All posts by Tony Camacho

Foundation Repair San Francisco, Foundation Repair San Francisco Bay Area, Uncategorized

Case Study
San Francisco Home Foundation

The Challenge
The Client had pur­chased a lot in San Francisco for a new home. As is typical of many City lots, there was a zero lot line condition: on one side there was an exist­ing home right at the property line and at 2 others, the edge of the foundation was right at the sidewalk. The plans called for excavating below both the founda­tion of the neighboring house and the City sidewalks.

Action:
The adjacent foundation was sta­bilized by hand-digging alongside and under the adjacent foundation and installing underpinning pits, before the mass excavation phase. Because the soils were type 1 it was not necessary to place shoring in between the shoring pits and it was also possible to make unshored vertical cuts at the sidewalk sides.
The foundation was then installed by placing drainage and water­proofing membranes directly against the cuts and shoring, and shotcreting the foundation walls.

Results:
Because of the techniques used, it was not necessary to over-excavate for double-sided forms and the excava­tion and foundation work were completed without any distress to the surrounding properties.

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

Uncategorized


Case Study San Francisco General Hospital

The Challenge
A structural analysis of one of the hospital’s buildings indicated that it was vulnerable to severe damage during a significant seismic event.
The retrofit design called for installation of new footings and large diameter piers around the pe­rimeter of the foundation. The new footings as well as the existing interior footings required a series of tiedowns locking them down against uplift.

Action:
In order to install the exterior footings and tie­downs, first it was necessary to construct soldier beam and wood lagging shoring to a depth to 30 ft.
An opening was cut into the basement area from the shoring pit. Finally a small track rig was lowered into the pit to perform the exterior and interior tiedown drilling.
The 36” diameter piers needed to be installed 40 ft. deep directly against the existing foundation, while avoiding damaging the building.

Results:
The work was completed successfully. This San Francisco General Hospital building now stands reinforced against the possibility of a devastating earthquake.

San Francisco General Hospital
Earthquake Retrofit Strengthens Hospital Against Seismic Peril

Captions:
Craning drill rig into shored pit for tiedown drilling
A San Francisco General Hospital building required seismic retrofit
Drilling tiedowns through interior foundation footings
Shored pit with tops of tiedowns showing
Bringing 35 ft. long pier cage to site
Continuous flight augers used in tiedown drilling
Setting cage for 36” diameter x 40 ft. deep pier
Craning in double hopper grout pump for tiedown grouting
Placement of reinforcing cage in cased 36” pier hole

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

Helical Anchors, 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

Earth Stabilization

The Challenge
The Brighton Gardens Retirement Complex was experiencing severe earth movement at several loca­tions on the Campus, threatening the infrastructure. The front of the the property sloping down to the boulevard below was a mix of weak soils and clay permeated with underground water. Several scarps had opened up and further slope failure was immi­nent. At the rear of the property, an existing 10ft. high masonry wall was starting to bulge.

Action:
The repair plan for the front of the complex called for a tiered installation of piers and grade beams to re­tain the below grade portion of the slide. Because of excessive underground water and caving, the piers had to be drilled, the reinforcing cages installed and con­crete placed via tremie all in one continuous operation. Above grade, a series of gravity walls using interlock­ing masonry units, pins and geofabric were installed. The saturated soils had to be left out and turned in order to bring the moisture content down a level where 90% compaction could be achieved. The back wall was stabilized by excavating behind the wall and installing a drainage system to relieve hydro­static pressure. Additionaly, series of tiebacks with steel plates were installed at the face of the wall to prevent any further movement.

Results:The owner’s investment in this large retirement complex is secure and the center is now a safe home to many of Santa Rosa’s senior citizens.

Captions:
Inspector watching tremieing operations with drilling going on in rear
Continuous drilling and pouring operations. Note continuous flight auger on ground and core barrel on drill rig.
Constructing interlocking walls. Wall drain cleanout pipes sticking up in background
Partially completed interlocking wall with com­pacted native soils and drainrock behind Tieback rig bolted to face of rear wall

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

seismic strengthening


Case Study Santa Clara Semiconductor Manufacturer
Seismic Strengthening Of Semiconductor Test Facility

The Challenge
Marvel Corp., a major manufacturer of semicon­ductors, needed to build test facilities at their North American Headquarters in Santa Clara. A large existing structure was being gutted and turned into a test laboratory.
In order to bring the building up to the demand­ing seismic specifications that were critical for the functioning of the sensitive equipment, the existing columns needed to be braced against any uplift motion. The design called for each column base to resist an uplift force of 440 kips.

