Client: Sonoma County, CA
Location: Sonoma County, CA
Project: Burn Lot Assessments

The October 2017 North Bay Wildfire was devastating for Sonoma County, CA., especially for the city of Santa Rosa. The fire destroyed approximately 5,300 homes in Sonoma County and left 24 people dead. Our firm was contracted to provide site assessments for 43 sites in Sonoma County, predominantly in the Santa Rosa area, for geotechnical considerations. Of the 43 sites, 35 were determined to not exhibit geological factors impacting them, primarily because the sites had minimal elevation relief and slope stability and erosion potential were not an issue. The remaining 8 sites were determined to require comprehensive site assessments. These site assessments included historical photo review, review of published geologic data, site reconnaissance, engineering and geologic analysis of data to evaluate slope stability, erosion potential, and general hydrology. Our individual Geotechnical Site Assessment reports for these 8 sites provided conclusions regarding geological factors currently impacting the sites, recommendations to mitigate adverse conditions, and our Engineering Estimates for the cost to implement recommended repairs.

At the time of our site reconnaissance for the 8 sites, about three years had passed and the debris left by the fires had generally been cleaned up and hauled off site. In many cases, new residences had already been constructed or were in the process of construction. Vegetation consisted of sparse to moderate growth of annual grasses, weeds, shrubs, and both live and dead trees. Large areas of slopes were near devoid of ground cover and woody vegetation. Some properties had local stands of live, mature trees present. Site drainage, and evidence of erosion and slumping were noted during site reconnaissance.

Erosion protection measures already in place were also noted and their effectiveness assessed. Our Geotechnical Site Assessment reports included descriptions of the regional and local geology, pre-fire and post-fire site conditions, and included before and after fire Google Earth photos.

Our reported conclusions for the 8 sites were generally consistent from site to site. We identified geotechnical issues that affected the properties and that could impact future redevelopment. 

Erosion was found to be the greatest factor of geotechnical concern observed. The importance of established vegetation was stressed as vegetation affects both the surficial and mass stability of slopes, ranging from mechanical reinforcement and restraint by the roots and stems to modification of slope hydrology as a result of soil moisture extraction via evapotranspiration. The loss of slope vegetation because of fire can increase rates of erosion and increase the likelihood of slope failure.

At all the sites it was noted that lack of vegetation had caused excessive erosion on sloping ground, and especially along site drainage paths. We recommended that permanent vegetation be planted as soon as practically possible. However, because sufficient deep roots of new growth can take years to develop sufficient protection, we recommended that interim measures for slope protection mitigation include the installation of stabilizing erosion mats, such as North American Green EroNet SC150, on slope surfaces, attached to the slopes using 11-gauge, 6-inch-long steel staples. As part of the installation, we recommended that herbaceous seeds should be mixed with a humus mixture placed within the entangled mesh and that an irrigation system be provided to sufficiently cover the areas to maintain the healthy growth of plants and to avoid overly dry surface conditions that can lead to excessive surface cracking.

At some locations we recommended temporary drainage weirs be constructed along drainage paths to slow the amount of storm water flow to minimize erosion. These weirs may consist of sandbags embedded 1 feet below grade and extend 2 feet above the drainage surface. These weirs are expected to be effective until adequate plant growth is established to naturally control the water flow.

As part of our site assessment reports, we provided Engineer’s Estimate of Repair Costs for each site. The cost estimates included project setup, mobilization, clear and grub, vermin control, installation of entangled mesh, installation of herbaceous seed and humus, an irrigation system, cleanup, and demobilization. 

These reports were written with the hope that the property owners understand and follow through with our mitigating recommendations, and that their insurance companies understand the importance of these measures and provide the owners with the funds to adequately complete them.

Client: West Basin Municipal Water District (WBMWD)
Location: El Segundo, California
Project: 42-inch Water Line

Ground subsidence of up to 2 feet was observed following the backfill of a 60-inch RCP storm drain pipe that crossed 35 feet under an existing and active 42-inch reclaimed water line for West Basin Municipal Water District (WBMWD) in El Segundo, California. The likely causes were attributed to consolidation of loose storm drain trench backfill and consolidation of native soil disturbed by the installation and removal of sheet piling that had been used along the sides of the storm drain trench during construction.

