Showing posts with label Geotechnical engineering. Show all posts
Showing posts with label Geotechnical engineering. Show all posts

Tuesday, 9 January 2018

Maximum Dry Density And The Optimum Moisture Content 

INTRODUCTION

For any soil, for a given amount of compactive effort, the density obtained depends on the moisture content. At very high moisture contents, the maximum dry density is achieved when the soil is compacted to nearly saturation, where (almost) all the air is driven out.

This test is done to determine the maximum dry density and the optimum moisture content of soil using heavy compaction as per IS: 2720 (Part 8 ) – 1983.

APPARATUS

(i) Cylindrical metal mould – it should be either of 100mm dia. and 1000cc volume or 150mm dia. and 2250cc volume and should conform to IS: 10074 – 1982.

(ii) Balances – one of 10kg capacity, sensitive to 1g and the other of 200g capacity, sensitive to 0.01g

(iii) Oven – thermostatically controlled with an interior of noncorroding material to maintain temperature between 105 and 110'C

(iv) Steel straightedge – 30cm long

IS Sieves of sizes – 4.75mm, 19mm and 37.5mm

PREPARATION OF SAMPLE

A representative portion of air-dried soil material, large enough to provide about 6kg of material passing through a 19mm IS Sieve (for soils not susceptible to crushing during compaction) or about 15kg of material passing through a 19mm IS Sieve (for soils susceptible to crushing during compaction), should be taken. This portion should be sieved through a 19mm IS Sieve and the coarse fraction rejected after its proportion of the total sample has been recorded. Aggregations of particles should be broken down so that if the sample was sieved through a 4.75mm IS Sieve, only separated individual particles would be retained.

PROCEDURE

(A) Soil not susceptible to crushing during compaction

 1. A 5kg sample of air-dried soil passing through the 19mm IS Sieve should be taken. The sample should be mixed thoroughly with a suitable amount of water depending on the soil type (for sandy and gravelly soil – 3 to 5% and for cohesive soil – 12 to 16% below the plastic limit). The soil sample should be stored in a sealed container for a minimum period of 16hrs.

 2. The mould of 1000cc capacity with base plate attached, should be weighed to the nearest 1g (W1 ). The mould should be placed on a solid base, such as a concrete floor or plinth and the moist soil should be compacted into the mould, with the extension attached, in five layers of approximately equal mass, each layer being given 25 blows from the 4.9kg rammer dropped from a height of 450mm above the soil. The blows should be distributed uniformly over the surface of each layer. The amount of soil used should be sufficient to fill the mould, leaving not more than about 6mm to be struck off when the extension is removed. The extension should be removed and the compacted soil should be levelled off carefully to the top of the mould by means of the straight edge. The mould and soil should then be weighed to the nearest gram (W2).

 3. The compacted soil specimen should be removed from the mould and placed onto the mixing tray. The water content (w) of a representative sample of the specimen should be determined.

 4. The remaining soil specimen should be broken up, rubbed through 19mm IS Sieve and then mixed with the remaining original sample. Suitable increments of water should be added successively and mixed into the sample, and the above operations i.e. (2.) to (4.) should be repeated for each increment of water added. The total number of determinations made should be at least five and the moisture contents should be such that the optimum moisture content at which the maximum dry density occurs, lies within that range.

(B) Soil susceptible to crushing during compaction

Five or more 2.5kg samples of air-dried soil passing through the 19mm IS Sieve, should be taken. The samples should each be mixed thoroughly with different amounts of water and stored in a sealed container as mentioned in Part (A)

(C) Compaction in large size mould

 For compacting soil containing coarse material upto 37.5mm size, the 2250cc mould should be used. A sample weighing about 30kg and passing through the 37.5mm IS Sieve is used for the test. Soil is compacted in five layers, each layer being given 55 blows of the 4.9kg rammer. The rest of the procedure is same as above.

REPORTING OF RESULTS

 Bulk density Y(gamma) in g/cc of each compacted specimen should be calculated from the equation..

