Bay Area Structural Shoring: Commercial & Residential Emergency Support
- Joe Lazzaretti
- Jan 2
- 14 min read
Updated: Jan 2
The Bay Area faces constant risks from earthquakes, unstable soil, and aging buildings. Emergency shoring is critical to protect structures - both commercial and residential - from collapse during seismic activity or construction. Here's what you need to know:
Earthquake Risk: A 72% chance of a 6.7+ magnitude earthquake in the next 30 years.
Soil Instability: Liquefaction and settlement in areas with soft soils like bay mud.
Aging Structures: Over 80% of San Francisco homes were built before 1980, often lacking seismic reinforcements.
Shoring Techniques: Methods like soldier piles, tiebacks, and underpinning stabilize structures while adhering to strict California building codes.
Emergency shoring ensures safety, stabilizes foundations, and prevents catastrophic failures. Whether addressing seismic retrofits or excavation support, professional solutions are essential for the Bay Area's unique challenges.
What Causes Structural Emergencies in the Bay Area
Earthquakes and Seismic Activity
The Bay Area is crisscrossed by active fault lines, including the notorious San Andreas fault, which can unleash powerful seismic energy [6]. Buildings not designed to handle these forces face severe risks. For instance, steel structures from the 1960s to 1990s and wood-framed apartments with open ground floors are particularly prone to damage. San Francisco has flagged 4,921 soft-story buildings for seismic upgrades, while Oakland and San Jose have identified 1,500 and 1,400, respectively [7]. These buildings often lack sufficient shear walls, leaving them vulnerable to collapse when the first floor gives way under lateral pressure.
"The challenge is that the older buildings are not up to those codes. When it comes to building safety, it comes down to when it was built." - Richard Allen, Seismologist, UC Berkeley [7]
Adding to the risk, local soil conditions can worsen the structural instability caused by earthquakes.
Soil Conditions and Ground Movement
The Bay Area's soil composition plays a major role in structural emergencies. Liquefaction and ground settlement are common in areas with deep, soft soils, such as Holocene bay mud beneath artificial fills. These conditions amplify ground shaking compared to more stable rock or stiff alluvium [6]. During the 1989 Loma Prieta earthquake, bayshore fills experienced peak accelerations of 0.11 to 0.29 g, significantly higher than the 0.08 to 0.12 g recorded at rock sites [6].
Uncompacted hydraulic fills are especially problematic. In October 1989, the Port of Oakland's Marine Container Terminal at Seventh Street settled by 0.3 meters due to liquefaction, leading to crane rail failures and damage to the piles supporting the wharves [6]. Similarly, the San Francisco-Oakland Bay Bridge Toll Plaza mole experienced 40 cm of differential settlement, resulting in pavement cracks up to 8 cm wide and damage to underground utilities [6].
But natural forces aren't the only culprits - older construction methods also contribute to these dangers.
Old Buildings and Poor Construction Methods
In San Francisco County, 81% of housing units were built before 1980, many without proper seismic reinforcements [9]. These older structures often lack anchor bolts, braced cripple walls, or foundations designed to handle anything beyond gravity loads.
"The majority of damaged structures had not been strengthened to increase earthquake resistance. Except for two deaths from landslides and one from fire, the remainder of the 62 deaths from the earthquake was due to collapse of older structures." - Hai S. Lew, Author, NIST [8]
The 2014 South Napa earthquake underscored this issue. While retrofitted homes remained stable, many older houses shifted off their foundations. Unreinforced masonry buildings and hillside homes on tall, narrow posts without diagonal bracing remain particularly vulnerable to collapse across the region [9].
Concrete Pour: Bay Area Retaining Wall Experts
Emergency Shoring Methods for Commercial Buildings
When emergencies strike commercial buildings, having reliable shoring systems in place is essential. These systems not only stabilize the structure but also protect nearby assets, utilities, and transit lines.
