Chapter 1.
Introduction to Engineering Geology
1.
How many major layers are in the Earth’s internal structure? What are their thicknesses?
Answer:
The Earth is divided into three main layers: crust, mantle, and core.
 The crust is the outer solid layer of the Earth and comprises the continents and ocean
basins. The crust varies in thickness from 35-70 km in the continents and 5-10 km in the
ocean basins.
 The mantle, a highly viscous layer about 2900 km thick, is located beneath the outer
crust. It includes the upper mantle (about 35 to 60 km thick) and the lower mantle (about
35 to 2890 km thick).
 Beneath the mantle and at the center of the Earth are the liquid outer core and the solid
inner core. The outer core is an extremely low viscosity liquid layer, about 2300 km
thick, and composed of iron and nickel, with an approximate temperature of 4400°C. The
inner core is solid, about 1200 km in radius, and entirely composed of iron, with an
approximate temperature of 5505°C.
2.
A geologic map in Monterey, CA is shown below (Figure 1.7).
(1) From the map, identify the following rocks (types and names): Mvqa, Qls, Mlt, and Kp.
(2) Identify what geologic features the following four lines represent.
Line 4
Line 2
Line 3
Line 1
Figure 1.7 Geologic map
Answer:
(1)
Myqa: the area labeled "Mvqa" represents an unnamed formation composed of a volcanic
rock (“vq”) called andesite (“a”) of the Miocene Epoch in the Tertiary Period
(between 23.7 to 5.3 million years ago).
Qls: the areas labeled “Qls” represent landslide (“ls”) deposits of Quaternary period,
Mlt:
Kp:
the arrows in the “Qls” deposits indicate the directions of the landslides.
Lone Tree Formation of Miocene Epoch in the Tertiary Period.
the area labeled “Kp” shows the Panoche Formation of Cretaceous period
(Panoche Formation is named after the Panoche Pass, a landform feature within a
mountainous area of San Benito County, California).
(2)
Line 1: a solid thick line, representing a precisely located fault.
Line 2: a dashed thick line, representing a fault with less certainty.
Line 3: a dotted line of thickness between depositional contact (thin) and fault (thick),
representing folds axis with most uncertainty
Line 4: a thin line, representing a depositional contact for two different rock formations.
3
Name the three major classes of rocks and briefly describe how they were formed.
Answer:
(1) Igneous rocks are formed due to igneous activities, i.e., the generation and movement of
silicate magma. There are two kinds of igneous rocks: extrusive or volcanic rocks that are
formed by cooling of lava from volcanic eruption, and intrusive or plutonic rocks that are formed
by the slow cooling of magma beneath surface.
(2) Sedimentary rocks are formed by the accumulated and hardened deposits of soil particles and
weathered rocks transported by wind, streams, or glaciers. Among sedimentary rocks, the most
widespread are shale, sandstone, limestone, siltstone, mudstone, claystone, and conglomerates.
They all display the characteristic stratification resulting from the gradual accumulation of layers
of compacted and cemented deposits.
(3) Metamorphic rocks are formed when igneous or sedimentary rocks have been subjected to
the combined effects of heat and pressure, resulting in compaction, cementation, and
crystallization of the rock minerals; the extreme pressure and heat transform the mineral
structure.
4
Provide generalized comments on the hardness, soundness, and durability associated with
the three basic types of rocks.
Answer:
Typically, igneous and metamorphic rock formations are hard and durable. Sedimentary rock
formations can also be sound and durable; but compared to igneous and metamorphic rocks,
more inconsistencies are expected in sedimentary rocks because of the presence and inclusion of
foreign materials at the time of formation or because of weak bonding and cementing. Shale and
mudstone generally soften when soaked in water, settle significantly under load, and yield under
relatively low stresses. Such weak rocks can provoke unpredictable difficulties in excavations
and foundations.
5.
What types of bedrock formations would offer good foundation support for structures?
What types of rock formations are likely to be poor foundation materials?
Answer:
Typically, igneous and metamorphic rock formations are hard and durable and can offer good
foundation support for structures. Shale and mudstone, types of sedimentary rocks, generally
soften when soaked in water, settle significantly under load, and yield under relatively low
stresses.
