Engineering - Assignment Example

Student’s Name Instructor’s Name Course Name: Date: 15th December, 2012. Question 2 a). active lateral earth pressure on a retaining wall Active lateral earth pressure on a retaining wall is earth pressure on wall cause slight movement from the backfill. In this case the wall rotates about the bottom to take a new position which is tilted to the point of plastic equilibrium. This is shown in the diagram below. b). Effective Ranking active Pressure at z=0, z=4 and z=8 Here one begins with determining surcharge which is calculated as follows In case q is the surcharge load is given as 30kN/m and Ka is or Ka = and we given as 35o and given c’ as 0 this is because the wall is no tilted in any way and we are not given for surcharge. Thus, surcharge coefficient of ranking active pressure is determined as follows Ka = = 0.271 Therefore at Z=0 Effective Ranking active Pressure will be consist of only surcharge which is – 2c 0.271 – (2 = At z= 4, the effective ranking active pressure is We are given c’ as 0 and 18kN/m3 is therefore, the upper layer of sand its coefficient of ranking active pressure is determined as follows, Ka = = 0.271 The effective ranking active pressure is = 0.271[30 + (4m x18kN/m3] = 27.642/m2 At Z=4 but in the lower layer the force will be 0.271[30 + (4m x18kN/m3] = 27.642/m2 . This is because is 35o as in the first layer At Z=8metres the effective ranking active pressure is = (27.642/m2 x 4 + 4(20kN/m3- 9.81)) x 0.271 =151.328kN/m c). Rankine active force per unit length of the wall Rankine’s active force per unit length =( ½)H Therefore at Z=0, Rankine’s active force per unit length is =( ½) x 27.642/m2 x 0 =0kN/m Therefore at Z=4, Rankine’s active force per unit length is =( ½) x 27.642/m2 x (4m) = 55.284kN/m At Z=8 Rankine’s active force per unit length =( ½) x 151.328kN/m2 x (8m) = 605.312kN/m d). When we have a factor of safety of 1.4 and we have calculated disturbing force. The formula is FOS against overturning = The wall represents the resisting moment Disturbing moment = 151.328kN/m +27.642/m2 += 187.07kN/m 1.4 = = 1.4 187.07kN/m = 240X X= 1.09m 2X=2.18m Question 3 a). Main types of shallow foundation Strip Footing- this is a continuous footing where columns are put in rows to increase load bearing capacity. The following diagrams shows the strip footing (The Constructor) Spread Footing- This is type of footing which is used to provide support to main footing or columns. The diagram below shows spread footing; (The Constructor) b). Square footing of 3m by 3m i) The formulae Square Footing is Where No is the bearing capacity factor (cohesion), B is the width or diameter of the foundation, D is the effective vertical strength of the soil, Nq is the bearing factor and surcharge friction, is the bearing capacity factor self weight and friction, C is the cohesion strength of the soil. In this case we are given unit weight as 19kN/m3, we have friction as 350, and we have depth base as 3m and a square footing of 3m by 3m Where is the ultimate bearing capacity, in this case we will use the formula Where Qu = In this case Nc=45, Nq=35.4, Ny=50 Qu =1.3x0x(45) + 19kN/m3 (3m) x 35.4) + 0.4 (19kN/m3 x 3m x 50 = 2,017.8 + 1,140 =3,157.8kN/m2 Allowable Bearing Capacity It is Qa = Qu Qa = kN/m2 ii) Shear failure Nc = 16, Nq = 4, N = 1.7 = 273.81 It is Qa = Qu Qa = kN/m2 Allowable total gross load Q= Qa(B)2 = 91.27 X (7)2 = 4,472.16kN The load of 1900 kN thus it is acceptable since the allowance load on the clay is 4,472.16kN c). In determining the consolidation settlement for the soil profile in the diagram with a load of 1900kN which is applied at two metres below the ground by a square footing with a size of 3m by 3m will be determined as follows. Where Sc is the consolidation settlement under the square footing, =wGs =0.35x2.75= 0.9625, Co is 0.009, H is height and is 6m po = (4x19) + 3(21-9.81)+3(22-9.81) = 146.14 kN Δp= [1900*(3*3)] / [(9+1)*(9+1)] = 171kN , K= 1-sin = 0.426 = 39.425125 ,, e0=0.987, = 0.00285m or 0.285cm or 2.85mm = 0.0001days Question 4 a. Deep Foundation this is suitable when the soil top layer is soft and has good bearing soil strata. This means that it can withstand super-embossed stress. If the two mention conditions are made, then deep foundation is used. b. There are a number of known types of deep foundations. These include: -steel piles -timber piles -composite piles -concrete piles -shaft piles c.i) where is the ultimate pile capacity, is the shaft resistance and is ultimate toe resistance. They are calculated as follows: Where is the area of the pile surface area which is pile perimeter length, is undrained shear strength of clay soil and is adhesion factor, is the area of the toe and is the pile adhesion or force. In our case we have 3 Qs because the clay has different adhesion that is 4 strata therefore it will be calculated as follows representing stratum 1, 2 and 3. + ( )+ )+) +( )+ ) Qs = 128 + 168 + 240 = 536kN = Qb = 2520 Qu = 2520 + 536 = 3056 This is ultimate load on the pile. Allowable load on the pile will be determined as follows: Since skin friction is different the toe will have its calculation different from the others, thus allowable load on the pile will be Qa = = 1108kN The allowable load on the pile is 1108kN ii) The design shown is not good enough to change or to be made in order to test the pile capacity. A flat pile should be used instead of toe method. The other method that is likely to be used to test is effective stress method where the friction angle is determined. Stress method considers coefficient for each soil type. Question 5 a).There are a number of reasons for carrying out site investigation. Some of the reasons are listed below 1. Site investigation is done to collect information about the conditions of the soil and ground in order to assist in designing a property that will be put up in the area without the information about the ground, the property foundation may not be strong. 