Problems 2 [PDF]

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NPTEL- GEOTECHNICAL EARTHQUAKE ENGINEERING

Module 3 DYNAMIC SOIL PROPERTIES (Lectures 10 to 16) PROBLEMS 1. At a level site, bedrock is overlain by a layer of overconsolidated clay of variable thickness. A seismic refraction survey is conducted with 13 receivers placed on a straight line between two shot points located 1,000 ft apart. From the p-wave arrival times listed below, determine and plot the subsurface profile in the central 800 ft portion of the survey. Determine the p-wave velocities of the over consolidated clay and the underlying bedrock. Receiver

A B C D E F G H I J K L M

Distance from SP 1 0 50 100 200 300 400 500 600 700 800 900 950 1000

Arrival time from Distance from SP 2 SP 1( ) 0 15 30 48 58 67 78 91 108 113 115 119 124

1000 950 900 800 700 600 500 400 300 200 100 50 0

Arrival time from SP 2 ( ) 124 119 114 105 96 85 75 73 68 47 30 15 0

2. The figure below shows the vertical response of geophones located at the same depths in vertical boreholes spaced 5 m apart. The waves recorded at the geophones resulted from downward (solid lines) and upward (dashed lines) impact on a mechanical source at the same depth in a third borehole that was collinear with the other two boreholes. Determine the average SV-wave velocity of the soil between the geophones.

Dept. of Civil Engg. Indian Institute of Technology, Kanpur

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NPTEL- GEOTECHNICAL EARTHQUAKE ENGINEERING

3. Portions of the time histories of deviator stress and axial strain from a stresscontrolled cyclic triaxial test are shown below. Compute the secant shear modulus and damping ratio of the test specimen. Assuming that the soil is saturated and its response is consistent with the Masing criteria, estimate the maximum shear modulus of the soil.

4. A site is underlain by about 14 m hydraulic fill sand with the following properties.

Saturated unit weight Average uncorrected SPT resistance Average cone tip resistance The groundwater table is located at a depth of 2m. (a) Estimate the shear wave velocity of the hydraulic fill at a depth of 5 m by as many procedures as the available data will support.

Dept. of Civil Engg. Indian Institute of Technology, Kanpur

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NPTEL- GEOTECHNICAL EARTHQUAKE ENGINEERING

(b) Shear wave velocity measurement at this site have indicated hydraulic fill shear wave velocities ranging from about 120 m/sec-200 m/sec at 5 m depth with an average value of about 170 m/sec. comment on the level of agreement between the estimated shear wave velocities from Part (a) and the measured shear wave velocities. 5. At the site described in problem 5, the hydraulic fill is underlain by a 15 m thick deposit of medium stiff, normally consolidated silty clay with the following properties: Water content = 40% Liquid limit = 46 Plastic limit = 23 Saturated unit weight Cone tip resistance Undrained shear strength (a) Estimate the shear wave velocity of the silty clay at a depth of 20m by as many procedures as the available data will support. (b) Shear wave velocity measurements at this site have indicated silty clay shear wave velocities ranging from about 120m/sec-180 m/sec at 20 m depth with an average value of about 155 m/sec. comment on the level of agreement between the estimated shear wave velocities from part (a) and the measured shear wave velocities.

Dept. of Civil Engg. Indian Institute of Technology, Kanpur

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