 May 3
Finalize Project May 1 May 3

Design

Preparation

Fern Relocation

The first step in our project was to relocate the existing vegetation. Our site was covered in large fern patches that needed to be removed before any work could be done. These fern patches also contributed to the restricted access around the Yurt, so their removal was necessary for Yurt maintenance. We used shovels and pickaxes to remove the ferns. Once removed, we planned to relocate them beyond the CCAT property line. HSU Plant Operations expressed their desire to make the foot trails behind CCAT more narrow and discreet. Thus, we planned to relocate some of these ferns along the trail.

Live Stake Preparation

Live stakes are crucial for our soil erosion control system. They are also very expensive. The alder trees that line the CCAT property border are a perfect resource for our live stakes, as there are many large branches crowning their tops. We plan to cut these branches using a large ladder and an extendable tree pruner. Each branch will be stripped of its offshoots, and cut down to size. We will need about 50 stakes that are 2 – 3 ft. long and ½ - 1 in. in diameter. Each stake needs to have a flat and a pointy tip. These cuts will be made using a table saw. All small branches, offshoots, and other alder leftovers will be used for branch packing. Finally, all stakes will be preserved in a bucket of water for at least 24 hours prior to use.[2]

Slope Grading and Shaping

After the site has been cleared of plant material, the slope will need to be graded. One of the objectives of the project is to ease concern over soil erosion therefore lessening the slope steepness will contribute to that goal. We plan to remove soil from the slope starting from the back of the site and working toward the Yurt and relocate it off site. In addition, the slope will be pushed back about a foot from the Yurt. We will do this by shoveling the earth away from the Yurt and relocating it off site. [1]

Installation

Installing the Live Stakes and Branch Packing

In order to implement the branches for the branch packing system, we will remove up to 1 ½ ft of soil from the slope. Once the soil is removed, we will install the live stakes. The stakes will be spaced in a 2 ½ ft square grid and tamped into the soil to a depth of 2ft. Once all of the stakes have been put into place we will lay the live branches into position. The live branches will be laid in a crisscross pattern across the site, in between the stakes. Once a layer of branches is in place will be fill the site back with the 1 ½ ft of soil we initially removed. This soil will then be compacted and wet. An additional layer of live branches may be laid down and covered, but this depends on the amount of material we can gather. If any extra live branches are left over, it is an idea to make live fascine bundles. These bundles will then be placed in a shallow trench that lines the bottom of the slope.

Construction

Preparation

Fern Relocation

The two large fern patches contained about a dozen large ferns and several small ones. Shovels were used to dig around the ferns and expose their roots. Pickaxes were then used to gently hack away at the ball of roots and free them from the soil. As each fern was pulled out of the ground, a new hole was dug nearby to accommodate it. This task proved much harder than anticipated.


We asked CCAT for some volunteers on a Friday. CCAT volunteers drastically reduced the time it took to relocate our ferns. However, even with the extra workers, this first phase of construction took several weeks.

It is important to note that a lot of care was taken to preserve the ferns and incorporate them into our system. Half of the ferns replanted were used to shape the foot trails on the edge of the CCAT property line. The other half were used to fill void space in the surrounding hillside.

We also thought it would be super eco groovy to incorporate some of the ferns into our branch packing part of our soil erosion control. Two whole ferns were saved and, later, stripped of their branches. The branches were incorporated into our branch packing to decrease top soil erosion. The remaining root masses were replanted around the area

Live Alder Stakes

Harvesting our live alder stakes was done concurrently with the fern relocation. A large aluminum ladder was secured to an alder by a piece of rope. A large extendable tree pruner (12 ft. reach) was used for the cutting of the branches. In addition to its cutting tip, our tree pruner has a large saw blade at the tip. This blade was covered up with newspaper and taped up to prevent any injury. The cutting phase was extremely dangerous, and a lot of care was taken to prevent injury. The felled branches were taken to a processing area where they were stripped of their offshoots, and cut down to size with a table saw. Each felled branch yielded 2 - 3 finished stakes and plenty of smaller branches and offshoots. A 44 gallon trash can was filled with water and used to soak about 60 stakes, pointy tip down. All smaller branches, offshoots, and other alder leftovers were set aside and treated with water every other day until used for branch packing.

Hillside Excavation

Some last minute changes by the client required us to make the Yurt all around accessible, according to the Americans with Disabilities Act (ADA). The desire was a five foot clearance between the Yurt and the hillside. Thus, an actual retaining wall structure, and not just a soil retaining system, was required. This was a very challenging change to our design, and excavation began immediately. An area around the Yurt was excavated to about 5 feet wide and almost 6 feet deep. The area was heavily rooted and required the use of Pulaski. Pickaxes and shovels were also heavily used. About a week later, the ADA idea got scrapped by our client.

