1. The Feasibility, Constructability, and Efficacy of Tire-Derived Aggregate as a Component in Slurry Cutoff Walls

2. Slurry Cutoff Walls
A slurry cutoff wall is a form of seepage barrier intended to stop the migration of water through an impervious barrier.
One of the methods used to construct a slurry cutoff wall is to excavate a trench and then backfill it with a mixture of soil, cement, and bentonite clay (SCB)

3. Slurry Cutoff Walls in Waterside Applications
In waterside applications, a cutoff wall is typically constructed either at the toe of the levee or along the crown (top) of the levee.
The process is typically:
A trench that is excavated.
The trench is filled with hydrated bentonite clay slurry to prevent the trench from caving in.
The soil that was excavated is mixed with bentonite and cement and placed back into the trench.
Samples are periodically taken to measure the permeability (ability of water to flow through the backfill material).

4. Slurry Cutoff Walls in Waterside Applications

5. The Recycled Tire Slurry Cutoff Wall Demonstration Project
In 1998, a research grant was awarded to the CSU, Chico Research Foundation to evaluate the feasibility of incorporating tires shreds into a levee slurry cutoff wall
The hypothesis for this project was that a large quantity of recycled tires could be incorporated into the backfill, alleviating the various piles of waste tires stockpiled in the State of California and providing an effective barrier to water migration.

6. The Recycled Tire Slurry Cutoff Wall Demonstration Project
The Recycled Tire Slurry Cutoff Wall Demonstration Project was funded by the California Integrated Waste Management Board as a potential source for the reuse of waste tires.
The project had four distinct stages:
Laboratory Testing
Medium Scale Testing
Large Scale Field Testing - Implementation
Monitoring of Results

7. Preliminary Investigations
In , preliminary laboratory work began to determine if in fact, there was a method in which the soil, cement, bentonite, and tire shreds could be mixed resulting in a product that behaved similar to backfill materials being used in traditional SCB cutoff walls
The target used for measurement of performance was the USACOE specifications with three major criteria including:
Slump – 100–150 mm (4-6 inches)
Permeability – Less than 5 x 10-7 cm/sec
Compressive strength (fc) – Less than 100 psi

8. Preliminary Investigations Continued
The following Project obstacles were quickly found as the preliminary investigations into the project began:
Method of mixing materials in a large scale field test
Method of testing permeability
Method of testing slump
Buoyancy of the tires
Variations of soil classification used in lab tests from those actually found at the site

9. Preliminary Investigations Continued
To address the obstacles of this project, the following ASTM standard’s were researched and incorporated into the project:
ASTM C-143: “Standard Test Methods for Slump of Hydraulic-Cement Concrete
ASTM D 5084: “Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter”
ASTM C-360: “Test method for Ball Penetration in Freshly Mixed Hydraulic Cement Concrete”
ASTM C 150: “Standard Specification for Portland Cement”
ASTM D 422: “Standard Test Method for Particle Size Analysis of Soils”
ASTM D 2487: “Standard Classification of Soils for Engineering Purposes”
ASTM D 4318: “Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils”
ASTM D 698: “Laboratory Compaction Characteristics”
ASTM D 1556: “Standard Test Method for Density and Unit Weight of Soil in Place by the Sand-Cone Method”
ASTM D 4832: “Preparation and Testing of Soil-Cement Slurry Test Cylinders”

10. ASTM C-143: “Standard Test Methods for Slump of Hydraulic-Cement Concrete”
This test method was used to provide the user with a procedure to determine slump of plastic hydraulic-cement concretes.
The process uses freshly mixed concrete and compacts it in a mold shaped liked cone and measures the displacement of the original and displaced center as the slump in the concrete

11. ASTM D : “Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter”
This test methods covered laboratory measurement of the hydraulic conductivity (also referred to as coefficient of permeability) of water-saturated porous materials with flexible wall permeameter at temperatures between 59 and 86 degrees Fahrenheit.
This test methods may be utilized on all specimen types (undisturbed, reconstituted, remolded, compacted, ect.)

12. ASTM C-360: “Test method for Ball Penetration in Freshly Mixed Hydraulic Cement Concrete”
This test method utilized a 6” diameter, 30 pound Kelly Ball, attached to a rod.
A sample of slurry mix was prepared and then struck with the Kelly ball.
The depth of penetration was measured and then correlated to the slump

13. ASTM C 150: “Standard Specification for “Portland Cement”
The Portland Cement standard specifications cover:
Concrete additions
Chemical Composition
Physical Properties
Sampling
Test Methods
Rejection Criteria
Concrete Storage

14. ASTM D 422: “Standard Test Method for Particle Size Analysis of Soils”
This test method covered the quantitative determination of particle sizes in soils as follows:
Particles larger than 75um (retained on the No. 200 seive) are determined by sieving
Particles smaller than 75um are determined by a sedimentation process, using a hydrometer

15. ASTM D 2487: “Standard Classification of Soils for Engineering Purposes”
This standard used a system for classifying mineral and organo-mineral soils for engineering purposes based on laboratory determination of particle-size characteristics, liquid limit, and plasticity index

16. ASTM D 4318: “Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils”
This test method covered the determination of a soils liquid limit, plastic limit, and plasticity index.
The results of these tests distinguish the boundaries of a plastic soils state of consistency.

