Failed slope

Introduction

Work was completed to stabilize a roadside slope located 5 miles south of Westpoint, CA on State Highway 26.
The slope sheds directly into the Mokelumne River via a drain inlet approximately 25 yards from the toe of the slope. CalTrans was faced with the challenge of stabilizing an eroding 0.5:1 slope potentially adding sedimentation to the Mokelumne River below and putting a home site in danger above. CalTrans needed a quick, effective method to permanently stabilize the slope.

Background

CalTrans had previously placed synthetic netting on the slope with intention of adding surface tensile strength at a low material installation cost. Unfortunately, this method did not maintain the slope and within one year of installation the slope failed.

Requirements

CalTrans, already under enormous pressure to comply with the NPDES regulations, has recently been under additional pressure to set the standard in the state in terms of storm water pollution prevention. Under those pressures District 10 maintenance managers placed the site under an emergency status with a maximum budget of $99,999 allowing CalTrans to hand select only the best installation contractors in the state.

Setting

The site represented an area of approximately 5000 square feet and an average slope angle of 0.5:1. The width of the slope was 50 feet and the height was 100 feet. Access to the top of the slope was restricted by access rights. A two lane paved road at the toe of the slope allowed unobstructed access from the bottom.

Construction Implementation

Early on it was determined that extensive preparation work would be needed before the turf reinforcement mat could be placed. The initial failure of the slope had left large reels and indentations. In order for the turf reinforcement mat to work most effectively it is necessary that the earthen surface area be smooth and without any major indentations.

The most effective method to remove the reels and indentations was to shave the slope with flat shovels and chip away the negative portions with a chipping hammer at the top. This was accomplished by rappelling down from the top of the slope. When finished the hillside prep ended up with approximately 12 cubic yards of loose soil and rock. K-Rails where placed at the toe of the slope to keep all spoils off of the paved road during this phase.

Hydroseeding the slope before laying TRM

Next a 2’x2’x50’ anchor trench was dug 6 feet back from the crest of the slope. The turf reinforcement rolls were then pinned into the anchor trench using 18″ galvanized pins. Guide lines where then installed to identify the perimeter of the project. Pine seedlings in the project area where flagged to be pulled through the mat during installation. Hydroseeding then took place using a native seed mix with tackifier. The seed mix was left overnight to allow for drying. After the seed mix had dried the turf reinforcement mat was deployed over the side of the slope. The mats then where aligned for accurate coverage and correct seam overlapping.

Pinning the TRM to slope

The seams where then diaper pinned together. After the diaper pinning additional 18″ straight pins were laid out on a grid of 2.5 pins per square yard. The pins were then driven into the slope using a bulldog rock hammer. Approximately 5800 pins were used. The purpose of the pins was to create intimate contact between the turf reinforcement mat and the slope.

Installing Earth Tendon Anchors

Additional anchoring took place using 650 mechanical anchoring devices driven into the slope. These mechanical devices are driven into the slope using a 40lb jackhammer. A steel tendon on each anchoring device is then pulled to engage the mechanical device. Once the device is engage the tendon is pulled through the turf reinforcement mat and a UV protected 4” plastic washer is slipped onto the tendon. After the washer is placed a one way washer is placed over the washer to lock the washer in place. Following the installation of the mechanical devices final cleanup took place resulting in a total export of 15 cubic yards.

Conclusion

Revegetated Slope

CalTrans expressed complete satisfaction with the project and plans to use this method of slope stabilization in many other similar situations. Vegetation was fully established by spring of 2006 resulting in a completely stabilized slope.

Polymer Stabilized Road Surface
Bear River Estates, Auburn, CA

Bear River Estates is a new rural subdivision near Auburn, CA.  The developer chose natural looking aggregate roads, but Nevada County DOT required the main road to be paved in order to comply with fire department access rules due to grades in excess of 10%.

Thunder Mountain provided the solution with the technology for a permanent pavement alternative to asphalt that was less expensive than asphalt and maintained a natural ambience.  Thunder Mountain’s Polymer Stabilized Road Surface, doesn’t introduce hydrocarbons to the environment, and provides a cooler surface than Asphalt to minimize heat island effect.

Foster Farm Fertilizer Plant, Livingston, CA
Lined Evaporation Pond

Customer: Foster Farm
Location: Livingston, CA
Project Manager: Beth Smiley

Environmental laws require that industrial applications protect water quality including runoff and what can infiltrate into the water table.

Thunder Mountain installed a High Density Polyethylene (HDPE) Pond Liner in the Foster Farm Fertilizer Plant evaporation pond.  A 60 mil HDPE liner was used due to its resistance to chemical degradation and ultraviolet light degradation.  The system was designed to withstand full exposure to the sun.

Highway 126 Drainage Improvements

Project Owner: Caltrans

Project Location: Napa County, California

Installation of 3 drainage systems across Highway 126 near Napa.  Thunder Mountain removed and replaced two 18” culverts, added downdrains and installed underdrain system to prevent further road deterioration from undermining from water seeping from the uphill bank underneath the road.

As an integral component of The Central Valley project, the Folsom Dam was built in 1955 by the U.S. Corps of Army Engineers roughly twenty-three miles northeast of the City of Sacramento.  It is currently operated by the U.S. Bureau of Reclamation.  Located right below Folsom Dam is the Folsom Power Plant, which produces approximately 198,207 kilowatts of electricity (equivalent to 10% of the power consumed by the City of Sacramento) through the use of three turbines.  These turbines generate electricity by harnessing controlled gravitational releases of water from Lake Natoma.  These releases eventually run into the American River which flows to the Sacramento River, and is subsequently expelled into the San Francisco Bay.

