Environmental & Engineering Geology Flashcards
1
Q
What intrinsic factors affect tunnel stability?
A
- Rock is not a manufactured material
- Discontinuous
- Inhomogeneous
- Anisotropic
- Nonlinear elastic
- Rock type - intact strength
- Rock structure - fractures (orientation etc) / spacing
- Condition of discontinuities
- In-situ pore water pressure
2
Q
What factors relating to tunnel setting affect tunnel stability?
A
- In-situ stress (depth, tectonic setting etc)
- Tunnel orientation wrt discontinuity sets
3
Q
What factors relating to design and construction/support affect tunnel stability?
A
- Shape and size of tunnel opening etc
4
Q
In the context of tunnelling, what are the rock mass characteristics that should be considered?
A
- Intact rock strength
- RQD (Rock Quality Designation)
- Joint spacing (of joint sets)
- Condition of joints
- Groundwater
Plus
- Fracture orientation
- State of in-situ stress
(note: each parameter is weighted differently according to its importance)
5
Q
What is RMR?
A
The Rock Mass Rating (RMR) classification system takes 5 or more important characteristics (i.e. parameters) known to influence overall strength.
Each parameter is assigned a rating and these are summed to give an overall RMR score or Index out of 100.
6
Q
Define RQD
A
Rock Quality Designation (RQD) is an index of the ratio between the sum of the lengths of core fragments longer than 100 mm and the total length of the Core run
7
Q
Give the equation for Rock Quality Designation (RQD)
A
8
Q
What are some criticisms of RQD?
A
- RQD is conveinient as it is obtained from core samples from a rotary drill, however artifically indiced breaks can be hard to distinguish.
- It can be argued that defining this indicator of fracture scarcity is arbitrary in using 100 mm; why not 200, or 50 mm?
- The RMR uses RQD and the average fracture spacing as a seperate parameter and so will tend to count the influence of fracture density twice!
9
Q
What are the effects of making a hole underground?
i.e. what are the effects of excavation on stress and groundwater?
A
- Rock moves inwards - bc material is essentially elastic (creates a ‘squeeze’ issue on rock boring machines)
- Stress refraction: Normal & Shear stresses on the excavation wall are zero
- Excavation acts as a sink if it’s a porous, fractured rock mass - bc pressure in excavation is reduced to atmospheric, fluids flow into excavation under pressure gradient
10
Q
What parameter is the most heavily weighted out of the RMR classification parameters?
A
Condition of discontinuities, with a rating of 30
11
Q
What parameter is the least heavily weighted out of the RMR classification parameters?
A
Strength of intact rock material
or
Ground water,
both w/ rating of 15
12
Q
The RMR system utilizes which six rock mass parameters?
A
- Uniaxial compressive strength of intact rock material
- Rock quality designation (RQD)
- Spacing of discontinuities
- Condition of discontinuities
- Groundwater conditions
- Orientation of discontinuities
13
Q
The ‘Condition of discontinuities’ parameter of the RMR system is split into what sub-parameters?
A
- Length, persistence
- Separation
- Smoothness
- Infilling
- Alteration / weathering
14
Q
The rating of each of the RMR parameters are summarized to give a value of RMR.
But how are the parameters measured?
A
All RMR parameters are measureable in the field and can also be obtained from borehole data.
15
Q
How is the RMR classification applied to a tunnel build project?
A
- The rock mass along a tunnel route is divided into a number of structural regions, i.e. zones in which certain geological features are more or less uniform.
- The 6 RMR classification parameters are determined for each structural region from measurements in the field.
- Once the classification parameters are determined, the ratings are assigned to each parameter according to the RMR Table. In this respect, the typical/average/overall conditions, rather than the worst (or every detail of) conditions, are evaluated.
- F.m. it should be noted that the ratings, which are given for discontinuity spacings, apply to rock masses having three sets of discontinuities. Thus, when only two sets of discontinuities are present, a conservative assessment is obtained.
16
Q
What does this figure show?
A
Stand-up time as function of unsupported span and RMR values
- An interpretation of time and span can be made from RMR class number due to experience of many projects and a lot of data
- Also: Continuum properties (cohesion of rock mass, friction angle of rock mass) can be approximated, taking the assumption that the whole rock mass behaves homogeneously (average/overall properties)
17
Q
What support in rock tunnels is suggested for a rock mass class stated ‘very good rock’, with an RMR score of 81-100?
A
- Generally no support required except for occasional spot bolting
18
Q
What support in rock tunnels is suggested for a rock mass class stated ‘good rock’, with an RMR score of 61-80?
A
- Locally bolts in crown, 3 m long, spaced 2.5 m with occasional wire mesh
- 50 mm shotcrete in crown where required
19
Q
What support in rock tunnels is suggested for a rock mass class stated ‘fair rock’, with an RMR score of 41-60?
A
- Systematic rock bolts 4 m long, spaced 1.5-2 m in crown and walls with wire mesh in crown
- 50-100 mm shotcrete in crown, and 30 mm in sides
20
Q
What support in rock tunnels is suggested for a rock mass class stated ‘poor rock’, with an RMR score of 21-40?
A
- Systematic rock bolts 4-5 m long, spaced 1-1.5 m in crown and walls with wire mesh
- 100-150 mm shotcrete in crown, and 100 mm in sides
- Light steel set ribs spaced 1.5 m where required
21
Q
What support in rock tunnels is suggested for a rock mass class stated ‘very poor rock’, with an RMR score <21?
A
- Systematic rock bolts 5-6 m long, spaced 1-1.5 m in crown and walls with wire mesh. Bolt invert
- 150-200 mm shotcrete in crown, and 150 mm in sides, and 50 mm on face (cutting face)
- Medium to heavy steel set ribs spaced 0.75 m with steel lagging and forepoling if required. Close invert
22
Q
Tunneling is normally done between 0-500 m depth.
What is the dominant stress at this depth?
A
Average horizontal stress is normally higher than vertical stress between 0 and 500 m i.e. normal Civ Eng Tunnel Depths
23
Q
Discuss the importance of the prevalent stress regime in relation to tunnels?
A
- Must know the depth to which a particular tectonic stress regime acts
- Affects how support around the tunnel is going to be designed
- What’s the stress across the tunnel, + along the line of the tunnel
- Stress regime is going to change across the tunnel section (consider channel tunnel example)
24
Q
What if a tunnel opening was rectangular and had corners - what affect would this have on the wall stress magnitudes?
