Site Improvement

Earthwork and Ground Technology

Site Improvement

Methods of site improvement

•        Removal and replacement

•        Preloading

•        Vertical drains

•        In-situ densification

Removal and replacement

•        One of oldest and simplest methods is  simply to remove and replace the soil

•        Soils that will have to be replaced include  contaminated soils or organic soils

•        Method is usually practical only above the  groundwater table

Preloading

•        Simply place a surcharge fill on top of the soil that  requires consolidation

•        Once sufficient consolidation has taken place, the  fill can be removed and construction takes place

•        Surcharge fills are typically 10-25 feet thick and  generally produces settlement of 1 to 3 feet.

•        Most effective in clay soil

Advantages of preloading

•        Requires only conventional earthmoving  equipment

•        Any grading contractor can perform the  work

•        Long track record of success

Disadvantages of preloading

•        Surcharge fill must extend horizontally at  least 10 m beyond the perimeter of the  planned construction, which may not be  possible at confined sites

•        Transport of large quantities of soil required

•        Surcharge must remain in place for months  or years, thus delaying construction

Vertical Drains

•        Vertical drains are installed under a surcharge load  to accelerate the drainage of impervious soils and  thus speed up consolidation

•        These drains provide a shorter path for the water  to flow through to get away from the soil

•        Time to drain clay layers can be reduced from  years to a couple of months

PVD (Prefabricated Vertical Drain)

•        Geosynthetics used as  a substitute to sand  columns

•        Installed by being  pushed or vibrated  into the ground

•        Most are about 100  mm wide and 5 mm  thick

Typical installation of PVD

•        Typically spaced 3 m  on centers

Prefabricated Drains Available

•Nylex

In-situ densification

·      Most effective in sands

·      Methods used in conventional earthwork are  only effective to about 2 m below the  surface

·      In-situ methods like dynamic deep  compaction are for soils deeper than soil can be  compacted from the surface

Vibratory probe compaction

•        Long probe mounted onto a vibratory pile  driver compacts the soil around the probe;  penetrations spaced in a grid pattern similar  to vertical drains

Vibroflotation

•        Probe includes the vibrator mechanism and water  jets

•        Probe is lowered into the ground using a crane

•        Vibratory eccentric force induces densification  and water jets assist in insertion and extraction

•        Vibratory probe compaction is effective if silt  content is less than 12-15% and clay is less than  3%

•        Probes inserted in grid pattern at a spacing of 1.5  to 3 m

 

Rocks And Its Types

Geology :

·      Geology is the branch of earth science is concerned with the both the liquid and solid earth, the rock which it is composed and the process by which they changed overtime.

Petrology:

·      Petro means rock and logos mean study, so it is the branch of geology which deals with the study of rocks.

Rocks:

·      Rocks are defined as an aggregate of minerals.

Importance of Geology in Civil Engineering

·      It provides an opportunity to interpret the physical properties of individual rocks, likewise texture, structure, mineral and chemical composition etc...

·      These help in knowing the strength, durability, color, appearance etc.

·      These properties are very important for the civil engineer to know because different rocks are suitable for different purposes and no rock is ideal or best suited for all purpose.

Igneous Rocks:

·      All rocks that have formed from original hot molten material (magma) through the process of cooling and crystallization may be defined as igneous rock.

Difference between Magma and Lava

·      Magma: Magma is hot viscous siliceous melt containing gasses. It comes from greater depth below the earth’s surface. This melt remains within the surface.

·      Lava: when magma comes out upon the surface of earth, it is called lava.

Igneous rocks can be further divided into three sub-categories

·      Volcanic Rocks

      -Cooling and crystallization of lava.

      -Cools down very fast so the grain size of

       The crystal is very fine.

·      Plutonic Rock

         -This igneous rocks formed at

           Considerable depth of about 7 to 10

           Kilometer below the earth surface.

         -Slow rate of cooling so coarse

           Grained.

         -For Example: Granite

·      Hypabyssal Rocks

         - Also known as Sub Volcanic Rock.