 Y(gamma) = (W2-W1)/ V

where, V = volume in cc of the mould

The dry density Yd in g/cc

Yd = 100Y/(100+w)

The dry densities, Yd obtained in a series of determinations should be plotted against the corresponding moisture contents,w. A smooth curve should be drawn through the resulting points and the position of the maximum on the curve should be determined. A sample graph is shown below:

 The dry density in g/cc corresponding to the maximum point on the moisture content/dry density curve should be reported as the maximum dry density to the nearest 0.01. The percentage moisture content corresponding to the maximum dry density on the moisture content/dry density curve should be reported as the optimum moisture content and quoted to the nearest 0.2 for values below 5 percent, to the nearest 0.5 for values from 5 to 10 percent and to the nearest whole number for values exceeding 10 percent.

Atterberg Limits - Plastic Limit 

INTRODUCTION

The plastic limit is one of 5 limits developed by A. Atterberg, a swedish scientist.  The plastic limit is one of the most commonly performed of the Atterberg Limits along with the Liquid Limit.  These 2 tests are used internationally to classify soil

The plastic limit is defined as the moisture content at which soil begins to behave as a plastic material.  A plastic material can be molded into a shape and the material will retain that shape.  If the moisture content is below the plastic limit, it is considered to behave as a solid, or a nonplastic material.  As the moisture content increases past the plastic limit, the liquid limit will be approached.  The liquid limit is defined as the moisture content at which the soil behaves like a liquid.

EQUIPMENT

Soil sample,Mixing dish,425 micron Sieve and pan Spatula ,Glass plate,Water.

PROCEDURE

 1. Obtain equipment outlined above for the Plastic Limit test.

 2. Weigh 3 metal moisture content containers and record the weights.  Keep track of the containers and their weights.

 3. Using the soil provided or your own sample of dry material, pulverize about a handful of it using the small soil pulverizer. The pulverizer breaks the material up into particle sizes that will pass the 425micron sieve in accordance with the ASTM standard for this test. Any material not passing through the pulverizer can be discarded.

 4. Put the soil into the mixing bowl and add enough water so that the sample can be easily molded into a ball.

 5. Obtain a ball about the same diameter as a nickel and place the ball on the glass plate.  Roll the ball into a thread of approximately 1/8 inch diameter. 

 6. If the thread crumbles before 1/8 inch diameter is reached, the sample is too dry and water must be added.  If the thread is easily rolled to 1/8 and even smaller, the sample is too wet and must be dried by working the soil with the hands.

 7. When the sample just begins to crumble at 1/8 inch diameter, this is the plastic limit.

 8. Immediately placed the thread of soil into a cup and obtain a wet weight of soil.  Place the soil in the oven and obtain the moisture content at the next lab meeting.

 9. Repeat test once more to obtain an average of 2 tests.

Atterberg Limits - Liquid Limit 

INTRODUCTION

The liquid limit is one of 5 limits developed by A. Atterberg, a swedish scientist. The liquid limit is one of the most commonly performed of the Atterberg Limits along with the plastic limit. These 2 tests are used internationally to classify soil

The liquid limit is defined as the moisture content at which soil begins to behave as a liquid material and begins to flow. The liquid limit is determined in the lab as the moisture content at which the two sides of a groove formed in soil come together and touch for a distance of 2 inch after 25 blows. Since it is very difficult to get this to occur exactly, we will run the test repeatedly until the groove closes 1/2 inch with over 25 blows and under 25 blows. We can plot these results as blow count versus moisture content and interpolate the moisture content at 25 blows from this graph.

EQUIPMENT

Soil sample, Metal Mixing Bowl,Small Spatula, Liquid Limit Device, Water, IS Sieve of 425 Micron, Weight Ballance.

PROCEDURE

1. Obtain equipment Required for the Liquid Limit test.

2. Weigh 3 metal moisture content containers and record the weights. Keep track of the containers and their weights.

3. Pass the soil sample through IS Sieve of 425 Micron.

4. Now take about 120gm soil sample passed through 425 micron sieve & put the soil into a metal mixing bowl and add enough water so that the sample has a creamy texture like smooth peanut butter.

5. Adjust the drop height of the liquid limit device to 10mm using the block end of the grooving tool. Measure from the block to where the bowl hits the block.

6. Place the wet soil sample in the liquid limit device as shown below. This should be done by first turning the crank so that the bowl is resting on the base. The soil should fill the bowl similarly to the way water would fill the bowl. The sample should be smoothed and curved somewhat towards the bottom of the bowl. The depth of the soil sample should be no deeper than the triangular extrusion on the end of the grooving tool.