Thursday, February 22nd 2007 marked the ground breaking ceremony for construction of the Folsom Bridge Project.  After the September 11th attacks on the World Trade Center buildings, a comprehensive review of sites that had potential to be terrorist targets was conducted by U.S. Bureau of Reclamation.  Due to the proximity and population density surrounding the Folsom Dam, it was determined that continued public access to the Folsom Bridge Road posed too great a risk.  As a vital artery for transportation across the city of Folsom, its closure would put undo stress on the remainder of the city’s thoroughfares, thus an alternative route had to be constructed.

The Folsom Bridge construction site is a joint venture between U.S. Army Corps of Engineers, U.S. Bureau of Reclamation and the City of Folsom.  The site itself occupies 380 acres, 80 acres were to be disturbed to construct the Roadway and Bridge.  The New Folsom Bridge was to be constructed over  the pristine American River that runs crystal clean most of the year.  During the first wet season significant changes were required to the initial design of the Storm Water Pollution Prevention Plan including shed-on calculations, site topography and soil characteristics.  Several slope failures, inadequate basin sizing and two notices of violation from the Regional Water Quality Control Board expedited the reevaluation of the SWPPP.  After these failures were identified, the City of Folsom hired Beth Smiley of Thunder Mountain Enterprises as an outside consultant for the purposes of assisting in SWPPP design update, site monitoring and help keep the site out of trouble with the State.

Thunder Mountain Enterprises worked in collaboration with City of Folsom, US Army Corps of Engineers and the prime contractor to address SWPPP design deficiencies.  The sheds were evaluated and diversions and pumping was implemented.  The slope stabilization for temporary erosion control was redesigned.  The contractor and original SWPPP design consultant assumed the permenant erosion control would be sufficient for the slopes and soil type.  Some critical areas were redesigned with Profile Products Green Armor System.  It was soon discovered that the premise behind the original Storm Water Pollution Prevention Plan was contingent upon the assumption that the decomposed granite, a major constituent of the soil on-site, would allow rapid infiltration of storm water.  When storm water did not infiltrate due to steep topography, abundance of rock granite formations below the surface and significant shed-on the rainfall that occurred on the site created massive amounts of watershed .by increasing erosive forces on unstabilized soil.  As the on-site hydrology failed to infiltrate and began to move, the topography of the project became an important factor to consider.  Cuts made through the hills adjacent to the Folsom Dam to facilitate road access to the Folsom Bridge, resulted in very steep (1:1, 2:1) slopes with very long runs (some in excess of 50 linear feet).  In most cases these very long running, steep slopes served to amplify erosion by increasing the sheer strength of storm water on already highly erodible soils.  To further complicate matters, the calculation of actual acreage that would shed storm water on to the project site was grossly underestimated.  All of these factors combined contributed to numerous instances of erosion, slope failure, pooling and turbid water discharge.

After the aforementioned problems were identified, Thunder Mountain began putting together a plan to address each of these particular concerns.  Beth Smiley was responsible for completely redesigning the existing slope protection in an effort to re-stabilize areas that had already failed, and ensure continued stability for the duration of the project.  This goal was achieved with the use of Profile Products’ Green Armor System for permanent slope stabilization around critical locations, and their general Erosion Control system for temporary erosion control.  The use of both temporary and permanent erosion control systems was necessary to satisfy multiple challenges that the Folsom Bridge Project involved.

Profile Products’ Green Armor System was developed as an alternative to what is known as “Hard Armor,” which mainly involves the use of stone or rock in storm water management.  Advantages to using the Green Armor System over a hard armor design abound.

Twelve Bridges, Village 9, owned by Placer Holding, Inc. infrastructure was constructed the winter of 2006 in the rolling hills of Lincoln, CA. The soils are very fine and tricky when constructing during wet season. The Storm Water Pollution Prevention Plan was prepared by Beth Smiley, CPESC, CPSWQ of Thunder Mountain Enterprises, Inc. The soils, hydrology, including 100 acres shed-on to the site, construction timeline and adjacent creek as receiving waters were significant considerations in the design. Advanced Treatment of Storm Water was considered highly likely early on due to the fine clayey soils, three outfalls directly into the creek and a construction timeline that would certainly get into wet season grading and underground utilities.

The 133 acre site had multiple other challenges. Experienced Construction Management of Rob Parish from Parish and Associates in this region emphasized proactive Storm Water Pollution Prevention Plan preparation. Among the many challenges were multiple outfalls into the creek that were designed to be vegetated instead or hard armor with the influence of Thunder Mountain. There were massive cuts and fills and many terraced lots. The slopes of the lots were seeded and blanketed due to the sensative nature of the soils. There is an open space to the east with many slopes that were also seeded and blanketed and silt fenced for protection until vegetative establishment.

The mild early winter allowed half of the site to pave prior to significant rainfall. So, the Advanced Treatment System could be downsized to treat less storm water discharge. However, the inability to dig a basin required multiple tanks to capture the rain event, be treated in secondary tanks, run through sand filtration before being discharged at below 10 NTU. The site treated millions of gallons.