[ Six Rivers National Forest Landslide Repair | City of Eureka Landslide Repairs ] 

[ Caltrans Landslide Repairs | Communication Towers | Hospital Expansion ]  

[ Mill & Shackleford Creeks Erosion Inventory | NCRA | PJ Murphy Road ]

[ Tank Gulch | Timber Harvest Plans ]

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Six Rivers National Forest-Grouse Creek Landslide, Forest Road Repairs

SHN conducted geotechnical investigations of three landslide damaged portions of Forest Road 6N06, in the Six Rivers National Forest. Forest Road 6N06 was damaged at several areas by a series of large, complex slides that occurred during the winter of 1997-1998. The slides are located in the steep inner gorge of Grouse Creek, and are often parts of much larger ancient slide complexes. Numerous reports of continued failure of portions of the road indicated chronic instability of these areas. An extensive, multi-phased boring program was completed, and slope inclinometers were installed and monitored for over a year. Because of the complex nature of the geology and slide movements, considerable uncertainties existed regarding potential mitigation options. Repair options were further complicated by the location of the slide within a steep inner gorge adjacent to a sensitive waterway. SHN presented three potential repair options, with brief descriptions of the advantages and disadvantages associated with each option, and assisted the USFS with selection of the most efficient mitigation option for each slide location. In some locations, retreat of the roadway off the larger slide mass was the most prudent and cost effective approach to mitigation; at others, partial retreat, removal of slide debris, and construction of engineered retaining structures (or some combination thereof) were appropriate. SHN designed the various mitigations and provided inspection services during construction to verify soil and geologic conditions and to ensure that the construction was completed in compliance with the intent of our design.



 

City of Eureka Landslide Repairs

Vista Drive Landslide and Road Failure

This slope failure had undergone previous repairs (recommended and designed by others), but by the winter of 2001-2002, significant new pavement cracking was evident along the outboard edge of Vista Drive, in the previously repaired area. SHN investigated the site, and prepared plans and specifications for a second repair of the instability.

Information obtained during SHN’s investigation suggested a relatively deep-seated landslide that extends north from the portion of Vista Drive that was affected. Evidence of minor movement also suggested creeping or associated movement extending east from, and to the south of, the apparent primary landslide scarp location.

SHN’s recommendations included a stabilization trench repair including a blanket drain installation. To date, SHN-recommended repairs have stabilized this site.

Slope Failure Repair Investigation Campton Road, Progress Avenue, and Manzanita Drive

SHN conducted geotechnical investigations of slope failures at three sites of chronic instability that were impacting or threatening three city streets. Other services included topographic mapping of the landslide features, an alternative repair analysis, and design documents.

The Campton Road site was experiencing accelerated slope failure. SHN installed soil borings to characterize subsurface soil conditions for the purpose of developing embankment stabilization alternatives. Work also included installation and monitoring of an inclinometer and several piezometers for monitoring groundwater conditions.

During the winter of 2002-2003, surface water runoff escaped the conveyance systems that parallel Manzanita and N Streets. Runoff saturated the fill prism and a series of parallel and sub-parallel tension cracks developed in the paved roadway surface with vertical displacements of up to several inches. SHN coordinated with the private landowners with regard to access and repair alternative scenarios. Soil borings were advanced to characterize subsurface soil conditions for the purpose of developing embankment stabilization alternatives. Work also included installation and monitoring of an inclinometer and conducting laboratory testing to determine general strength parameters of the soils encountered in the borings.

A bluff face failure adjacent to the west side of Progress Avenue was primarily the result of erosion by concentrated runoff from the Progress Avenue paved surface. The bluff was experiencing continued retreat that was threatening the City street and adjacent homes. SHN advanced borings at the base of the bluff, where a buttress or retaining wall were recommended to mitigate further bluff failure. Laboratory testing was conducted to determine general strength parameters of the soils encountered in the borings.

Based on the results of the geotechnical investigations and topographic surveys, SHN prepared three schematic-level design alternatives and related construction cost opinions for each site. These alternatives were presented to City staff in an informal meeting, which allowed us to eliminate the costs of preparing technical reports. Once the City and SHN had mutually selected preferred repair methods, SHN prepared plans, specifications, construction cost estimates, and bid schedules for the repairs. We were again able to keep costs down and stay on budget by producing one-sheet plan drawings of the repairs and the necessary details for each site.

E Street Embankment and Shoulder Repair

As a result of the December 28, 1996, Northern California storms, the City of Eureka experienced an embankment failure along one of its major cross-town arterial streets. SHN provided a geotechnical investigation, including the installation of inclinometers; a site topographic survey; conceptual design; reviews with the City; and final construction plans and technical specifications.