A
- Firstly, the stress has to refract around the hole
- Therefore, even in a cylindrical tunnel, there is a high localized stress on the tunnel walls, partiularly at the crown on the tunnel, or in the wall opposite to σ3.
- Stress is amplified bc of the stress concentration in these areas.
- In a rectangular tunnel, stress concentration is near/just below the corners, and is greatly amplified - with a magnitude 6.8 x greater than the original horizontal stress.
25
What is shown in the image below?
The effect of an excavation intersecting a pervasive planar rock fabric, i.e., foliation, on the potential location of rock failure at the excavation periphery. This potential is a function of both the magnitude of the rock stress acting parallel to the excavation boundary and the orientation of the foliation relative to the excavation boundary, as indicated by the white arrows and the shading in the individual rock samples, respectively
26
What is the optimal orientation of tunnels to avoid damage caused by stress concentrations?
The optimal orientation of tunnels to avoid damage caused by stress concentrations is parallel to the maximum principal stress component, i.e., as in the right-hand sketch.
The stress concentration around the tunnel in the left-hand sketch will be higher than that in the right-hand sketch
27
What are the two main causes of failure in rock engineering?
How can these be mitigated?
Adversely high rock stresses and the movement of rock block
Key block theory (kinematic analysis) allows joint mapping to try to get good representation of discontinuities;
Here, you can map out most problematic part of structure from a point of view of sliding and falling blocks (w/ stereographic projections)
28
Re: discontinuity properties and assessment, how might one be objective about spacing?
scanline mapping
What's the persistence, trace length etc?
29
When assessing discontinuities, what properties must be made note of?
1. Length, persistence (how many sets etc)
2. Seperation
3. Roughness
4. Infilling (gouge)
5. Weathering (wall strength)
Also:
* Aperture
* Seepage rates
30
Software can be used to stereographically project discontinuity data. This can help with what?
* Deriving **block distributions**
* **Kinematic analyses** in tunnels (just like for rock slope failure problems)
* Discontinuity sets (bedding and joints) can be plotted on a stereonet and considered in terms of _kinematic stability_ and _sliding_ into the tunnel
31
What tunnel orientation relative to the strata is more favourable?
More favourable for tunnel to run perpendicular to the strata than for the tunnel to run parallel to strike.
If tunnel runs parallel to strike, it can lead to problems.
32
What is the benefit of using RMR classifications, other than safety?
* More economic to know that there's some good rock (e.g. dolomites) that doesn't require expensive support
* Also get an idea of how difficult the rock is going to be to excavate.
33
Is RMR the only classification system that can be used for tunnel support design?
* No
* Q-Index
* Tunnel engineers tend to prefer the Q-index System for rock mass classification
34
What's the difference between RMR and Q-Index?
* The Q-Index is obtained by multiplying together three ratios (not the sum of 5):
* Block size
* Shear strength between blocks
* Influence of state of stress
* The interpretation chart for Q-Index is more practical and offers suggested reinforcement categories
35
How are Numerical Models used in tunneling?
* Continuum approach
* RMR numbers used to generate failure envelopes that can be put into software that can predict:
* Deformation
* Squeezing of tunnels
* What support is needed
* Etc.
36
What determines whether continuum or discontinuum approaches are used in numerical modelling in tunnelling?
* Size of domain controls how many fractures we're going find (domain size defined in numerical model)
* Scale of interest tells what type of technique that can be used (continuum or discontinuum)
37
Give a summary of the empirical approach to tunnel construction.
1. Perform **Site Investigation** for proposed tunnel of given cross section shape
2. _Characterize_ the **geology** and important **rock mass properties**
3. Perform **kinematic stability prediction** from _discontinuities_ - key blocks
4. Evaluate **zones of tunnel support** from _RMR_ or Q class (along tunnel sections)
5. Consider tunnel **excavation methods** available and support
6. **Design** portal and or shaft access
7. Begin **exploratory** tunnel construction and adopt _forward borehole survey_
8. **Update RMR** with continuous mapping, monitoring and data analysis
9. Drill **forward boreholes** for grout injection if to seal and minimise water seepage
10. Advance **excavation-construction** with support
11. _Adapt_ to changing geological conditions during advance
12. _Monitor_
38
In recent years a number of high‑latitude permafrost regions have begun to thaw due to increased average air temperatures. As successful construction in these environments depends on preservation of the permafrost, it is likely that infrastructure in regions like Alaska will be adversely affected by such climatic change.
Sketch a typical North‑South cross section through a high‑latitude region showing the spatial relationships of relevant features. Include those geological features indicative of the freeze/thaw processes taking place in such an environment and explain breifly how they form.
* **Permafrost** currently covers 20% of Earth's land surface; **Active layer** (1-3 m thick) thaws during summer; Impearmeable subsoil prevents drainage → waterlogging and flow.
* **iw = ice wedge,**
* **il = ice lens**
* Freezing of water → expansive forces → shattering of frozen material → ground heave.
* **Pingos** (h→50m; Ø→300m) have been unheaved by intrusions of ice; usually deeply fissured, may have crater in top.
39
In recent years a number of high‑latitude permafrost regions have begun to thaw due to increased average air temperatures. As successful construction in these environments depends on preservation of the permafrost, it is likely that infrastructure in regions like Alaska will be adversely affected by such climatic change.
The Dalton Highway in Alaska extends North from Fairbanks almost 800 km to Prudhoe Bay. Much of the highway crosses the Arctic Coastal Plain where polygonal ground is commonly encountered.
How does polygonal ground form, and what are its principal features both during and after formation?
* Polygonal ground is created by **nets of ice wedges**;
* Occurs where permafrost is over 60% ice.
* Typical polygons are **15-75 m across**, bounded by almost straight ice wedges each **10-40 m long** between 3 or 4 point junctions.
* A uniform distribution of ice wedges creates polygons that tend to hexagonal.
* Many polygons have **no surface expression where they are stable** or growing slowly in undisturbed frozen ground. Others are visible as **slight ridges or vegetational contrasts** over growing ice wedges.
* **Polygons are most conspicuous where their ice wedges are thawing**, to create **meltwater troughts** over them.
* Any slight melting of the permafrost creates a **hollow that then fills with water**.
* _Summer water levels stand below the level of the frozen ground_, and each _ice wedge is melted back_ at that level, to form a **cave**, that then _collapses_ to create a **gully** - revealing the network of ice wedges (Fig. 10).
40
Where else are you likely to see polygonal ice wedges, like those in the Arctic Costal Plain?