Action:
RWR Construction provided a design-build pro­posal to install helical pier tiedowns around all columns, consisting of (6) piers each with a 73.3 kip design rating and a 110 kip test (150%) rating per pier. 3.5” galvanized tubular helicals were installed to a depth of 56 ft. The helicals were driven through and below a 7 ft. thick dense sand lens located at an invert elevation of 28 ft. The sections in and below the sand lens were then pres­sure grouted. This locked the helicals into and up against the bottom of the sand lens, which increased the uplift resistance to the required specifications. The piers were then cut off at the proper elevation, anchor plates and nuts were installed and the pier caps were cast into the new foot­ings surrounding the column bases.

Results:
All helicals were tested to 150% of design load and passed. The test facility is now able to keep functioning through any minor seismic event, and is structurally protected from major events.

Captions:
Installing helicals around perimeter column base
Starter sections with helix flights visible
Existing column and base surrounded by installed helical pier group
Pressure grouting operations for test pile
Detail of end section of typical helical pile showing sand lens, helix flight configurations and grout ports.
Performing helical test pile installation in parking lot adjacent to testing facility.

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

retaining wall problems, tiebacks

Case Study: Mill Valley Slide Repair Soldier Pile Walls with Tiebacks Save Property

The Challenge
During the winter of 2017, a large section of this hillside property in Mill Valley started to slide downhill. RWR was called in on an emergency basis to stabilize the property before further catastrophic failure occurred. An existing soldier beam retaining wall at the head scarp was becoming undermined and a section of a wall at the bottom of the slide had begun to yield and was out of plumb. The yielding section of the lower wall was directly downhill from a corner of the residence and a collapse would have caused the slide to fail directly up to the foundation, putting the house at risk.

Action
The head scarp was stabilized by installing a system of tiebacks and walers to restrain the majority of the existing upper retaining wall, while an older section of wall directly under a small guest house was completely removed and replaced with a new steel soldier pile wall and the same tieback and waler system.
The failing section of the lower wall was completely demolished and replaced and the wall was then ex­tended across the entire hillside to retain the bottom of the slide. The same wall design was used: a steel soldier pile and p.t. wood lagging system restrained at the top with tiebacks and steel walers. Tiebacks and walers were also installed across the remaining existing lower wall to prevent any further failures.
The hillside was rebuilt by benching the slide area, installing sub-drains and then reinstalling the soil in compacted lifts. The project was completed by seeding then placing erosion control netting over all disturbed areas.

Results:
The property has been successfully and completely sta­bilized, and has cy­cled through several heavy winters with no further move­ment or distress. The subsurface drainage systems in the earth benches and behind the lower wall are preventing any hy­drostatic buildup in the soils as well. The owner’s property has been returned to its full use and value.

Captions:
Yielding Lower Wall Undermining Of Wall At Head Scarp
Uphill View Of Landslide With Fissures And Sloughing Visible
Tearing Out Failed Section Of Lower Wall
Midway Through Construction With Slope Rebuilt
Aerial View Of Stabilized Property

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

landslide repair



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

micropiles


Case Study: Deep Micropile Installation Under Existing Multistory Building
The Challenge
The Owners of a former warehouse located in the vibrant tech start-up area south of Market St. in San Francisco made the decision to bring the building up to current earthquake standards and to have the option to add on another 3 stories.
The very large structure was situated on fill and bay muds to depths of up to 130 ft. and the foundation was supported on driven wood pilings from the early 1900s that only extended 60ft. from grade. The building had experienced marked differential settlement from pe­rimeter and point loads along with down-drag on the wood pilings from the settling fill.
Access was a major issue, with only 20ft. wide alleys on the exterior of the long sides of the building and 8ft headroom inside the basement. Driven piles were not an option because of settlement concerns for the neighboring properties and inaccessibility in the in­terior. The bay muds and debris-laden fill presented a problem in being able to install drilled piles down into bedrock without having to insert and remove casing in 130 ft. of clinging, collapsing material in tight and/or low headroom conditions.

