Shotcrete Retaining Wall Shoring on Yerba Buena Island Residential Development

Joe Lazzaretti
Aug 12
9 min read

Updated: Sep 2

Why Shotcrete? Yerba Buena Island's steep land and quake risks needed a wall fix that could work in small spots. Shotcrete, put right on slopes, cut out the need for big frames and saved costs by 10–30%.
Challenges Faced: The island's mix of hard stone and soft bay mud made it hard to stay fixed, while small ways in and quake risks called for a tough, bendy build.
Two Jobs: The wall helped right away when digging and kept strong against dirt push, water in the ground, and quake forces long-term.
New Bits: Dirt pins with rust-proof coats, strong shotcrete, built-in water paths, and quake breaks made it last and stay tough.
Checks and Tests: Top tools like Leica Nova™ TM60 watched the site all day and night, while test pins made sure the setup was safe.

This work shows how shotcrete fixed to the needs can beat tough city build challenges with little room and big quake worries.

Work Site Issues and Limits

Yerba Buena Island Building Plan

Yerba Buena Island sits in the middle of San Francisco Bay, close to the Bay Bridge, and faces big building challenges. Its sharp, sloped land and limited ways in call for smart build plans to fit this tight city spot. These issues are key in shaping how we hold up the land.

Ground Types and Earthquake Threats

The island's ground is a mix of hard rock with a top layer of Bay mud, which has soft, wet dirt, peat, and loose sand. Bay mud is tough for engineers as it is weak and squeezes tight under weight. Also, the top soils grow and shrink with wet and dry times. Data from the 1989 Loma Prieta quake showed a top shake of 0.06 g on rock but 0.3 g in soft Bay mud near San Francisco Airport. This big gap shows why it's so key to design supports that can stand up well in quakes.

Construction of Sculpted Shotcrete Soil Nail Wall Start to Finish

Setting Goals and Making Standards

The sprayed concrete wall on Yerba Buena Island was made to meet two big needs: helping with digging in the short run and keeping strong over time under different weights. This two-use plan looked at what the building needed now and what it would need to last.

Needs for Digging Help

All through the digging in parts, the system kept the slope safe and kept nearby utilities safe too. It let workers dig deep while keeping the land around it stable and open for putting in utilities and making bases.

As the space was tight, keeping the nearby stuff safe was very important. The setup was made to cut the risk of things settling which could break key services, making it a simple and strong choice over older ways.

Needs for Loads and Limits of How It Performs

The wall was made to take on lots of different weight conditions. It held back the push of the earth, water in the ground, and weights from building. It also thought about shake risks from quakes known in that area. This made sure the wall could handle moving forces without losing its strength.

To deal with water push, it had built-in water systems, and steps to control bending kept the nearby buildings safe. The mix of sprayed concrete was picked to cut shrinking and fight rust, making it last for over 50 years. These steps all help make sure the wall stays strong as long as the project goes.

Shotcrete Keeping Wall Plan

The work team chose a soil nail wall with shotcrete on the front to deal with issues like tight space, changing ground types, and needing dual support.

Why Pick This System

The small space on Yerba Buena Island made normal wall types hard to use as they often need big tools and a lot of room to set up. The soil nail wall with shotcrete on the front was a better fit for the space we had. This method cut down digging and let us use small, easy-to-handle tools. It was just right for the island's ground that changes a lot. The place also shakes a lot, so the wall had to handle quake moves. All these things led to the needs we set below.

Parts of the Wall and What They're Made Of

The wall plan had a thin shotcrete layer made to hold back soil while fitting in soil nails. A steel mesh inside the shotcrete stopped cracks and made the structure strong. The soil nails, the wall's main hold, were made long or short and close or far as needed for the ground here. To last in the sea air, the nails had a cover that stops rust. The shotcrete mix got extra stuff to keep out water, last longer, and save the steel from the salty air.

Water control was key too. A built water system, with holed pipes and well-placed small holes, took care of water flow behind the wall. Steel plates where the nail heads were spread out forces well, while screws that could be turned helped make sure the setup was just right.

Quake Plan and Long-Last Wall

To deal with shakes, given the hard ground and small ways to get there, the design had heavy-duty parts to face quaking. Tests on quaking helped us decide to put quake gaps along the wall at good spots. These gaps, closed with bendy materials, were made to let the wall move without letting water in during or after quakes.

To keep the wall strong for a long time, all steel was covered to stop rust. We put in checks like where the ground and water stand, how well points hold up, and regular looks at the wall to spot any early trouble or wear. Lasting hold points and easy-to-reach spots for up-keeping were part of the plan too, fitting with our goal to keep the wall good for a long time.

Building the Place and Running the Site

The Yerba Buena Island task made sure safety was watched all the time, by using top tools to keep an eye on and handle site states well. Let's dig into the tools that helped do this.

Tools to Watch and Check

To keep a tight watch on weight and change as needed by the rules, the group used up-to-date watch tools. They picked tools for checking changes from Leica Geosystems, a firm known for being good for more than thirty years. The Leica Nova™ TM60 tool for watching, along with Leica GeoMoS and Leica GeoMoS Now! programs, gave non-stop data and study. This setup let them track changes all day and night, helping the team spot problems fast and stick to both building and long-term aims[1].

