Geology Chapter: Sedimentary Rocks

Geology and Civil Engineering

• Sedimentary rocks are formed through deposition and solidification of sediment, often deposited in layers and containing fossils.
• Sedimentary rocks can be used as construction materials, e.g., coarse (gravel) and fine (sand) aggregates in concrete, and raw materials for structural steel.
• Soil is important for embankment, fill material, and reclamation, and proper soil investigation is crucial to prevent calamities like landslides.

Rock Cycle

• Sediments are formed through weathering and erosion, and then undergo pressure and cementation to form sedimentary rocks.
• Sedimentary rocks can be exposed to high pressure and temperature, resulting in metamorphic rocks.
• Metamorphic rocks can melt to form magma, which then cools and solidifies to form igneous rocks.
• Igneous rocks can undergo erosion to form sediments, completing the rock cycle.

Plate Tectonics

• Plate tectonics is the process that determines the structure and characteristics of the lithosphere through time.
• The movement of plates causes different events on the lithosphere, such as earthquakes, volcanic activities, and the formation of mountains and oceanic trenches.
• The Philippine Plate is located at the border of the Eurasian Plate, and the movement of these plates causes earthquakes and volcanic activities in the Philippines.

Earth's Structure

• The Earth is composed of the crust, mantle, outer core, and inner core.
• The mantle is divided into the upper mantle and lower mantle, and is capable of flowing due to heat and pressure.
• The outer core is made up of liquid iron and nickel, and the inner core is solid iron and nickel.

Earthquakes and Faulting

• Earthquakes occur when there is a sudden release of energy in the Earth's crust, usually due to faulting.
• Faulting is the process of brittle deformation of the Earth's crust, resulting in the formation of faults.
• There are three types of faulting: normal, reverse, and strike-slip faulting.
• Faults can be recognized by geological evidences, such as offset of rock units, repetition and omission of strata, and stratigraphic sequence.
• Fault plane evidences, such as feather joints, slickensides, and drag, can also indicate faulting.

Development of Pull-Apart Basins and Restraining Bends

• Pull-apart basins are formed when there is a large-scale pull-apart movement of plates, resulting in the formation of normal faults.
• Restraining bends are formed when there is a push-up or uplift of plates, resulting in the formation of reverse faults.
• The combination of normal and strike-slip faults can produce a pull-apart basin, while the combination of reverse and strike-slip faults can produce a restraining bend.

Fault Zone Processes

• Fault zones can serve as conduits for rapid fluxing of large amounts of water, leading to dissipation of heat during deformation.
• Fluids play an important role in faulting, having a lubricating effect and reducing the shear stress necessary to permit fault slip.
• Focal mechanism, which includes the type of faulting (reverse, normal, strike-slip, etc.), can be used to determine the orientation of the fault plane and the direction of shear.### Soil Sampling Techniques
• 15 minutes to 15 blows are considered to relieve water pressure and suction during soil sampling
• Sampler is rotated one revolution and slowly retracted to avoid falling out of the soil sample
• Tubes are sealed with cheesecloth and paraffin wax on both ends and stored in an upright position
• Soil samples are extruded in the same direction as the soil entered the sampler

Cone Penetration Test (ASTM D5778)

• Uses electric steel probes with a 60° apex tip
• Probe is pushed into the soil at roughly 20mm/s
• Continuous readings of tip resistance, sleeve friction, and possibly water pressure are taken
• No boring is necessary and limited disturbed samples can be recovered

Sample Disturbance

• Samples collected in split spoon are disturbed
• Degree of disturbance affects sample quality
• Rod is slowly penetrated to minimize disturbance

Rock Coring

• Simultaneous and continuous hole advancement and core sampling
• Various components are used depending on the condition of the rock site
• Samples are recovered and stored in core boxes for analysis
• Rock Quality Designation (RQD) is used to evaluate the quality of the rock core

Rock Core Handling

• Rock cores are transferred from core barrels to core boxes and marked accordingly
• Cores are stored securely in place and left to right in the core box
• Weathered rocks are sensitive to moisture and need to be wrapped in plastic for protection
• Drilling is limited by equipment length and cores are recovered in intervals with block placed between them

Rock Quality Designation (RQD)

• Measures the quality of the rock core from a run as a percentage
• Calculation is based on the total length of sound pieces divided by the length of the core run
• Sound pieces of core are at least 100mm and not highly weathered
• RQD is used to classify rock quality into different categories (e.g. Very poor, Class 2, Class 3)