All posts tagged retaining walls

Completed Project: Retaining Wall Replacement

This project brings us to Baker Street in Pacific Heights where we are replacing a failed retaining wall that was installed just 15 years ago.  The project is a typical example of an architictural/engineering firms failure to design a project with construction costs in mind.  Since the client wanted to obtain building permits for this project,  she hired Smith Engineering in Oakland to draw up plans.  Once the plans were complete, the client proceeded to obtain several estimates for implementation.  The estimates that came in were astronomical and out of reach for the client due to the nature of the design and the plans abandoned. Thats when Tamate Landscaping was called to discuss options.   The original plans called for massive steel i-beams, timber and an elaborate sump pump drain system.  Yes, it would have been a solid wall that would hold up 50 plus years.  But any design is a failure if it can’t be built due to budget constraints.   Basically we had to start from scratch and draw new plans .  We ended up working with our own architect/engineer who has extensive experience working with San Francisco Department of Building Inspection as an employee there.  We designed a wall that would pass DBI’s stringent permitting criteria but more importantly could be built within the clients budget.  The outcome was a wall that we contracted to build for approximately 1/3 the cost of the original design.

Pictured here is the failed wall bowing out.

Demolition and excavation.

The main foundation of the new design are these 6″x6″ posts that were sunk in a hole in  excess of 4′ deep and 18″ wide and back filled tons of concrete.

September 28th, 2012.  The end of the 6th day on site.  Pressure treated planks were secured to posts with 1/2″ bolts.  To date we used almost 4 yards of concrete just to set the posts.  This wall won’t be budging for quite some time.  Next week we’ll be adding a Mira drain system to keep hydrostatic pressure off the wall and finish the project with a redwood fence and final inspection..

Below, a Mira Drain system is installed.  Basically, Mira Drain is a multi layer membrane with channels in between to allow water to stay of the retaining wall and travel down towards the base of the wall.  Typically, this water is then collected by an additional drainage pipe and directed out of the vicinity but in this case, with the sandy soil, is readily absorbed into the ground.

Project is completed by backfilling the ditch and building a redwood fence on top of wall.

Pressure Treated Lumber (PT)

Pressure treated (PT) lumber is the predominant wood material used in San Francisco landscapes where the exposure will be in a wet enviorment or when there is earth/wood contact.  Its identified by a greenish or very brown color with staple size slits on all surfaces except the ends.  PT lumber is basically a douglass fir or equivalent lumber that has been infused with preservatives.  The preservative used until 2004 for home applications was CCA or chromated copper arsenate with the arsenate component being highly toxic and a known carcinogen.  Today we use PT that has been infused with amine copper quat (ACQ) or copper azole (CA) or micronized copper quatemary (MCQ), all products without the arsenate and much safer.  Does that mean we would recommend building a raised vegetable planter out of it?  Although the manufacturer says its safe, we still would not recommend it.  But we at Tamate Landscaping do use it for the structural components of decks and fences since its the most economical and will last the longest.  Still there are some options in some applications.  For example, instead of a PT retaining wall, consider concrete.  Or for fences, consider all redwood instead of PT structural components.  These options will cost much more but they are options none the less.  Do your own research regarding these products and feel free to contact us for different options for your specific application.

 

Completed Project: Difficult Terrain in Forest Knolls

Our current project brings us to the Forest Knolls neighborhood of San Francisco. Much of the Forest Knolls neighborhood is shrouded in Eucalyptus Trees and set amongst a hilly terrain. Landscaping can be a bit challenging. Reclaiming usable square footage usually involves creating level areas by building decks and or retaining walls. Here you see the rear yard right before the project began on June 25, 2012.1

Project Update: Excavation

It was decided that for this project we would build a series of retaining walls to create level areas. The picture below shows the end of the 5th day. All foliage has been removed, existing concrete pad broken up and hauled away, and the process of carving into the hillside is underway. By the end of the excavation, we removed 40 cubic yards of material or 6 dump trucks. As is typical in San Francisco, all work is done by hand due to limited access. With this job, we were lucky in that we were able to remove debris by wheel barrel instead of the normal 5 gallon Home Depot bucket.

Project Update: Construction of Concrete Walls

Below you see the progress of the project on July 6, 2012, 9 days into the project. We salvaged the lower existing concrete wall since it was solid. Since it was not built level, we extended it with concrete. Whenever such an extension is added, its important to add steel reinforcement. Before the concrete pour, we drilled holes in the existing wall and epoxied vertical re-bar into the wall and tied horizontal re-bar on to these. In the background, you see additional walls being put up. For wall material, we decided on CMU to save on costs since all concrete work would have to be done in many stages.

 

Project Update: Hydrostatic Pressure

The walls are finished and below you see us installing a drain behind each wall.  Hydrostatic pressure occurs when the water run-off accumulates and puts added weight behind the walls.  With the weight of water at 8.3 pounds per gallon, an extended rainy season can compromise the integrity of the wall if hydrostatic pressure is not factored in.  Our drainage system consist of digging a trench behind each wall, installing a 3″ perforated drain pipe wrapped in fabric, connecting it to the municipal drain and backfilling the trench with drain rock.

At day 14 since the start of the project, the black limestone wall cap is installed, stairs stringers are cut and the concrete base for the Silver Quartzite Flagstone patio is being poured.

 

Project Update: End of the 4th week, July 20th, 2012.

Here you see the the Silver Quartzite Flagstone being mortared in over a 3-4″ concrete base.  Each piece is carefully selected and fit into place, kind of like a gist jigsaw puzzle.  Silver Quartzite is a favorite at Tamate Landscaping due to its natural characteristics: Its the hardest, most non porous of all flagstones and the colors and patterns will not fade over time.

Redwood stairs and safety rails are in, the retaining walls are being veneered with Beijing Green wall panels and planting work has begun.

 

Project Update:  July 26, 2012 Project Complete