SHN’s geologists used their knowledge of the local geology and soil forming processes to determine fill/native material contacts and make recommendations for additional sampling sites. SHN installed, monitored, and analyzed slope inclinometer equipment and data to pinpoint the landslide slip zone.

Because of the threat to this high volume traffic corridor, the project was fast track. SHN completed the construction plans within 3-1/2 weeks of receiving notice to proceed. The City solicited bids for construction and completed the repairs at a cost of $85,000. SHN was able to complete this project on time and within budget.



Caltrans Landslide Repairs

SHN worked as a subcontractor to Boyle Engineering, providing civil and geotechnical engineering and geologic, surveying, and right-of-way services for storm damage and construction disposal sites in Caltrans District 1.

These projects included culverts, stabilization trenches, embankments, slide removal and stabilization, rock buttresses, rock slope protection, and retaining walls.

Text Box: Contact: Ms. Kathleen Sartorius, Caltrans, 1656 Union Street, Eureka, CA 95501-2229; 707-441-5815 SHN conducted geotechnical/geological investigations and evaluation including subsurface drilling, sampling, laboratory testing, and piezometer and slope inclinometer installation and monitoring. We provided a geotechnical/geologic report summarizing the results and providing recommendations for the sites listed below.

Surveying services included topographic, boundary, construction, monitoring, and existing right-of-way and right-of-way acquisition.

SHN, working directly for Caltrans, also provided botanical inventories, prepared permits, and obtained environmental clearance including categorical exemption/categorical exclusions under CEQA and NEPA, Army Corps of Engineers Regional General and Section 404 permits, Coastal Development Permits, California Department of Fish and Game 1601 Agreements/ Certifications, Section 4(f) Agreements, County Grading Permits, Water Quality Control Board 401 certifications, and National Marine Fisheries Service and US Fish and Wildlife Service Biological Assessments.

Site

Description

Est. Constr. $

Geo

Survey

ROW

Permits

Hum 36 PM 21.4

Seismic refraction studies and movement monitoring

750,000

x

x

x

Hum 36 PM 22.1 and 23.8

Survey and right-of-way, Geologic review

430,000

x

x

x

Hum 36 PM 25.6

road stabilization; alternate route

1,750,000

x

x

x

Hum 96 PM 19.9 and 21.4

Stability trench, subdrainage, rock slope protection (RSP), and embankment reconstruction

1,550,000

x

x

x

Hum 101 PM 23.0 and 41.5

Rock Buttress, Subdrainage, Stability, & Culverts

3,960,000

x

x

x

Hum 101 PM 24.55

Culvert

140,000

x

x

Hum 101 PM 26.23/26.26

Rock Buttress

585,000

x

x

Hum 101 PM 29.3/29.5

Stab Trench

940,000

x

x

x

Hum 101 PM 86.60

RSP Buttress

90,000

x

x

Hum 101 PM 89.77

RSP Buttress

140,000

x

x

x

Hum 254 PM 12.782/12.76

Retaining Wall

640,000

x

x

x

Hum 254 PM 15.40

Stabilization Trench

505,000

x

x

x

Hum 254 PM 22.49

Embankment, RSP

42,000

x

x

x

Hum 299 PM 25.0

Seismic refraction, subdrainage gallery, & embankment reconstruction

6,890,000

x

x

x

Men 101 PM 84.9/85.1

Slide removal/drainage

400,000

x

x

Men 101 PM 87.0/87.3

Slope Repair

2,325,000

x

x

Men 101 PM R010.86

Slide removal/ drainage

105,000

x

x

Men 101 PM R100.7/R100.8

Stabilization trench

445,000

x

x

Men 101 PM97.5/97.6

Slide Removal

520,000

x

x






Geotechnical Engineering Foundation Investigations & Survey Services
SHN has conducted geotechnical engineering foundation investigations for cellular telephone and television communication towers, for several communications companies, at locations throughout Northern and Central California. The work subsurface exploration and sampling, laboratory testing, and report preparation, including specific foundation recommendations, for each site.





Geotechnical Investigation, Design Criteria, and Construction Inspections

SHN has provided geotechnical and construction observation services for this hospital renovation and expansion project. The facility was in an extraordinarily heavy concrete building, immediately adjacent to the existing hospital. SHN conducted a detailed subsurface exploratory drilling program which included Dutch cone penetrometer studies.

