Aspek Geoteknik

Type of Foundation

Summary of types of shallow foundations

Factors of safety (modified after Vesic 1975) Category Typical Structure Observations Soil exploration Through Limited A Railway bridges Warehouses Balst furnaces Reaining walls Silos Maximum design load likely to occur often Ultimate limit states with disastrous consequences 3 4 B Highway bridges Light industrial and public buildings Maximum desighn load may occur occasionally serious consequences 2.5 3.5 C Apartement Buildings Office Buildings unlikely to occur 2

Safety Factor Method for Determine Bearing Capacity Load Minimum Safety Factor Compression Tensile Theory or empirical + loading test 1. Dead Load, live load and water pressure 2. Dead Load, Live Load Earthquake Load and Flood 50 years 2,50 1,50 Theory or empirical + PDA Test 3,00 2,00 Theory or empirical without Loading test and PDA Test 3,50 2,25

Acceptable Probability of Failure Design Factor of Safety, F Classification of Structure Acceptable Probability of Failure Design Factor of Safety, F Good Control Normal Control Poor Control Very Poor Control Monumental 10-5 2,3 3,0 3,5 4,0 Permanent 10-4 2,0 2,5 2,8 3,4 Temporary 10-3 1,4

Load Maximum Lateral Defflection Service Load without earthquake load 1,27 cm (0,5 “) Service Load with earthquake load 1,905 cm (0,75”) Ultimate Load 3,5 cm

Typical Allowable Total Settlement, a Type of Structure Typical Allowable Total Settlement, a (in) (mm) Office buildings 0,5-2,0 (1,0 is the most common value) 12-50 (25 is the most common value) Heavy industrial buildings 1,0-3,0 25-75 Bridges 2,0 50

Differential Settlement Ratio of maximum total settlement Wmax to maximum angular distortion max ( modified after Skempton and MacDonald 1956) Soil type Isolated foundations Mat foundations Sand / sand fill 15 LR 20 LR Clay 25 LR 30 LR LR = reference length = 1 m  40 in. Tolerable angular distorsion for special – purpose structures Structure  = w/L Machines Frames with diagonels Overhead cranes Tilt of tall buildings/ structures Steel tanks 1/750 1/600 1/300 1/250 1/25

θa Type of Structure 1/25 Steel tanks 1/125 Bridges with simply-supported spans 1/125 Bridges with continous spans 1/250 Buildings that are very tolerant of differential settlements, such as industrial buildings with corrugated steel siding and no sensitive interior finishes Typical commercial and residential buildings 1/500 Overhead traveling crane rails Buildings that are especially intolerant of differential settlement, such as those with sensitive wall or floor finishes 1/1000 Machinery 1/1500 Buildings with unreinforced masonry load-bearing walls Length/height ≤ 3 Length/height  5 1/2500 1/1250

Geotechnical Concerns To determine the approximate minimum depth of boring, engineers may use the rules established by the American Society of Civil Engineers (1972): Determine the net increase in the effective stress, ’, under a foundation with depth as shown in figure. Estimate the variation of the vertical effective stress, ’0, with depth. Determine the depth, D = D1, at which the effective stress increase ’ is equal to 0,1q (q = estimated net stress on the foundation). Determine the depth, D = D2, at which ’/’0 = 0,05. Choose the smaller of the two depths, D1 and D2, just determined as the approximate minimum depth of boring required, unless bedrock is encountered.

GEOTECHNICAL CONCERNS Two types of soil samples can be obtained during subsurface exploration : Disturbed Undisturbed Disturbed, but respresentative, samples can generally be used for the following types of laboratory test : Grain-size analysis Determination of liquid and plastic limits Specific gravity of soil solids Determination of organic content Classification of soil Undisturbed soil samples must be obtained for these types of laboratory tests such as : Consolidation Hydraulic conductivity Shear strength tests

No. of stories Boring depth 1 3,5 m (11 ft) 2 6 m (20 ft) 3 10 m (33 ft) 4 16 m (53 ft) 5 24 m (79 ft) Type of project Spacing Multistory building 10-30 m (30-100 ft) One-story building 20-60 m (60-200 ft) Highways 250-500 m (800-1600 ft) Residential subdivision Dams and dikes 40-80 m (130-260 ft)

Average Properties of Cohesionless Soils Relative Density Blow Count, N, (blows / ft) Voila Ratio, e Simple Field Test with ½ -in. Diameter Rod Usable Bearing Strength ( k / ft2 ) ( kPa ) Loose < 10 0.65-0.85 Easily pushed in by hand 0-1.0 0-50 Medium 10 – 30 0.35-0.65 Easily driven in by hammer 1.0-2.0 50-100 Dense 30 – 50 0.25-0.50 Driven in by repeated hammer blows 1.5-3.0 75-150 Very dense > 50 0.20-0.35 Barely penetrated by repeated hammer blows 2.5-4.0 125-200

Average Properties of Cohesive Soils Consistency Unconfined Compressive Strength (k/ft2) Simple Field Test by Handling of an Undisturbed Sample Usable Bearing Strength ( k / ft2 ) ( kPa ) Very soft < 0.5 Oozes between fingers when squeezed Soft 0.5 – 1.0 Easily molded by fingers 25 – 50 Medium 1.0 – 2.0 Molded by moderately hard squeezing 1.0 – 1.5 50 – 75 Stiff 2.0 – 3.0 Barely molded by strong 50 – 100 Very stiff 3.0 – 4.0 Barely dented by very hard 1.5 – 3.0 75 – 150 Hard 4.0 or more Dented only with a sharp instrument 3.0 + 150 +