Action
After RWR analyzed the test borings, load require­ments, and access and overhead issues, a hollow bar injection drilling system was selected as the best method to obtain the necessary up to 183 kips design compression load: The bars are drilled down with a sacrificial bit as grout is continuously pumped under high pressure through the annulus and out the bit ports to form a cement column around the drilling bar. When the necessary depth has been reached, the bar is left in place and is the reinforcing member of the composite column.
Frictional resistance factors were assigned to the var­ious layers of fill and muds below the top 30ft, which was still settling, and used to calculate diameter and depths for the piles. The size of the building and the addition of 3 more stories required that a total of 352 piles needed to be installed and extended 10ft into bedrock.
The perimeter micropiles were installed with a 45,000 lb. rotary drilling rig plumbed for continuous injec­tion. The interior piles were installed with 18,000 lb. drill rigs similarly plumbed.
A portable silo and a 10,000 lb. automatic grout plant were installed in one of the alleys to batch and pump the grout to the drill rigs.
Since the soil borings had stopped at the top of the bedrock, it was discovered during installation of the test piles that the bedrock was of extreme hardness. Even with 30,000 lbs. of down pressure the rock could only be penetrated to approximately 3-5 ft. with the ported carbide tipped cross bits that were standard for rock drilling with the hollow bars. Rotary percussion was ruled out because the impact energy would mostly be lost through the extreme depths of the muds.
The bits were taken to RWR’s welding shop and after pre-heating, conical carbide tipped drill teeth were welded on to the cross bits. This adaptation allowed penetration through the bedrock to the necessary depths.
In order for the piles to have the necessary resistance to lateral earthquake forces, the top 13 ft. of all the piles were reinforced by first installing 10” diameter x ½” thick steel casing, then injection drilling through the casings. Footing trenches were already excavat­ed in the basement so the casing was installed 13 ft. below the bottom of excavation. But the exterior was 11 ft. above bottom of footing, so a casing driver was constructed and used to insert the top of the 13 ft. long exterior casing to the proper depth. Disposable plastic piping was then inserted that reached from grade into the top of the steel casing to prevent collapsing and guide the drill bars into the casing.
The exterior micropiles were installed using 3” diam­eter hollow drill bars in 3 meter lengths. Due to the 8 ft. headroom, the casings in the basement were thread­ed and installed in 1 meter lengths and the bars in 1 meter lengths as well. All bars were connected using couplers with special metal seals that could withstand the up to 600psi grout pressures.
Due to the tight schedule, there were 2 low overhead rigs and crews operating inside, 1 rig and crew out­side and a grout plant with crew. The grout plant was modified to be able to pump grout to 2 machines at once: a Y valve was installed that would direct the batched grout to either the high pressure pump on the grout plant or to a double-hopper grout plant in the basement that fed a 2nd machine. A dance of casing installation and injection grouting between the 3 rigs required constant oversight and careful scheduling.
Up to 20 tons of cement were delivered in a dou­ble hopper truck every-other morning and blown into the silo to feed the grout plant.
The grout, which consisted of neat cement and a retarder to allow for the hard rock drilling time, had a specified strength of 8000psi. There was continuous sampling of grout batches during the installation and crush results ranged from 8000 to 10,000psi after 40 days.
Three initial compression tests were performed to verify the loading requirements. 20% of all production piles were pull tested to 133% of compression design loads, which also verified tension load requirements.

Results:
Almost 7 miles of micropiles were installed successfully in tight access and very chal­lenging subsurface condi­tions, around and under the existing structure. This was a key element to bring the building up to current seis­mic standards and allowed the Owners to lease out the entire building, including the additional 3 stories, to a large Bay area tech Company.

Captions:
Bringing A Drill Rig Into The Basement
Installing Casing Driver On Drill Rig
Limited Access: Installing Micropile At Perimeter Of Building
Tops Of Micropiles Visible In Trenches
Two 18k Drill Rigs In The Basement
Crossbit Customized In RWR Welding Shop, To Penetrate Extremely Hard Bedrock
Exterior: Top Of Micropile With Bearing Plate & Nuts Visible Along With Plastic Sleeving At Far End
Casing And Hollow Bars For Exterior Installation
2nd Grout Pump In Basement
2 Drill Rigs Working Opposite Trenches
Production Micropile Testing Using Adjacent Piles As Reactions
And To Suspend Testing Frame Over Footing Reinforcement
Compression Test On Sacrificial Pile, Using Production Piles As Reactions. Failure Occurred At 350 kips
Plan View Of 352 Micropiles Layout

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

Bowed, Cracked, Sinking Wall Repair, retaining wall problems, underpinning

The Challenge
A large exterior retaining wall was starting to fail and endanger a Presidio Heights home.
Because the house was built above and close to the retaining wall, a failure would have meant severe settlement and structural damage or partial collapse of the house.

Action:
Since the wall could not be removed without first supporting the house, a system of drilled piers with grade beams was installed under the house and extended beneath the exterior foundation and fireplace. These cantilevered beams supported the house while the retaining wall was demolished and replaced with a new shotcrete wall. After the struc­tural work was complete, the wall was stuccoed and painted and the landscaping was replaced.

Results:
The house sits on the corner of Walnut St. doubly supported by the cantilevered shoring system left in place and the new retaining wall. Safety and property values have been fully restored and the residence is an enhancement to the neighborhood.

Captions:
Underpinned house with top of old retaining wall removed
Closeup of underpinned foundation showing ends of earth-cast cantilevered beams projecting through foundation.
Removing failed retaining wall
Shotcrete wall ready for finish work
Finished wall with house secured
The final result

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

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