DHLA has provided geotechnical services for various projects within nine southern California counties (Los Angeles, Orange, Riverside, San Bernardino, San Diego, Imperial, San Luis Obispo, Santa Barbara, and Ventura). Our firm offers a wide range of geotechnical services for both new development projects and for existing sites and structures affected by geotechnical problems.
Third-Party Geotechnical Review
DHLA has provided third-party geotechnical and geological review services for numerous development projects. These services have been provided to private developers as well as public agencies.
These reviews verify report compliance with grading and building code requirements, and with the standards of practice for the geologic and geotechnical engineering aspects of new residential and commercial projects.
Mr. Lee also performs Peer Reviews for the California Board of Professional Engineers and Land Surveyors.
New Building Developments
DHLA has conducted geotechnical design and construction services for various new development projects, including residential buildings, commercial/retail and industrial structures, fire station facilities, multi-level parking structures, retaining walls, and other appurtenances.
Our project experience also includes infrastructure projects such as roadway improvements, bridges, flood control, pipelines, harbor studies, and shipyard improvements.
We are experienced in evaluating many types of geologic seismic hazards, including special studies zones, historical and probabilistic seismicity, liquefaction, and landslides.
Our services include, but are not limited to, geotechnical and geologic investigations, laboratory testing, seismic studies, slope stability analysis, shallow and deep foundation design, geotechnical reports, plan review, construction observation/testing and foundation excavation inspection, and quality control during construction.
Typically, our due diligence as the responsible geotechnical/geologic firm on a new project includes a thorough evaluation of applicable geologic hazards, site-specific engineering design in accordance with applicable state and local codes, review of the project plans/specifications to verify conformance with the geotechnical design, and final grading certification.
Evaluation and Stabilization of Landslides
DHLA has performed numerous geologic and geotechnical evaluations of landslides and slope failures. Our services have been provided on an emergency on-call basis, as well as through a standard proposal bidding process, for various clients including property managers, insurance claim adjusters, law firms, and public agencies. Many of these projects have involved site inspection, geologic mapping, subsurface investigation by drilling/trenching (including down hole logging by a Certified Engineering Geologist), instrumentation installation and monitoring, slope stability analysis, geotechnical design of cost-effective construction mitigation, construction monitoring, and field testing.
Case Example: Via Cerro Rebal Landslide Stabilization
DHLA is especially proud of the design work we performed for the stabilization of a large, active landslide in a residential community in the City of San Juan Capistrano, California, known as the Via Cerro Rebal Landslide Stabilization. In late 1997 to early 1998, a large, ancient landslide had re-activated as a consequence of the heavy El Niño rainstorms. The landslide occurred in a park site, and was initially believed to be confined within the park. Subsequent exploration, and installation and monitoring of slope inclinometer casings, disclosed that the slide was moving and threatened a number of residences downslope. Stability analyses indicated that the only practical method of remediation was the use of high-capacity tieback anchors. DHLA provided the geotechnical design and construction monitoring for a tieback anchor and grade beam system, with over 860 high-capacity (300- to 365-kip) permanent tieback anchors to stabilize the landslide, and remedial grading to restore the slope face. Mr. David H. Lee, our principal geotechnical engineer, co-authored a technical article on the Via Cerro Rebal Landslide Stabilization project for an ADSC publication. This project also won the 2002-2003 Outstanding Project Honorable Mention Award from the California Geotechnical Engineers Association (CGEA).
Case Example: Pegasus Street Landslide Stabilization
DHLA also provided the design work for the stabilization of an active landslide in a 100-foot-high cut slope on a residential cul-de-sac in the City of Anaheim, California, known as the Pegasus Street Landslide Stabilization. During the rainy season of 1978-1979, a large, deep-seated landslide had mobilized and damaged two homes. Subsequent forensic investigations revealed a number of possible causes for the landslide, namely, (a) adversely oriented and continuous slip surfaces present beneath a shallow, compacted fill buttress, (b) elevated groundwater levels caused by heavy rainfall and exacerbated by landscape irrigation, (c) the placement of fills without adequate subdrainage, and (d) inadequate design of the slope.
In 1999, DHLA was retained to evaluate the landslide. Preliminary stability analysis supported what had been established some years earlier, namely, that lowering the groundwater table through a permanent dewatering program would only marginally increase the static long-term factor of safety, and that another method would be required to stabilize the landslide.
DHLA provided the geotechnical design and construction monitoring for a tieback anchor and grade beam system, with 127 permanent tieback anchors loaded to 100- and 150-kips, and remedial grading to restore the slope face.
Assessments of Structural Damage Caused by Geotechnical Problems
A large portion of DHLA’s consulting practice is concerned with providing expert geotechnical engineering services in the evaluation of structural damages for insurance and litigation claims that have arisen as a consequence of ground movement (i.e. landslides, mudflows, and debris flows), flooding, settlement, heavy rains, groundwater migration, and construction defects. We have also provided insurance assessments and repair designs for structures damaged during several major seismic events in central and southern California, including the Sierra Madre, Landers, Big Bear, Northridge, and San Simeon Earthquakes. Our services have been provided on an emergency on-call basis, and also according to a less urgent timetable. Many structural damage assessment projects have involved site inspection, subsurface investigation, instrumentation installation and monitoring, research pertaining to site geology and rainfall records, seismic ground motion studies, geotechnical design of cost-effective construction mitigation, construction monitoring and field testing. Our professionals often collaborate with structural engineers to provide a more complete damage evaluation and repair design for our clients. When implemented, typical repairs have included contact grouting, compaction grouting, mechanical jacking, foundation underpinning, soil nails, tieback anchor systems, re-grading, subsurface and surface drainage improvements, etc., to mitigate geologic and geotechnical hazards.
Case Example: Weseloh & Sons MSE Wall Repair
DHLA provided a geotechnical and geologic evaluation into the cause of failure in a newly constructed, 650-foot-long, 30-foot-high Mechanically Stabilized Earth (MSE) wall at an automobile dealership in the City of San Juan Capistrano, California. The existing wall was constructed at the top of a natural slope that descended approximately 75 feet to the Metrolink railroad below. An approximately 80-foot section of the wall failed near the completion of the wall’s construction due to settlement within a poorly compacted fill, and a consequent irrigation line break. Subsequent forensic investigations revealed a number of construction-related problems in need of mitigation, without which, the remaining portion of the wall was deemed likely to fail. Additionally, the client preferred to supplement the wall repair with a new import fill pad further downslope supported by a new Reinforced Earth wall.
DHLA provided the geotechnical design and construction monitoring for several phases of construction, including compaction grouting within the existing wall backfill, installation of 122 tieback anchors loaded from 47 to 91 kips, installing 121 temporary soil nails and 62 permanent soil nails, temporary excavations, and observation and testing of fill placement.
Case Example: San Simeon Earthquake Damage Assessment
DHLA provided structural damage assessment and seismic ground motion studies for approximately 75 properties in the central coast region of California, including residential, commercial, and industrial buildings, following the Magnitude 6.5 San Simeon Earthquake of December 22, 2003. Many of the properties were red-and yellow-tagged after they sustained heavy damage. Our services assisted insurance carriers in processing claims.