Environmental Engineering Reference
In-Depth Information
TABLE 6.6
Geologic Nomenclature for Joints
Joints
Characteristics
Figure
Joint type
Longitudinal
Parallel bedding or foliation planes
6.47
Normal or cross
Intersects bedding or foliations at right angles
6.47
Diagonal or oblique
Intersects bedding or foliations obliquely
6.47
Foliation
Parallel foliations
6.46
Curvilinear
Forms parallel sheets or slabs; often curved
6.42
Joint systems
Joint set
Group of parallel joints
6.45
Joint system
Two or more sets or a group of joints with a characteristic pattern
Conjugate system
Two intersecting sets of continuous joints
Orthogonal system
Three sets intersecting at right angles
6.40
Cubic system
Forming cubes
6.40
Rhombic
Three sets parallel but with unequal adjacent sides and oblique angles
Pyramidal
Sets intersecting at acute angles to form wedges
6.47
Columnar
Divide mass into columns: three- to eight-sided, ideally hexagonal
6.41
Intense
Badly crushed and broken rock without system: various shapes and
6.44
sizes of blocks
TABLE 6.7
Classification of Joint Surface Roughness
Surface
Roughness
Origin
Undulating
Rough or irregular
Tension joints, sheeting, bedding
Smooth
Sheeting, nonplanar foliation, bedding
Slickensided
Faulting or landsliding
Planar
Rough or irregular
Tension joints, sheeting, bedding
Smooth
Shear joints, foliation, bedding
Slickensided
Faulting and landsliding
of these features affect their engineering characteristics. Silt, clay, and mylonite are common
fillings. A classification of surface configuration or roughness is given in Table 6.7.
Engineering
In general, deformation occurs by closure of joints and by displacement of the bounding
blocks. Strength is derived from joint surfaces in contact or from the joint filling materials
6.4.3
Jointing in Various Rock Types
Igneous Rocks
Solid Masses
In solid masses, joints are widely spaced and tight as shown in
Figure 6.39.
Systematic Orientation
Systematic orientation of joints results from the cooling and contraction of the mass
during formation from magma. Normally, three joint sets form more or less according to