Check and Test Work

Nail and Hold Test Ways

After we build, we test a lot to make sure the wall will last and stay strong. To keep the real build safe, we use test nails instead of the usual nails. As dirt tech expert PEinc says:

"For my soil nail projects, I specify sacrificial test nails designed with a short, unbonded length. That way, I can test them to the assumed ultimate bond stress or to failure. Testing production nails to twice the design load risks overstressing the nail tendon or shotcrete facing." [2]

The test made sure each nail moved less than 2 mm. Then, some nails got more weight to test their top strength. This test checked that the design had enough safe space. In these tests, the contractor put blocks under the jack to keep the shotcrete safe and guard the wall. As PEinc points out:

"I have no problem with testing against the shotcrete because my test loads are relatively low. However, I do have the contractor use sufficient cribbing beneath the test jack to prevent damage to the shotcrete and punching shear failure of the jack into the dirt face." [2]

If nails made for use broke in a test, we wrote down the weight they held up to, and used just half of that weight as the okay weight for putting them in. For nails not put in yet, workers could fix this by using longer nails, making bigger holes, putting nails nearer to each other, or filling the holes again. PEinc adds:

"If the contractor tests production nails and they fail, he needs to know at what load they failed and then use 50% of that load as his allowable load, then install supplementary soil nails. For nails not yet installed, the contractor has the option of using longer nails, larger diameter drill holes, closer nail spacing, or regrouting the nails." [2]

These test steps show the detailed checks that were key to the project's win.

Lessons and Tips from the Project

The Yerba Buena Island shotcrete wall project showed us how to deal with building on urban hills in areas that can get hit by earthquakes. The island's tough layout made clear that deep ground checks and flexible designs are key, and gave us important lessons for other like projects.

Changes in Design for Different Soils

The island's mixed soil made the team change designs many times while building. First tests showed fill stuff on top of old rock, but when they dug in, things were not that set. They had to change how they put in anchors in parts of the wall. Doing more soil tests as they dug helped them change plans fast, saving money.

For other such works, it's vital to start with a full ground study by a good engineer. The island's story shows how good it is to use designs that can shift as you go, from how things connect to the shotcrete used, rather than just stick to a set plan.

Earthquake thoughts were big in shaping the project's design and build ways.

Building to Stand Earthquakes

Building in a quake area meant the wall had to be made to stand firm during shakes without breaking. They used steel-shotcrete and tough links to make this happen.

The foundation's design was key to the wall staying up in quakes. Deep roots firmly put in rock gave the steadiness needed. Strong links let the wall bend under quake forces, cutting the chance of breaks.

While building, quake-safe holders and parts were used to fix the steel mesh and rods right, making sure they stayed put during shotcrete work. For similar works on hills in quake zones, start with a strong base and use tough, bendy links to help it last and cut care needs.

Golden Gate Shoring Work and Past Jobs

Golden Gate Shoring takes on tough quake and space issues with jobs like Yerba Buena Island by using shotcrete walls made for city places at high risk of quakes. The project at Yerba Buena Island shows how firm design and smart building plans can meet the needs of hill homes in areas that get a lot of quakes. They know a lot about special shoring and wall work.

Wall and Shoring Know-how

Golden Gate Shoring has a lot of past work in making sure walls hold up. They mix great design with ways to fix spot needs like moving earth and quake danger. By making old designs better, they make sure all supports are strong and follow local build laws during the work.

Tools and Ways of Building

Golden Gate Shoring uses top ways to keep building strong in tough spots. For the Yerba Buena Island job, they made a plan just for that land and its limits. They used good concrete mixes, made sure of quality, and set the work steps to handle tight spots and sharp slopes. They thought about quakes from the start to end of the building, making sure both short-term and long-term walls could face still and moving forces. These steps fix problems now and keep their builds strong for a long time.

End Thoughts: Yerba Buena Island Work Outcomes

The Yerba Buena Island home project shows that shotcrete wall supports can be a solid choice for hard city building spots. Golden Gate Shoring took on sharp hills, quake risks, and small areas with a tailor-made shotcrete wall setup that fit tight build rules. Later steps proved the setup's strength in many settings.

A main point is the focus on materials' strength and quake safety. The crew made shotcrete blends that could take on both the weight of building right then and long push from the land, well tackling the sharp hills and quake dangers. These walls were built to hold up against quake shakes, making sure of safety in a spot with high risks.

Getting to the place was also handled well. The island's tight roads and steep land meant they needed a step-by-step build plan. Golden Gate Shoring used small gear and timed things well to keep the project moving smooth with no big waits.

Another key thing was the check on quality. Often testing the shotcrete's firmness and the anchor setups made sure each part was better than planned. This extra firmness gives long-stay sureness for the homes built.

Golden Gate Shoring’s job on Yerba Buena Island shows their skill in handling tough city shoring jobs. Their good use of shotcrete walls in a quake-ready spot starts a strong example for new projects in the Bay Area.

The finished walls now keep digging and building safe, with the work done on time and hitting all safety targets. This win shows the worth of well-made shotcrete systems in tough city spots.

FAQs

How does the shotcrete wall work with mixed soil and quake risks on Yerba Buena Island?

Shotcrete walls are made to meet the tough cases of mixed soil and shakes, like those on Yerba Buena Island. They have steel inside to make them strong and bendy so they can stand up to dirt moves and quake hits.

In places with high quake risks, shotcrete helps keep the ground firm, cutting down dangers such as dirt turning to liquid and earth shifts. To make it even more steady and long last in hard soil places, shotcrete is used with ground making firm methods like making denser and adding more support.