All posts by Tony Camacho

landslide repair

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

seismic strengthening

Case Study: Beresford Arms Hotel Earthquake retrofit

The Challenge
This hotel was built on unstable fill and sands and was in danger of collapse in the event of a severe earthquake. A structural analysis showed that the inner core of the building needed to be reinforced with shear walls and underpinned with cast-in-place reinforced concrete piers.

Action:
The inner courtyard was inaccessible except for an 8 ft. tall x 5 ft. wide opening. The height of the build­ing prevented the use of cranes to place equipment or material into the courtyard. Furthermore, since the soils were noncohesive, all piers had to be cased for the top 25 ft.
A small track rig was used that fit through the narrow opening. Groups of 4 piers 40 ft. deep were placed in each of the 4 corners. 18” diameter contin­uous flight augers and steel casing were used for the pier drilling.
The cages were winched through the opening in sections and then assembled to full length with rebar couplers. They were then raised over the piers and lowered in using temporary tube steel pole and winch systems bolted to the sides of the building. The piers were then poured as the casing was re­tracted.

Results:
This initial phase of a multi-phase retrofit program helped bring the Beresford Arms Hotel up to current earthquake standards.

Captions:
Multi-story Hotel, San Francisco
Detail showing rebar couplings
Starting a new pier hole before inserting casing
Overhead shot of pier drilling in corner of courtyard
Raising a reinforcing cage consisting of #8 rebar and spiral ties
Overview of construction site showing continuous flight augers and one set of completed piers at upper left corner.
Placing a reinforcing cage into a pier hole in the corner
Lowering a cage down into a pier hole with the temporary winch system
Picture showing temporary winch systems bolted to building and suspended cage at right side. Access opening visible at center bottom.

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

landslide repair

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

micropiles

Case Study: Montgomery St Building SF Financial District
Foundation Improvement with Micropiles In San Francisco

The Challenge
The owners of an older 3 story building in San Fran­cisco’s financial district wanted to add an additional story on for their growing practice as well as earth­quake-proof the building.
The existing inadequate foundation consisted of shallow spread footings sitting on up to 35ft. of arti­ficial fill and marsh deposits.
The site presented a very difficult challenge besides the overburden: there was no access to the basement for the 20,000lb. micropile drill rig that needed to be used.

Action:
To gain access, the front of the building was opened up at the street level and the floor was shored underneath from the basement. The drill rig was then tracked inside and onto a cribbed platform that went from the basement up though an opening in and level with the first floor. The rig was then slowly and carefully jacked down to the basement level.
After reviewing the soils data, RWR decided to use a rotary percussion drilling technique to install 8” diam­eter micropiles reinforced with a solid 1 3/8” diameter 150KSI bar.
The drilling proceeded by advancing a retractable casing through the overburden until the tip was seated into the top the bedrock. A Down-The-Hole hammer was then advanced through the casing using 1050cfm of 350psi (high pressure) air to power the hammer and clear the cuttings. The DTH hammer continued to advance through the bedrock until the desired bond length was achieved. The bedrock consisted of layered shale and sand­stone but the sandstone layers were much weaker than expected, which necessitated a recalculation of the overall shear strength and the bond lengths being deepened. This caused pile lengths to be increased to up to 60ft. As an added precaution, all piles were post grouted 24 hours after installation. Tension testing was per­formed on 20% of the piles to 133% of the design load of 75 kips and all passed.

Results:Successful installation of the piles allowed construction of the additional story on top the of the building and provided greatly enhanced safety against seismic uplift, settlement and lateral movement

Captions:
Case Study Montgomery St Building SF Financial District
1050cfm high pressure compressor in front of job site
Drill rig being jacked down from mezzanine level to basement
DTH hammer being pulled out of hole after drilling to 60ft
Lowering reinforcing rod with 2 postgrout tubes into hole
Retractable casing being installed through the overburden

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