Soldier Piles and Lagging Systems
Soldier piles paired with lagging are a go-to solution for stabilizing excavations up to 40 feet deep. This method involves driving steel H-beams or I-beams vertically into pre-drilled holes, which are then backfilled with concrete to create a sturdy foundation. As the excavation progresses, timber lagging (at least 3 inches thick and with moisture content under 19%) is placed between the piles to hold back the soil [10].
Take the 1100 Broadway project in Oakland, for example. Engineers used soldier beams with wood lagging, tiebacks, and internal bracing to secure a 20-foot deep excavation at the bustling corner of 12th Street and Broadway [4]. The system maintained vertical deviation to less than 0.5% [10]. To prevent hydrostatic pressure, sand was packed between the lagging and the excavation face, allowing the system to drain freely [10].
Another impressive example is the Molecular Foundry project at Lawrence Berkeley National Laboratory. Here, a 68-foot deep excavation on a steep hillside required a combination of soldier beams, tiebacks, and shotcrete to handle the challenging terrain and depth [4]. California regulations stipulate that shoring systems over 14 feet must be designed and approved by a registered civil engineer, with a minimum design load of 100 pounds per square foot [3].
These methods are especially useful in tight, urban environments where space is limited, and stability is paramount.
Sheet Piles and Secant Piles
Sheet piling is another effective approach, particularly for projects near water. Prefabricated steel sections (U or Z shapes) are driven into the ground using a Vibro hammer, providing both soil retention and water resistance [11]. For urban areas where buildings are closely packed, secant piles offer a more tailored solution. This method involves overlapping concrete piles - alternating between unreinforced "soft" piles (20 N/mm² strength) and reinforced "hard" piles (40 N/mm² strength) - to create a watertight barrier [10]. Guide walls, which ensure proper alignment of boring equipment, must be at least 500 mm deep with a shoulder width of 300 mm [10].
A noteworthy example is the 30 Otis project in San Francisco. Here, a 30-foot deep excavation was stabilized using a soil-cement cut-off system, soldier beams, and tiebacks. Additionally, slant-drilled underpinning was employed to protect nearby three-story brick and two-story wood-framed buildings [4][12].
Tiebacks and Anchors
For added lateral support, tiebacks and anchors are often integrated into shoring systems. Tiebacks anchor walls into stable soil or bedrock, transferring loads through a capping beam. Steel anchors are drilled at an angle through the wall, grouted into place, and tensioned to distribute forces evenly [10].
At 1900 Broadway in Oakland, a shoring system was designed for an excavation exceeding 30 feet in depth. This system protected the nearby 19th Street BART Station while avoiding interference with underground utilities [4]. California building codes require that lateral loads be resisted at each floor level by diagonal bracing or similar measures, with resistance calculated at no less than 100 pounds per lineal foot of floor edge or 2% of the total dead load - whichever is greater [3].
"Shoring has to work during normal digging AND during an earthquake. That's a pretty big ask." - West Coast Drilling Co. [13]
To ensure stability, the base of the shoring system must extend at least 5 feet below the excavation depth or reach bedrock [10]. A project at a Porsche dealership in San Francisco demonstrated the efficiency of this approach. The shoring design allowed for the demolition and construction of new foundations, saving the client $100,000 and speeding up the timeline by over two months [14].
These strategies for commercial shoring lay the groundwork for more specialized approaches in residential settings, which will be covered next.
Emergency Shoring Methods for Residential Properties
Residential properties present unique challenges when it comes to shoring. Unlike commercial buildings, homes often have limited space and are occupied daily, meaning the methods used need to be precise, minimally invasive, and cost-conscious. These specialized techniques are designed to address the specific demands of residential structures without causing significant disruption.
Underpinning and Foundation Reinforcement
When a home's foundation starts to sink or crack, underpinning is a go-to solution for stabilizing the structure. Techniques like helical piers and push piers are commonly used to lift and secure foundations, often backed by warranties that can last up to 25 years [16].