17. ASTM D 698: “Laboratory Compaction Characteristics”
This test method covered laboratory compaction methods used to determine the relationship between water content and dry unit weight of soils

18. ASTM D 1556: “Standard Test Method for Density and Unit Weight of Soil in Place by the Sand-Cone Method”
This test was used to determine the in-place density and unit weight of soils using a sand cone apparatus
The test is applicable for soils without appreciable amounts of rock or coarse materials in excess of 1 ½ in (38mm) diameter

19. ASTM D 4832: “Preparation and Testing of Soil-Cement Slurry Test Cylinders”
This test method covered procedures for the preparation, curing, transporting and testing of controlled low strength material (CLMS)

20. Laboratory Work
Upon completion of the preliminary investigations and discussions with the experts in the field of slurry cutoff walls, the project was deemed feasible and initial mix design testing began
More than 500 pounds of shredded tires were supplied to the CSU, Chico Research Foundation varying in size ranges from 2” x 2” up to 8” x 8”.
Using these tire shreds, preliminary tests were conducted using soil from the surface of the proposed construction site and it became apparent that 2” minus tire chips would provide the best workability and efficiency

21. Mix Design
In the mix design, it was found that twenty four hours fully assured full hydration of the bentonite and provided an effective slurry for testing
Mixes were tested using a three cubic foot electric concrete mixer and each test mix was tested for slump and compressive strength
When a mix met both of these requirements it was sent to a Independent lab for permeability testing
The permeability testing had to be specially conducted at a second lab due to the size of the tire chips.
Special test cylinders were constructed that had twelve inch diameter plastic pipe with a plywood bottom
The test procedure ASTM D-5084 was used to accommodate the USACOE requirements that hydraulic conductivity was not to exceed 5 x 10-7 cm/sec
After approximately two months, a proposed mix design was achieved.
The achieved mix design, due to the viscosity of the mix, found that it appeared the separation of the tires from the slurry was unlikely thus alleviating most of the concern about the tires floating in the bentonite.

22. Mix Design and Parameters
proposed mix design:
Slurry Mix Item
Percent by Weight
Soil
67%
Bentonite Clay 3%
Cement 5%
Tire Chips
25%

23. Mix Design

24. Medium Scale Testing
In spring of 1999, After a design mix was established, a second larger round of tests began at a independent testing lab
At this lab, two medium scale mixes were prepared, using soil obtained from the site in a ready-mix concrete truck
Both of these mixes were tested for both permeability as well as compressive strength
From the results of this test, it was deemed the mix was adequate to proceed with construction of large scale project.

25. Large Scale Field Test
Excavation of the cutoff wall commenced on June 17, 1999.
The equipment utilized included:
2 Caterpillar excavators – One at each end of the trench. The lead excavator was digging the trench and the second excavator was mixing and placing the Soil-Cement-Bentonite-Tire mix for backfill.
1 Caterpillar Integrated Tool Carrier (ITC) – This piece of equipment served many purposes. With it interchangeable components, it can serve as a forklift to offload cement and bentonite from the delivery trucks. The ITC can also attach a front end bucket to serve as a loader, and a boom which allowed carrying heavy loads. The primary function of the ITC was to deliver cement to the mixing bin.
1 Caterpillar 953 Track Loader – The track loader is similar to a rubber tired front end loader only it is mounted on tracks for traction and flotation. The track loader was used to load soil and tire chips into the mixing bin. Once all materials were measured and placed into the mixing bin, the front end loader would agitate the materials to mix them prior to placement.
1 – 6” contractors pump – the pump was used to supply water to the bentonite hydration and mixing tanks. The water was supplied from the canal which is fed from the Feather River.

26. Large Scale Field Test: Equipment

27. Large Scale Field Test: Equipment

28. Large Scale Field Test
The project consisted of a 30 foot deep, 1,400 lineal feet long, cutoff wall on a DWR levee in Gridley, CA and utilized 475 tons of recycled tires.
This location was selected because the canal adjacent to the levee is drained and filled annually thus providing a good opportunity for monitoring

29. DWR levee

30. QA/QC
During construction, due to Quality Assurance and Quality Control, slump measurements were conducted on a regular basis, as well as, permeability and Compressive strength tests
The process of Quality Assurance and Quality Control was conducted by the USACOE specifications

31. Monitoring of Results
After the project was constructed, nine-four inch diameter monitoring wells were installed
The monitoring wells provide an opportunity to measure the depth of the ground water to determine if water was migrating from the canal, through (or around) the cutoff wall.
Weekly groundwater measurements were taken over the course of two years which determined that the water appeared to be migrating through the levee at both ends of the cutoff wall (not through the wall).

32. Groundwater Measurements

33. Groundwater Measurements

34. Groundwater Measurements

35. Monitoring of Results

36. Secondary Monitoring
To answer the question of how the water was migrating from the canal to the adjacent field, a water level data logger was installed in each well prior to the canal being filled in April, 2005
The water level data logger took elevation readings every 15 minutes a 2 week period
Following the 2 week period it was determined there was sufficient data to opine that the water was migrating around or under the cutoff wall and the project was successful.

37. Ending Results of using Tire-Derived Aggregate as a Component in Slurry Cutoff Walls
The project successfully showed that the cutoff wall construction process was not affected by the incorporation of recycled tires
Furthermore, the following was discovered through the project:
Using Tire-Derived aggregate increased the per square foot cost of the project by $0.51 but also had the added result of recycling 475 tons of disposed tires
Future projects could implement this technology and possibly recycle up to 63,980 tons of tire material per year in similar projects
This would equate to approximately 6.4 million tires recycled each year.