Geotechnical Validation for Sydney Tunnels Tim Nash, Bernard Shen, Rob Bertuzzi 16th Australasian Tunnelling Conference 30 October - 1 November 2017, Sydney Pells Sullivan Meynink

Objective Application of Sydney Classification System (Pells et. al., 98) to rock masses in mined tunnels Practical challenges and suggested improvements/alternatives Endoscopes - pros and cons

Routinely Determining UCS OPTIONS CHALLENGES 1. Coring and testing • Timeframe Equipment in tunnel Coring correct interval/orientation Expensive 2. Point load testing • Sample size and number In situ position Relies on good UCS correlation Lacks repeatability 3. Field guide to strength (normally adopted) • No access to tunnel face/crown/sidewall Small ranges of UCS in classification Sample size/insitu position

UCS – Improvements Field estimation Specify field est. strength intervals rather than specific UCS values adequate SI to substantiate field est. strengths Only at critical locations - specify min. UCS values that require testing, not for routine verification

Defect Spacing Challenge 1: Distinguishing between a true defect and rock fabric “a discontinuity, fracture, break or void in the material across which there is little or no tensile strength.”

Groundwater seepage/Iron staining Infill Overbreak or delamination back to a plane Shearing observed in an endoscope

Defect Spacing Challenge 2: Scale Consider 6 m high tunnel face with 3 bedding planes, 2 being 0.5 m apart. The defect spacing could be reported as 0.5 m (min) or as 2 m (average over defined interval). Addressed by Bertuzzi and Pells (2002) “the classification system be applied to portions or units of rock mass having similar UCS, defect spacing and seam characteristics”

Defect Spacing Suggested solutions Specify intervals over which class should be assessed (assumes portions or units of rock mass have similar UCS, defect spacing and seam characteristics) Specify min defect spacing if important to design Establishing common approach for all mappers at beginning of construction (training)

Allowable Seams Definition “…clay, fragmented, highly weathered or similar zones” Challenge: Access - permissible only after ground is fully supported, almost always includes shotcrete At best, the character and infill thickness is based on remotely observed behaviour

Allowable Seams Suggested solutions Seams specifically defined in design to be practically verifiable and confidently assessed at (near) the face. Example for endo: “allow any subhorizontal defect infilled with clay or any fragmented/highly weathered rock that is between 25 mm and 200 mm thick”.

Endoscopes Holes drilled in crown Commonly with rock bolting rig, top hammer percussion, 45-65 mm diameter Challenge: Percussion drilling can inadvertently damage the borehole - rifling, overbreak and fracturing of the rock mass

Endoscope inspections

Endoscope Inspections Endoscope inspections becoming more common for alleged validation of Defect type and characteristics Rock mass class Geological structural models Lithological changes Hole closure caused by shearing along defects Validation of many of these aspects by endoscope is virtually an impossible task.

Endoscopes Suggested improvements Non percussive/rotary drilling techniques, hole diam. ≥ 65 mm and well flushed Avoid incorporating the identification of infill thicknesses <25 mm Consider endos as informative method to assess lithology and shearing/hole closure

Concluding Remarks Incumbent on tunnel designers to consider the inherent difficulties and accuracy in field observations align with common, pragmatic solutions for validating geotechnical / geological attributes Outline how each design component will be validated at start of construction (collaboration).