"Our helical pier and deep driven pile systems can address many of these concerns [unlevel flooring, cracked concrete] with the underpinning process." - Foundation Solutions [16]
In tight spaces or areas with nearby structures, micropiles are an excellent option. These small-diameter steel rods, grouted into place, provide high load-bearing capacity without causing vibrations that could damage neighboring homes [5][18]. For example, at the 270 Brannan Office Building in San Francisco, engineers used groups of micropiles to stabilize shear walls through 60 feet of compressible soil and liquefiable fill. This method is equally effective for residential properties facing similar soil challenges [15].
In cases where properties are hemmed in by adjacent buildings, slant-drill underpinning offers a practical alternative. A notable example is the Symphony Towers project in San Francisco, where engineers used slant-drilled supports to stabilize five buildings, navigating challenging dune sand conditions at depths of up to 35 feet [4]. Homeowners should keep an eye out for early warning signs of foundation issues, such as gaps between baseboards and floors or doors and windows that no longer align properly. Addressing these problems early can make emergency shoring far more effective [16].
Temporary Bracing and Hydraulic Shoring
When immediate stabilization is required, hydraulic shoring provides a fast and reliable solution. Hydraulic pistons push outward to brace walls, delivering instant support for shifting foundations or trench work [17]. This speed makes hydraulic systems ideal for emergencies where quick action is critical.
For short-term fixes with lighter structural loads, timber bracing is a budget-friendly option. Wooden beams can provide adequate support for smaller projects without the cost of more advanced systems [17]. However, for deeper or more complex repairs, steel shoring systems offer the strength and durability needed to transition to permanent solutions [5][17].
Choosing the right method depends on the situation. Hydraulic shoring is perfect for urgent scenarios, timber bracing works well for cost-conscious projects, and micropiles or helical piers are ideal for tight spaces where low-clearance equipment is required [5][18]. In California, residential projects taller than 14 feet must use engineer-designed systems that account for the unique challenges of occupied homes [3].
How the Emergency Shoring Process Works
Emergency shoring involves three key phases: assessment, installation, and removal. Each step requires strict adherence to engineering standards and safety protocols, especially in areas like the Bay Area, where seismic activity and challenging soil conditions demand extra care. These steps ensure stability throughout the process while aligning with the shoring techniques mentioned earlier to meet rigorous safety and performance requirements.
Site Evaluation and Structural Analysis
The process starts with engineers conducting an on-site evaluation to assess the structure's condition. This analysis focuses on two main factors: soil stability and load requirements. The soil must be stable enough to support vertical members, and engineers also consider potential changes caused by weather or nearby construction activity [3]. Historic facades and unreinforced masonry buildings, which are common in San Francisco, often require additional attention [2].
Each shoring design must meet specific load standards, such as a minimum total design load of 100 pounds per square foot for combined live and dead loads [3]. Engineers also calculate lateral loads, which are supported by diagonal bracing at a minimum of 100 pounds per lineal foot of floor edge or 2% of the total dead load, whichever is greater [3]. For structures taller than 14 feet or spanning more than 16 feet, a registered civil engineer must approve and sign off on detailed calculations and drawings [3]. In the Bay Area, evaluations often follow the ATC-20 Post-Earthquake Safety Evaluation of Buildings standards to ensure stability after seismic events [2].
Installation and Monitoring
Once the design is approved, the next step is to create a stable base for vertical supports. Engineers must verify the soil's ability to bear the required load before installation begins [3]. For more complex setups, a registered civil engineer or an authorized representative must inspect the system and certify in writing that it complies with the approved design before any material is loaded [3].
Safety measures include installing protective guardrails around the perimeter after the supports are in place [3]. Engineers conduct regular inspections throughout the project, reviewing shop drawings, addressing questions, and confirming the system’s stability [2]. If motorized carts are used on the shored surface, the design load must be increased by an additional 25 pounds per square foot [3]. A copy of the shoring layout and the engineer’s certification must remain onsite to ensure compliance [3]. Once the installation is secure and monitoring is ongoing, the process moves to the final phase: safe removal.
Removing Shoring and Project Completion
Shoring systems can only be removed once the supported structure has gained enough strength to handle its weight and any applied loads [3]. For concrete structures, this means waiting until the material reaches the specified strength outlined in the engineering plans. Structures exceeding 14 feet in height or 16 feet in span require inspection by a registered civil engineer, who must certify that the transition to permanent structural elements has been carried out correctly [3].
