Aggregate pier ground improvement systems have been used for over 25 years to provide shear reinforcement for unstable slopes and failed slopes for a wide range of projects, both public and private. Recent innovations in design and delivery methods have resulted in great value to owners and contractors by providing long-term, engineered solutions that save time and money compared to traditional earthwork solutions for shallow slide failures. This presentation will provide a brief description of short pile-and-plate slope repair methods and will use case histories where shallow slides have impacted existing pipelines and infrastructure to illustrate applications where this innovative and minimally invasive ground improvement solution has been utilized to repair failed slopes.
About the speaker:
Adam Killinger, P.E., G.E. is Geopier's Region Engineer in Northern California and Nevada. Adam has over 15 years of geotechnical consulting experience prior to joining Geopier – a specialized design-build ground improvement company. He completed his BS in Civil Engineering and Geotechnical Engineering at California State University - Chico and received his MS in Geotechnical Engineering from California State University - Sacramento. Adam has experience in business development, project management, ground improvement design, and construction support. When Adam is not working, he enjoys traveling and spending time with friends and family.
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1.) What are the limitations of SRT?
Depth of slide (less than 15 ft) and performance in clean sands.
2.) RE Page 5 - slide 1 - Can you refer us to a technical paper in the literature justifying the shear strength increase from stress concentration?
Stress concentration decreases with depth and should only be used with good engineering judgment and understannding of the mechanics. A stress concentration factor of 1 is typically used for design where piers are not confined between bedrock or a stiff layer.
3.) Why do you use stress concentration in addition to area replacement when analyzing geopiers for slopes? Slope failure will occur through weakest soil, and we dont account for stress concentration with other systems.
Stress concentration decreases with depth and should only be used with good engineering judgment and understannding of the mechanics. A stress concentration factor of 1 is typically used for design.
4.) Can SRT be used to stablize crust on top of liquefiable layer (flow failure)? if yes, how do you make sure there is no flow failure in between piles in liquefiable layer?
To date SRT has not been consdiered for protection against flow failure resulting from liquefaction. One way to reduce these effects might be to lengthen the plates and close the spacing to reduce the potential for flow between the plates. The piles would also need to be designed for adequate bending and shear resistance. This may or may not be cost effective.
5.) Do we see any improvement in shear wave velocity and site class?
Yes for rammed aggregate pier improvement. No for SRT slope stability improvement. The site class with RAP improvement can often be improved from Site Class F. However, improvement for other site classes such as E or D are typically not practical or warranted because the site class is based on a weighted shear wave velocity in the upper 30m of the soil profile and boundary effects.
6.) Thanks for the interesting presenetation. What is the maximum depth of unstable soil layer SRT can be used for? What are the typical spacing?
SRT can be used for slide depths up to 15 ft. Typical lateral spacing is 4 ft. Design dictates spacing up and down the slope.
7.) Do you have capacity curves for Geopiers? I mean vertical load versus displacement?
Geopier has an internal set of set of guidelines used for preliminary design by it's design builders. A site specific load-deflection or stress-deflection curve is provided on most projects where a site specifc modulus load test is performed.
8.) How do you model GeoPier in codes like Flac/PLAXIS? How far away from the Geopier we should enhance soil properties?
This is a good yet complex question. Typically an axi-symmteric model with mohr coulomb failure criteteria or strain hardening model can be used. However, selection of appropriate soil parameters such as stiffness moduli and ko can vary based on the soil types, spacing of elements, and loading stresses. These parameters requires careful consideration and judgment. Typically hand or spreadhseet calculations provide excellent prediction of RAP performance based on prior research and empircal observations.
9.) Can SRT be used for shallow shoring systems (<10ft) if so are there any limitations in terms of installation lengths into dense sands?
SRT is not typically used for shoring applications. It has been used in a limited capacity for temporary shoring of excavations of about 5 ft or less on projects with other Geopeir supported applications. We would be pleased to discuss any project specific needs with you.
10.) What is the typical inclination of SRT system?
The piles are typically installed vertical from horizontal plae for ease of instalaltions. There is typically a small batter upslope.
11.) What is the typical plate pile input in Slide?
The shear resisance in plf is entered from the Lpile analsyis.
12.) Can SRT be installed with inclination angle?
SRT can be installed on slopes as steep as 1:1 (H:V). The installation is usually slighly battered towards the uplope side because the piles are installed normal to a horizontal plane.