Polygonal nets characterize periglacial lowlands, and **East Anglia** has many that are relics from the Pleistocene.
41
The Dalton Highway in Alaska extends North from Fairbanks almost 800 km to Prudhoe Bay. Much of the highway crosses the Arctic Coastal Plain where polygonal ground is commonly encountered.
The presence of the Dalton Highway has dramatically affected the polygonal ground over which it passes. Describe this situation.
* **Cut slopes** were initially **unstable and unsightly as the frozen ground thawed and collapsed**, but after about five seasons the slopes had slumped to stable profiles with established vegetation, and the permafrost was preserved behind the new organic mat.
* Most modifications to the road have been modest drainage features to eliminate inter accumulations of ice.
* E.g. the road crosses a slope of frozen **soliflucted** till.
42
In areas of frozen ground and periglacial conditions, construction may cause a particular problem to the landscape.
Describe this kind of problem, paying attention to its cause and nature, and when and why they occur. How might a natural analogue of these conditions form?
* **Solifluction** is downslope movement of saturated debris as a viscous flow, 10 mm/a \> v \> 300 mm/a.
* Most significant form of mass movement in tundra.
* Solifluction deposits are poorly sorted, poorly bedded, display fold structures, t→3m.
* Tend to be found at the foot of slopes, are easily reactivated by drainage changes, erosion, construction.
* Called ***head*** in the UK;
* Usually weak, compressible, permeable, if derived from chalk, can be weakly cemented with CaCO3.
43
What features of the polygonal ground formed in Southern England during the Pleistocene, should geotechnical engineers be alerted to, in order to determine whether or not it suffered solifluction?
Solifluction lobes
| (e.g. Dartmor)
44
What effects can a glaciation have on the landscape?
* **Frost splitting** d→30 m in chalk of SE England.
* **Hill creep/solifluction** influenced by valley sides in frozen material being over-steepened.
* **Valley bulging** caused by removal of weight of ice.
* **Rockhead** may be unrelated to modern topography; depth to r/h may be irregular.
* **Buried channels** may lie beneath or be unrelated to modern valleys; irregular and variable depth/width.
45
Draw a suggested mechanism for Valley Bugle situation.
46
What is a periglacial environment?
cold climate; non-glacial with ground freezing
47
What is permafrost?
Ground at or below 0°C for \> 2 yrs:
Can occur from cold air and winter snowfall.
48
What is the active layer?
Sees annual freezing and thawing.
Thickness of AL is ~cm scale (near pole) to ~10 m in doscount permafrost regions.
49
What is the 'transition zone' in periglacial regions?
Uppermost permafrost - much segregated ice in lenses.
Much evidence in Kent.
50
What is ground ice?
Will be in the form of pore, segregated, wedge and lense.
Wedge ice leaves vertical ice laminae where single thermal contraction crack occurs.
51
What weathering processes take place in periglacial landscapes?
* From features seen in Kent:
* Freezing and thawing - in situ expansion on freezing, thermal suction and segregation leads to fracturing - brecciation.
* Type 1: Angular fragments with infilled fractures having matched sides. By ice wedging, fewer F-T cycles.
* Type 2: Subangular to rounded lumps - lithorelics in a chalky matrix lacking stratification. See infilled dray valleys at Pegwell Bay. Often grades downwards into..
* ..Type 3, by many F-T cycles and possibly some ground movement; e.g. seen folded flint bands.
52
What peri-glacial processes formed the landscape we see in Kent today?
* Weathering processes
* Cold-climate aeolian processes and deposits
* Deformation processes and structures in soil and rock
* Slope processes and deposits
* Cambering strata and widened vertical joints (gulls)
53
What peri-glacial cold-climate aeolian processes and deposits do we see example of in Kent?
* Loess - wind blown mainly of coarse silt size, trapped by vegetated cover.
* Often find calcareous tubes marking positions of roots, clays help bind.
* BGS call it 'brickearth' or 'head brickearth'.
* Several m thick.
* Hydroconsolidation is possible.
54
What peri-glacial deformation processes and structures in soil and rock do we see example of in Kent?
* Periglacial **Involutions** or **Cryoturbations** are structures caused by _repeated frost action_ processes deforming the unconsolidated soils or breccias.
* **Flame-like structures** caused by soft sediment during _active layer deepening_.
55
What peri-glacial slope processes and deposits do we see example of in Kent?
* Mass wasting, in the form of solifluction (soil flow) of 'head' deposits - deposits that are periglacially derived from underlying weathered bedrock moving on slopes.
* Porewater pressure increases immediately after ice melts often enough to initiate sliding.
* Gravelly sediments may accumulate near bottoms of valleys.
56
How are the cambering strata and widened vertical joints (gulls) that we see in Kent formed?
* Large-scale **flexing and stretching** of _competent caprocks_ over the upper parts of valley side slopes lead to _beds dipping towards valley floor_ and _blocks tilting_.
* Probable mechanism is **incompetent mudrock beneath harder beds** flowing towards valley.
* In valley itself where river has cut through competent layer to reveal mudrocks and clays, greatest deformation is in lowest point of valley.
* **Gulls are widened by tilting of blocks** in strata next to deeply incised valleys unsupported on downslope sides, e.g. High Weald (Ardingly Sst.)
57
How might one decide what types of geomaterials are appropriate for use in the chosen construction?
Think about **loads**, **stability**, **performance**
Identifying the **functional requirements** of your construction project will lead you into thinking about what geomaterials are needed
58
How would one figure out how much geomaterial is needed for a given project?
* Detailed and average **cross-sections** and **plans** lead to the **_bulk volumes_** required.
* A range of different **packing densities** will affect quantities
59
Where does the geomaterial come from ?
As close to site as possible (transport costs are a massive part) Quarries, cuttings, hills/borrow areas, (+ cement and bitumen bound aggregates?)
60
What are the logistics of geomaterial supply?
What is a typical yield of material from a normal aggregates quarry or a dedicated quarry – per week?
More plant can make a job go faster – but there may be limits on construction rates
61
What is the first question a consultant asks about any project when it is being conceived for the first time (before any design)?
What are the needs and purposes of the project - the Client's needs?
i.e. what are the functional requirements? - leads you to the geomaterials required
* e.g. when building a motorway:
* don't want it to be smooth - want friction to allow breaking and steering at high speeds - t.f. tarmac will need to have coarse parts to it too.