During removal, stripped forms and shoring materials must be stockpiled promptly. Any protruding nails, wire ties, or temporary accessories must be removed or cut to prevent tripping or puncture hazards [3]. For example, at the San Francisco Conservatory of Music, engineers designed temporary support for a historic facade over 100 feet tall, including underpinning for a basement excavation before transitioning to a permanent mat foundation [2]. Similarly, during the California Memorial Stadium retrofit in Berkeley, temporary shoring supported the historic west wall while permanent seismic reinforcements were integrated, preserving the integrity of the original masonry [2].
Bay Area Emergency Shoring Projects
Emergency shoring techniques come to life in various real-world projects across the Bay Area. These examples highlight how these methods solve structural challenges in both commercial and residential settings.
Commercial Project: San Francisco Office Building
In March 2019, the Fox Plaza Tower in San Francisco - a 30-story office building - underwent a seismic retrofit that lasted 10 months. Plant Construction Company led the project, addressing complex beam-to-column issues by conducting full-scale tests at UC San Diego. The solution involved installing 14 viscous dampers on the lower floors to minimize drift, while also reinforcing the upper connections. This method kept beam rotations under 0.02 radians and limited tenant displacement to under 5%, thanks to phased unit construction that allowed the building to stay partially operational throughout the project [1].
Residential Project: Oakland Family Home
Shoring projects for residential properties, like an Oakland family home, require a more customized approach due to space constraints and the need to maintain occupancy. The process starts with a licensed engineer drafting a site-specific plan. Temporary shoring is installed to stabilize the home, especially when soil movement jeopardizes the foundation's integrity. Once stabilized, crews demolish the damaged foundation sections to reach stable soil. In densely populated areas, such as those near BART stations, excavations often exceed 30 feet. These conditions demand careful coordination of shoring, demolition, and reconstruction to ensure safety and efficiency [19][20][4].
Building Codes and Seismic Requirements for Bay Area Shoring
Emergency shoring in the Bay Area must comply with stringent state and local regulations to ensure the safety of both structures and workers. The California Code of Regulations (CCR) Title 8, Section 1717 outlines the standards for designing, erecting, and inspecting shoring systems. These systems must be capable of safely handling all expected loads during both construction and removal phases [3][22]. For shoring taller than 14 feet or spanning over 16 feet, detailed design calculations and drawings signed by a California-registered civil engineer are mandatory [3][22]. These regulations form the foundation for more specific load and inspection requirements.
Building Codes and Permits
State law requires shoring systems to be designed for a minimum total load of 100 pounds per square foot (psf), accounting for both live and dead loads. Additionally, lateral loads must be resisted at each floor using diagonal bracing or other methods, calculated at a minimum of 100 pounds per lineal foot of floor edge or 2% of the total dead load, whichever is greater [3][22]. Before concrete placement or any supported work begins, a registered civil engineer or authorized representative must inspect the shoring and provide written certification confirming compliance with approved drawings. A shoring layout or falsework plan must also be accessible at the job site at all times [3][22].
The San Francisco Building Code (SFBC) Chapter 16 adds further structural requirements, such as live load standards for sidewalks (250 psf) and driveways, which follow AASHTO HS-20 guidelines. These requirements may impact shoring installations [21]. Vertical supports must be set on properly compacted, level, and stable bases, with soil load-bearing capacity verified to handle applied loads, including potential weather-related impacts [3]. Beyond these structural considerations, seismic safety introduces additional complexities.
Seismic Retrofitting Requirements
Shoring and retrofit designs in the Bay Area must account for seismic forces using base shear calculations. This involves multiplying the expected ground acceleration by the building's weight to determine the force the structure must withstand [23]. With a 72% probability of at least one magnitude 6.7 or greater earthquake striking the San Francisco Bay Area between 2014 and 2044, these calculations are critical [9]. Compounding the risk, about 81% of housing units in San Francisco County were built before 1980, meaning they were constructed without modern seismic standards [9].