The storm drain was constructed for the Plaza Del Segundo commercial/retail development by Comstock Crosser & Associates. This firm was contracted by the developer to come up with a plan to mitigate future settlement and resulting damage to the reclaimed water line (RWL). Considering the sand nature of the onsite soil, we proposed that the loose soil supporting the water line be treated with a chemical grout to provide some compaction and to cement the soil, giving it strength to support the RWL, and to treat the remaining loose soil by removals to near the top of the storm drain pipe and water jetting along the sides to consolidate the sand shading. Following the water jetting, the backfill could be replaced with the soil removed, placed in lifts compacted to the specified relative compaction values. These proposed measures were adopted, and we were contracted to develop and oversee the mitigation measures.

This firm developed the construction plans and technical provisions for the work, which included setting up settlement monitoring devices prior to construction, laying out chemical grout injection points and injection sequencing, performing Cone Penetrometer Testing (CPT) within the treatment zone following completion of grouting, providing a sand/cement slurry cradle along and under the RWL, and construction methods for mitigating the loose storm drain backfill.

Prior to the work, we set up 6 settlement plate monitors placed directly on the 42-inch pipe and installed Sondex settlement monitoring devices within the grout treatment zone at 4 locations to monitor settlement during chemical grout operations. Reading of these devices was taken multiple times a day during grouting operations. Minor measurable changes were observed during the initial grouting work resulting in an adjustment of time and distance between injection points to allow curing and hardening of the grout-infused soil.

164 injection points were used to inject grout to varying depths and treatment intervals. The treatment zone was centered on the 42-inch RWL and extended about 24 feet on either side, and from 10 to 15 beyond the centerline of the 60-inch RCP storm drain. The injection points were typically spaced at 2.5-feet center to center.

The injection work was performed by Pressure Grout Company of Long Beach, CA. They provided the drill rig that drilled the injection points, the injection casing, the grout mixing equipment and supplies, and the injection pumping equipment.

Grouting was done in two phases. In the first phase, 5 of the outermost grout rows on both sides of the centerline of the RWL were grouted, and the effects of wetting the underlying soil resulting in collapse were determined through settlement monitor readings. Readings indicated some settlement, and the sequencing of installing casings and injecting were modified to allow more time, at least 5 days for adjacent points, for materials to set before installing and injecting adjacent points.

Grout was injected through a 1-inch diameter PVC pipe, capped at the bottom and with pre-drilled injection holes at 15-inch stages. The injection hose nozzle (packer) had gaskets to seal within the injection hole stages. Injections began at the bottoms and advanced upward in 15-inch increments, injecting a pre-determined quantity of grout, or until injection pressures indicated that the surrounding soil was already well compacted and did not require additional grout. 

Chemical grouting operations were completed in about 30 calendar days. A total of 36,449 gallons of chemical grout was placed within the treatment zone.

Five days after the completion of grouting, Cone Penetrometer Testing (CPT) was performed by Fugro, under our direction and observation, at 6 locations to evaluate the effectiveness of the grout treatment. Project specifications called for the treated material to exhibit an unconfined compressive strength of at least 10 psi or 0.72 tons/sqft. From analyzing the CPT data, we concluded that the treatment met or exceeded the 10 psi target strength.

Following the chemical grout treatment, excavations were made to expose a 36-foot-long section of the 42-inch RWL, centered over the underlying 60-inch storm drain pipe. Excavations were then made to expose the sides and bottom of the RWL. To provide continuous support of the RWL, excavations were made in four alternating sections, each approximately 9 feet in length, to at least 3 feet lateral clearance from the pipe edges, and below the pipe to expose soil treated with chemical grout (but not less than 1 foot). A spray of water and phenolphthalein was used to identify that treated soil was exposed, with the spray turning magenta in color when it reacted with the cement in the grout. 

A representative of WBMWD was present when sections of the pipe were exposed to inspect the condition of the pipe. No damage to the pipe was noted except for some tears in the plastic membrane covering the pipe. At the direction and observation of the WBMWD’s representative, new plastic membrane was installed over the damaged sections.