* corners not too sharp
* slopes not too steep
* hold weight of vehicles
* e.g. if **dam**, specify _volume of water_ and the _head_ to be able to generate a certain amount of electricity
62
What is needed to achieve the functional requirements of a given project?
Design and Construct ensuring the design geometry and material strengths will withstand the loads (not just after construction but for the design life i.e. durable, e.g. wave action or vehicles on a road)
Engineering Geology skills input, especially on SI
63
Where are geomaterials sourced from?
* **Quarries** (local open quarry *or* is there a requirement to open a new quarry bc of remote location for e.g.),
* **local borrow areas** (not legal in UK, but can get planning permish.),
* **ready-mix suppliers** (transport this in?)
* Different **Contractor companies** may suggest various suitable sources at time of bidding for the contract.
* **Transport costs are key** (moving huge volumes of rock or earth).
* Engineering Geology skills input
64
What principles are applied when designing a particular project?
The consulting engineering company (structural, geotechnical and coastal expertise as a given) applies **soil mechanics, rock mechanics, coastal hydrodynamics, codes of practice** etc. to arrive at an **optimal design** that is _dimensioned_ and with the _geomaterials types specified._
i.e. from design you get sense of shape (**width, height, slope** of sides, etc) and t.f. **cross-sectional area** - then define **length** = **volume**
**\*\* from CSs and plans you can calculate volumes of geomaterials needed**
65
What would be the functional requirements of this project?
* West Bay (Dorset) being eroded
* **Create harbour protection** (to let boats in and out safely during rough seas; make calm water behind breakwater), **trap beach materials** (prevent erosion), **provide amenity beach** etc
* **Design** plan shape, profile shape, to _resist loads from wave and storm action_ (e.g. breakwater needs to be strong enough so...)
* Calculate **volumes** needed, **define construction materials requirements** and _source_ them -\> Engineering Geology
66
What might be some of the functional requirements for building stone?
* Colour aesthetic for architect
* What sort of tests would you think might be most useful?
* Abrasion resistance? Skid resistance?
* Compressive strength?
* Resistance to weathering in engineering time?
* Freeze thaw ?
67
What are the phases involved in a construction project?
* Planning phase
* Design phase
* Construction phase
* Monitoring and maintenance phase
68
Using an example, describe how to get from the planning phase to the design phase in a construction project?
* The process starts with **identifying the functional requirements** of the design: e.g. in the **West Bay Harbour coastal project** example, it was to create harbour protection, trap beach materials, provide amenity etc.
* **Site Investigation**: Ground conditions and environmental factors (probing) e.g. waves, storms are investigated to _ascertain loading conditions_
* **Alternative designs** with plan shape and profile sections, _designed to resist loads_ from wave and storm action are proposed.
* **Construction materials requirements** are defined and volumes needed are calculated.
* **Sourcing geomaterials** of the required amounts of each material type (often this becomes the job of the contractors).
* *_Engineering Geology_ may be involved at all stages by Consultants and Contractors*
69
What does the 'construction phase' of a construction project involve?
Quarrying
Transportation
Construction
70
While it is the consulting engineering company that is responsible for the design of a civil engineering construction project, it is the pieces of rock that make up the construction materials that eventually deliver the functional requirements of the construction project to the client.
Draw a labelled flow diagram that explains the geomaterials properties to be controlled and tested at the subseqent different stages in the life of a construction project.
A conceptual understanding of properties and functions of any geomaterial used in construction (such as gabion stone, recycled materials, concrete units, grouted stone, and the many and varied applications of aggregates and armourstone) is given by the scheme, illustrated here for armourstone.
71
In relating properties to functions, it is useful to distinguish the three types of property that relate to different phases in the life cycle of armourstone, for instance.
What are the three types of property?
1. Intrinsic
2. Production-induced
3. Construction-induced
4. *(System response under loads)*
**Undertaking these steps is important to end up with the right rocky material for the functional requirements of your project!
72
In relating properties to functions, it is useful to distinguish the three types of property that relate to different phases in the life cycle of armourstone, for instance.
Describe what is meant by the '**intrinstic**' properties of a geomaterial.
* Relate to the rock **source properties**, its geological history or the industrial process involving thermal or other modification.
* They account for engineering geology considerations such as:
* **mineral fabric characteristics** (mineralogy, density, intact strength, Young's modulus etc)
* **discontinuity sets** (spacing etc)
* **weathering grade** (thickness of joints, colour staining etc)
* Colour
* **tectonic context** of the quarry
* Choose by _fitness-for-purpose_ (by above) and _transport cost_ as well.
73
In relating properties to functions, it is useful to distinguish the three types of property that relate to different phases in the life cycle of armourstone, for instance.
Describe what is meant by the '**production-induced**' properties of a geomaterial.
* **Properties of geomaterial following excavation**
* Relate to the armourstone as an individual piece or as a granular material composed of individual pieces.
* They are affected by the **intrinsic properties** and controlled by the **production technique**/affected by excavation process such as:
* blast design,
* selection,
* handling and sorting techniques or devices
* Controls **block integrity**, **shape** (expressed as ratio; slab-shapes break more easily than cuboid-shaped rocks), **size**, **size distribution (grading)**
* Size distribution determined after **stockpiling**
74
In relating properties to functions, it is useful to distinguish the three types of property that relate to different phases in the life cycle of armourstone, for instance.
Describe what is meant by the '**construction-induced**' properties of a geomaterial.
* Such as **layer thickness** or **layer porosity (packing density)**, **permeability**, are controlled by the construction of the armourstone as a granular material and are..
* Heavily influenced by the **placement technique, the shape and the conditions of execution**, for example above or below water.
* e.g. **Shear strength** as a granular material depends on layout (porosity, interlocking?), size etc - e.g. low porosity with slab-like shape, w/ gaps only 20% of whole vol. (other shapes nearer to 40%).
* Important for _wave-energy dissipation_.
* Each property is also _susceptible to change with time_ as a **function of loadings** from the _physical_, _chemical_ and _biological environment_.
* These are considered further in terms of **durability**.
75
In relating properties to functions, it is useful to distinguish the three types of property that relate to different phases in the life cycle of armourstone, for instance.
At the end of the cycle is the '**system response under loads**' phase. What does this entail?
Desinger calculates (using appropriate equations) the **performance of the material in fulfilling its _functional requirements_**.
e.g. withstanding **loads** like wave action, or weight of vehicles on a road
76
In relating properties to functions, it is useful to distinguish the three types of property that relate to different phases in the life cycle of armourstone, for instance.
