Marin General Hospital Soil-Nail Wall Expansion Case Study

Joe Lazzaretti
Aug 12
6 min read

Updated: Sep 2

To grow Marin General Hospital, they needed a special wall to keep a steep hillside safe while the hospital stayed open. The work had to deal with small space, tight times, and keeping things calm for patients and emergency paths. Here's what made it good:

Site Issues: Rocky land, little room, and hospital still working meant a need for good plans.
Building Method: They built the wall in stages from the top down to keep it sturdy and cut down on mess.
Careful Planning: Soil tests helped decide where to put the nails, how deep, and how far apart for the best hold.
Watching for Safety: Tools like slope meters and plates to measure settling helped watch the wall’s safety as it was being built.

The work was done on time in 2016, and they spent $500,000 less than the $21 million they had set aside. This win shows that using soil nails is a strong way to make hospitals bigger when keeping things safe and working well is key.

Soil Nail Wall Installation

Project Plan and Site Details

The Marin General Hospital expansion in Greenbrae, CA, aimed to fix the problem of not having enough parking by making a rocky hillside safe. This part of the work needed the making of a hard soil nail wall to keep the hill from moving.

Digging Deep and Holding It Up

The work called for a hard soil nail wall that could reach up to 40 feet high to hold up the hillside [1]. This need came from very tight space limits that asked for exact and very careful plans.

Site Limits and Building Bounds

The task came with hard tests due to the rough ground and the hospital work that was still going on close by. It was very important to keep the hospital running smooth and to keep paths clear for urgent care. This made it necessary to plan very carefully at all parts of the task.

Team and Jobs

The making of the special wall was done by Tuan and Robinson Structural Engineers, Inc. [1]. Also, Geo-Engineering Solutions, Inc. used their deep know-how in dealing with hard ground tasks, showing the deep tech parts of the work [2].

Making the Right Wall Choice at the Hospital

The team used tried and true earth and build rules to make the wall system for the Marin General Hospital bigger. They looked at the land and what the hospital does day-to-day and saw that using nails in the soil was a good way to hold up the hospital's busy setting. This choice led how they made and built the wall.

What the Land is Like and What They Knew

Knowing all about the soil was key in making the plan. Things like the layers of soil, water in the ground, and how strong the materials were got a close look. This info helped make big choices, like how deep the nails should go, how far apart, and the full set-up.

Why Picking Nails Works for Hospitals

For hospital jobs, it's super key to keep things calm. Soil-nailing is good because it shakes less and uses less big machines, which means the hospital can work like normal. This way is solid for places that need to be careful.

How They Made the Plan and Looked at Loads

Looking at loads in detail, which includes checking slip spots and how loads spread out, helped pick the best spot and way to put the nails. The plan also looked at things like local shakes from the earth and water pressure to make sure the wall system would stay strong in many situations.

Building Steps and Setting Up

The crew used a top-down way to build, making sure to work in small 3–6 ft parts so the hospital could keep running without problems. Let's dive deeper into the main parts of setting up and making sure everything was right during the build.

Digging in Stages and Putting in Nails

The work moved ahead in 3 to 6 ft chunks, finishing one level before digging down to the next. At each stage, the team dug out a bit, put in soil nails, and added a shotcrete layer before going lower. This kept the ground firm and let them manage the work well.

After digging each part, workers made near-flat holes in the soil. They put nail bars into these holes at set angles and depths, and used neat cement grout to fix them firmly. To share out the weight, bearing plates were put on the nails, which sat in a 3–6-inch thick shotcrete layer with wire mesh. A draining setup with synthetic strips and pipes was also put behind each part to keep water away.

Drilling, Filling, and Testing

It was key to check that the holes were the right width and depth during drilling, ensuring the soil nail bars fit well. They used the tremie way to fill the holes, making sure the grout tube was set right with marks. They kept an eye on the grout mix with a mud balance, and tested samples to be sure of quality.

Before starting, they looked over all materials - like steel bars, wire fabric, rebar, shotcrete mix, centralizers, and drainage parts - to see they were up to the plan's needs. Mill certifications were checked too. As they dug each part, they inspected the soil face to make sure it matched what was expected. Any issues were quickly sent for an engineer's look.

To make sure the design's grout-to-ground bond values were good, they put in and tested two or more extra testing nails before the main work started. Also, about 5% of the nails used in the project were tested often to keep checking the bond's quality.

Checking and Results

A full check system was put in place to see how the wall did during and after it was built, making sure it met what the design hoped for.

Tools for Checking and Gathering Data

To watch for any shifts in the wall and the land, the team used common tools during the build. They placed inclinometers by the wall to catch any side moves or bending. They also put survey points on top of the wall and its shotcrete side to keep an eye on both up and down and side shifts. Plus, they put settlement plates behind the wall to watch the earth moves in the kept soil mass. Regular looks at the data let the team see trends and do engineering checks when needed. These tools and ways gave a clear view of how the wall was doing at each step of the project.

Wall Moves vs. What Was Thought

The checks showed that the wall moves and earth sits were all in the design's safe zone. Using a stage-by-stage build method worked well, as it let the team catch and handle small shifts early on. All through the time they kept an eye on it, the wall did just as the design said it would.

Making Sure Things Were Right and Keeping Records

Making sure things were done right was key to the project's win. Tests for how much load the wall could take and the grout’s strength showed that the setup met all the design's needs. Full as-built drawings showed how it was put in place and any changes made in the field. Daily check reports kept track of how the dug areas looked and marked spots where more temporary holds or better water flow help were needed. This careful keeping of records not just made sure the wall met all design rules but also gave good tips for making future projects better.

Work Outcomes and Simple Learnings

The team at McCarthy | Watry Design, Inc. finished the job in 2016, on time and $500,000 less than planned. From a full budget of $21,000,000, the task took out 53,000 cubic yards of earth. The ongoing use of the soil-nail wall method for making the campus larger shows it works well and does the job right. These results show that this system works as a good answer for more growth work in the future.

FAQs

How did the group make sure the wall of dirt and nails was safe and steady while they built at Marin General Hospital?

The group set up the dirt-nail wall to be a forever side hold system to keep it safe and steady. By pushing dirt nails deep into the rocky hillside, they made it strong, stopping any shift and building a firm base for the new car park.

This wall was made to reach 40 feet high, using smart building plans and safety steps to keep it steady. Working on the site's hard parts took top skills and careful plans, all to end up with a strong, lasting fix.

Why did the Marin General Hospital soil-nail wall expansion project keep to its time frame and stay within money limits?

The Marin General Hospital soil-nail wall expansion project did well because of good planning, new work ways, and direct site control. By using top soil-nail methods and keeping a close watch all through, the team kept on track and cut down extra costs.

Also, smooth teamwork between contractors and picking tools and stuff right for the hard land made sure the work was fast and cheap. These joint actions helped keep the project on budget while still getting top-quality outcomes.