Category Archives: landslide repair

Case Study
Fair-Anselm Plaza

The Challenge
Creek bank erosion underneath a retail commercial center was starting to expose foundations and risked destabilizing the entire structure. A retaining wall adjacent to a parking lot area had also been severely affected. Action was needed to prevent serious dam­age or the entire loss of a high value complex.

Action:
The eroding bank under the Center required installa­tion of a 350 foot long, by 15 foot high concrete slope protection system. The existing retaining wall needed to be replaced with a new 15 foot high wall installed at the edge of the parking lot. Both structures re­quired vertical and lateral support.
Subsurface soils consisted of a mixture of sandy silt, gravel, and weak sandstone. Because of the certainty of collapsing soils, as well as tight access conditions and limited overhead under the building, helical piers and tiebacks were chosen over a traditional pier and drilled tieback solution.
After installation of creek protection measures and grading, 180 vertical pier and horizontal tieback
helicals were installed. A first layer of shotcrete was then applied which was laterally supported with steel plate and nut assemblies on the tensioned tiebacks.
A second layer of shotcrete was then applied to the entire project and was sculpted and colored at the parking lot to resemble native soil and stone.
Because the project was located adjacent to a creek, a total of 8 federal, state and local agencies had juris­diction and required permits, inspections and coor­dination. The Federated Indians of Graton Ranche­ria were also involved due to the discovery of human bones during the investigation and design phase.
Because the project was on a protected waterway, all work under the Complex had to be completed by Sept. 30th, giving a construction schedule of only 2 months. RWR not only met the schedule, but also completed the job a week early.

Results:
Today, the property is sound and fully occupied, and the creek no longer threatens the structure. Recent photos show the creek water crystal clear, while the building sits securely on a solid foundation over the creek banks.

Captions:
Track Machine Installing Helical Piers & Tiebacks In Tight-Access Conditions

Extensive Erosion Under Plaza Had To Be Mitigated

RWR Crew Installs Drainage Strips & Reinforcing Wire

Shotcrete Applied By RWR Nozzleman

Proof Testing Of Tieback

Completed Retaining Wall Supporting Parking Lot Adjacent To Building

Shotcrete Sculpting To Match Native Rock Surfaces

Today Fair Anselm Plaza Sits Securely Above Crystal-Clear, Flowing Creek Water

RWR Construction Inc. 200 Gary Place, San Rafael, CA 94901 (415) 457-5658 www.RWR-inc.com

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Case Study

Case Study: Tiburon Slide Repair – Failing Retaining Wall Endangered Residence

The Challenge
A sloping property in Tiburon was experiencing deep-seated movement that threatened the house. This landslide needed to be stopped before significant structural damage occurred along with loss of property value.

Action:
The repair consisted of installing a soldier beam wall with tiebacks at the rear of the property. Piers were drilled down through the slide and into bedrock. Steel beams were then placed in the piers and filled with concrete. The top 6ft. portion of the slide was restrained with pressure treated wood placed between the beams. Tiebacks were also installed near the top of the beams. The portion of the slide below grade was halted by a bridging effect between the steel beams.
The Tiebacks were necessary because the beams need­ed to be restrained at both the top and bottom in order to resist the slide forces.
Results:
The slide has been stopped and the house and grounds are se­cure. Property values have been restored.

Captions:
Small tieback rig frame
Track Drilling For Soldier Beams
Soldier beam steel and double corrosion protected tiebacks with post-grout tubes.
Cut-to-size pressure-treated lagging starting to be installed
Grouting tiebacks with grout hopper in background

RWR Construction Inc. 200 Gary Place, San Rafael, CA 94901 (415) 457-5658 www.RWR-inc.com

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Case Study
San Rafael Slide Repair

The Challenge
A large slide was endangering several homes on a steep slope in San Rafael. The slide plane ran at a depth of up to 30 ft. below the surface and the scarp measured over 200 ft. wide x 300 ft. in length.

Action: The repair called for removal of the slide material, benching into competent bedrock and re-installation of the slide material in compacted lifts.
A series of sub-surface drains were placed at the back of the benches.
Surface improvements were also installed, including concrete V-ditches and drop inlets to channel rain­water away from the slope. Finally, re-vegetation with perennial rye-grass was installed along with surface erosion protection using jute netting, allow­ing the grasses to take hold.

Results: This neighborhood is now safe, with the full value of the properties restored. The slide repair has been through many heavy winters with no sign of any further movement or distress.

RWR Construction Inc. 200 Gary Place, San Rafael, CA 94901 (415) 457-5658 www.RWR-inc.com

Captions:
Landslide In San Rafael Endangered Homes
Spreading out slide material in 8” lifts
Working our way up the hill, excavating a bench into competent material
Wrapping a sub-drain at the back of a bench, in filter fabric
Excavating out unstable soils
Endangered structure at top of landslide.
Drain pipe and sub-drain installation, with sheeps-foot compactor in foreground
Sitting on compacted bench
Compacting slide material with sheeps-foot roller. Top of sub-drain gravel showing.
Finished slide repair. Hillside re-seeded and erosion protection matting installed.

RWR Construction Inc. 200 Gary Place, San Rafael, CA 94901 (415) 457-5658 www.RWR-inc.com

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Belevedere Slide Repair
Property Saved From Sliding Into San Francisco Bay

Case Study

The Challenge
Heavy rains and a broken drainage system caused the lower section of a steep property on the water’s edge in Belvedere to fail. A large amount of soil was swept down­hill, knocking a series of tiered access stairs off their foundations and worse, threatening the stabil­ity of the large home above. Access to the site was extremely difficult: egress to the home itself was via a funicular tram that runs from the street to the front door below or, a series of steep stairs. The slide area below the home could only be reached by a steep foot path along the side of the house.

Action:
After analyzing the subsurface conditions and taking into con­sideration the steep site and the extremely limited access, it was decided that the best approach was to use RWR’s portable drilling equip­ment to construct a retention system consisting of 24” diameter drilled piers extending above grade into cast concrete columns. The columns were restrained at the top with 1” diameter double corrosion protected tiebacks grouted in 6” diameter drilled shafts. After casting of the 24” diameter columns and installation of the tiebacks, 6” x 12” .6 ACZA pressure treated timbers were installed for lagging, then a sub-drain system consisting of perforated pipe and class II permeable drain rock was placed behind the lagging. The hillside was then rebuilt by bringing back up the slide soils from below and placing them in compacted lifts behind the new wall system. The tiebacks were initially lighted loaded so as not to pull the columns out of plumb. After all backfill was placed, the tiebacks were proof tested and locked off at full design load. A new surface drainage system was installed to collect rain runoff over the entire repair area, the access stairs to the dock were jacked back onto and reconnected to their foundations and all damage to the stairs was repaired. Lastly, all disturbed areas were seeded then covered with a layer of erosion control blanket and galvanized steel chain link netting anchored to the new piers.

Results:
This valuable property has been saved and restored to its former unblemished condition and the Own­ers sleep well knowing that their property has been safely stabilized.

Captions:
1st Section Of Wall Built And Scarp Visible Behind Restored Hillside
View of the repaired property with dock access stairs visible Stabilized Deck With Stunning Views

RWR Construction Inc. 200 Gary Place, San Rafael, CA 94901 (415) 457-5658 www.RWR-inc.com

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