Recommendations and Design

Following a site investigation program, the information is evaluated and engineering analysis performed to develop the most appropriate recommendations for the project. For some projects, it is the geotechnical engineering recommendations only that are required to allow the design team to proceed with their work. Our knowledge and experience with a wide variety of projects gives us a unique understanding of the design and construction requirements in order to provide recommended and alternate systems and their appropriate design parameters. We provide recommendations for:

Because of our experience working for various public and private agencies, we are familiar with the policies and procedures for providing geotechnical design recommendations according to the most current requirements.

Yeh and Associates also believes that the geotechnical engineer should be a part of the design team and as such we also provide geotechnical design services for:

Landslide Stabilization

Foundations

The most appropriate foundation system should be selected based on geotechnical, geologic and groundwater conditions, lateral and vertical load demands, and construction considerations. We have extensive experience with foundation systems, from small bridges in complex geologic conditions to historic structures on constrained sites to large heavily-loaded multi-span bridges and high-rise urban buildings. Our expertise in foundation systems includes spread footings, mats, driven piles, drilled shafts, micropiles, post-tensioned slab and composite systems incorporating deep foundations with ground anchors.

With our years of experience working within AASHTO and FHWA guidelines, we are intimately familiar with the policies and procedures for providing foundation design recommendations according to the most current requirements. We are well versed in the current design requirements covered in the AASHTO Specifications for Highway Bridges 16th Edition both under Service Load Design and Load and Resistance Factor Design procedures.

Retaining Wall Design

We are experienced in designing all types of wall systems, including: concrete cantilever, ground anchor, mechanically stabilized earth (MSE), gravity systems, soil nail, soldier pile, drilled shaft, and micropile walls. Our design of the most appropriate wall type for a cut or fill is based on the soils, rock and groundwater conditions and the aesthetics, cost, and performance considerations prescribed by our clients.

Wall design analysis and recommendations are provided in accordance with the most current design requirements. Our MSE wall designs utilize the recently released program MSEW and our soil nail design procedures follow the Manual for Design and Construction Monitoring of Soil Nail Walls.

Landslides

Several of the Yeh and Associates staff are contributing authors to the Transportation Research Board publication Landslides, Investigation and Mitigation.
Beginning with reconnaissance, our engineers and geologists make a preliminary assessment of the type of slide and its feasibility for remediation. Our personnel are experts in exploration and instrumentation of landslides to understand their mode of initiation and movement. This is critical to determining the appropriate engineering solution.

We offer multiple options for landslide stabilization in which cost, constructability, and factor of safety are the integral components. We provide emergency response services to local government agencies, including CDOT, and railroads to effect quick temporary remedial measures so roadways and railways can be re-opened safely.

Geologic Hazards

Yeh and Associates is considered a national leader in geologic hazard assessment. Our experience includes rockfall, debris/mud flows, avalanche, collapsible soils, sensitive and swelling clays, and mining hazards and subsidence.

Our staff has participated in the development of many of the rockfall hazard rating systems used in the United States including the most widely used rockfall modeling software, the Colorado Rockfall Simulation Program. In addition to evaluating geologic hazards, we also provide design services to mitigate rockfall hazards. We have participated in the testing of rockfall barriers, which we have designed and have worked to establish the standards used for barrier design.

Slopes

We are experienced in slope stability evaluation and analysis, slope stabilization measures including rock mechanics and rock slope stability throughout the United States. Our services include geologic mapping, site investigations, evaluating slope stability and designing new excavations and stabilization measures for existing slopes.

Our staff has developed rock sculpting methods for appropriate structural conditions to simulate weathered rock slopes in aesthetically sensitive areas. We have assisted transportation agencies, municipalities, and public utilities with designs for construction or stabilization of soil and rock slopes. We are currently under contract to the CDOT to develop a manual of practice for rock slope stabilization.

Fill

For fills, whether for roadway embankments, dams or site grading for development, the existing soil and rock conditions are explored and fill parameters developed so that earthwork on the project can be optimized. Swell factors are established for soil or bedrock excavations based on the material type and excavation or blasting methods. Shrink factors are given based on the fill material properties and placement requirements for density and moisture. Slope stability for the fills is evaluated based on our experience with a wide range of soil and rock materials and our analysis using current computer programs and other methods. We work closely with our clients to obtain the most practical and effective borrow excavation and fill design. Through our design studies, we prepare recommendations for site preparation, grading, fill materials, fill placement and compaction, and excavation support and drainage based on subsurface conditions encountered and the project needs.

Erosion

Yeh and Associates provides innovative design solutions to difficult soil stability issues. Our experience ranges from traditional erosion control through effective cut and fill slope designs to active mitigation measures in sensitive high altitude, alpine tundra environments. We have worked closely with U.S. Forest Service specialists on many of our projects to develop effective measures to stabilize soil erosion resulting from poor construction practices in the past.

Pavement Design

Pavement design recommendations are provided for review and compliance with the local governing agency. Localized areas of poor subgrade that have been identified receive specific recommendations including over excavation and replacement with select material, chemical stabilization, and/or reinforcement with geosynthetics. Many of the staff members at Yeh and Associates have extensive experience working on projects involving pavement design and reconstruction and subgrade rehabilitation.

Tunnel Engineering

Yeh and Associates has provided engineering and management services on nearly all of the highway tunnels in the state of Colorado. Our personnel serve on several national committees on tunneling and underground structures.

With this experience, we are able to provide clients with a full-range of tunnel engineering services including feasibility studies, route selection, assessment of local geology, geotechnical/geological investigations, management consulting, preliminary and final design, and construction engineering.

Underground works and tunneling can provide outstanding possibilities for resolution of limited space constraint challenges. However, creation of underground structures is usually an expensive and difficult undertaking. With our unique experience and successful record, our clients can be assured of a well-integrated, multi-disciplinary approach to their tunnel engineering needs.

Ground Modification

Yeh and Associates staff is familiar with and has used most of the current ground modification techniques. We are also working with the FHWA on a manual of practice for ground modification using injection of polyurethane resins. Where site conditions or project requirements dictate modification of the existing soil properties, we can provide the recommendations for the appropriate modification techniques and design the application methodology depending on the technique selected. On several of our projects, the use of ground modification resulted in significant saving in construction by eliminating costly construction methods intended to mitigate the site conditions.