7. When the soil sample as adequately placed in the bowl, use the grooving tool to cut a groove through the sample as shown below. The bottom of the brass cup should be seen.

8. At this point, turn the crank at a rate of 2 turn per second until the groove closes 1/2 inch, as shown below and keep track of the blow count. Record the blows on the data sheet and obtain a sample for a moisture content.

9. Repeat the test. If the blow count from the first try was greater than 25 blows, add some water and repeat. If less than 25 blow were obtained, add dry soil, mix extremely well, and repeat until a data point above and a data point below 25 blows is obtained.

Sieve Analysis Of Soil 

INTRODUCTION

Sieve analysis of different types of soil is necessary to know the percentage of material of different size in it. Each type of soil contains materials of different size & properties. By Sieve analysis we can break the soil sample in different size of particles & hence we can know the percentage of materials of different size. Each type of soil has a limit for each size of material, which can be checked by sieve analysis.

Sieve Analysis Of Soil For Granular Sub Base

APPARATUS

A set of IS Sieves for gradation of soil for GSB (75mm, 53mm, 26.5mm, 4.75mm, 75 micron, pan)

Weight Ballance

Observation Sheet

PROCEDURE

A Representative sample of soil will be taken for sieve analysis of soil.Take weight of Sample & note it on Observation sheet.Now Arrange the sieves in decreasing order.Sieve the soil sample with the sieves & note down the weight retained on each sieve on observation sheet.Calculate the % of weight retained on each sieve, passing of material on observation sheet

RESULT

If Your soil sample passed 100% from 75mm sieve then it means that your GSB is of grade-I

If Your soil sample passed 100% from 53mm sieve then it means that your GSB is of grade-II

If Your soil sample passed 100% from 26.5mm sieve then it means that your GSB is of grade-III

Check the desired limits for each size of material on observation sheet.

Wednesday, 15 June 2016

Types of Stairs


The stairs may be built with wood, concrete masonry or with cast iron. Wooden stairs are not safe, because of the danger of fire. However they are used in buildings to access to small areas in the upper floors.

 Cast iron or steel stairs in the spiral forms were used commonly to reduce stair case area. In many residential buildings masonry stairs are also used. Reinforced concrete stairs are very commonly used in all types of buildings.

PLASTERING


Applying mortar on the surfaces of walls, columns, ceiling etc. to get smooth finish is termed as plastering.

Mortar used for plastering may be lime mortar, cement mortar or lime-cement mortar.

Lime mortar used lime to sand ratio of 1 : 3 or 1 : 4.

Cement mortar of 1 : 4 or 1 : 6 mix is very commonly used for plastering, richer mix being used for outer walls.

CELLULAR CONCRETE


It is a light weight concrete produced by introducing large voids in the concrete or mortar. Its density varies from 3 kN/m3 to 8 kN/m3. It is also known as aerated, foamed concrete.

Properties of cellular concrete
1. It has low weight.

2. It has good fire resistance.

Compaction factor test.


This is another test to  identify the workability of concrete. This test is conducted in the laboratory.

The test equipment consists of two hoppers and a cylinder fixed to a stand, the dimensions and the distances between the three vessels being standardized. Vessel A and B are having hinged bottoms whereas cylinder C is having fixed bottom.

What is uses of timber?


1. For heavy construction works like columns, trusses, piles.

2. For light construction works like doors, windows, flooring and roofing.

3. For other permanent works like for railway sleepers, fencing poles, electric poles and gates.

4. For temporary works in construction like scaffolding, centering, shoring and strutting, packing of materials.

Uses of Stones.


(i) Stone masonry is used for the construction of foundations, walls, columns and arches.

(ii) Stones are used for flooring.

(iii) Stone slabs are used as damp proof courses, lintels and even as roofing materials.

What are the Properties of Stones?


(i) Structure

(ii) Texture

(iii) Density

(iv) Appearance

Tuesday, 7 June 2016

DETERMINATION OF MOISTURE CONTENT


OBJECTIVE 

Determine the natural content of the given soil sample.  

NEED AND SCOPE OF THE EXPERIMENT

In almost all soil tests natural moisture content of the soil is to be determined. The knowledge of the natural moisture content is essential in all studies of soil mechanics. To sight a few, natural moisture content is used in determining the bearing capacity and settlement. The natural moisture content will give an idea of the state of soil in the field. 

