50-ft Soil-Nail Wall Installation at Sunol Valley Water Treatment Plant
- Joe Lazzaretti
- Aug 12
- 7 min read
Updated: Oct 3
The Sunol Valley Water Treatment Plant got a big fix with a new 50-ft wall made of soil nails. This work made it so the plant could clean 40 million more gallons of water each day, and stay safe near shaky ground. They had to deal with a few tough bits, like being close to the Calaveras fault, handling water underground, and keeping the plant going while they built.
Key Parts of the Project:
Goal: Make room for big water tanks and boost the plant’s power.
Place: Sunol, California, by the Calaveras fault.
How They Built it: Built from the top down using steel nails, sticky mix, and spray-on stone.
Tough Parts Tackled: Staying strong in quakes, dealing with underground water, and small space to work.
Main Folks Involved: SFPUC, ECS, Keller North America, and others.
This work gave us a tough and long-lasting wall, making sure the plant runs smoothly and stays safe for a long time ahead.
Plan Info
Site Spot and Plant Info
The Sunol Valley Water Treatment Plant is in Sunol, California. It is a key part of the water system in the Bay Area. The SFPUC owns it. They had to put in a new soil-nail wall when they made the plant bigger. This work was a big step to make the plant better. It needed a lot of teamwork between the people who planned and built it.
Plan Aims and Main People
A few main groups came together to make sure the plan worked:
This way of working let pros in different jobs handle each step, from first plan to last build.
Job Needs
The big aim was to build a 50-ft permanent soil-nail wall. This wall had to hold back soil and keep the water tanks safe [1].
Site Conditions and Design Requirements
Earth and Ground Tests
The wall's plan grew from deep earth tests. At the Sunol Valley Water Plant, AGS did big earth checks as part of the Phase II Upgrades, done in 2014 [2]. These checks helped fix the key earth and water under earth traits needed for the right wall plan.
Water under earth showed up as a key thing changing how the wall worked. More water under earth cuts down how safe the wall is and adds push on the wall [5]. In places with this water, the push that keeps the earth-to-nail setup strong acts less well than in dry spots [5]. These facts were key in setting how close nails should be and how to put them in, forming the plan path that came next.
Plan Ways and Rules to Follow
The plan thought about how water under earth changes how nails work. Tests show that this water can push on the top nails, while bottom nails keep things steady [5]. This point set the plan for how to put nails in, making it clear there was a need for more moves to start nail push in dry earth [5].
Place Limits and Work Rules
Plan steps were set up to fit well with what the water plant needed to keep working right. The way of making and putting things in made sure tasks could go on without messing up the plant’s key jobs, going well with its day-to-day work.
Soil Nail Wall Installation
Building Steps and Methods
In 2011, AVAR Construction made a 50-ft wall with soil nails at the Sunol Valley Water Plant using a top-down way. This was part of a big, $50 million job to make the plant bigger for the San Francisco Public Utilities Commission (SFPUC) [4]. This way let the team work in order while the plant kept running.
Getting Ready to Build
Before they dug up the earth, the crew made sure to find where the utility lines were and set paths for machines. They set up a space for big tools, such as drill rigs on tracks, mixers for grout, and pumps.
How They Put Up the Wall
Putting up the wall was a step-by-step job. Each part began with digging out 3 to 6 feet of dirt to keep the side from falling. Then, they drilled side holes 3 to 6 feet apart, put in steel nails that fight pull, and filled the holes with grout. After the nails were stuck in place, the workers set up drains, put on strong spray-on concrete, and put plates on the nail tops. They did this again and again until they dug down to 50 ft [3]. After putting up the wall, it was heavily tested to check it was built right.
Checks and Making Sure it was Good
All through the job, the crew did different tests like pull-out, load, grout, and concrete checks. These tests made sure the wall was strong and would stay up for a long time [6].
