Introduction

Engineering Geology studies geological materials and structures that affect the design, construction, and operation in Civil Engineering Projects. Some key influencing factors:
1. Material: Soil, Rock, Water.
2. Structure: Faults, Folds, Bedding Planes, Joints.
3. Environment: Topography, Stress Condition, Groundwater, Climate.
4. Engineering Activities: Excavation, Retaining, Drainage, Shotcrete, etc.

Application of Engineering Geology:
1. Tunnel design and support
2. Slope stability analysis
3. Dam foundation assesment
4. Reservoir leakage control
5. Foundation type selection

 

Geological Processes and Earth Interior

Earth Internal Structure:

• Crust : Upper layer, Lower layer
• Mantle: Upper mantle, transition zone, lower altitute.
• Core: Outer core (liquid), Inner core (solid)

Plate Tectonics

Type	Description	Example
Divergent	Plates move apart, creating new crust.	Mid-Atlantic Ridge
Convergent	Plates collide, leading to subduction or mountain building.	Himalayas (continental-continental), Mariana Trench (oceanic-continental)
Transform	Plates slide horizontally past each other.	San Andreas Fault

Fault and Stress

According to U.S. Atomic Energy Commission, a fault is considered as an active fault if:

• Movement occurred within the last 35,000 years, or
• Multiple movements occurred within the last 500,000 years, or
• Clear morphological evidence of recent displacement exist, or
• Instrumental evidence shows fault activity.

Type of Faults:

Fault Type	Dominant Force	Principal Stress
Normal Fault	Tension	σ1 vertical
Reverse Fault	Compression	σ1 horizontal
Strike-slip Fault	Shear	σ1 and σ3 horizontal

 

Rock Mass Classification

1. Rock Load Classification (Terzaghi)

Classifies rock masses as Intact, Stratified, Moderately Jointed, Blocky, Crushed, Squezing, and Swelling.

2. Rock Quality Designation (RDQ, Deere)

Formula:

RQD (%)	Rock Quality
<25%	Very Poor
25–50%	Poor
50–75%	Fair
75–90%	Good
90–100%	Very Good

3. Rock Mass Rating (RMR, Bieniawski)

There at least six parameters that must be considered, such as:

1. UCS
2. RDQ
3. Joint Spacing
4. Join Condition
5. Ground Water Level Condition
6. Joint Orientation Adjustment.

Weak Plane in Rock Mass

Type of Weak Planes:

Type	Definition	Examples
Primary Weak Planes	Weakness planes formed during the sedimentation process, before lithification.	Bedding planes, Unconformity surfaces
Secondary Weak Planes	Weakness planes formed after lithification, due to tectonic deformation or stress changes.	Cleavage, Schistosity, Joints, Faults, Fissures
Failed Weak Planes	Planes that have already undergone failure, often serving as active shear surfaces.	Shear surfaces, Fault gouge zones

Some important key words related to weak planes:

Property	Description
Spacing	Distance between adjacent discontinuities.
Persistence	Extent or length of the discontinuity plane.
Roughness	Surface waviness or irregularity.
Wall Strength	Strength of the rock adjacent to the discontinuity surface.
Aperture	Width between the surfaces of the discontinuity.
Filling	Materials filling the discontinuity (e.g., clay, calcite).
Seepage	Water flow along discontinuities.
Number of Sets	Number of discontinuity orientations present.
Block Size	Size of rock blocks bounded by discontinuities.
Orientation	Dip direction and dip angle of the plane.