New Cross Shaft Ground Improvement Chalk Grouting | Keller UK

New Cross Shaft Ground Improvement Chalk Grouting

Chalk Fissure Grouting
The process is undertaken by initially drilling small diameter boreholes through the chalk, then injection of a fluid cementitous grout via inflatable packers.

Contract Statistics
Number of holes drilled = 71
Total Length of drilling = 2295m
Number of grout injections = 241
Volume of grout injected = 102m^3
Average permeability achieved = 1.5 Lugeons

As part of a new deep cable tunnel between New Cross and Wellclose Square substations, ground improvement was required to allow the New Cross shaft to be constructed in stable ground conditions.

Keller Geotechnique were contracted by J Murphy & Sons  to  design and construct the ground improvement scheme, with the aim of improving the shear strength and reducing the permeability of the chalk which surrounded the proposed shaft location.

The works were undertaken by drilling small diameter rotary percussive boreholes through the Chalk, then the injection of a low viscosity, microfine cement based grout under pressure, and in controlled stages. 

The grouting targeted the fissures within the Chalk, such that the overall permeability was reduced in line with the specification to 2 to 5 Lugeons.  The reduced permeability of the Chalk was proven by post treatment using separate boreholes at a centroid grid position, then 10 minute permeability tests were performed using an in-situ packer.

System: Chalk Grouting

Client: London Power Networks

Contractor: J Murphy & Sons

Engineer: AECOM

Year of Execution: 2013

 

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