2. Site investigation is very important as it is able to assist, locate grounds which can accommodate some infrastructure. Some grounds may not have the ability to host some infrastructure b). There are a number of insitu tests which are carried out and they include standard penetration test, cone penetration test, vane shear test and many others. In this case we are interested in standard penetration test and vane shear test. Standard Penetration Test—this test is used in soil that has been disturbed by other factors to provide the properties of the test. The test is simple and cheap that’s why it is normally used in testing the relative density and shear strength of soil as well as ground. The method involves the use of a thick walled tube which is driven to the ground using a hammer to scoop the soil. Usually it is driven to the ground to cover 6 inch to 18 inch where each stage of 6 inch penetration is tested for N-value. N-value gives information about the density of the soil and the shear strength of soil properties. Equipments—the equipment that is used in this method include a penetration tube which is sometimes called spoon sampler, a hammer that drives the tube 6 inch, 12 inch, and 18 inch sizes of spoon sampler. Procedure 1). The ground is identified 2). The above named equipment is prepared 3). One goes to the site with the equipment where the thick walled tube is driven to the ground using a hammer. 4). Samples are taken Factors Affecting the Results—there are a number of factors that affect the results of standard penetration test. This include -Using boreholes that have been opened for long therefore the ground has been disturbed so much -While driving the spoon sampler, the field officers may exceed the casing area, thus obtain soil that is not within the area -Field officers may also have their attitude which would affect the result -They may use wrong equipment that would affect the result -There is also sampling the wrong ground by field officers or switching results. This method is very important because it requires cheap equipment to carry out the result. The result obtained is usually calculated using the following formula N(60) = NmCnCeCbCrCsCaCcCBF Where Cm is the blow counts, N(60) is STP number that is to be adjusted to 60%, Ce is the energy correction factor, Cn is overburden correction factor, Cb is the borehole diameter correction factor, Cr is the rod length correction factor, Ca a anvil correction factor, Cs is the correction factor, Cc is hammer correction factor, and CBF is blow count frequency correction factor Vane Shear test—this method of testing is suitable in ground whish are clay and of saturated strength that has not been disturbed. The method is used when the protection identified is to be put in clay ground. The method is simple and cheap thus, making it cost-effective. This method is usually done on undisturbed soil because the ground is having undrained soil. Apparatus—this method requires four stainless blades which will be fixed at right angles but attached to a tensile rod. Test Procedure—this method is used to test the sensitivity of the ground. The procedure followed is as follows -Once the ground has been identified the equipments are taken there. -The equipment is driven to the ground and ensuring that the vane and rod are below the borehole. -It is then rotate at a constant speed -Soil is extracted. The result obtained is calculated using the following formula Where is the undrained shear strength of the soil, is the maximum torque to failure, is the height of the vane and the diameter of the vane There are a number of factors that affect the result that is obtained. This include -The field officers may affect the result through their attitude. -An envelope may not be horizontal thus giving the wrong soil for testing. -It may be conducted on other soils other than clay thus giving a wrong answer. -Borehole pressure will also play an important role in determining the result c. Description SPT Test Results SPT Number SPT Details (Seating & Test) 75 mm 75 mm 75 mm 75 mm 75 mm 75 mm Firm Greyish brown sandy CLAY 14 2 4 3 3 3 1 d. They should not continue because it is sandy clay and having STP number of 50 is too large. Works Cited Coduto, Donald, Man-chu Ronald Yeung and William Kitch. Geotechnical Engineering: Principles & Practices. Boston: Prentice Hall, 2010. Print Lommler, John. Geotechnical Problem Solving. NEW York: John Wiley & Sons, 2012. Print. Sivakugan, Nagaratnam & Braja Das.Geotechnical Engineering: A Practical Problem Solving Approach. New York: J. Ross Publishing, 2009. Print The Constructor. Types of shallow foundations. Apr. 2012. 15 Dec. 2012 Wyllie, Duncan. Foundations on Rock: Engineering Practice. CRC Press, 1999. Print Read More

