Unit – 6
Geological Hazards, Groundwater and Building Stones
Q1) What is earthquake and causes of it?
A1) The sudden release of stored energy due to sudden vibrations of earth’s crust that creates seismic wave is termed as earthquakes. Earthquakes are measured using observations from seismographs. Earthquake may occur naturally as a result of human activities. The magnitude of an earthquake and intensity of earthquake is reported on Richter scale.
Causes of earthquakes
Always obey law of reflection and refraction because as they pass through Earth materials of varying density.
P-waves (Primary waves)
- = >8 km/s in earth mantle and core
- = 1.5 km/s in water.
S- waves (Secondary waves)
- 2.5-3.0 km/s in inner core.
L Waves (Long waves)
Description Richter Magnitude Earthquake effect Micro less than 2 not felt Very minor 2.0-2.9 only recorded. Minor 3.0-3.9 rare causes Light 4.0-4.9 sharing of items. Moderate 5.0-5.9 major damage Strong 6.0-6.9 area of = 100 miles can be damaged. Major 7.0-7.9 serious damage Great 8.0-8.9 damage up to 100 miles across. Rarely >9.0 1000 miles destruction. |
Q2) Explain seismic zone of India?
A2)
Q3) Explain landslide and stability of hill slope and preventive measures?
A3) Landslide
Factors which cause landslide-
Types of landslides are:
Q4) What is groundwater and its types?
A4) Groundwater
Uses:
It is used for agricultural, municipal and industrial use by constructing and operating extraction well.
Groundwater is mainly found in aquifers. There are two types of aquifers-
Confined aquifer:
Q5) What is the hydrogeological properties of rocks?
A5)
Voids are obtained by following-
Q6) What are the types of aquifers and groundwater?
A6) Types of aquifers
1. Unconfined aquifers:
2. Confined aquifer:
Types of groundwater
Q7) Write short note on water table depth zones?
A7) Water table is the table at which soils are saturated with water at the upper level of an underground surface.
Subsurface water –
1) Soil water zone
FC to OMC is called as Readily Available moisture.
RAM = FC – OMC {RAM= (60-70%) of AM}
Example: 1) For loamy soil, FC = 28%, OMC =15%, PWP =8%
AM = FC -PWP = 8℅
RAM = FC -OMC = 13℅
2) For clayey soil, FC=25℅, PWP= 5℅, OMC=12℅
AM = FC – PWP=20℅
RAM =FC – OMC = 13℅
RAM =65℅AM
2) Intermediate zone
It is grown in between soil water zone and capillary zone.
3) Capillaryzone
Capillary fringe is subsurface layer in which groundwater seeps up from water table by capillary action.
Saturated zone is classified into 4 groups-
Aquifer- It is porous layer that contains and transmit groundwater. Aquifer is present at various depth.
Types of aquifers– (a) Confined aquifer (b) unconfined aquifer
Aquiclude- It is impermeable layer underlying or overlying an aquifer. It absorbs water but cannot transmit it in significant amount.
Aquifuge- It is impermeable body rock that contains no interconnected opening. Hence, neither absorb nor transmit water.
Aquitard-Low permeability adjacent to aquifer or serves as storage unit for groundwater.
Q8) Explain cone of depression and circle of infulnce?
A8) Radius of influence
OR
Q9) What are the artificial recharge method of groundwater?
A9) Artificial Recharge Techniques
Direct surface techniques
Direct subsurface techniques
Subsurface techniques
Basin tank with pit, shaft or wells.
Indirect techniques
Percolation Tank
Q10) What are the requirement of good building stones?
A10) Following are the quality requirements of good building stones: -
1) Durability: Building stones should be able to resist the adverse effect of forces such as wind, rain and heat. The stone should not be deteriorated due to adverse effect and hence must be durable.
2) Hardness:
3) Strength-Most of the building stones have high strength to resist load coming from superstructure or substructure. Hence, it is the first step to check the quality of stone. Compressive strength of building stone generally falls in the range of 60 to 200 N / .
4) Specific gravity-
Toughness-
Appearance-
Fire resistance-
Limestone can with stand temperature upto 800°C
Types of stones Max. limit of water absorption
Sandstone 10 Limestone 10 Shale 10 Quartzite 3 Granite 1 Slate 1 |
9) Dressing-
Giving proper and required shape is called as dressing in stone. Care should be taken so that dressing will not cost of required strength.
10) Fracture-
For good building stone, its fracture should be
11) Texture-
A good building stone should have cavity free crystalline structure which are fully compacted. Stones with this type of texture are strong and durable (cavities= loose or soft material).
12) Mineral-