Durability characteristics are also considered in this process. Why is that?
Don't want properties of the material to start changing with time, especially when the project is designed to last, say, 100 yrs.
e.g. if a granite has feldspars that are weathering to kaolinite, that part of the rock is going to disintegrate causing the integrity of the rock to fail.
77
Discuss the main controls of geomaterials supply to a construction site.
* Here, one would:
* Choose a geomaterial type e.g. rockfill, aggregates
* Indicate if supplies come from sources 'dedicated' to the project or if from established supplier company.
* Propose the most likely vessel/truck type and its capacity (tonnes or volume) by which the material arrives on site.
* If there is a time limit, e.g. 2 yrs (~100 weeks), to construct the geomaterials part - calculate how many transporter vessels would need to arrive per working hr/day/week. Is construction acheivable?
78
Not all material complying with the definition "aggregates" has come from a crushed rock quarry.
What are the other sources of aggregates?
* Sand and gravel (land, e.g. beach)
* Marine sand and gravel
* Secondary aggregates
* Recycled aggregates
79
What is an aggregate?
A granular material used in construction
80
What is a primary aggregate?
Crushed rock, land or marine won sand and gravel
81
What is secondary aggregate?
Indistrial by-products,
e.g. powerstation ash (pfa, fba), blastfurnace and steel lags, colliery spoil, china clay wastes, slate wastes
82
What is recycled aggregate?
Generated from demolition and construction arisings
e.g. crushed concrete, bricks and mortar, road planings
83
What are 'alternative aggregates'?
Secondary and recycled aggregates
84
List the geomaterials/aggregate test methods.
* Sampling (not a test as such)
* Size
* Shape
* Physical
* Mechanical
* Weathering resistance
* Chemical
85
Give examples for some end uses for aggregates
Concrete, track ballast
86
What are the reasons for testing aggregate?
* To predict likely **in-service behaviour**
* To compare between **competing sources**
* To help the producer in the **quality control** of the production process
* To establish if a supplied aggregate will **satisfy a specification clause** in the contract
87
What are the aggregate specifications for the **geometrical requirements** of bituminous mixtures and surface dressing for roads, airfields and other trafficked areas?
* Requirements for coarse aggregate and fine aggregate (sand)
* Geometrical requirements
* Grading (i.e. upper and lower sieve limits defined)
* Shape (i.e. flakiness)
88
What are the aggregate specifications for the **physical requirements** of bituminous mixtures and surface dressing for roads, airfields and other trafficked areas?
* Requirements for coarse aggregate and fine aggregate (sand)
* Resistance to **fragmentation of coarse aggregate**
* Resistance to **polishing and abrasion of coarse aggregate** to be used for _running surfaces_
* Resistance to **wear of coarse aggregate**
* Resistance to **abrasion** from studded tyres
* **Particle density**
* **Bulk density**
89
What are the aggregate specifications for the **durability requirements** of bituminous mixtures and surface dressing for roads, airfields and other trafficked areas?
* Requirements for coarse aggregate and fine aggregate (sand)
* Resistance to **freezing and thawing**
* Resistance to **salt crystallization**
* **Weathering** resistance of coarse aggregate
"Sonnenbrand" of basalt
* *Remember also the chemical requirements*
90
What are the specifications for the **requirements for filler aggregate** of bituminous mixtures and surface dressing for roads, airfields and other trafficked areas?
* Geometric
* Physical
* Stiffening
* Chemical requirements
91
List the aggregate tests given in the lecture.
* **Los Angeles** test for aggregates
* **AIV** test
* **Micro-Deval** test
* **Aggregate Abrasion Value** (**AAV**) test
* **Polished Stone Value** (**PSV**) test
92
What are the aggregate properties being tested for in the Los Angeles test?
Resistance to **degradation** by
abrasion or attrition, impact, and grinding
93
What are the aggregate properties being tested for in the AIV test?
Resistance to **impact**
94
What are the aggregate properties being tested for in the Micro-Deval test?
Resistance to **wear**
95
What are the aggregate properties being tested for in the Aggregate Abrasion Value (AAV) test?
Resistance to **abrasion of coarse aggregates**
to be used for _running surfaces_
96
What are the aggregate properties being tested for in the Polished Stone Value (PSV) test?
Resistnace to **polishing** of coarse aggregates
to be used for _running surfaces_
97
Aggregates have a wide range of uses, for each "end-use" the important properties are specified by...
...indicating the values that must be achieved with a standard test method
98
Aggregate test methods tend to fall into what categories?
* Geometric,
* Physical (Mechanical)
* Chemical
* Durability
99
How much aggregate goes into one km of new motorway in the UK?
100,000 tonnes
100
The roas network of 345,000 km in the UK is at least 95% constructed with at least one layer of material consisting of bituminous mixes.
What are the kinds of bituminous mixes for roads?
Asphalt and Macadam
101
The road network of 345,000 km in the UK is at least 95% constructed with at least one layer of material consisting of bituminous mixes (asphalt and/or macadam).
What are the characteristics of asphalt?
* Dense mortar providing strength and stiffness
* High bitumen content
* High filler/fines content
* Low coarse aggregate content
* Load transmitted through mortar
102
The road network of 345,000 km in the UK is at least 95% constructed with at least one layer of material consisting of bituminous mixes (asphalt and/or macadam).
What are the characteristics of macadam?
* Well graded aggregate giving dense stable aggregate structure
* Low bitumen content
* Load transmitted through aggregate structure
103
With aid of a diagram, describe the cross section of a motor way road.
104
Re: roads, what are the requirements for the wearing coarse?
* **Waterproof**, with **skid-resistant** chips rolled into its top to give _high friction_ to the final road surface; it must *not deform* under braking conditions.
* The **lower the AAV and MDE**, the better the *wearing* properties; for a good wearing-coarse aggregate chippings, an _AAV \< 14_ is needed (sometimes as low as _10_) or _MDE \< 36_.
* The **higher the PSV**, the better the *resistance to polishing*, and the better the aggregate.
For a good wearing course, the _PSV \> 60_, and sometimes values as high as _70_ are called for.
* Most **igneous** and **metamorphic** rocks are *strong* enough to have sufficiently _low AAV and AIVS_, but often they are *easily polished*, and so have a _PSV value which is too low_.
This is understandable, since it is ig. and met. rocks which are most widely used as decorative slabs that take a polish.