Installation

Retaining Wall

Excavating a large amount of hillside behind the Yurt left us with no real option but to continue with the construction of a retaining wall structure. The decision to erect a vertical, rather than horizontal, log wall was heavily influenced by our available resources in the area. Piles of decent sized logs littered the hillside behind our work site and would be ideal for vertical building. Also, the height and intensity of the wall made it unrealistic to consider contour wattling.

We selected our logs based on strength and desired length for the different sections of our wall. The center pieces have to provide the most structural support so we chose the largest and sturdiest of the logs. We started building at the center and worked our way out. The side of the hill was carved out to accommodate the log’s dimensions, and a 1 ½ - 2 ft. trench was dug at the bottom of the wall. We fit each log into the trench and tinkered until everything was snug against the wall, before filling with dirt. A tamper was then used to tamp each log into place. Lastly, the logs and the soil around them were tamped, watered, and tamped again.

Slope Grading and Shaping

The log retaining wall negated the initial design requirement of grading the slope. Instead, grading was incorporated into our live stake installation, and began after most of the log retaining wall was installed. We used shovels to dig about 1 ½ ft. deep into our soil erosion grid. The recovered soil was relocated close by for later use. We started digging near the back of the grid, and moved toward the retaining wall. This helped naturally back fill soil behind our logs and helped better secure them into the ground.

Live Stakes

The installation of our live stakes was done after the ‘grading’ of our slope. The alder stakes were positioned 2 ½ ft. from each other in each direction. A long heavy metal pole, called a digging stick, was used to poke holes in the soil a little over a foot deep. The stakes were inserted pointy tip first, and tamped down with a rubber mallet. Only 40 out of our 60 stakes were used, which gave us the opportunity to be a little selective. The remaining stakes were incorporated into the retaining wall structure or into the branch packing system. The larger stakes were used to fill some of the gaps between the logs in the wall. This will prevent soil erosion through the cracks while providing proper drainage for the wall. The smaller stakes were used in the final layer of branch packing

Branch Packing

The installation of our branch packing system was done right after stake installation. All of the smaller branches, offshoots, and other alder leftovers were laid down in crisscross patterns across the site and covered with a layer of soil. Another layer of fern branches was laid out in crisscross patterns and finally filled with the remaining soil. The soil was lightly compacted and saturated with water.

Finishing Touches

The soil retention system was almost complete, but we felt there were still a few things that needed to be worked on. A lot of watering was done to help promote the rooting of our alder stakes and help to further secure the logs in the ground. The soil around the logs sank further in with each watering. We continued to water and tamp around the wall until no changes were observed. Last of all, we decided to use a chainsaw to shave a little bit off the tops of some of the logs to create a nice tier down the wall.

Finalized Product

January 2013

May 2013

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Update October 2014

Most of the retaining wall is working well; however, the edges of the wall are letting some of the soil into the path area. The soil that is falling from the retaining wall is currently not enough to warrant immediate action, but the heavy rain fall of this environment could cause problems eventually and the retaining wall would do well to be improved or rehabilitated sometime soon. Additionally a number of the logs used in the retaining wall appear to be rotting, the rain and high humidity of the environment that the wall is in would allow for degradation of the wood faster than that of a dry environment, still logs appear to be the best material for the job, they may require more maintenance than other materials but they are the most available materials for the best price. It should be stressed that the wall is holding back just about all the soil at this time and the improvements or rehabilitation of the wall would be good future projects. A good number of the Live stakes appeared to be standing and in satisfactory condition.

References

Template:Reflist

  1. 1.0 1.1 1.2 Eubanks, C.. "Soil Bioengineering Techniques." A soil bioengineering guide for streambank and lakeshore stabilization. San Dimas, CA (444 E. Bointa Ave., San Dimas 91773): U.S. Dept. of Agriculture, Forest Service, Technology and Development Program, 2002. 75 - 131. Print.
  2. 2.0 2.1 Gray, Donald H., and Robbin B. Sotir. "Brushlayering." Biotechnical and soil bioengineering slope stabilization: a practical guide for erosion control. New York: John Wiley & Sons, 1996. 231. Print.
  3. "Patios and Courtyards." The complete backyard book. New ed. Sydney, NSW: Murdoch, 2002. 99. Print.
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