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Numerical simulation of concrete dam foundation seepage and uplift pressure distribution
Published in W.A. Hustrulid, G.A. Johnson, Rock Mechanics Contributions and Challenges: Proceedings of the 31st U.S. Symposium, 2020
Figure 5 indicates that increasing grout curtain depth effectively reduces uplift pressures if the grout curtain reduces rock mass conductivity by two orders of magnitude or more. Greater pressure reduction is realized at points closer to the grout curtain. If the grouting only reduces the conductivity of the grouted zone by about one order of magnitude little additional benefit is derived from increasing the depth of the grout curtain below approximately 33 percent of flow layer thickness (in this case, a curtain depth of about 100 feet). If the grouting is more effective and reduces the grouted zone conductivity by two to three orders of magnitude, a point of diminishing returns is reached between 35 to 40 percent of the flow zone depth. Grouting to this depth reduces the uplift pressures by approximately 75 percent of the nearly full depth grout curtain pressure reduction. Thus it appears that grouting to a depth of more than 30 to 40 percent of the depth of a flow zone may not be cost effective under many circumstances.
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Published in C.P. Chugh, Ken Steele, V.M. Sharma, Design Criteria for Drill Rigs: Equipment and Drilling Techniques, 2020
C.P. Chugh, Ken Steele, V.M. Sharma
Grout Curtain: to impede the flow of water under or around a dam a grout curtain is usually provided. The depth to which this should extend will depend on the type and condition of the rock mass. The suggested depth of grout curtain is D=1/3H+C,
Trenchless construction of Phase IIIA district cooling system (DCS) by TBM pipejacking and hand-dug tunnelling on Kai Tak Development: part I – design and construction considerations
Published in HKIE Transactions, 2018
Wilson W S Mok, Victor K Y Lo, Germaine T M Chau, Louis Y M Lau
A hand-mining shield tunnelling technique was adopted at three locations where there was insufficient space to construct a working pit to accommodate a TBM, and for a short section of tunnel excavation. This technique requires larger over-excavation which causes more ground settlement. The ground settlement for each tunnelling drive, using the same approach as the TBM pipejacking, was estimated to be in the range of 35 mm to 55 mm. Prior to excavation, a grout curtain, about 1.5 m thick, was provided above the ground and at the two sides of the tunnel alignment, by drilling horizontal grout holes from the working pit, to strengthen the ground.
Design of grout curtain for temporary embankments on rock foundation
Published in Geomechanics and Geoengineering, 2022
Ahsan Saif, Khyzer Ahmed Sheikh
In soils, seepage occurs through the small, closely spaced voids present between the soil particles scattered throughout the medium while in rocks seepage majorly occurs along discrete joints and fractures. In soils hydraulic conductivity is mostly controlled by the size, shape and arrangement of its voids (Terzaghi et al. 1996), while in rock masses, the hydraulic conductivity depends on the aperture, spacing and infilling characteristics of its discontinuities (Goodman 1980). Providing an impermeable cut-off under the embankment (sheet pile or curtain grouting) to lengthen the path of incoming seepage is one of the most commonly used seepage control methods. In soils, installing sheet piles may prove a better option but for embankments on rock foundations, curtain grouting is almost always the better, quicker and economical solution as installing sheet piles in rock could take more than the anticipated time and may also get damaged during drilling. Curtain grout is a drilled hole filled with cement mortar under pressure to fill the voids, fissures, cavities in the surrounding rock/soil and decrease the permeability or in other words, block the path covered by seepage water. Grouted holes are constructed in series, forming a curtain in the path of seepage, hence the name grout curtain. The cut-off lengthens the seepage path under the foundation of the embankment and ensures piping does not occur, which is the most common failure cause in embankments (ICOLD 2013). Since piping through foundation usually starts from the downstream end of the embankment, the purpose of providing cut-off is to reduce the exit gradients and seepage velocity at the downstream end of the embankment, where seepage exits the soil/rock. Additional seepage control measures may also be introduced along-side constructing cut-offs, depending upon the type and scope of the embankment structure, such as upstream blankets, relief wells, downstream berms, toe drains, etc.