105
What is the relationship between abrasion and skid resistance in ig. and met. rocks?
Good abrasion resistance (i.e. low AAV) sometimes inversely correlated with good skid resistance (i.e. high PSV)
## Footnote
*But why?*
106
Is the insistence of high PSV specification cost effective to the Tax Payer?
* Micro-friction and skid resistance can be maintained by abrasive plucking of surface minerals which retains jagged chipping surfaces but leads to material losses and high road maintenance needs.
* The abrasion, and associated loss of macro-friction is also very detrimental for safety at higher speeds and with very wet conditions, so rapid wearing down caused by low abrasion resistance is also a problem for safety.
107
For granular geomaterials, define **void ratio**, giving the equation.
***e* = VV / VS**
***e* = n/(1-n)**
(Volume of void over volume of solids within an aggregate body).
Gives indication of the porosity (and permeability).
In the image, void = liquid + gas (non-solid).
108
For granular geomaterials, define **porosity**, giving the equation.
Porosity is governed by what?
***n* = VV / Vt**
***n* = *e*/(1+*e*)**
where *e* = void ratio
Volume of void over total volume of aggregate body.
_Porosity (and permeability) is governed mainly by particle geometry i.e. sizes and shapes of particles_.
109
For granular geomaterials, define **bulking factor**, giving the equation.
**B = Vt/V**s = swell factor
**B = 1 + *e***
where *e* is the *void ratio*
If n=0.30 or 30% (n=porosity), bulk volume = 143% of solid volume,
swell factor = 1.43 = 1 + *e*
e.g. after blasting, rock takes up larger volume
110
Re: particle packing characteristics (e.g. for geomaterials applications), what are the general properties of particulates?
* Shear strength
* Porosity
* Porosity
* Void ratio
111
Shear strength is one of the general properties of packed particulates.
What is the shear strength of a particulate body governed by, and explain how the particulate characteristics affect the shear strength.
* Shear strength is governed mainly by the **number of contacts per unit area**.
* This coordination gives the *intergranular friction*, which is greater if there is a greater difference in the sizes of the grains.
* I.e. **higher _grading_ gives higher coordination numbers** - that allow the body to **harness more shear strength**.
112
Re: aggregate packing properties
A wide grading encourages:
* Lower porosity
* Greater packing density
* Higher shear strength when compacted
* Poor drainage
113
Re: aggregate packing properties
A narrow grading (single size) encourages:
* Higher porosity
* Lower packing density
* Lower shear strength when compacted
* Greater drainage
114
Re: aggregate packing properties
A well rounded compared with a highly angular aggregate encourages:
* Lower porosity
* Greater packing density
* It is not clear cut the effect regarding shear strength
115
Re: aggregate packing properties
A highly angular compared with a well rounded aggregate encourages:
* Higher porosity
* Lower packing density
* Effect not clear re: the shear strength
* Beware that with a high vibro-compaction, angular pieces can find the geometric positions to pack tightly
116
Porosity/Packing density is a function of what?
* Ranges of sizes
* Range of shapes
* Absolute sizes (adhesive forces ~\<0.5mm)
* History of coalescence
* Compaction / vibration
* Degredation
117
Can one accurately predict the porosity of particulates?
No, real porosity of particulates is hard to predict accurately.
118
Construction of a 10 km motorway section of the M62 between Leeds and Manchester is to cross a flat lying section which then traverses a valley just before an inclined section that climbs up onto the Pennines.
What are the functional requirements of the motorway?
* **Major transport pathway** (at least 4 lanes) for vehicles moving at high speeds 50-70 mph in **safety** for some **50 years design life**.
* Safety will *restrict* **sharpness** of bends and **steepness** of inclines.
119
Construction of a 10 km motorway section of the M62 between Leeds and Manchester is to cross a flat lying section which then traverses a valley just before an inclined section that climbs up onto the Pennines.
With the functional requirements of the project in mind, outline the factors that an engineering geologist would need to take into account to identify the types of geomaterials to be considered to complete the project
* _Rockfill_ for **road foundation**,
* _Rockfill_ for **possible dam** *if* river is to be dammed (e.g. solution eventually adopted at Scammonden) or _concrete aggregates/readymix_ concrete for a **bridge** over the river.
* _Rockfill_ from making a **cutting into Pennines** to reduce incline is used for **embankment fill** as new *grade line* for the road rises towards Pennine *scarp*.
* Several **concrete bridges to cross the motorway** might be expected in 10km together with possible **junctions/slip roads**.
* **Road pavement** requires series of _various quality aggregates_ from *sub-base – to bituminous bound wearing courses*.
* _Local geology determines rock types excavated in road cut and types from borrow area fills_.
120
Construction of a 10 km motorway section of the M62 between Leeds and Manchester is to cross a flat lying section which then traverses a valley just before an inclined section that climbs up onto the Pennines.
Outline how the required quantities of the main types of geomaterials involved in the project would be estimated.
(Note: you are not required to perform specific calculations.)
* **Plans** and **cross section** to calc volumes is the *issue*.
* Ease of excavation (by **ripping**) affects route; route affects road **foundation thickness** required and engineering geology estimation of **capping layer depth**.
* **_Cut and fill detailing from drawings and highway width allows calculation of rock fill volumes_**.
* The **average width** (e.g 6-8 lanes with shoulders and central verge) and **depth** of the _motorway pavement layers_ provide **average cross sections**.
* For given lengths (10 km in total) the **bulk compacted volumes** of required *sub base* and *aggregate* materials can be _calculated_.
* If a _dam_ is to be built from rockfill, to make a reservoir in the valley, the **plans and sections** give bulk compacted volumes of the fill.
* **Concrete structures** created from *readymix*. – _calculate volumes from dimensions_.
121
Construction of a 10 km motorway section of the M62 between Leeds and Manchester is to cross a flat lying section which then traverses a valley just before an inclined section that climbs up onto the Pennines.
Identify the most probable sources of the main types of geomaterials involved in the project.
* _High valued ready-mix and bituminous bound aggregates_ **trucked in** from depots and quarries **up to 30km away**.
* _Embankment fill_ from **borrow areas** – suitable superficial (sands and gravels). Can also use **clay rich deposits** - but at *gentler embankment angles* and *more materials* needed.
* Several established **Carb limestone aggregates quarries** are available for supplying _subbase_ in this region – also **high PSV gritstones from Carboniferous Coal Measures** for _wearing course_ are available from **quarries** in the area.