DEFINITION

The natural water content also called the natural moisture content is the ratio of the weight of water to the weight of the solids in a given mass of soil. This ratio is usually expressed as percentage.

APPARATUS REQUIRED

    1. Non-corrodible air-tight container.       2. Electric oven, maintain the temperature between 1050 C to 1100 C.      3. Desiccator.      4. Balance of sufficient sensitivity. 

PROCEDURE

1. Clean the container with lid dry it and weigh it (W1).  2. Take a specimen of the sample in the container and weigh with lid (W2).  3. Keep the container in the oven with lid removed. Dry the specimen to constant weight maintaining the temperature between 1050 C to 1100 C for a period varying with the type of soil but usually 16 to 24 hours.  4. Record the final constant weight (W3) of the container with dried soil sample. Peat and other organic soils are to be dried at lower temperature (say 600 ) possibly for a longer period. 

  Certain soils contain gypsum which on heating loses its water if crystallization. If itb is suspected that gypsum is present in the soil sample used for moisture content determination it shall be dried at not more than 800 C and possibly for a longer time.

OBSERVATIONS AND RECORDING

Data and observation sheet for water content determination  

S.No. Sample No. 1 2 3

1 Weight of container with lid W1 gm

     

2 Weight of container with lid +wet soil W2 gm

     

3 Weight of container with lid +dry soil W3 gm

     

4 Water/Moisture content

W = [(W2−W3)/(W3−W1)]100

     

   

  RESULT

The natural moisture content of the soil sample is ________ 

 REMARKS

1. A container with out lid can be used, when moist sample is weighed immediately after placing the container and oven dried sample is weighed immediately after cooling in desiccator.

2. As dry soil absorbs moisture from wet soil, dried samples should be removed before placing wet samples in the oven.

Monday, 6 June 2016

Self compacting concrete.


A concrete which is capable to compact itself by its own self-weight under gravity without any external efforts like vibration is called as self compacting concrete. the mix is required to have ability of passing, filling and being stable.

Following ingredient are used to prepare self compacting concrete.

1. cement :- OPC 43 or 53 grade.

2. Aggregates:- well grade rounded or cubical aggregate of size 10 to 20mm uniformly graded fine aggregates.

3. Good quality of mixing water.

4. Super plasticizer like poly-carboxylated ether to improve the workability and viscosity modifying agent.

5. Mineral admixture like fly ash, ground granulated blast furnace slag, silica flume, fiber, finely crushed lime stone, dolomite or granite

6. Under self weight , scc should level and deform itself without any compaction and external vibration. There should be not be any entrapped air in concrete.

7. SCC should be fully flowable but without segregation and bleeding. This is achieved by keeping higher viscosity of cement and mortar to ensure flowability while maintaning no sedimentation of bigger aggregates.

Slump Test


Slump test is the most commonly used method of measuring workability of concrete. the apparatus for conducting the slump test essentially consists of a metallic mould in the form of a frustum of a cone having the internal dimensions as follows:-

Bottom diameter   20cms

Top diameter          10cms

Height                      30cms

The mould is the place on a smooth, horizontal, rigid and non absorbent surface. the mould is then filled in four layer each approximately 1\4 of the mould. each layer is tamped 25 times by the tamping rod taking care to distribute the stroke evenly over the cross sections. After the top layer has been rodded, top is struck off level with a trowel and tamping rod. the mould is removed from the concrete immediately by raising it slowly and carefully in a vertical direction. this allows the concrete to subsidence. this subsidence is referred as slump of concrete. the difference in level between the height of the mould and that of the height point of the subsided concrete is measured. this difference in height in mm is taken as slump of concrete.

slump requirement for beams and slabs 50mm to 100mm

for walls and columns 75mm to 100mm

Vibrated concrete 15mm to 25mm  

Tuesday, 31 May 2016

Standard Penetration Test (SPT)


One of the most common in-situ tests is the standard penetration test or SPT. This test which was originally developed in the late 1920s.

SPT is most commonly used in situ test, especially for cohesionless soils which cannot be easily samples. the test is extremely useful for determining the relative density and the angle of shearing resistance of  for cohesionless soils.

it can also used to determine the unconfined compressive strength of cohesive soils.

