1. Advanced Geotechnical Engineering
Groundwater and Seepage flow
in jointed rock mass (i)
Advanced Geotechnical Engineering
EAG 442
By: Dr Mohd Ashraf Mohamad Ismail

2. Properties of joint networks
Rock mass properties:
Filling
Wall strength
Block size
Joint set
Roughness
Persistence
Aperture
Joint spacing
Dip and dip direction
Seepage
Rock type
Weathering grade

3. Fluid flow through RM
“This topic concerns with fluid flow through rock mass which is one of the most difficult topics facing practicing engineer”
“The basic idea is rock mass contains discontinuities and discontinuities are preferential flow paths”

4. What is groundwater?
Rainfall that soaks into the ground and moves downwards into pore spaces and cracks in the rocks becomes groundwater.
The rocks that store groundwater are aquifers.
The study of groundwater is called hydrogeology.
The study of groundwater requires an understanding of the hydrological cycle as it pertains to the recharge and discharge of groundwater and
The study of the geological formations that store groundwater is essential for a comprehensive understanding of groundwater.

5. Key aspects of Groundwater
Groundwater occurs as a result of specific geological conditions in combination with specific hydrological conditions.
Aquifers exhibit porosity – the capacity to store water.
Aquifers exhibit permeability – the capacity to transmit water
Groundwater flows down the hydraulic gradient – from high head to low head (m).
Flow occurs as seepage / matrix flow or fracture flow or both.
Groundwater flows from recharge areas to discharge areas.
Aquifers may be unconfined or confined – open to atmospheric pressure or sealed by an overlying impermeable layer.
Groundwater chemistry changes naturally due to rock-water interactions in the aquifers.
Groundwater management requires reliable aquifer characterization.

6. Interaction between SF and GW

7. Hydrogeological diversity
Unconsolidated rocks:
Primary Porosity
Large storage
Locally high permeability
Consolidated rocks:
Secondary fracture porosity
Small storage
Low permeability
Consolidated rocks:
Karsts (enlarged fractures)
Moderate storage
High permeability

8. Porosity and Permeability
Porosity: the percentage of rock or sediment that consists of voids or openings
Permeability: the capacity of a rock to transmit a fluid such as water or petroleum through pores and fractures
Porous: a rock that holds much water
Permeable: a rock that allows water to flow easily through it
Impermeable: a rock that does not allow water to flow through it easily

9. Primary and secondary permeability
Fluid flow through intact rock and fractured rock
Intact rock: small scale
(Rock matrix)
Low K
Fluid in
Fluid out
Rock mass: Large scale
High K
Fluid in
Fluid out
(Discontinuities)

10. Table of content Simulation model for GWF in JRM
Parallel Plate model & Cubic law
Actual Flow Observation in JRM & its simulation
Permeability value of rock mass
How water will affect rock mass

11. Table of content
Review of Darcy’s Law and exercise on flow through discontinuity networks
Next Tuesday 30 / 4 / 2013

12. Table of content Simulation model for GWF in JRM
Parallel Plate model & Cubic law
Actual Flow Observation in JRM & its simulation
Permeability value of rock mass
How water will affect rock mass

13. Simulation model for JRM
(1) Continuum model (Equivalent Porous media)
Model assuming an equivalent porous rock containing a discontinuity plane
(2) Discontinuum model(Network Model)
Assumed to exist in the water path discontinuity in the rock surface, forms a network of pathways of groundwater models

14. Simulation model for JRM
Extremely Porous Rock
Porosity
CO2 Injection
Pumice
Permeability
Scoria
Oil and Gas reservoir

15. Geometrical Modelling
Roughness
orientation
filling
aperture
size
Number of joints
2-dimensional model
3 dimensional model

16. Mechanical modelling of rock mass
Equivalent Continuum
Discontinuum
Input: properties of elements
Input: properties of discontinuities
Output: averaged stress in elements, displacement of nodal points
Output: force between blocks displacement of rock blocks

17. K1 K2 K3 K4 Hydraulic modelling of rock mass K1 K2 K3 K5 K6 K7 K8 K4
Equivalent Porous Media
Network
Input: properties of elements
Input: properties of discontinuities
Output: averaged velosity in elements, head of nodal points
Output: actual velocity through flow path head of discontinuities intersection points

18. EPM model Good points ●Easy to constitute
●Can consider vast number of joints
Weak point
●Can not grasp the actual velocity
●Applicable only to the elements of REV

19. Network model Good point ●Actual velocity ●No need to assume the REV
Weak point
●Accurate model is required
●Large computation

20. Table of content Simulation model for GWF in JRM
Parallel Plate model & Cubic law
Actual Flow Observation in JRM & its simulation
Permeability value of rock mass
How water will affect rock mass

21. Darcy’s Law Henry Darcy (or D’Arcy?) (1803-1858), Hydraulic Engineer.
The ”discoverer” of Darcy’s Law, 1856.
His law is a foundation stone for several fields of study including ground-water hydrology, soil physics, and petroleum engineering.