Following the inspection of the pipe and repairs to the membrane, the excavations were filled to at least mid-pipe with a 2-sack slurry. Slurry for sections 1 and 3 were allowed to set for 2 days before excavating for sections 2 and 4.

After the RWL was sufficiently supported, excavations were made to remove and treat the backfill and edges of the 60-inch storm drain trench excavation. 15 feet of the trench backfill was removed on either side of the RW to expose the soil backfill to be jetted. Excavations along the RWL stopped at the exposed the chemical grout treated soil (note the white 1-inch PVC injection casings in the photos below). 

The remaining 26 feet of storm drain backfill was treated to consolidate the sandy soil with water jetting, from the bottom up. A 20-foot long, 1.5” PVC pipe was used, attached by a 2” fire hose connected to a fire hydrant. With water flowing through the pipe, it was pushed into the jet zone to depths of 22.5 to 25 feet, held until water returned to the surface or settlement of surficial material was observed. The pipe was then pulled up in approximately 5-foot intervals and the jetting repeated. Jet points were spaced 2.5-foot center to center. Onsite sands at the removal surface were flushed into holes left by the jetting pipe until holes were filled. Material exposed at the surface within the jet zones were observed to settle from 0.5 to 0.75 feet during jetting.

The materials removed to expose the jetting zone surface were used to backfill those excavations. The backfill was placed in 6- to 8-inch loose lifts that were moisture conditioned to near the optimum moisture content, and then compacted by wheel-rolling using a large rubber-tire loader. At the direction of the WBMWD onsite representative, lighter, manually operated compaction equipment was used to compact the backfill directly over the 42-inch RWL until at least 5 feet of backfill over the pipe had been placed.

This firm provided observation and field density testing of the backfill operations to verify that work was performed in substantial conformance with the project specifications and technical provisions, the grading codes of the City of El Segundo, and applicable portions of the project geotechnical requirements.

Based on our observation during work and the results of CPT testing, the chemical grout treatment of soil materials supporting the 42-inch reclaimed water line and placement of slurry were considered suitable to mitigate the potential for future settlement of the pipe.

Also, based on our observations and field density testing, the removal of loose storm drain materials, water jetting of soils loosened by previous sheet-piling, and compacted backfill replacement was considered suitable to prevent settlement of overlying surface improvements.

Comstock Crosser & Associates was very pleased that the problem was repaired in-place, as opposed to major removal and replacement operations.  West Basin Municipal Water District was equally pleased that their waterline was protected and sufficiently supported and that mitigation work was performed without damage or undo risk to the integrity of the 42-inch reclaimed water line.

Client: Knott’s Berry Farm
Location: Knott’s Berry Farm, CA
Project: Xcelerator Amusement Attraction

The Xcelerator is a high-speed thrill ride at Knott’s Berry Farm.  The ride hydraulically launches a train holding 20 passengers to reach a top speed of 82 mph in 2.3 seconds.  The train travels through a vertical 205-foot ascent and immediate descent at a 90-degree angle.  The track encompasses a total of 2,201 feet.  The extreme speeds and changes of direction produce relatively large forces on the supporting pile foundation system.

Albus & Associates, Inc., was retained to investigate the site to characterize geotechnical conditions and provide design parameters.  Our investigation included drilling borings to a maximum depth of 50 feet and selected sampling of soils encountered.  Our recommendations included design parameters for single and group capacities of free- and fixed-head piles.  Each side of the tower required a pile group consisting of 20 piles in a non-symmetrical configuration.  

During construction, representatives of Albus & Associates, Inc., were present to observe and test the contractor’s work to verify compliance with our recommendations.  Our services consisted of providing soils engineering and materials testing for construction of the ride foundations, queue station, and other site improvements.  Our services included observation of excavations for CIDH piles, inspection and sampling of fresh concrete placed for the CIDH piles, preparation of concrete compression specimens, performing concrete compression tests to verify specified strengths, and observation and testing of structural backfill placed for utilities and around structures.

