Soil friction angle,friction angle for different soils according to USCS,Correlation between SPT-N value, friction angle, and relative density,Number of Cement bags required for a specific cement concrete ratios,What is stress and how does it develop?Advantages of using LRFD method and Comparison of ASD and LRFD,Disadvantages of Using LRFD method.

1. “For Civil Engineering” Soil friction angle Soil friction angle is a shear strength parameter of soils. Its definition is derived from the Mohr-Coulomb failure criterion and it is used to describe the friction shear resistance of soils together with the normal effective stress. In the stress plane of Shear stress-effective normal stress, the soil friction angle is the angle of inclination with respect to the horizontal axis of the Mohr-Coulomb shear resistance line. Typical values of soil friction angle for different soils according to USCS some typical values of soil friction angle are given below for different USCS soil types at normally consolidated condition unless otherwise stated. These values should be used only as guidelines for geotechnical problems; however, specific condition of each engineering problem often needs to be considered for an appropriate choice of geotechnical parameters.
Correlation between SPT-N value, friction angle, and relative density Correlation between SPT-N value and friction angle and Relative density (Meyerhoff 1956)
Description USCS Soil friction angle [°] Reference min max Specific value Well graded gravel, sandy gravel, with little or no fines GW 33 40 [1],[2], Poorly graded gravel, sandy gravel, with little or no fines GP 32 44 [1], Sandy gravels - Loose (GW, GP) 35 [3 cited in 6] Sandy gravels - Dense (GW, GP) 50 [3 cited in 6] Silty gravels, silty sandy gravels GM 30 40 [1], Clayey gravels, clayey sandy gravels GC 28 35 [1], Well graded sands, gravelly sands, with little or no fines SW 33 43 [1], Well-graded clean sand, gravelly sands - Compacted SW - - 38 [3 cited in 6] Well-graded sand, angular grains - Loose (SW) 33 [3 cited in 6] Well-graded sand, angular grains - Dense (SW) 45 [3 cited in 6] Poorly graded sands, gravelly sands, with little or no fines SP 30 39 [1], [2], Poorly-garded clean sand - Compacted SP - - 37 [3 cited in 6] Uniform sand, round grains - Loose (SP) 27 [3 cited in 6] Uniform sand, round grains - Dense (SP) 34 [3 cited in 6] Sand SW, SP 37 38 [7], Loose sand (SW, SP) 29 30 [5 cited in 6] Medium sand (SW, SP) 30 36 [5 cited in 6] Dense sand (SW, SP) 36 41 [5 cited in 6] Silty sands SM 32 35 [1], Silty clays, sand-silt mix - Compacted SM - - 34 [3 cited in 6] Silty sand - Loose SM 27 33 [3 cited in 6] Silty sand - Dense SM 30 34 [3 cited in 6] Clayey sands SC 30 40 [1], Calyey sands, sandy-clay mix - compacted SC 31 [3 cited in 6] Loamy sand, sandy clay Loam SM, SC 31 34 [7], Inorganic silts, silty or clayey fine sands, with slight plasticity ML 27 41 [1], Inorganic silt - Loose ML 27 30 [3 cited in 6] Inorganic silt - Dense ML 30 35 [3 cited in 6] Inorganic clays, silty clays, sandy clays of low plasticity CL 27 35 [1], Clays of low plasticity - compacted CL 28 [3 cited in 6] Organic silts and organic silty clays of low plasticity OL 22 32 [1], Inorganic silts of high plasticity MH 23 33 [1], Clayey silts - compacted MH 25 [3 cited in 6] Silts and clayey silts - compacted ML 32 [3 cited in 6] Inorganic clays of high plasticity CH 17 31 [1], Clays of high plasticity - compacted CH 19 [3 cited in 6] Organic clays of high plasticity OH 17 35 [1], Loam ML, OL, MH, OH 28 32 [7], Silt Loam ML, OL, MH, OH 25 32 [7], Clay Loam, Silty Clay Loam ML, OL, CL, MH, OH, CH 18 32 [7], Silty clay OL, CL, OH, CH 18 32 [7], Clay CL, CH, OH, OL 18 28 [7], Peat and other highly organic soils Pt 0 10 [2],
SPT N3 [Blows/0.3 m - 1 ft] Soi packing Relative Density [%] Friction angle[°] < 4 Very loose < 20 < 30 04-Oct Loose 20 - 40 30 - 35 Oct-30 Compact 40 - 60 35 - 40 30 - 50 Dense 60 - 80 40 - 45 > 50 Very Dense > 80 > 45

2. Number of Cement bags required for a specific cement concrete ratios
1. For cement concrete of ratio 1:1:2(1 cement: 1sand/coarse sand: 2graded stone aggregate) require 11no bags of 50kg.
2. For cement concrete of ratio 1:1.5:3 require 7.8no bags of 50kg.
3. For cement concrete of ratio 1:2:4 require 6 no bags of 50kg.
4. For cement concrete of ratio 1:3:6 require 4.25no bags of 50kg.
5. For cement concrete of ratio 1:4:8 require 3.2 no bags of 50kg.
6. For cement concrete of ratio 1:5:10 require 2.50 no bags of 50kg.
7. For cement concrete of ratio 1:6:12 require 2.25 no bags of 50kg. What is stress and how does it develop? When an object is subjected to an external force, the object tends to build up internal resistance within itself (material). This resistance is termed as “stress”. In short, stress can be defined as load per unit area. Stress can be classified into four types: Compressive stress Tensile stress Bending stress Shear stress Stress = Load/Area = W/A = N/mm2 Where, N = Newton Calculation of Modular ratio values for different grades of concrete Grade of concrete Modular ratio M15 m = 280/3×5 = 18.66 M20 m = 280/3×7 = 13.33 M25 m = 280/3×8.5 = 10.98 M30 m = 280/3×10 = 9.33 It should be remembered that rounding off the modular ratio values is not permitted by Indian Standard. Advantages of using LRFD method and Comparison of ASD and LRFD 1. LRFD is another tool for design of steel buildings. It provides flexibility to the designer in selecting design methodology. 2. When dead load is larger as compared to live load then LRFD becomes economical. 3. The behaviour at the collapse including ductility, warning before failure are considered in LRFD. This is not directly possible in ASD method because here the structure is considered at service stage. 4. Plastic design concepts may be employed in LRFD method but cannot be applied in ASD method. 5. Every type of load may be given different factor of safety depending upon its probability of overload, number of occurrences and changes in point of application. But in ASD same factor of safety is used for different loads. 6. Safer structures may result under LRFD method because of considering behaviour at collapse. But behaviour at collapse is not considered in ASD method. Disadvantages of Using LRFD method 1. Elastic behaviour considered for load analysis and ultimate plastic behaviour for material strengths are not compatible. However, percentage difference is less. 2. Engineers experienced in ASD have to become familiar with this technique. 3. Old books are according to ASD method and become ineffective. 4. Validity of previous designs is still to be checked according to ASD.