22. Hydraulic Conductivity Medium(cross-sectional area,A)
Darcy’s Law
Q = K A ー
DHL
Hydraulic Gradient Q
Hydraulic Conductivity L DH Q
Medium(cross-sectional area,A)

23. Hydraulic conductivity of the aperture Kf
Parallel Plate Model
vf=
gt2
12n i
Gravity：g
Kinematic viscosity：n
The simplest model of flow through a rock fracture is the parallel plate model (Huitt, 1955; Snow, 1965).
This is the only fracture model for which an exact calculation of the hydraulic conductivity is possible; this
calculation yields the well-known .cubic law. (Witherspoon et al., 1980). t vf
Hydraulic conductivity of the aperture Kf
tKf
gt3
12n
transmissivity
Cubic Law

24. Results of applying the parallel plate model
– 8　–7　–6　–5　–4　–3　– 2 2 1 -1 -2 -3 -4
Log(measured K [cm/s])
Log(calculated K[cm/s])
1：1

25. Seepage condition in the in-situ rock mass

26. Spacing of disc opening = aperture
Radial pipe flow model
Spacing of disc opening = aperture

27. Result of applying the radial pipe flow model-2 -3 -4 -5 -6 -7 -8
1：1
Log(calculated K[cm/s])
– 8　–7　–6　–5　–4　–3　– 2
Log(measured K[cm/s])

28. Examination result of flow model
Insitu
Seepage flow experiment ？

29. Table of content Simulation model for GWF in JRM
Parallel Plate model & Cubic law
Actual Flow Observation in JRM & its simulation
Permeability value of rock mass
How water will affect rock mass

30. OBJECTS of Pathways Surveys
Single Joint
Super-Conductive Joints
Joint System
“One of the most intensive in-situ test to characterize the channeling flow in fractured rock mass”

31. Experimental area (Kagawa prefecture, Japan)
Okayama Prefecture
Shodoshima
Wells Island
Uno City
Toyoshima
Naoshima
Yashima
Geology: granite
Aji Quarry
Takamatsu City
Highest quality of Japanese Tombstone
Kagawa Prefecture

32. METHOD of Pathways Surveys
Super Fine Grout Injection
Removal of the Rock Blocks
Observation of Grout Lumps on Both Joint Surfaces

33. Pathways Survey Method
1. Single Joint
sealed

34. Pathways Survey Method
2. Super Conductive Joints

35. Pathways Survey Method
3. Joint System
sealed
sealed

36. Pathways Survey Method
3. Joint System
water chamber
concrete
side
front
side
front
water pipe
Rock Block
Specimen

37. Pathways Survey Result
Single Joint IN
OUT

38. Pathways Survey Result
2. Super Conductive Joints
Borehole

39. Pathways Survey Result
2. Super Conductive Joints

40. Pathways Survey Result
3. Joint System
Removal

41. Pathways Survey Result
3. Joint System
OUT

42. Notable Points
Pathways in joints are what is called “channeling” pathways.
Area ratio of pathways – joint plane is varied and normally distributed.
Aperture(grout thickness) is log-normally distributed in a joint.

43. Historical perspective Fractures as parallel plates
Constant width

44. Historical perspective
Cubic Law of Fractures
Aperture half width
Fracture length

45. Historical perspective
Fractures cannot be assumed as parallel plates. w

46. Historical perspective
Fractures cannot be assumed as parallel plates.
A real fracture surface is rough and tortuous.

47. Historical perspective
The flow through a fracture follows preferred paths because of the variation in fracture aperture.
Witherspoon (1980)
Iwai (1976)
Neuzil(1980)
Tracy (1980)

48. Historical perspective
The friction associated with the rough fracture surface affects the flow performance.
Tsang&Tsang(1988)
Brown (1987)

49. Historical perspective
Stochastic aperture simulations
Experimental support
Aperture Width ?
Effect of friction in fracture flow simulations

50. Historical perspective
How do we obtain fracture aperture width?
How do we simulate flow through fractures effectively?
Application of water-resource research technology into petroleum engineering

51. Experimental Analysis
The approach
Experimental Analysis
Aperture width, qm, qf
Fracture simulation
Simulation
Aperture distribution
Stochastic Analysis

52. Experimental Analysis
The approach
Experimental Analysis
Aperture width, Qm, Qf
Fracture simulation
Simulation
Aperture distribution
Stochastic Analysis

