Geological factors considered in the construction of :

Geological Factors

Tunnel

5. Running Ground

6. Gases in rocks

1. The type of the rock and their strength and deformation behavior

3. Groundwater conditions

7. Rock temperature

8. Topographical conditions

2. Geological discontinuities and associated strength and deformationbehavior

4. Squeezing and swelling rock conditions

-the arrangement of the natural and artificial physical features of an area.

A. The type of the rock and their strength and deformation behavior

B. Geological discontinuities and associated strength and deformation behavior

C. Groundwater conditions

D. Squeezing and swelling rock conditions

E. Running Ground

F. Gases in rocks

G. Rock temperature

H. Topographic conditions.

-Is often saturated and the presence of water can encourage liquefaction whendisturbed by tunneling activities.

-Can arise at a later stage due to the progressive collapse and formation of asignificant cavity tapping a major aquifer and overlying unconsolidated saturated deposits.

- Gases are frequently in the sedimentary rock.

- Organic-rich sedimentary rocks have significant amounts of organic material, generally in excess of 3% total organic carbon.

1. Folds- Folds are sometimes the natural traps of natural gases, which might beharmful to the persons working in tunnels.

2. Faults- The orientation of the faults in relation to the tunnel line is vitallyimportant since this govern the length of tunnel affected by the faults andits accompanying faults zone

3. Joints - Are structural plane of weakness and greatly affect shear strength of propertiesof rock and rock masses.

a. Igneous rocks- The crystalline nature of the igneous rocks signifies high compressive strengthwith potential difficulties in rock excavations process, but can also indicate themark competence with the advantages of decreased support needs to achieve anacceptable degree of stability.

b. Sedimentary rocks- The effects of stress and advanced weathering, and weakening by the action of water can give rise to the problems especially where such rock type containsappreciable clay minerals.

c. Metamorphic Rocks- Rock containing micaceous minerals have well defined planes of weaknessand can easily split along these planes of weakness and show very ratherproperties in terms of both strength and deformation properties.

-The presence of groundwater is recognized as a major hazard in addition tocausing operational difficulties in respect of tunnel construction works. Encountering large quantities of water in weak ground conditions can lead torapid formation of cavities around the tunnel excavation and can be producethe potential for the significant quantities of wet and loose ground to flow thetunnel.

- Temperature increases about 10c for every 60-80metres in geologically stableareas and 10c for 10-15 meters in volcanically active areas.

-Effective ventilations is perhaps the only means which can alleviate theproblem.

-Squeezing is in the effect a type of displacement into an excavation due tostress gradient created around the tunnel by excavation.Stress released due to excavation may cause shear displacement to take placeof hundreds of meters beyond the excavation surfaces.

Swelling is a time dependent process and involves physico-chemicalreactions with water.Swelling behaviour denotes the response of rock to the presence of water.

3. Weathering

4. Groundwater Conditions

1. Topography

2. Geological Structures

Road Cuttings

Geology of Dam Sites Narrow River Valley

Dams

5. Lithological Character

Geology of Dam Sites Effects of Associated Geological Structures

Geological factors considered in the construction of :

Geology of Dam Sites Competent Rocks for Safe Foundation

Geology of Dam Sites Bedrock at Shallow Depths

1.Narrow River Valleys

2.Occurrence of the bedrock at a shallow depth.

3.Competent rocks to offer a stable foundation

4.Proper Geological Structures

- Single most important factor

- Reveals the existence of Land Features

- Knowledge of Topography is essential:

1. To decide cuttings

2. To give Retaining walls

1. Topography

2. Lithological Character

3. Geological Structures

4. Joints and Faults

5. Weathering

6. Groundwater Conditions

- Necessary to investigate thoroughly the position of water table. Water exerts influence on the bearing capacity of the rocks and soil. In case of ground with rich moisture, properties of ground have been determined. Condition of free-flow of groundwater through the soil is quite dangerous.

-At the proposed dam site, if the river valley is narrow, only a small dam is required, which means the cost of dam construction will be less. On the other hand, if the valley is wide, a bigger dam is necessary which means the construction cost will be very high.

- Structural Features of rocks have very important bearing upon.

1. Design of cuts

2. Stability of Roads

1. Dams

2.Tunnels

3. Road Cuttings

4. Buildings

- Softer layer of rocks get weathered at a faster rate than the overlaying harder rock

- the alteration of rocks to more stable material from their exposure to the agents of air, water, and organic fluids

- For the stability of a dam, the occurrence of favorable geological structure is a very important requirement. Under structural geology we have learnt that those rocks bear certain inherent or original physical properties, such characters get modified either advantageously or disadvantageously when geological structure occurs in those rocks.

-If Igneous rock occurs at the selected dam site, they will offer a safe basis, and weak sedimentary rocks, particularly shale's, poorly cemented sandstones and limestone's shall naturally be undesirable to serve as foundation rocks.

-This provides details like:

1. Composition of Rocks

2. Texture of rocks

3. Structure of Rocks

4. Origin of rocks

- To ensure its safety and stability a dam has to necessarily rest on (Physically) very strong and (Structurally) very stable (i.e. bedrocks). If such competent bedrocks occur near the surface or at shallow depths, the foundation cost of the dam will naturally be less. On the other hand, if competent bedrocks occur at great depths, the cost of the foundation will be very high because it involves extensive work of excavation of loose overburden and concrete refilling.

Buildings