Attach_10_Memorandum,_Paradise_Inn_Annex_Preliminary_Geotechnical_Review,_Dec_22,_2010.pdf

DRAFT

MEMORANDUM

Date: December 22, 2010

To: Mr. Tom Hamann, Otak, Inc.

From: Stuart Albright, P.E.

cc:

Re: Paradise Inn Annex

Preliminary Geotechnical Review Mount Ranier National Park, Washington 1794-00

We have reviewed the geotechnical report prepared for the project by Northwest Geotech Inc. This memorandum summarizes our impressions of that work, initial recommendations, and summary of intent for further work.

The field work completed for the report is relatively thorough and covers the corners of the buildings. The wide variability in conditions encountered leads to a need to complete additional explorations in order to improve the quality of data available relative to foundation installation and drainage improvements. However, on proposing for a project of this nature, not having completed geotechnical explorations there before, our scope of work for field explorations would have been similar to what was accomplished here.

The recommendations portion of the report takes less than two pages. There is very little to that content and not much to be gleaned relative to their intent on how the original project would be constructed. Of particular note is the section that covers construction dewatering and permanent dewatering. It is three sentences long and contains no project specific content.

In general, the subsurface conditions consist of mudflow deposits (similar to the Mt. Saint Helens flows) overlying volcanic ash and intact bedrock. The mudflow deposits generally occurred as silty sands to sandy silts with varying contents of gravel and cobbles. Groundwater was encountered from 2.5 to 5 feet below the ground surface at the end of summer.

From a water issue standpoint, the conditions are such that shallow groundwater will nearly always be present across the site. Surface water can rather easily infiltrate into the mudflow soils where further infiltration is likely slowed or stopped entirely by the lower permeability ash and bedrock. Water ultimately migrates downhill and erupts as

Paradise Inn Annex – Preliminary Geotechnical Review Page 2 December 22, 2010

1794-00 springs but given the irregular bedrock and ash surfaces, the flow pathways are anything but direct. This is particularly acute at the Annex structure where the rock appears to have been encountered at a higher elevation on the downslope side of the building than at the upslope side. If this is true, the water may be somewhat contained by a natural subsurface dam and as such, doesn’t drain, even during Summer.

It is worth noting that the cross sections included in the report are full of errors and are not particularly representative of the conditions encountered (as but one issue, they don’t reflect surface topography). The surface elevations are also not captured in the logs. Assuming the site plan represents the drilling locations fairly accurately, it shouldn’t be difficult to redraft the data based on actual topography.

The soils and rock formations encountered are generally suitable for the support of foundations. The relatively thin soil cover (4 to 21 feet) is generally good for foundation support. The deeper depth to rock found on the upslope half of the site (13 to 21 feet) is potentially troubling if we are trying to get support uniformly from bedrock. We will have to evaluate that further during our subsurface work. As we have discussed, deep foundations (micropiles) may be necessary.

We should be able to install a cutoff drain on the upslope side of the building. This, plus better surface drainage, and perhaps some waterproofing of the basement foundations below grade would address the majority of the water intrusion into the basement. As we discussed in the field, it would be advantageous to install the cutoff drain before starting excavation in order to provide some level of dewatering for the Contractor. Additional dewatering would also likely be necessary.

Surface drainage currently ponds water adjacent to the building. Although this issue may persist during spring melt due to inadvertent dams created from unmelted snow, it is important to direct as much water as possible away from the foundations. This should be accomplished with both grade changes and pavement maintenance. Further, some level of waterproofing below grade (such as a membrane system) could be applied. These two systems, coupled with a drain system that will address groundwater are the best lines of defense to limit flow into the basement area.

We have discussed water disposal with Otak. We understand that a direct pipe into the adjacent drainage is unlikely to be permitted. As such, a flow spreader with no surface manifestation could be constructed below the Annex building. Obviously this structure should be built as far away from, and as far below, the existing structure as feasible. We are aware that it may need to be installed relatively close to the downhill side of the building. This is feasible, although perhaps not the most desirable.

Going forward, a further exploration program will assist in defining the cross-section through the building. This is important in order to better understand how subsurface water flow works as well as to get a hand on construction quantities. The presence of a large unexcavated mound of soil in the basement is troubling since one would assume that it represents a rock outcrop. However, based on existing exploration data, the presence of an outcrop at that location is highly unlikely. This needs to be evaluated as it represents a potential large expense relative to the structural upgrades.