b. There are a number of known types of deep foundations. These include: -steel piles -timber piles -composite piles -concrete piles -shaft piles c.i) where is the ultimate pile capacity, is the shaft resistance and is ultimate toe resistance. They are calculated as follows: Where is the area of the pile surface area which is pile perimeter length, is undrained shear strength of clay soil and is adhesion factor, is the area of the toe and is the pile adhesion or force. In our case we have 3 Qs because the clay has different adhesion that is 4 strata therefore it will be calculated as follows representing stratum 1, 2 and 3. + ( )+ )+) +( )+ ) Qs = 128 + 168 + 240 = 536kN = Qb = 2520 Qu = 2520 + 536 = 3056 This is ultimate load on the pile.

Allowable load on the pile will be determined as follows: Since skin friction is different the toe will have its calculation different from the others, thus allowable load on the pile will be Qa = = 1108kN The allowable load on the pile is 1108kN ii) The design shown is not good enough to change or to be made in order to test the pile capacity. A flat pile should be used instead of toe method. The other method that is likely to be used to test is effective stress method where the friction angle is determined.

Stress method considers coefficient for each soil type. Question 5 a).There are a number of reasons for carrying out site investigation. Some of the reasons are listed below 1. Site investigation is done to collect information about the conditions of the soil and ground in order to assist in designing a property that will be put up in the area without the information about the ground, the property foundation may not be strong. 2. Site investigation is very important as it is able to assist, locate grounds which can accommodate some infrastructure.

Some grounds may not have the ability to host some infrastructure b). There are a number of insitu tests which are carried out and they include standard penetration test, cone penetration test, vane shear test and many others. In this case we are interested in standard penetration test and vane shear test. Standard Penetration Test—this test is used in soil that has been disturbed by other factors to provide the properties of the test. The test is simple and cheap that’s why it is normally used in testing the relative density and shear strength of soil as well as ground.

The method involves the use of a thick walled tube which is driven to the ground using a hammer to scoop the soil. Usually it is driven to the ground to cover 6 inch to 18 inch where each stage of 6 inch penetration is tested for N-value. N-value gives information about the density of the soil and the shear strength of soil properties. Equipments—the equipment that is used in this method include a penetration tube which is sometimes called spoon sampler, a hammer that drives the tube 6 inch, 12 inch, and 18 inch sizes of spoon sampler.

Procedure 1). The ground is identified 2). The above named equipment is prepared 3). One goes to the site with the equipment where the thick walled tube is driven to the ground using a hammer. 4). Samples are taken Factors Affecting the Results—there are a number of factors that affect the results of standard penetration test. This include -Using boreholes that have been opened for long therefore the ground has been disturbed so much -While driving the spoon sampler, the field officers may exceed the casing area, thus obtain soil that is not within the area -Field officers may also have their attitude which would affect the result -They may use wrong equipment that would affect the result -There is also sampling the wrong ground by field officers or switching results.

This method is very important because it requires cheap equipment to carry out the result. The result obtained is usually calculated using the following formula N(60) = NmCnCeCbCrCsCaCcCBF Where Cm is the blow counts, N(60) is STP number that is to be adjusted to 60%, Ce is the energy correction factor, Cn is overburden correction factor, Cb is the borehole diameter correction factor, Cr is the rod length correction factor, Ca a anvil correction factor, Cs is the correction factor, Cc is hammer correction factor, and CBF is blow count frequency correction factor Vane Shear test—this method of testing is suitable in ground whish are clay and of saturated strength that has not been disturbed.

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