Geotechnical & Tunnel Consultants

A consultant is a universal observer who can look at a problem outside the environment in which the problem came to be, thereby creating a solution that was never possible before.  Fernando Flores

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B-Type 1 or 2?
C-Jacked Pipe Failure
D-Top of Rock
E-PI Litigation Support
F-Geotech Assessment
G-Microtunneling Hard/Soft
H-Machine Failure
I-Boulders-Tunnel Boring
K-Plowing Utilities
L-Rock Socket Overrun
M-Bored Tunnel Inflow
N-Rock Comminution
O-Sub-Std TBM Performance
P-Bored Tunnel-Shear Zone
Q-Disputes Resolution
R-Problem Proj. Completion
S-Bored Tunnel Overbreak
T-Auger Sampling Problems
U-Bored Tunnel Delay
V-Hoe Ram - Failure to Rely
Peter J. Tarkoy

---on behalf of contractor---

Inspection Ignored Conditions Leading to Collapse - Did not direct contractor

The misrepresentation of ground conditions, the attempted post-contract modifications, and Inspection's inattention to actual ground conditions , were and continue to be the cause of collapses.

The entire landslide mass in which the tunnel is driven is at risk of failure. 


Misrepresentation of Ground Conditions

The original RMR scale, Ground Classes (AA through E), & associated stand-up times as presented by Bieniawski (Figure 4.2, 1988) are illustrated below:  

Four 4 distinct Ground Classes (A, B, C, & D) were defined in the project contract with associated standup times, yet each ground class fell into Ground Class D rather than in their respective and appropriate Classes.  It is immediately obvious, that Ground Classes were used to imply ground conditions superior to those indicated by the contract specified standup time. 

A further misrepresentation of the character of the Ground Classes was made by arbitrarily shifting Ground Classes A, B, C, & D to lower standup times without specific notice as shown below.

Inspection enforced this counterfeit classification even though it had not been a part of the contract.  After months of failing to deal with these issues by Inspection, the tunnel is undergoing progressive failure, with shotcrete cracking, movement of the lining, and ultimate fallout.  Inspection's response: NOTHING 

Non-Contractual Modifications by Inspection

After contract signing, inspection revised the description and, classification of the ground, its behavior, support requirements, (including number and diameter of bolts, spacing of steel sets), and stand-up time of Ground Classes.  This change was made & enforced despite it being outside the signed contract.  As a result, it was impossible for the contractor to achieve the original excavation rates (blue) and having to recalculate and modify his progress rates (red) illustrated below:

The encountered excavation suffered delays as a result of several differing site conditions, consequential and associated difficulties with roadheader excavation, and associated delays.  In addition, the  client imposed various non-contractual changes.  All of these impacted the encountered progress rates (in magenta) as illustrated below:

"But for" the delays imposed by the various differing site conditions and client imposed non-contractual changes, the contractor could have exceeded even his anticipated baseline rate as illustrated by the green line below:

In effect, inspection modified, misrepresented, and enforced a non-standard, non-contractual, false set of conditions on the contractor.  It appears that the intention was to mislead and coerce the contractor into accepting a decrease in the price of the work by making fraudulent calculations of RMR to indicate better quality rock than actually encountered. 

The contractor sought our assistance to determine if his claims were valid.  Our investigation revealed a number of differing site conditions, excavation issues, and the contrived classifications, all, independently and without ever reading the contractor's claim.

In effect, the contractor's original claim amount was far less than our investigation uncovered.

It is a miracle that this good natured contractor continued the work despite the difficult geological conditions and the oppressive environment created by the Inspection.


Unanticipated Short Standup = Excess Shotcrete

The encountered material did not behave as indicated in the contract documents, instead it air slaked and raveled faster than indicated in the contract requiring excessive amounts of shotcrete to fill the voids to the steel sets.  The air slaking stopped when ventilation was turned off.

Delays were experienced throughout the tunnel as a result of excessive shotcrete required to fill the voids left by unanticipated slaking and raveling. 


Tunnel Collapse @ Unanticipated Fault

There was a collapse of the left wall of a tunnel being excavated in volcanic clast and landslide material.  The unanticipated fault's failure plane was located beyond the length of the bolts required by inspection for support.

Delays were experienced as a result of necessary re-stabilization.