Project Name: SVE Underground Manifold & Infrastructure
Location: Los Angeles, CA
Job Type: Remediation System Construction
Internal demolition, civil structural renovation and subsurface construction of a large volume underground manifold designed to be hidden from view; within one half of a pre-existing house, located in a densely populated, long standing residential neighborhood. The pipework consisted of sixteen conveyance pipes varying in size between 14”, 12” and 10” in diameter for removal of petroleum hydrocarbons below the neighborhood. The entire internal working space was only 1900 square-feet (sf) with less than 9 feet (ft) of headspace, with internal excavation required to 11ft below ground surface (bgs). The entire lot area was less than 3000sf leaving a small perimeter footprint. A 16ft deep excavation with shoring (within 30ft space between back of house and block wall fence) was also performed under power and comm lines. The overall excavation required exacting planning and execution to perform all tasks safely and efficiently. To meet current industrial structural code, the house required structural modifications (while maintaining the original façade) before and after the manifold construction.
Structural Demo and Modification to Existing House
This included demolition of internal house pad and house structural framing, installation of footings, and modification to ceiling and wall framing structures. Internal demolition of foundation and internal bearing walls required temporary shoring of the internal structure. 40% of original internal wall foundation footings were removed. Extensive removal of existing ceiling joists, rafters, wind braces, struts, bearing walls etc. and subsequent installation of new and upsized parallam beams, Simpson strong walls, and installation of fully sheathed shear walls were constructed throughout entire structure. Extensive termite damage required replacement of top plates and shouldering of various ceiling support structures.
Excavation of 45% of Subgrade
Excavation of Class A soil to depth of 11 feet below house within the confines of the perimeter footing of the house. The area excavated was 59 feet long and total area of 960 square feet. Excavation with skid steers was executed ramping down into the garage and to back of house for the full length of the house. To meet Oil Company safety standards, extensive shoring was used in the primary area where the 16 large diameter manifold pipes had to be stacked and fitted within a total width of only 10 feet. Excavation and use of build-a-box shoring was used to install the backyard manifold sub-structure under the rear wall of the house to tie internal house piping to a 16” riser installed to a depth 14 feet below grade.
Pipe and Lower Manifold Construction
The subsurface horizontal piping with wye risers to intermediate flanges were constructed. Tolerance for setting the 16 large diameter pipes the length of the house was extremely tight. The gang of 16 incoming pipes were not in the position anticipated by the plans and in turn the tie-in had to compensate for the differences to achieve the necessary alignment within the tight foot-print of the house. This lower half of the large manifold structure had to be constructed such that the wye risers were precisely plumb and spaced to ensure future construction of the manifold (by others) would result in plumb risers from the floor to ceiling within the house.
The project required completion within 38 working days. Working hours were limited due to the project location within residential neighborhood. Equipment options were limited due to the proximity of adjacent homes, and the small site footprint. Excavation challenges were further compounded by the low headroom and the temporary structural shoring of the new, much larger beams that needed to be installed prior to construction of permanent posts and wall footings. These site conditions combined with tight tolerances required very labor-intensive construction methods and repositioning of shores to accurately fit the stacked configuration of the large diameter PVC pipes. The approach angles of the pre-existing pipes that fed into the house required substantial field adjustments and the use of small-angle couplers with precise rotation to achieve accurate placement and connection of the manifold pipes. Space constraints, low hanging overhead power lines, 16ft high perimeter sound barriers and railroad easement abutment to the property, presented significant challenges to complete excavation safely and within schedule.
Pipe fitting of the large diameter piping within tight space constraints, required precise cutting and dry fitting before final assembly. QC of welded joints was highly critical to ensure pipe could sustain pressure testing of 7 psi (14.25 in Hg) for 1 hr. Extensive sacrificial anchoring was required to ensure zero movement of highly buoyant pipe during the slurry backfilling process. E&E was successful mitigating any damage to external stucco and veneer materials during structural renovations, termite repairs and movement of heavy equipment around and within the house so that the external house maintained the original appearance of when it was originally built, allowing it to remain seamlessly integrated aesthetically into the surrounding neighborhood.