The completed amphitheater
FA info icon.svgAngle down icon.svgProject data
Status Verified
Completed 2012
Made Yes
Cost 136
OKH Manifest Download

The goal of this project was to build a low-embedded energy amphitheater for Friends of the Dunes at the Humboldt Coastal Nature Center. The Sandy Cove Amphitheater consists of three arced retaining walls made from urbanite, or reused concrete, to form its structure. It will mainly be used as an environment to instruct and lecture young students about the dunes between Arcata Bay and the Pacific Ocean. It may also be utilized as a seating area for the general public.


Introduction[edit | edit source]

The Builders of the Bay are a part of Cal Poly Humboldt's spring 2012 Engineering 215 course. Engineering 215 Intro to Design The Builders of the Bay consist of Cory McGill, Tyler Lowe, and Jairo Luque Villanueva. The team worked with Friends of the Dunes on building an amphitheater for the Humboldt Coastal Nature Center. Friends of the Dunes is a non-profit organization working to conserve the natural diversity of coastal environments through community supported education and stewardship programs[1]. The Sandy Cove Amphitheater will be used as a main center of teaching and learning at the Humboldt Coastal Nature Center. The Sandy Cove Amphitheater is constructed of stacked slabs of recycled concrete obtained from Kernen Construction. The Sandy Cove Amphitheater is a 137 degree section of a circle with three retaining walls increasing in height and length from the front to the back.

The Sandy Cove Amphitheater design

Problem Statement and Criteria[edit | edit source]

The objective of the Builders of the Bay is to design and construct a low-embedded energy amphitheater for the Friends of the Dunes organization.

Criteria Description Weight
Safety Children can safely occupy the amphitheater. 10
Durability The lifespan of the amphitheater is at least five years with only minor repairs done to the structure. 9
Aesthetically Pleasing The amphitheater demonstrates professionally appealing attributes according to the clients standards. 8
Capacity 30 or more people can easily be seated and properly instructed on the amphitheater. 7
Environmental Impact Over 80% of the materials used to construct the amphitheater are recycled materials. 4
Cost The total cost of the amphitheater does not exceed $325. 6

The Sandy Cove Amphitheater Solution[edit | edit source]

The Sandy Cove Amphitheater begins with three retaining walls constructed of stacked urbanite. The blocks of urbanite composing the three retaining walls are stacked in an offset manner to create a more structurally sound structure. These walls are then backfilled with sand. The first retaining wall is 16 inches high and each level of the amphitheater increases by that measurement as you move up the amphitheater. Each retaining wall is 3 feet wide. Each wall follows the same angle of curvature, which is of 137 degrees from a single, central point that is 5 feet in front of the first wall. The first wall has an arc length of 12 feet, the second wall has an arc length of 19 feet, and the third wall has an arc length of 26 feet. The mortar used in the construction of the amphitheater is concrete.

Area is staked to plan schematics at site of implementation.

Stake Schematics

Urbanite is found at various demolition sites.

Retrieve Urbanite from a Demolition Waste Facility

Place first tier without mortar to be sure your wall ends us strong throughout and level on the top layer.

Piece together wall by stacking retrieved Urbanite

Dye is added to make mortar look like the sand that the amphitheater is built on.

Mix Mortar and add brown concrete dye. Dye should be added in a ratio of one bottle per two 60 lb bags of mortar.

Mortar is now applied to the wall built.

Take apart wall and rebuild while applying mortar this time.

Back fill wall to the top of this wall with sand to create the wide walls of this amphitheater.

Place landscaping fabric at the back of the wall and backfill sand once mortar has dried.

Completed first wall.

The first wall is now completed

Costs[edit | edit source]

The cost of The Sandy Cove Amphitheater was $136.53 for all the necessary materials. Friends of the dunes donated $100.00 to the total cost of the amphitheater project and therefore the cost of $36.22 was split between the three team members.

Quantity Material Source Cost Total
6 8" stakes Ace Hardware $0.68 $4.08
7 2' Stakes Ace Hardware $0.92 $6.08
13 Urbanite Kernen Construction $162.50 $0.00
1 Ball of string Ace Hardware $1.50 $1.50
7 Concrete mortar Ace Hardware $6.99 $48.93
1 Landscaping fabric Ace Hardware $28.99 $28.99
1 Chisel Ace Hardware $10.99 $10.99
4 Mortar dye Ace Hardware $8.99 $35.96
Total Cost $136.53

Maintenance Costs[edit | edit source]

The amphitheater will require an occasional upkeep and additional materials as applicable. Monthly inspections of the amphitheater should be made to make sure that none of the urbanite has been removed each retaining wall. Extra urbanite is being kept on site to provide the client with the appropriate material to fix the damage.

Labor[edit | edit source]

The following image shows the work involved in this project.

This chart shows the compilation of hours spent on each phase of the design process. The total amount of time spent on this project was 287 hours.

Testing Results[edit | edit source]

The Builders of the Bay built and tested two separate retaining walls before the final installation of the walls at the Humboldt Coastal Nature Center. The purpose of these tests was to practice the actual building of the walls and to make sure the material we were recovering from Kernen Construction would be suitable to use for stacking and building the walls.

A practice wall we built to be sure that the urbanite was usable.

Summary and Next Steps[edit | edit source]

A total of 287 hours were spent on the design and completion of The Sandy Cove Amphitheater project. The Sandy Cove Amphitheater fits all specifications given to The Builders of the Bay. The amphitheater is safe due to wide steps, adequate step height and using sand as backfill. These are safety measures to keep the amphitheater from being too steep and to provide a soft surface to fall on instead of using solid concrete for the entirety of the amphitheater. Because the amphitheater is made of concrete and uses concrete mortar, the amphitheater is durable and will last five or more years with only minor repairs. Urbanite is an aesthetically pleasing material due to the fact that it matches all other retaining walls surrounding the facility. The capacity also meets the standard of seating 30 people or more. Using urbanite as the primary material meets our criterion of lowering the environmental impact by using mostly recycled materials. Lastly, using urbanite helped keep our cost low and well under our initial budget.

Update October 2016[edit | edit source]

The amphitheater is a hit and used all the time. It is used as a place to gather during many FOD activities including weekly during field trip visits from local schools. The amphitheater could use some minor maintenance to fix the side stairs so they stay in place.

Kids in Sandy Cove on a field trip

Update October 2017[edit | edit source]

The Sandy Cove

The amphitheater that is used by students that are on field trips. It is used weekly if the weather allows it. It is evident that it needs some maintenance. Weeds need to be picked and some sand must be added to the stairs.

References[edit | edit source]

  1. . Friends of The Dunes, 2012. <> (Apr. 5, 2012)
FA info icon.svgAngle down icon.svgPage data
Authors Cory McGill
License CC-BY-SA-3.0
Language English (en)
Related 0 subpages, 9 pages link here
Impact 532 page views
Created April 5, 2012 by Cory McGill
Modified August 22, 2023 by Lonny Grafman
Cookies help us deliver our services. By using our services, you agree to our use of cookies.