Client: City of Los Angeles
Location: Los Angeles, CA
Project: 182nd Street Bridge Expansion and Seismic Retrofit

The 182nd Street Bridge was built in 1964, and was recently upgraded to meet the current seismic codes.  The Bridge is 35-foot-wide and 226 feet in length, a 3-span (max span 74 feet) pre-tensioned concrete I- Girder construction, simply-supported on concrete pile foundations. 

Albus & Associates, Inc., was retained to evaluate and redesign a deep foundation system using 48-inch-diameter Cast-in-drilled-hole (CIDH) piles as part of the value engineering (VE) services.  We performed analyses for vertical and lateral pile capacities under static and seismic conditions. 

Our services also included observation, testing and consultation during construction of eight CIDH piles, four at each abutment.  Our staff logged the drilled holes to confirm subsurface conditions and to verify design assumptions.  We observed the installation of inspection pipes and concrete placement in accordance with project plans and specifications.  After concrete placement, we performed Gamma Gamma Logging (GGL) services through the pre-installed inspection pipes to verify concrete quality and pile integrity, and prepared a construction report summarizing our findings and test results.  

Client: Trammel Crow Residential
Location: Orange, CA
Project: Alexan Pacific Grove Residential & Retail Project

Recently featured as one of the top 10 projects in Southern California in the magazine “Real Estate & Construction Review”, the Alexan Pacific Grove project is a mixed-used redevelopment in the city of Orange, California.  The project includes approximately 200 luxury residential units and 12,000 square feet of retail space.  The complex consists of a four-story residential/retail structure surrounding a 6-level integrated parking garage.

Albus & Associates, Inc., was retained to perform a geotechnical investigation of the site for use in design of proposed development.  Our work included drilling of 5 borings and laboratory testing of representative soil samples.  A key issue requiring careful evaluation was differential settlements between the relatively large foundations supporting a heavy parking structure and the smaller, lighter residential foundations located immediately adjacent to the parking structure. Our geotechnical report provided recommendations for design and construction including parameters for heavily-loaded shallow spread footings, ground preparation and fill placement, underground utilities, and pavement.

During construction, representatives of Albus & Associates, Inc., were present to observe and test the contractor’s work to verify compliance with our recommendations.  Our services consisted of providing observation and testing during the preparation of ground, placement of compacted fill for general grading and utility trench backfill, compaction of paving subgrade, and placement of pavement materials.

Client: Centex Homes/Elsinore Valley Municipal Water District.
Location: Lake Elsinore, CA
Project: Interstate 15 Sewer and Water Undercrossing at Third St., Lake Elsinore

The I-15 undercrossing project involved 417 feet of sewer and water at the terminus of Third Street in the city of Lake Elsinore.  Installation of the lines was prompted by large residential developments by Centex Homes east of the freeway that required connection to existing infrastructure west of the freeway.  The crossing involved the installation of 44-inch steel casing for a 30-inch ductile-iron water line and 30-inch steel casing for a 15-inch PVC sewer line.  The casings were installed using a jack and bore method.  The jacking pit was located westerly of the Caltrans right-of-way at the terminus of Third street while the receiving pit was located easterly of the right-of-way.  The lines were installed nearly 40 feet below the travel lanes of I-15.

Albus & Associates, Inc., was retained to investigate the proposed jack and bore alignment in order to characterize the subsurface conditions and develop design recommendations.  Our investigation included exploratory borings and laboratory testing of representative soil samples.  Our analyses of data included estimation of potential ground displacement and distortion in the travel lanes overlying the proposed alignment, shoring parameters, temporary excavation stability, and corrosion. 

Albus & Associates, Inc., also provided services during the installation process.  During the boring, samples of drill cuttings were evaluated to verify soil conditions were as anticipated in our investigation.  Survey points were established on the travel lanes and monitored by a land surveyor.  The data was provided to our office for review to verify ground subsidence was within tolerable limits. Field representatives of Albus & Associates were present during grouting of the annular space outside the carrier pipes to verify compliance with project specifications.

Client: Centex Homes/ San Bernardino County Flood Control District
Location: Fontana, CA
Project: Hawker-Crawford Flood Control Channel

The Hawker-Crawford Channel is located in the city of Fontana and consists of approximately 2 miles of concrete box and open trapezoidal channel.  The project extends the storm drain box in Summit Avenue and Frontage Road to San Bernardino Flood Control Basin No. 5.   The project also included the construction of several levies to divert drainage from local tributaries of Lytle Creek to the Hawker-Crawford Channel.