Issues and Fixes
The 50-ft dirt nail wall job at the Sunol Valley Water Treatment Plant had many hard parts to it. Each issue was met with smart fix plans to keep the job on its path.
Road and Room Issues
One big problem was the hard way to get to the site, which you could only get to by a one-lane bridge that couldn't hold too much weight. To fix this, Monterey Mechanical made and put in short-term support to make the bridge stronger [7]. They also set up a good plan for traffic to help control cars well and keep things working smooth between the building work and the plant's needs. These moves were key to getting the wall put in on time, within the money limit, and with no issues [7]. Also, very tight checks on quality were kept in other parts of the work to keep high grades.
Shotcrete Quality Checks
Keeping the shotcrete good was very big. A strong program for checking quality was used to watch every part of the steps. This had checking mix plans, slump, heat, steel bar line-up, and squeeze power through set tests. For example, hot-shotcrete orders were turned away to make sure the stuff met needed marks [8]. Before putting it on, deep checks were done to see that the steel mesh, iron bars, and chair heights were right as per the plans [8]. Concrete bits were also taken to test for squeeze power, and shotcrete cores were pulled out and tested to make sure they hit the needed squeeze strength marks [8][9].
Results and Lessons Learned
The 50-foot wall at the Sunol Valley Water Plant did its job well, even though it was hard to do. Good plans and careful work made sure the project was done right without stopping the plant's usual work. We'll look at how well the wall did, what we learned about building in the area, and how it changed the plant's day-to-day jobs.
How Well the Wall Did
After they built the wall, checks showed that it worked as they thought it would. The wall didn't bend too much, and nail tests did better than what was needed. This made the engineers feel good about the wall lasting a long time. The wall's strength was just right, and tests on core samples proved it. Also, the wall's drain system worked well, using holes and layers to handle water, even when it rained a lot.
What We Learned About Building Here
This work taught us a lot about building in the Bay Area's special setting. Plans for earth shakes were key, needing parts that fit well with both the nails and the wall face. These parts did their job well when the earth moved a bit during the build. The area's high water level made things tough, asking for nail work to be done when it was dry. The ground, made of clay and sand, showed how vital it was to test the soil as they drilled. Changing how long and far apart the nails were based on these tests made the wall more steady. Getting tools to the tight site was hard too. Smart ways, like using drills that could be taken apart to fit into small, heavy spots, were very helpful.
How the Plant Kept Running
One big win was how the build barely messed with the plant's work. The water plant worked well because the build team and plant workers talked every day. They kept the noise down with sound walls and set work hours. They kept dust low with water sprays and covered up stored stuff. A strong safety plan meant no bad incidents, setting a good example for future work in busy places. After the wall was done, plant bosses felt sure about its steadiness, especially since it held up well in small earth shakes.
Wrap Up
The 50-foot wall made of soil nails at the Sunol Valley Water Treatment Plant shows that smart design can build a strong hold for new storage tanks. This effort shows that using nails in the soil can solve hard design tasks, even in small areas. Its win sets the way for more use like this in the future.
Main Results of the Project
This work met its design aims and proved that using nails in the soil is a bendy and money-saving way to keep slopes in place and help dig areas.
Future Use
What we learned here gives useful tips for big jobs that shore up land. Using soil nails fits well for jobs in tight spots and tough earth settings.
FAQs
How did the team keep the soil-nail wall safe and solid even with problems like the Calaveras Fault and lots of water in the ground?
The building team paid close attention to making the soil-nail wall strong and secure by creating it to follow tight safety rules: a bottom safety score of 1.5 for short-term builds and 2.0 for long-term builds. This setup kept in mind the earth shakes from the Calaveras Fault and the issues from changing water levels in the ground.
To deal with too much water in the ground, they picked ground with low rain soak when putting in the nails and put in top-notch water flow systems. These systems were made to deal with yearly shifts in water in the ground, making sure the wall was tough and steady no matter the outside forces.
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