122
Construction of a 10 km motorway section of the M62 between Leeds and Manchester is to cross a flat lying section which then traverses a valley just before an inclined section that climbs up onto the Pennines.
For the motorway project, give examples of where packing characteristics *(void ratio, porosity, bulking factor)* may be important in design and construction.
* From rock in-situ – after ripping or blasting to create rockfill, it will have ***swelled*** in volume _by a bulking factor_.
* These volumes may be _compacted_ somewhat during _laying of rockfill_ layers and foundation fills but **considerable porosity** will remain.
* Truck loads of aggregates and mixtures are paid for by the tonne and **conversion of weight to volumes in order to make the volumes in the design drawings require an understanding of porosity** achieved and the **density** of the rock material itself (usually **~2.7 t/m3**).
123
Construction of a 10 km motorway section of the M62 between Leeds and Manchester is to cross a flat lying section which then traverses a valley just before an inclined section that climbs up onto the Pennines.
List four geomaterials test methods that would be required in the quality control of the project, identifying in each case the part of the construction and the property that is being tested for.
* **Point load test** for _intact strength_ to assess _rippability_ and _blastability_ to excavate *highway cutting* and *capping horizon* across top of Pennines.
* **Los Angeles test** for _resistance to fragmentation_ of the *subbase aggregates*.
* **Micro-deval test** for _resistance to wear_ of *wearing course aggregates*.
* **PSV** to test for _skid resistance_ of *wearing course aggregate*.
124
Construction of a 10 km motorway section of the M62 between Leeds and Manchester is to cross a flat lying section which then traverses a valley just before an inclined section that climbs up onto the Pennines.
Explain which properties of an aggregate will help contribute towards a high skid resistance.
* Require **micro** *and* **macro-friction**.
* **High PSV** and hence microfriction requires _polyminerallic rocks_ (not very coarse grained igneous) with mainly **hard but varying strength minerals** prone to _revealing new uneven surfaces during continuous wear_.
125
In the engineering geology of igneous rocks, it is useful to characterise these materials in terms of (i) the form of their emplacement and (ii) their mineral chemistry.
**Outline the main engineering geological characteristics of extrusive rocks.** Your answer should include, but not be limited to, comments on the following: effects of cooling; permeability; weathering potential.
* Extrusives are **episodic** in origin and lead to _complex banded structures._
* **Jointing is polygonal** from *cooling* of intrusive, but _surface cooling_ of extrusives often leads to **lava tubes.**
* **Inter-Layering** is common and is associated with *gaps* between eruptions and *complex reworking* of the ground surface can **introduce soils**.
* **Permeability is highly variable** because of highly variable porosity of lavas through to _ashes_ and agglomerates forming _tuffs_.
* _Alteration_: many **weak and deleterious minerals**
* Can have further local thin intrusives **cross cutting**.
* Geol Complications include: very complex topography is possible, blocky heterogeneous materials interlayered but not necessarily in horizontal beds. Non-systematic history, interlayers of soil, original and thermally induced rock properties
126
In the engineering geology of igneous rocks, it is useful to characterise these materials in terms of (i) the form of their emplacement and (ii) their mineral chemistry.
What are the specific geological complications that an engineering geologist should be aware of, regarding the engineering geological characteristics of extrusive rocks.
* Very complex topography is possible, blocky heterogeneous materials interlayered but not necessarily in horizontal beds.
* Non-systematic history, interlayers of soil, original and thermally induced rock properties
127
In the engineering geology of igneous rocks, it is useful to characterise these materials in terms of (i) the form of their emplacement and (ii) their mineral chemistry.
Describe the principal weathering processes and products in **acidic igneous rocks**, and describe how these may affect engineering projects.
* Fractures → increase surface area → carbonic acid solutions replace silicate cations leading to decomposition of plag and k-feldspars to kaolinite, illite.
* Quartz is unaffected.
* Complete disintegration leads to a metastable loose sand after the clay has been removed.
128
In the engineering geology of igneous rocks, it is useful to characterise these materials in terms of (i) the form of their emplacement and (ii) their mineral chemistry.
Describe the principal weathering processes and products in **basic igneous rocks**, and describe how these may affect engineering projects.
Mg and Fe are abundant and combine to produce hydrated aluminosilicate – montmorillonite – key problem due to crystalline structure allowing swell/shrink.
129
Construction of the Ataturk dam in south eastern Turkey was completed in 1990, but within 2 years settlement of the vesicular basalt rock fill from which it is built had caused a considerable reduction of the dam’s crest level. Investigation revealed that this settlement was due to slaking of the basalt.
**Define slaking**.
Slaking is the deterioration and breakdown of a rock resulting from its exposure during excavation.
130
Construction of the Ataturk dam in south eastern Turkey was completed in 1990, but within 2 years settlement of the vesicular basalt rock fill from which it is built had caused a considerable reduction of the dam’s crest level. Investigation revealed that this settlement was due to slaking of the basalt.
## Footnote
**Under what circumstances do vesicular basalts form, and how might they become susceptible to slaking?**
* Vesicles in basalt are due to expansion of dissolved gases in magma forming bubbles.
* Subsequent mineralisation can lead to vesicles filling with slake susceptible minerals.
* The amygdules were largely montmorillonite and calcite at Ataturk dam.
* Slaking potential is very high with montmorillonite, therefore very high susceptibility of basalt to slaking.
131
Construction of the Ataturk dam in south eastern Turkey was completed in 1990, but within 2 years settlement of the vesicular basalt rock fill from which it is built had caused a considerable reduction of the dam’s crest level. Investigation revealed that this settlement was due to slaking of the basalt.
## Footnote
**Write down a checklist that an engineering geologist could follow on site in order to properly identify the presence and slake susceptibility of such basalts. In what ways might this checklist differ for the identification of slake susceptibility in mudrocks?**
* Are we dealing with **basalt rocks**?
* Is this basalt likely to be assoc. with **vesicular basalt**? Search and identify samples with vesicles.
* Are they **amygduloidal** and if so what minerals have crystallised?
* Use **Methylene Blue spot test** and/or **XRD**.
* Difference with mudrocks – the **entire rock** and not just the inclusions are **potentially prone to slaking**.
* Therefore _lumps of rock_ rather than crystalline products are _investigated_.
* Two suitable tests for mudrocks are the **slake durability test** and the **jar slake test.**
132
What is the Methylene Blue spot test?
Titration of amount of methylene blue adsorbed by the ground clay sample
133
How long did it take for excavation and supply of the geomaterials required for the M62 Motorway project and why did it take this long?