The standard penetration test is conducted in a borehole using a standard split-spoon sampler. 

When the borehole (55 to 150 mm in dia) has been drilled to the desired depth, the drilling tools are removed and the split-spoon sampler, attached to standard drill rods of required length is lowered to the bottom of the borehole and rested at the bottom.

The split-spoon sampler is then driven into the soil for a distance of 450 mm in three stages of 150 mm each by blows of a drop hammer of 63.5 kg mass falling vertically and freely through a height of 750 mm at the rate of 30 blows per minute (IS 2131 – 1981). The number of blows required to penetrate every 150-mm is recorded while driving the sampler. If full penetration is obtained, the blows for the first 150 mm is retained for reference purposes, but not used to compute the SPT value because the bottom of the boring is likely to be disturbed by the drilling process and may be covered with loose soil that may fall from the sides of the boring. The number of blows required for the next 300 mm of penetration is recorded as the SPT value. The number of blows is designated as the “Standard Penetration Value” or “Number” N.

The slit-spoon sampler is then withdrawn and is detached from the drill rods. The split barrel is disconnected from the cutting shoe and the coupling. The soil sample collected inside the split barrel is carefully collected so as to preserve the natural moisture content and transported to the laboratory for tests. Sometimes, a thin liner is inserted within the split-barrel so that at the end of the SPT, the liner containing the soil sample is sealed with molten wax at both its ends before it is taken away to the laboratory. 

Precautions

The drill rods should be of standard specification and should not be in bent condition

The split spoon sampler must be in good condition and the cutting shoe must be free from wear and tear

 The drop hammer must be of right weight and the fall should be free, frictionless and vertical.

 The height of fall must be exactly 750 mm. Any change in this will seriously affect the N value.

 

The standard penetration number is corrected for dilatancy correction and overburdon correction.

Undisturbed soil samples


Undisturbed soil samples are those in which the in-situ soil structure and moisture content are preserved.

• They are representative and also intact

• These are used for consolidation, permeability or shear strengths test (Engineering properties)

• More complex jobs or where clay exist

• In sand is very difficult to obtain undisturbed sample

• Obtained by using Shelby tube (thin wall), piston sampler, etc., 

Disturbed soil samples


Disturbed soil samples are those in which the in-situ soil structure and moisture content are lost, but the soil particles are intact.

• They are representative 

• They can be used for grain size analysis, liquid and plastic limit, specific gravity, compaction tests, moisture content, organic content determination and soil classification test performed in the lab

 • e.g., obtained through cuttings while auguring, etc.

Depth of exploration


The depth of the exploration required at a particular site depend on the degree of variation of the sub-surface data in the horizontal and vertical directions. It is not possible to fix the number, disposition and depth of borings without making a few preliminary borings or sounding at the site.

Generally exploration should be carried out to a depth upto which the increase in pressure due to structural loading is likely to cause perceptible settlement or shear failure. such a depth known as the significant depth, depent upon the type of the structure, its weight.  It is generally safe to assume the significant depth upto a level at which the net increase in vertical pressure become less than 10% of the initial overburden pressure.

Stages of the sub-surface exploration


1. Reconnaissance

site Reconnaissance is the 1st step in the exploration. it include a visit to the site and to study the maps and other relevant records. it helps in deciding the future programme of the site investigation. types of sample adopted to be taken and the laboratory testing and in-situ testing.

2. Preliminary or general exploration

the aim of the general exploration is to get an approximate picture of the sub-soil condition at the relatively low cost. the information so obtained should suffice for the design and execution of minor and routing engineering works.

the preliminary exploration are generally in the form of few borings or test pits. test are conducted inthe form of the borings or test pits. test are conducted with cone penetrometers and sounding rods to obtain information about strength and compressibility of the soil

3. Detailed exploration

it is a supplement to general exploration when large engineering works, heavy loads and complex costly foundation are involved, such as bridge, dam, and multistory building. however for small projects especially at sites where the strata are uniform, detailed exploration may not be required.

the purpose of detailed exploration is to determine the engineering properties of the soils in different strata. it include the  extensive boring programme, sampling and testing of the samples in the a laboratory.

field test, vane shear test, plate load test and permeability test are conducted to determine the properties of the soil in natural state.

the test for the determination of the dynamic properties are also carried out.