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Underground Parking Garage

Shoring Plan for

PlumpJack Squaw Valley InnOlympic Valley, CA

January 20, 2016

PlumpJack Group & Meriwether Companies / 1PlumpJack Squaw Valley Inn - Olympic Valley, CA

Underground Parking Garage Shoring Plan - January 20, 2016

IntroductiondavisREED has been asked by Meriwether Companies to assemble a revised plan to mitigate high groundwater conditions during construction of the PlumpJack Squaw Valley Inn parking garage. Through the construction of a horizontal barrier utilizing Cement Deep Soil Mixing (CDSM) to form the perimeter wall of the shoring and Jet Grouting to form the bottom, vertical barrier of the excavation, this plan will achieve the necessary site conditions to build PlumpJack’s new underground parking garage while maintaining the natural state of the surrounding hydrogeologic environment.

As stated in our November 3, 2015 Temporary Construction Dewatering Plan, davisREED understands that the parking garage will require some excavating to a depth of 6192’ (MSL) and that the groundwater levels seasonally fluctuate between a low of 6190’ and a high of 6200’. The purpose of this plan is to describe how we will create watertight shoring within the fluctuating groundwater system in order to construct the underground parking garage within the schedule presented in our initial report. To this end, davisREED has coordinated with Holdrege and Kull and our shoring subcontractor, Condon-Johnson & Associates, to design virtually impermeable shoring that will render large-scale construction dewatering unnecessary.

Garage Construction ScheduledavisREED’s proposed schedule for the construction of the PlumpJack underground parking garage will be approximately seven-and-a-half (7.5) months from demolition commencement to foundation completion. Our projected milestone durations for the major categories involved in this portion of construction are as follows:

• Apply for Lahontan RWQCB Permit: February 1 – March 31, 2017• Demolition: April 1 – April 30, 2017• CDSM for Horizontal Barrier (Walls): April 15 – June 30, 2017• Jet Grout for Vertical Barrier (Bottom): June 1 – August 15, 2017• Install Tiebacks: August 16 – September 15, 2017• Excavation: September 16 – October 15, 2017• Foundation: October 16 – November 15, 2017

Midway through the demolition phase davisREED will mobilize our shoring subcontractor to commence CDSM and Jet Grouting activities. We will begin with CDSM activities to install the shoring walls. Employing a drill rig equipped with paddles for mixing and a nozzle to introduce the cement, the rig will drill down to the designed depth of the walls, introduce the cement into the void and begin combining the soil/cement mixture to create grout columns that form a contiguous, impermeable grout wall for shoring. The columns will be placed around the entire perimeter of the proposed garage excavation, or approximately 1,876 linear feet. Halfway through the CDSM process, the Jet Grouting will begin inside the perimeter of the proposed excavation area. A contiguous series of drill points will be plotted to create an impermeable grout bottom that will withstand the calculated hydrostatic pressure and uplift exerted on the eventual underground parking structure. The Jet Grout plug will cover the entire area of the excavation, or approximately 64,000 square feet (please refer to page 3 of this davisREED report for layout and equipment examples).

Once the walls and bottom of the grouted shoring have been completed, davisREED will begin excavating and install a series of approximately 470 tiebacks to support the walls of the excavated area. By October 15 we will have excavated approximately 22,000 cubic yards of soil. davisREED will finally waterproof and form the foundation floor and walls directly against the grouted shoring and complete the underground foundation work by November 15, 2017.

Grouting Equipment & MethodologyThe purpose of the grouted shoring is to create vertical and horizontal barriers within the high groundwater area where we are to construct the underground parking garage and, in so doing, create a virtually impermeable barrier where water intrusion will be so insignificant that a simple sump pump will address any possible leakages in the shoring during construction.

The grout mixture created in the CDSM process for the walls of the shoring will have a compressive strength of approximately 150 psi. As briefly described above, this CDSM process will deliver grout columns to form the walls of the shoring by introducing a

Shoring Plan Narrative



cement mixture at a relatively low velocity, while the auger of the drill rig utilizes paddles to mix the cement mixture with native soil. The grout thickness of the perimeter shoring wall will be three (3) feet.

Jet Grouting will involve direct injection of a similar cement material to CDSM, but does not involve mixing with soil and has a higher compressive strength of approximately 250 psi. The grout is injected at a much higher velocity in order to displace the surrounding soil to achieve the designed thickness of the grout plug. The grout thickness of the PlumpJack vertical barrier will be five (5) feet, the specified thickness necessary to withstand hydrostatic pressures and uplift caused by the surrounding groundwater forces.

On occasion we may experience relatively slight leaks in the shoring system. However, we anticipate any water intrusion caused by leaks to be relatively insignificant and, should such an event occur, we have procedures to properly treat and handle the water.

SummaryThis plan is designed to wholly mitigate high groundwater and its seasonal fluctuations throughout the months of the parking garage construction of the PlumpJack Squaw Valley Inn. We have tailored the grout specifications to prevent water intrusion into the excavation area, thereby allowing our team to shore, excavate and construct the underground parking garage during the spring, summer and fall months. The methods described in this plan are industry standards that allow for effective underground construction within high water tables, while sustaining the native surrounding environment.

Shoring Plan Narrative



Shoring Site Plan (Example)

Plan View, CDSM Shoring

Plan View, Jet Grouting

CDSM Installation

Jet Grouting


Cement Deep Soil Mix (CDSM) Plan Layout CDSM Drill Rig

Jet Grout Plan Layout

Jet Grout Rig

Plan View, CDSM ShoringPlan View, CDSM Shoring




VISIOnS ReAlIzed

Documents

Appendix T