6.
Describe the three major types of rock weathering.
Answer:
(1) Mechanical weathering. The physical mechanisms contribute to mechanical weathering
include temperature, pressure, unloading water in rocks, flow of water, glaciers, and wind.
(2) Chemical weathering. The chemical reactions contribute to chemical weathering include
hydrolysis, reduction/oxidation, and solution of rock minerals due to carbonation.
(3) Biological processes, including physical penetration and growth of roots in rocks, digging
activities of animals, and metabolisms of microorganisms in rocks.
7.
What are the four major types of mineral soils? List them in decreasing order of sizes.
Answer: Gravel, sand, and silt, and clay.
8.
Briefly describe the types of transported soils.
Answer:
The residual soils or weathered bedrocks can be transported by various physical mechanisms and
then deposit elsewhere, they are called transported soils, including:
 Aeolian soils: Aeolian soils are transported by wind and deposit elsewhere. They include
sand dunes and loess. Loess is windblown silt and usually forms the characteristic vertical
cut. Both sand dunes and loess are very unstable material and are usually avoided as a
foundation soil.
 Alluvial (fluvial) soils: Alluvial soils, or alluvium, include all sediments that are transported
and deposited by streams. The deposits are usually stratified into layers of clay, silt, sand,
and gravel. In mountainous areas, alluvium consists largely of boulders; in areas dominated
by sluggish streams, alluvium typically is clayey silt.
 Colluvial soils: When soils and weathered bedrocks slowly move downslope due to gravity,
they form colluvial soils, or colluvium. Typical colluvium consists of unstratified, seemingly
randomly oriented angular blocks of bedrock in a clayey mix. In geologic time, colluvium is
actively moving.
 Glacial soils: Glacial soils, or glacial drifts, include all deposits formed by glaciers. There are
two types of glacial drifts: glacial till (nonstratified drift) and stratified drift. Glacial till is
deposited directly by glacial ice, is typically nonstratified and unsorted, and contains angular
to sub-rounded rock particles of all sizes. Glacial till generally has favorable engineering
characteristics. Sediments that are deposited by streams of water of melting glaciers are
called stratified drift. It is, in fact, alluvium and therefore has the properties of alluvium.
 Marine soils: Marine soils are the coastal deposits that are transported by rivers and deposit
in the ocean. It can include clay, silt, sand, and gravel.
 Lacustrine soils: Lacustrine soils are the fine-grained sediments that are deposited in lakes.
Lacustrine deposits are usually under-consolidated and can be very troublesome for
foundation.
 Engineered fills: Engineered fills are transported by human to construction sites; they
typically have satisfactory strength and deformation.
9.
What soil types would be expected in a river or stream delta?
Answer: Granular soil (fluvial or alluvial soil), mainly sand and silt.
10. For each of the following multiple-choice questions, select all of the correct answers.
Answer: the correct answers are underlined.
(1) The smallest geological time unit is:
A. Epoch
B. Age
C. Period
D. Era
E. Eon
(2) What are the important features on a geologic map:
A. Color
B. Shade
C. Letter symbols
D. Contact lines
E. Contour lines
(3) The following mechanisms play roles in the weathering of rocks:
A. Pressure or stress on the rock
B. Cementation and crystallization
C. Movement of glaciers
D. Oxidation
E. Igneous activities
(4) Granite is:
A. Intrusive rock
B. Extrusive rock
C. Igneous rock
D. Sedimentary rock
E. Metamorphic rock
(5) The sedimentary rocks are formed due to:
A. Compaction
B. Crystallization
C. Cementation
D. Cooling of lava
E. Extreme heat
(6) The mechanical properties of rocks include:
A. Rupture strength
B. Deformation characteristics
C. Reactivity
D. Density
E. Texture
(7) Shale is:
A. Igneous rock
B. Sedimentary rock
C. Metamorphic rock
D. Stratified in its structure
E. A sound foundation material
(8) Loess is:
A. A transported soil
B. An Aeolian soil
C. An Alluvial soil
D. A mineral soil
E. An organic soil