ASK J.P. BC I CANT FIND THE INFO FOR THIS
134
What is the purpose of weathering classification of ingeous rocks?
Need to incorporate degree of weathering (**rock-material characterization**) and relative abundance of altered materials (**rock-mass characterization**).
135
How might one classify the weathering of an igneous rock?
Put into one of six grades
136
Describe the different criteria that classify the weathering grade of a **Grade 1** igneous rock.
State whether this kind of rock is suitable for foundations.
* Fresh
* Sound minerals
* Knife cannot scratch feldspars
* Samples need repeated hammer blows to break
* Foundations: Sound
137
Describe the different criteria that classify the weathering grade of a **Grade 2** igneous rock.
State whether this kind of rock is suitable for foundations.
* Slightly weathered
* Biotites show edge staining
* Microfissures \> 1 cm apart
* Feldspars difficult to scratch
* \>1 hammer-blow needed to break
* Foundations: Good for anything execpt large dams.
138
Describe the different criteria that classify the weathering grade of a **Grade 3** igneous rock.
State whether this kind of rock is suitable for foundations.
* Moderately weathered
* Fsps and biotites moderately decomposed
* Some grain boundaries open
* Fsps can be scratched
* One good hammer blow breaks samples
* Foundations: Good for most small structures
139
Describe the different criteria that classify the weathering grade of a **Grade 4** igneous rock.
State whether this kind of rock is suitable for foundations.
* Highly weathered
* Fsps and biotites highly decomposed
* Open grain boundaries
* Fsps can be peeled
* Hammer crushes samples
* Foundations: Variable and unreliable
140
Describe the different criteria that classify the weathering grade of a **Grade 5** igneous rock.
State whether this kind of rock is suitable for foundations.
* Completely weathered
* Recognisably crystalline but all fsps and biotite completely decomposed
* Geology pick will indent outcrops/samples,
* Samples disintegrate when saturated
* Foundations: Assess by soil testing
141
Describe the different criteria that classify the weathering grade of a **Grade 6** igneous rock.
State whether this kind of rock is suitable for foundations.
* Residual soil
* No crystalline texture
* All non-qtz minerals feels clayey
* Thumb will indent outcrops/samples
* Foundations: Unsuitable
142
Arkose is sandstone that contains 25% or more feldspar, and as a result it can be misinterpreted in borehole core as granite.
Using your geological knowledge of these rock types, what features should an engineering geologist look for in a short length of borehole core (say, 5 m) to help determine which of these two materials is present?
* _Arkose is sedimentary_ so **sed structures** such as *grading* and *bedding* should be evident,
* _Granite_ will contain other **accessory minerals** and **micas**, and have **crystalline structure**...
* The **particulate clastic nature of arkose** will be visible with a hand lens.
* **Hydrothermal activity** much more commonly associated with _granite_
143
Arkose is sandstone that contains 25% or more feldspar, and as a result it can be misinterpreted in borehole core as granite.
Considering the engineering characteristics of these rocks, what could be the engineering consequences of misinterpreting arkose as granite and vice-versa?
* The **weathering profiles are different**.
* **Corestones** in granites may grade rapidly into tropical soil.
* _Permeability_ assoc with _porosity of sst_ is much greater in arkose.
* _Granite weathering_ is likely to be very much **more extensive** than arkose.
* **Variability and structural changes** (bedding discontinuities) are more likely in _arkose terrains_.
144
Arkose is sandstone that contains 25% or more feldspar, and as a result it can be misinterpreted in borehole core as granite.
A water supply company is proposing to construct a new reservoir in a valley that is underlain by arkose. Although most of the valley is covered by glacial till to a thickness of about 5 m, there is some outcrop evidence of mineralised veins that suggest hydrothermal activity.
How might the hydrothermal activity have altered the mineral composition of the arkose?
feldspars altered/decomposed to **kaolinite**
145
Arkose is sandstone that contains 25% or more feldspar, and as a result it can be misinterpreted in borehole core as granite.
A water supply company is proposing to construct a new reservoir in a valley that is underlain by arkose. Although most of the valley is covered by glacial till to a thickness of about 5 m, there is some outcrop evidence of mineralised veins that suggest hydrothermal activity.
What could the consequences of this be for the stability of the dam foundation?
* kaolinite is a clay and is _weak_, and **easily eroded** by water and *redeposited in joints and fractures*.
* It will **lower shear strength** – easy planes of shear for *instability*, and will further _increase the permeability_ of the unweathered arkose
146
Arkose is sandstone that contains 25% or more feldspar, and as a result it can be misinterpreted in borehole core as granite.
A water supply company is proposing to construct a new reservoir in a valley that is underlain by arkose. Although most of the valley is covered by glacial till to a thickness of about 5 m, there is some outcrop evidence of mineralised veins that suggest hydrothermal activity.
What techniques would you employ to investigate the quality of the foundation rocks, firstly at the preliminary site selection stage and secondly at the detailed design stage?
* Prelim stage - **Geophysics** – to get depth to foundation level (weathering grade 1-2) rock head and possibly identify weathered zones.
* Detailed stage requires **exploratory trenches** to locate weathered zones.
* During construction – trenches are used in a flexible manner to account for the very **variable foundation levels** likely to be encountered
147
Rock breakage by blasting can lead to a range of undesirable environmental impacts in and around surface mines and quarries. By outlining the mechanisms operating during the blasting process, explain the types of environmental impacts that may arise from blasting.
* Explosives _converted to gases_ at high T and P
* Gas impulse on borehole wall, crushing of borehole wall (**creates fines that contribute later to dust nuisance**)
* _Stress pulse_ radiates beyond crush zone and tangential (hoop stresses) become tensile à radial cracks
* Creation of many _free faces_, reflected compression waves become tensile making it ~10 times easy to break rock. When stress amplitudes no longer break rock – this energy **sets up heavy ground vibrations that propagate and attenuate**.
* _Stemming_ in boreholes confine the gases so this forces gas volume to *expands* inside holes and along cracks and helps push and heave the blocks out of front face. The pressure pulse then extends out into the air causing _air blast vibration_ which is manifest as both **noise nuisance (higher frequencies) and sub-audible airblast (lower frequencies)** is very uncomfortable and will damage eardrums if too intense because too close.
* The main cause of excessive airblast levels and **flyrock** is when unexpected cavities, locally burden is too small and not accounted for, or drilling accuracy is poor.