53. The approach Information from experiments? Fracture permeability
Fracture aperture
Matrix and fracture flow contributions
How these properties change with overburden stress

54. The approach Apertures measured physically Sand grains
Impermeable surface
Flow experiments
Sand grains
Apertures measured physically

55. The approach
The fluid flow through a fractured rock mass will depend on:
The aperture of the fractures which in turn will depend on,
The normal stress acting across the fractures which in turn will depend on,
The depth below the ground surface

56. The approach
500 psi
1000 psi
1500 psi
To quantify the change in aperture with overburden pressure

57. km Experimental setup Core : Berea Accumulator Graduated Cylinder Pump
CORE HOLDER
Permeameter
Accumulator
Graduated Cylinder
Pump
Hydraulic jack
Matrix
L=4.98 Cm
A=4.96 Cm2
Core : Berea

58. Experimental Analysis
The approach
Experimental Analysis
Aperture width, qm, qf
Fracture simulation
Simulation
Aperture distribution
Stochastic Analysis

59. From experimental analysis
The approach
From experimental analysis
waperture
Is it possible to create an entire aperture distribution from a single value of mean aperture?
Yes !

60. Apertures distributed log-normally
The approach
Apertures distributed log-normally
Log-Normal Mean
Log-Normal Deviation
Variable
( Aperture )

61. Through a mean and a variance
The approach
Through a mean and a variance

62. Smooth fracture surface
The approach
Smooth fracture surface

63. Slightly rough fracture surface
The approach
Slightly rough fracture surface

64. Highly rough surface fracture
The approach
Highly rough surface fracture
Larger Aperture Size

65. Creation of the aperture map
The approach
Creation of the aperture map
Lag distance
Co- variance
Variogram
Kriging

66. The approach
Outcome of Kriging 3D 2D

67. Not the real picture but effective
The approach
Comparison
Not the real picture but effective

68. Experimental Analysis
The approach
Experimental Analysis
Aperture width, qm, qf
Fracture simulation
Simulation
Aperture distribution
Stochastic Analysis

69. Table of content Simulation model for GWF in JRM
Parallel Plate model & Cubic law
Actual Flow Observation in JRM & its simulation
Permeability value of rock mass
How water will affect rock mass

70. Primary and secondary permeability
Permeability: Ability of the medium (either rock matrix, discontinuities) to transmit water
Hydraulic conductivity: Ability of water (or any fluid) to passing through (transmit) between the medium

71. Primary and secondary permeability

72. Primary and secondary permeability

73. Table of content Simulation model for GWF in JRM
Parallel Plate model & Cubic law
Actual Flow Observation in JRM & its simulation
Permeability value of rock mass
How water will affect rock mass

74. Effect of water to rock mass
Deterioration of rock
Excessive amount of seepage inflow in confined/limited space area (underground excavation)
Reducing effective strength in discontinuities

75. Effect of water to rock mass
Deterioration of rock due to water causes instability of the excavation and rock slope.
In the tropical region, such as Malaysia, Indonesia, the weathering process of rock is more extensive, which causes the rock deteriorate is accelerated.
Very important subject to understand about the deterioration mechanisms of rock strength due to water, an increase in stability of the rock mass and how to improve the safety and performance of excavation.

76. Effect of water to rock mass
The presence of moisture or water (at atmospheric pressure) can have several effects on the discontinuities’ behaviour. If the water is migrating, there can be a mechanical action in which softer material, such as clay or other decomposition, is washed out from the joints or faults. Chemical action may dissolve some of the more soluble mineral components, resulting in a change in the mechanical properties of the rock. Chemical hydration (gain or loss of water by hydration) in certain rocks may cause a volumetric change when accompanied by a change in mechanical properties. The alternation of wetting and drying will cause some rocks to expand and contract and will thus affect their properties. Some rocks will suffer to separate on bedding planes or, in more extreme cases, to completely disintegrate.
Hence, in an underground operation where the humidity is seasonable or otherwise variable, the deterioration of surface rocks may be expected, especially in sedimentary rocks containing clay or other decomposition products. Major accidents, due to falling rock or the roof falling, have been reported particularly in underground works. Most cases are caused by the presence of underground water which decreases the rock mass strength. In coal mining operations where the roof and floor are mainly composed of clay-mineral bearing rock, the deterioration of the rock strength may cause the roof to fall and the floor to heave.
Some rocks, which may be categorized as clay-bearing rocks such as shale and mudstone, will break without applying any compression to them. These rocks are characterized by a wide variation in their engineering properties, particularly by their resistance to short-term weathering by wetting and drying. For example in underground coal mining operations, shales are normally found in the roof and the floor of the roadway. The problem arises when the strength of shale is deteriorated due to the presence of water/moisture.

77. Thank you very much for your attention