Albus & Associates, Inc., was retained to prepare a soils investigation of the project area that was used in the design of the Hawker-Crawford channel and associates levies.  This investigation included numerous backhoe test pits and borings to examine the underlying soil conditions and collect soil samples for laboratory testing.  Samples were tested in our laboratory to determine engineering characteristics and design parameters.  

During construction, representatives of Albus & Associates, Inc., were present to observe and test the contractor’s work for compliance to our recommendations.  Our services consisted of providing soils engineering and materials testing for construction of the channel and associated levies.  Our services included verification of suitable ground for support of the structures; inspection and sampling of fresh concrete placed for the box and trapezoidal structures, preparation of concrete compression specimens, performing concrete compression tests to verify specified strengths, and observation and testing of the structural backfill placed around the structures and levies.

Client: Unocal Land Development
Location: Fullerton, CA
Project: Rehabilitation of E. Bastanchury Road

Bastanchury Road is a 4-lane arterial roadway traversing through the city of Fullerton, CA.  Extensive development along this corridor resulted in a significant increase in traffic volume above the original design criteria.  As a result, portions of this important transportation route became structurally damaged and required rehabilitation.  A section of roadway approximately 1 mile in length was selected for evaluation and rehabilitation in connection with a proposed residential project.

Albus & Associates, Inc., was retained to perform a comprehensive evaluation of the existing roadway in order to develop recommendations for rehabilitation.  Our evaluation consisted of visual observations of the pavement conditions to record types and extents of damage to the pavement.  The pavement was then evaluated by performing a falling-weight deflectometer test to measure the pavement’s resistance to traffic loads.  This test was followed by coring of the existing pavement and sampling of the underlying soils.  With the data gathered, the roadway was divided into zones with similar conditions and overlay rehabilitation was developed.  During construction, representatives of Albus & Associates, Inc., were present to observe and test the contractor’s work to verify compliance with our recommendations.  Asphaltic concrete was checked for thickness, temperature, and in-place relative compaction.  Construction materials were sampled and then tested in our laboratory facilities to verify compliance with required specifications.

Client: Signal Hill Petroleum Company
Location: Signal Hill, California
Project: Fault Investigations

Signal Hill has a long history of oil production, and a longer history of bedrock faulting. This firm has been investigating fault locations since 1999, when we were the Geotechnical firm of record during development of the hilltop from oil fields to residential homes by Comstock, Crosser & Associates. In the years since we have investigated numerous properties for the Signal Hill Petroleum Company and for private owners of properties wanting to develop their properties. Fault studies provided the property owners the locations of active and inactive fault locations, or the absence of faults, on their properties so that they could design their site development with safe buffer zones between the faults and proposed habitable structures. After years of fault investigations by us and various other geotechnical firms, we developed the composite Fault Location Map presented below for the Signal Hill Petroleum Company, a major owner of properties in Signal Hill, so that their planning team can anticipate the limitations that active faults may present on their properties not yet developed.

A typical fault trench investigation involved the excavation of trenches semi-perpendicular across the anticipated location and trend of a fault. These trenched were excavated with excavators to depths of 20 feet or more, with the sides laid back and benched to provide safe access for our geologists. The trench sidewalls were cleaned off to expose the geologic formations and characteristics that showed the history of ancient and near geologically recent activity.

Our geologists painstakingly mapped, with pencil on graph paper, at least one sidewall of the trench, concentrating on areas showing faulting and fracturing, and on areas near surface which might give clues to how recent of how far in the past the faulting and fracturing occurred. The field trench logs were then illustrated using AutoCad to produce the graphic trench logs like the one shown here.