         -Formed at intermediate depth, 2

           kilometers below the surface of

          Earth.

         -Mixed characteristics of volcanic

           And plutonic.

On The Basis Of Silica Content Igneous Rocks:

·      Acidic/Felsic Rock:

 -In these rocks silica content is more than 65%.

 -The light colored rocks are formed.

 -For example: Granite

·      Intermediate Rocks:

 -Silica content ranges from 55-65%.

 -Medium colored rocks are formed.

 -For example: Diorite

·      Mafic/Basic Rocks:

 - Silica content ranges from 45-55%.

 -Dark color rocks are formed.

 -For example:  Basalt

·      Ultra Mafic Rocks:

 -Silica content is less than 45%.

 -The ultra dark colored rocks are formed.

 -For example: Kimber lite

Texture of Igneous Rocks

There are three factors we define the texture of the igneous rocks

·      Degree of crystallization.

·      Granularity.

·      Fabric

Types of Texture

There are total five types of igneous rocks according to the texture:

1.  Equigranular Texture

2.  Inequigranular Texture

3.  Directive Texture

4.  Intergrowth Texture

5.  Intergranular Texture

 

INTERIOR OF EARTH

INTERIOR OF EARTH

Earth is composed of three layers (major concentric zones). Their names are given below as:

Crust:

The crust is the outermost layer of Earth.

•      “Crust” describes the outermost shell of a terrestrial planet .Beneath the crust lies Mantle.

•      The between crust and mantle is called is the Moho boundary.

•      Just as the depth of the crust varies so as the temperature and pressure

•      The crust is primarily (roughly 95%) made up of igneous rock and metamorphic rock. The remaining 5% is made up of sedimentary rock

Types of Crust

Earth’s crust is divided into two types:

Continental Crust

•      Continental crust is mostly composed of different types of granites.

•      Geologists often refer to the rocks of the continental

  Crust as “sial.” Sial stands for silicate and aluminum,

  The most abundant minerals in continental crust.

•      Its density is 2.7 grams per cubic centimeter.

Oceanic Crust

•      Oceanic crust, extending 5-10 kilometers beneath

•      the ocean floor

•      It is mostly composed of different types of basalts.

•       Geologists often refer to the rocks of the

     Oceanic crust as “sima.” It stands silicate and magnesium,

    The most abundant minerals in oceanic crust.

•       Oceanic crust is dense, almost 3 grams

     Per cubic centimeter

Mantle

•      The mantle is the mostly-solid bulk of Earth's interior.

•       The mantle lies between Earth's dense, super-heated core and its thin outer layer, the crust.

•       The mantle is about 2,900 kilometers thick, and makes up a 84% of Earth’s total volume.

Layers of Mantle

Upper Mantle

•      The upper mantle extends from the crust to a depth of about 410 kilometers. The upper mantle is mostly solid, but its more malleable regions contribute to tectonic activity.

Lower Mantle

•      The lower mantle extends from about 660 kilometers to about 2,700 kilometers beneath Earth’s surface. The lower mantle is hotter and denser than the upper mantle and transition zone

Core

•      Earth’s core is the very hot, very dense center of our planet.

•      It lies beneath the cool, brittle crust and the mostly-solid mantle.

•      The core is found about 2,900 km below

    Earth’s surface, and has a

    Radius of 3,485 km.

•      Unlike the mineral-rich crust and mantle,

   The core is made almost entirely of

    Metal—specifically, iron and nickel

Outer Core

The outer core, about 2,200 kilometers thick, is mostly composed of liquid iron and nickel. The NiFe alloy of the outer core is very hot, between 4,500° and 5,500° Celsius. The liquid metal of the outer core has very low viscosity, meaning it is easily deformed and malleable. It is the site of violent convection.

  Inner Core

•      The inner core is a hot, dense ball of (mostly) iron. It has a radius of about 1,220 kilometers. Temperature in the inner core is about 5,200° Celsius. The pressure is nearly 3.6 million atmosphere (atm).