For retrofits, the International Existing Building Code (IEBC) allows using 75% of the base shear required for new construction [23]. Similarly, the California Historic Building Code permits reduced lateral force requirements for historic structures, also at 0.75 times the standard code forces [23]. Specific regional guidelines, such as Standard Plan A and FEMA P-1100 (ICC 1300), provide detailed methods for strengthening wood-frame buildings. For example, Standard Plan A uses the formula V = 0.186W to calculate base shear [23]. Retrofitting homes can be a cost-effective investment, as homeowners may save between $10,000 and $200,000 in earthquake repair costs. Typical residential retrofits for homes with raised foundations generally cost between $3,000 and $7,000 [9].
Conclusion
Emergency shoring plays a vital role in safeguarding lives and property, especially in the Bay Area, where seismic activity is a constant concern. Whether it's stabilizing a high-rise project or addressing residential foundation issues, customized shoring solutions are key to managing the unique challenges of this region. Beyond just safety, professional shoring services ensure adherence to California's strict regulations, protect nearby structures, and help avoid failures that could impact critical infrastructure - all while addressing the complexities of local geology and building codes.
Golden Gate Shoring offers reliable emergency structural support services across the Bay Area. With licensed engineers and proven construction methods, their team is ready to respond to structural emergencies 24/7. They bring years of experience working in challenging conditions, such as near BART stations, supporting unreinforced masonry walls, and managing the area's tricky soil conditions.
If you're dealing with a structural emergency or preparing for seismic retrofitting, Golden Gate Shoring is ready to help. Their engineers will assess your site, design a compliant shoring system, and handle the installation with the urgency your situation requires. Don’t wait until the next earthquake - take action now to protect your property and ensure safety.
FAQs
What are the most common shoring methods used for residential projects in the Bay Area?
In the Bay Area, residential shoring projects typically rely on three main techniques to maintain structural stability during repairs or renovations.
Raking shoring uses angled braces to support walls and counteract lateral forces. This method is particularly useful for tasks like basement excavations or when removing a load-bearing wall. Dead shoring, on the other hand, provides vertical support to beams or floors when columns or other structural elements are temporarily removed. For below-grade projects - such as basement retrofits or utility trenches - trench shoring is the go-to method. It prevents soil collapse by using hydraulic systems combined with timber lagging.
In certain situations, especially when dealing with historic or masonry walls, flying shoring comes into play. This technique spans openings without requiring ground contact. Each method is carefully selected to address the Bay Area’s specific seismic challenges and soil conditions, all while ensuring adherence to California’s strict construction regulations.
How does unstable soil cause structural emergencies during earthquakes?
During an earthquake, unstable soil conditions like liquefaction or lateral spreading can wreak havoc on structures. These phenomena weaken the soil's ability to support foundations, which can cause buildings to tilt, shift, or even collapse. The result? Immediate safety hazards that often call for emergency measures to stabilize the structure.
When the ground loses its strength or begins to deform, the foundation's stability is at serious risk. This creates urgent situations where fast and effective solutions are critical. Using the right shoring techniques can help stabilize the structure, reduce risks, and prevent further damage to homes and commercial buildings alike.
What are the main steps in the emergency shoring process?
The emergency shoring process kicks off with a swift on-site evaluation to pinpoint structural dangers like unstable walls or floors and to assess the loads requiring support. Engineers thoroughly examine the building’s condition, layout, and any immediate risks - such as falling debris or shifting ground - to devise a temporary support plan tailored to the situation.
After the assessment, a specialized engineering design is created to align with safety protocols, including California’s strict regulations. This phase involves choosing the appropriate shoring method - whether it’s raking, trench shoring, or another approach - and prepping the site by removing obstacles and setting up essential equipment. Once the design passes approval, contractors proceed to install and secure the shoring system, ensuring it can bear the necessary loads.
The final step involves continuous monitoring and upkeep of the system during the repair or renovation process. Once permanent structural fixes are in place, the temporary shoring is carefully dismantled. This step-by-step approach ensures the structure remains safe and stable throughout the emergency response.
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