Here is an example I came across where a client was asked by the Mexican government to grout an existing dam. This governmental request came BEFORE (really?!?!?) they knew anything geotechnically about the dam. Some background to consider:
- Dam was built using alluvium and colluvium materials and compacted over near-surface bedrock.
- Dams are meant to seep and will last a long time if designed properly
- The dam had a clay core and a HDPE liner on the upstream face where it impounded water
- Dam had a seepage collection / underdrain pipe network installed at the base of the dam foundation to reduce saturation at the interface
The government agency was "demanding" a grouting program be performed because the dam had minor seepage at the downstream face and the impounded water was low Ph; improving the downstream water quality being the ultimate concern.
While I haven't gone into the deep details of the problem, here are some issues that needed to be considered to AVOID CATASTROPHIC FAILURE OF THE DAM!!!!!
- If the grouting does not create a deep curtain down to bedrock you are merely shifting seepage paths and pore pressures to a different zone in the foundation (possible stability problem)
- If the grouting isn't planned properly, you could plug off the seepage collection pipes
- If the grouting isn't planned properly, you can damage the clay core and actually increase seepage
- If you only grout the foundation (vs. the whole dam to the crest) you may change the seepage flow path to a shorter distance near the top of the dam and increase chances of local slope failures or piping.
- If the water or the soils are acidic, special concrete will need to be used otherwise the concrete will breakdown in a short period and make the improvements null.
It takes a seasoned contractor and engineering team to properly grout a dam. I haven't even mentioned the monitoring program needed to evaluate pore-pressures (effective stresses) before, during, and after construction. Analysis should be performed for both static and pseudo-static stability as well as seepage based on local regulations or commonly accepted best practices.
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Randall Rice P.E., M.ASCE
Golder Associates Inc.
Reno NV
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Original Message:
Sent: 05-09-2017 15:09
From: Michael Byle
Subject: What major safety hazards related to grouting, deep mixing, and diaphragm walls must engineers be conscious of?
As the ground improvement industry continues to expand, factors like large buildings, extensive underground work, and more exacting specifications from clients all contribute to the need for new methods of ground improvement, along with more intricate operations onsite. While bigger and more complex equipment enable sophisticated ground improvement elements, they also pose new and equally-complex safety issues.
Working platforms, silica exposure, and situational awareness are 3 such safety issues to be conscious of when working around grouting and deep mixing equipment. Rick Marshall, Director of Safety at ADSC, the International Association of Foundation Drilling, will be discussing means to mitigate them at Grouting 2017 in Honolulu Hawaii, July 9-12, 2017. Read more about the keynote session in the event program and register for the event: http://www.groutingconference.org/.
What kinds of safety issues have you encountered – or do you expect to encounter -- as technology, client expectations, and more drive new methods of ground improvement?
P.S. I've posted this in LinkedIn as well, but wanted to see what kind of discussions we can get on ASCE Collaborate as well.
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Michael Byle P.E., D.GE, F.ASCE
Tetra Tech Inc.,
Langhorne PA
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