As shown on the FT-4 trench log above, main fault traces can be identified by having different bedrock units on either side of a fracture, such as San Pedro Formation of the left side and Lakewood Formation on the right side of the Cherry Hill Fault Main Trace. Other identifying evidence could be the offset of sand and gravel beds, offset of near surface features such as krotovinas (infilled rodent burrows). The development of argillic soil horizons, which in a simple definition is the weathering of bedrock into soil, can give an indication of how long ago a fracture occurred. Our firm has employed experts in determining the age of argillic soil to visit the site and determine if a fault can be considered inactive or not. This can be a very important determination. A fault considered active required a structural setback restricting the construction of habitable structures, where a fault considered inactive would not require any restrictions.

When mapping and assessment has been completed, the trenches are backfilled using the materials excavated from the trenches, The backfill is placed in moisture-conditioned and compacted lifts of about 8- to 12-inches in thickness. A soil technician from our firm observes the backfill operations and performs field density tests to demonstrate that the backfill in properly compacted.

Client:  OMYA, Inc.
Location:  Lucerne Valley, California
Project: OMYA Mine

Our firm was contacted by OMYA, Inc., to help them with mitigating a safety issue at one of their calcium carbonate surface mines in Lucerne Valley. To satisfy the safety requirements of their mining permit OMYA needed to provide minimum haul road widths for their 50-ton and 100-ton rock trucks that transported crushed materials from the mine to their processing facility. There was an area approximately 160 feet long at one of their haul roads where the width was not wide enough and the topography above and below the road was too steep to safely grade the road wider. We were asked to assess the area and come up with a means to widen the road from the existing 15 feet to the required minimum width of 20 feet and provide a required 4-foot-tall berm along the downhill side.

Working with HI-TECH Rockfall Construction Inc., a plan was developed to accomplish the road widening by constructing a retaining system along the downhill side of the road. The retaining system used 7-inch-diameter, 0.75-inch-thick, steel pipe posts, embedded in drilled holes at least 5 feet into solid rock, connected with 0.75-inch-thick wire rope. The space between posts were faced with wire rope net by Geobrugg that was covered with Tencate Mirafi filter fabric. To prevent overturning, each post was anchored in front with wire rope tie-back struts anchored in drilled holes. Posts and anchors were secured in the drilled holes using 6,000 psi non-shrink Rapid Set grout.
At the upper end where the retained height exceeded 15 feet, the post tie-back struts were anchored to an 8-foot by 20-foot, 1-inch-thick steel plate that was buried after connections were made.

The retained height ranged from 8.5 to 21 feet from competent rock to top of berm. HI-TECH Rockfall Construction Inc. completed the construction of the retaining system and grading of the road in front of it. We had an engineer on site every day to verify embedment depth of the posts and to monitor the various stages of construction. The result was a semi-temporary robust retention system that help up the widened portion of the haul road and the berm.
Challenges were faced daily during construction. The greatest challenges were safety issues, and after just a few hours on the side of the giant hillside one realized that there are many hazards and constant vigilance was required.
Falling rocks from the 240’ high rock face above the road was a constant hazard. To minimize rock falls, HI-TECH personnel rappelled from the top to bottom and removed loose rocks before any work started on the road. Still, rocks occasionally fell, and personnel were reminded to stay on the outside of the road whenever possible.

The hazard of working along the outside of the road was falling over the edge. The descent to the bottom of the steep hillside was about 130 feet. HI-TECH had a crew member dedicated to watching the others working along the edge.

The nature of the calcium carbonate rock and soil presented a few unique hazards. Being predominately white, the soil and rock faces reflected the sun quite well and fatigued the eyes and beat on exposed skin. This was an issue until about 2 PM when the sun moved behind the ascending rock face. Sunglasses, long-sleeved shirts, and sunblock helped. The crystalline nature of the rock and soil made it very sharp, which would cause abrasions to exposed skin in a fall, even from the dust from the almost constant wind. Wearing gloves and long-sleeved shirts helped to protect against this.

OMYA had their own safety protocols for vehicles traveling on the 5 plus miles of the haul road between their office facility and the work site. All vehicles were required to sign in at the office and check out a radio to broadcast their location at every mile marker. Rock trucks traversing the haul road would request vehicle to stop in turnouts at designated mile markers until the truck passed. Radios were turned in and vehicles signed out at the end of each day. At the work site, a blast of the horn would notify the crew that one of the massive trucks was about to drive though the area, and all work would stop until the truck had moved on.