Building Retaining Walls to Withstand Nature’s Fury: Essential Seismic Design Considerations for Benton County Properties
In earthquake-active Benton County, Washington, constructing a retaining wall requires more than just basic engineering—it demands specialized seismic design considerations that can mean the difference between structural integrity and catastrophic failure when the ground starts shaking. Washington has the second highest risk in the U.S. of these large and damaging earthquakes because of its geologic setting. For property owners in this seismically active region, understanding these critical design factors is essential for protecting both your investment and your safety.
Understanding the Seismic Reality in Benton County
Earthquakes occur nearly every day in Washington. Most are too small to be felt or cause damage. However, the potential for significant seismic events in the region cannot be ignored. Based on data from the past 55 years and our earthquake archive back to 1900, there are about 2,700 quakes on average per year in or near Washington State, USA, making proper seismic design crucial for any retaining structure.
The seismic environment in Benton County is influenced by several geological factors, including proximity to major fault systems and the complex tectonic setting of the Pacific Northwest. This reality makes it imperative that retaining walls be designed to withstand not just static earth pressures, but also the dynamic forces generated during earthquakes.
Key Seismic Design Principles for Retaining Walls
When designing retaining walls for seismic conditions, engineers must consider several critical factors that differ significantly from standard static design approaches. The program computes KAE (coefficient for combined active and earthquake forces) per the Coulomb formula, modified by Mononobe-Okabe/Seed-Whitman, to account for earthquake loading, which represents the fundamental approach to seismic retaining wall design.
The Mononobe-Okabe equation is the modification of coulomb equation and it considers seismic forces. This methodology accounts for both horizontal and vertical ground accelerations, providing a more accurate assessment of the forces that will act on the retaining structure during an earthquake.
Critical Design Considerations
Several specific factors must be addressed when designing retaining walls in seismic zones:
- Ground Acceleration Parameters: Common kh values range from 0.05 to 0.30, depending upon area seismicity. Some sources indicate that kh = SDS / 2.5, but jurisdictions and interpretations vary.
- Wall Movement Tolerance: If the structural designer reviews the design and agrees that average permanent wall movements of 1 to 2 inches at the excavation level are acceptable, the seismic coefficient used for design (after reducing for scattering effects) can be further reduced by a factor of up to 0.5. The acceptability of the 0.5 factor is based on several considerations
- Drainage Systems: Proper drainage becomes even more critical in seismic design, as the presence of water in the backfill further increase the dynamic pressure during seismic excitation
Performance-Based Design Approach
Modern seismic design for retaining walls emphasizes performance-based approaches that allow for controlled movement rather than rigid resistance. For these systems, energy dissipation on shaking, leading to reduced inertia forces, can be achieved by allowing the activation of ductile plastic mechanisms. These must be correctly identified to guarantee the desired strength hierarchy
This approach recognizes that some movement during seismic events is not only acceptable but can actually improve the overall performance of the structure by reducing the forces transmitted to the foundation and surrounding soil.
Material and Construction Considerations
The choice of retaining wall system can significantly impact seismic performance. When properly designed and constructed, these systems seem well suited for handling seismic conditions. The wall facing, soil mass and geosynthetic reinforcement all moved in phase with the earthquake induced forces. Structures that are both flexible and coherent are ideal for these conditions
For properties in Benton County, working with experienced professionals who understand both local seismic conditions and construction requirements is essential. Designer must understand the local seismic code requirements before starting design.
Professional Expertise Matters
Given the complexity of seismic retaining wall design, it’s crucial to work with contractors who have specific experience in earthquake-resistant construction. When searching for a qualified retaining wall contractor Benton County, WA, look for professionals who understand the unique seismic challenges of the region and can provide comprehensive design and construction services.
Local contractors like Nailed It Construction TC bring valuable regional expertise to seismic retaining wall projects. Based in Kennewick, WA, we understand the unique needs of Tri-Cities properties, from navigating local building codes to choosing materials suited for Eastern Washington’s climate. With over 30 years of experience in the industry, we take pride in our reputation for high-quality craftsmanship, attention to detail, and unwavering dedication to our clients.
Code Compliance and Safety Factors
Seismic design requirements are not optional recommendations—they’re code requirements for structures in seismically active areas. International Building Code 2009 at section 1613 stated that every structure, and portion thereof, including nonstructural components that are permanently attached to structures and their supports and attachments, shall be designed and constructed to resist the effects of earthquake motions in accordance with ASCE 7. This obviously necessitate the design all structures for earthquake loads.
Safety factors for seismic conditions are also different from static design. Safety factor for sliding and overturning when earthquake is present is 1.1. These reduced safety factors reflect the temporary nature of seismic loading while still providing adequate protection.
Long-Term Performance and Maintenance
Properly designed seismic retaining walls can provide excellent long-term performance. SRW performance during earthquakes is generally considered to be excellent. Observations of SRWs within 31 miles (50 km) of the epicenter of both the Loma Prieta and Northridge earthquakes have shown that this type of retaining wall system can withstand considerable horizontal and vertical accelerations without experiencing unacceptable deformations.
The key to achieving this level of performance lies in proper initial design, quality construction, and ongoing maintenance that addresses the unique challenges of seismic environments.
Moving Forward with Confidence
For Benton County property owners, the seismic design of retaining walls represents both a challenge and an opportunity. While the additional considerations may seem complex, working with experienced professionals ensures that your retaining wall will not only serve its intended purpose but will do so safely for years to come, even when faced with significant seismic events.
The investment in proper seismic design pays dividends in terms of safety, longevity, and peace of mind. In a region where earthquake activity is a geological reality, there’s simply no substitute for professional expertise and proper engineering when it comes to retaining wall construction.