Investigations focused on characterizing a competent sand strata that was saturated in lower portions. Pier design criteria were developed to allow for end bearing above water table such that foundations could be excavated and installed without requiring casing or slurry drilling which would have been very expensive. Liquefaction potential of lower portions of the sand strata was also evaluated.


SHN geotechnical professionals provided design and drilled pier construction criteria, floor slab support and subdrainage criteria, and site preparation and grading recommendations. During construction, SHN monitored and logged all drilled piers, determined appropriate drilling depths, and monitored installation of reinforcing cages and placement and testing of concrete. We also provided fill material, filter material, and soils compaction testing services.






SHN conducted and erosion inventory of the Mill and Shackleford Creek Watersheds in Siskiyou County. The study area was composed of densely forested, steep mountains containing over one hundred miles of logging roads and associated skid trails.

SHN and Vestra Resources initially developed a comprehensive map of the road system, based on digital road base maps and historic air photos. SHN modified the established protocol for evaluating past and present erosion within the study area.

This protocol was issued in a two week field erosion inventory and sediment analysis of the identified logging roads. Culverts and crossings encountered along the logging roads were characterized and volumes were estimated for past and future erosion potential. SHN also inventoried significant erosional features such as slides, rills, and gullies, estimating past and future sediment deposition volumes.

The final product of the investigation was an Erosion Mitigation and Prevention Plan that prioritizes the sites identified in the field inventory, according to the cost-effectiveness of the proposed treatment. The plan is being used to prevent continued erosion and sediment delivery to the stream channel system, or degradation of the riparian corridor.





Engineering & Geotechnical Support
SHN worked with the North Coast Railroad Authority (NCRA) on its Willits to Eureka line. SHN provided engineering and geotechnical services on over 125 storm damage sites located between Fortuna and Longvale. These sites range from re-structuring tunnels and bridges, to securing tracks as they cross slide-prone slopes. SHN provided assistance to OES and FEMA in preparation of PDA's and DSR's, and provided geologic investigations, topographic surveys, earthwork design, RSP design, pile design, bridge design, culvert design, and permitting through and US ACOE.

Two of the largest projects include the Boulder Creek Bridge design and the Van Duzen Bridge erosion protection project.





P.J. Murphy Memorial Drive Structural Repair

Landslides resulting from severe storms in January 1997 damaged a large section of P.J. Murphy Memorial Drive, above Requa, Del Norte County, California.

SHN prepared damage assessment documents, preliminary and site specific geotechnical evaluations, topographic surveys, conceptual design of various repair alternatives, preparation of repair plans and specifications in accordance with Caltrans standards, preparation of bid documents, assistance with evaluations of bids and qualifications of prospective contractors, and full time management of construction activities.

The mitigation work included a 300 foot long by 36 foot high welded wire wall with 50 foot high cut slope buttress to repair this damaged road.






SHN provided engineering services to complete a Waste Characterization Study, site, design, permit, and perform construction management for this new, 10 acre, Class III, ash monofill with a composite liner and a Leachate Collection and Removal System.

In addition to the problems associated with designing a facility in a high rainfall area, SHN addressed the significant environmental factors, such as Spotted Owl habitat and the hydrogeology of the Eel River basin. SHN also conducted fieldwork relating to soils, geology, seismicity, groundwater, and hydrology to support the design effort.


SHN developed an innovative program to divert the ash waste stream into agricultural and forest land soil amendment projects. We also developed and implemented the vadose zone, groundwater, and surface water monitoring programs.

This project received the 1993 ASCE, North Coast Region Project of the Year award. It was 1 of only 4 Class III landfills permitted in California over a 5 year period.





Road Cut and Road Fill Failures, Timber Harvest Plans
SHN geoscience professionals conduct landslide investigations, and provide stabilization evaluation and remediation design for haul road cuts and fills associated with several Timber Harvest Plans across Northern California and Southern Oregon, including projects in Six-Rivers National Forest, Shasta-Trinity National Forest, and Klamath National Forest.

SHN conducts geologic investigations for design of rock buttress cutslope support, fill failure repair, surface drainage and subsurface drainage.


SHN also provided geotechnical services for Option "A" Timber Harvest Plan preparation. We provide geologic reports and maps depicting geologic and geomorphic features related to landsliding, for harvest plans. The Option "S" plans are intended to guide timber management in these areas for 100 years. Ths scope of the investigation include field (and occasionally, aerial) reconnaissance, aerial photograph interpretation, identification of active and dormant landslides, and development of site specific mitigation recommendations and best management practices for unstable areas, road construction and reconstruction, and silviculture practices.

SHN also provides biological and botanical inventories for THPs.




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