August 2019 Report

There was some concern while analyzing the test data over the last 18 months that some movement is occurring in the slope and that the berm is not performing as designed.   Additional testing on the stability of the berm was performed during March and June which confirmed that the berm has moved slightly,  probably due to the unusually wet winter and spring this year.   The original engineering planned for a level of safety of 1.25 and the new data indicates that the berm is not to that standard.  The ultimate goal is to reach a level of safety of 1.5 (50% more that what may be required to stabilize the slope).  Currently GTS is designing modifications to the berm that would hopefully accomplish the goal of completely stabilizing the affected slope.   Once the design is available it will be reviewed by the city and we will obtain cost estimates and determine the financial feasibility of making additional changes to the berm.     

March 2019 Update

I met with Chris Volksen of Geotechnical Testing Services this week for an update on his response to questions from the City and AGEC regarding his most recent report.  The report concluded that the slope appeared to be stable based on nine tests made over the past five years.  However, there were some questions from the City consultant, Jim Nordquist of AGEC, who reviewed the report and requested more information. 

GTS performed additional tests this month and discovered that there may be some slight movement after all.  Attached is a graph of data from one of five inclinometer wells, this one from a well located within the berm itself.  If you compare the test dates, it shows both positive and negative movement, back and forth, which can be attributed to instrument inconsistency.  The measuring instrument is extremely sensitive and it's not unusual to have slight inconsistencies among tests. The positive/negative differences in the early readings were averaged and the conclusion was that the slope had moved very little.  
The concern now is that the three most recent tests over the last 18 months for this particular well show a possible trend (all positive, no negative data points) indicating the possibility of slope instability.  The graph indicates movement of about 1/8 inch.  Very small but it could indicate some instability.   There is a blockage in one of the well shafts near N building about 40 feet down and Chris is trying to locate a camera this week to find out if the shaft has separated (minor inconvenience) or is sheared (major problem which could be proof of substantial earth movement).  Chris has yet to plot the other three inclinometer data readings and will compare the data from those locations to see if there is a similar trend.

It may be necessary to wait another six months (we have become very accustomed to waiting) and conduct additional tests.   If the readings indicate a negative direction, as in earlier tests, those results would be averaged with prior data and would again support the conclusion that the slope is stable.  If future readings show a continued positive trend the conclusion may be that the slope is still moving, if ever so slightly.  Further work to mitigate the problem may be necessary.  The engineers are being extra cautious as no one wants to declare the problem solved and spend a lot of money fixing things up, only to discover that the slope is still unstable. At present the test results remain somewhat inconclusive and further testing may be required to increase the confidence level in the conclusions and recommendations.