all Verizon 44 2031 mailattachmentgoogleusercontentcom Univ

all Verizon * 44% 20:31 mail-attachment.googleusercontent.com University of North Dakota HHSGGE Spring 2018/Ho Engineering Geology 14. Subsoil exploration is an important stage of site investigation, the samples have to be recovered using different samplers for laboratory tests based on different engineering purposes. Usually, for certain tests, the undisturbed samples are required for laboratory tests. In engineering, the undisturbed sample recovered depends upon the samplers used. In terms of area ratio, please describe how to define a sampler which can be used to collect undisturbed samples. Please also list one example of samplers you know to recover undisturbed soils samples. (15 pts) 15. The CPT and SPT tests are two typical in-situ field tests to be performed for subsoil exploration. As a geological engineer, if you are assigned to propose a testing plan for a site with a complex stratification and seasonal change of groundwater table. Please explain what test you may select if only either CPT or SPT can be chosen and state why you think it is a proper in-situ test to be performed. (15 pts) 16. (2) Please briefly describe how to count the Standard Penetration Number, N

Solution

Prob. 14

The main factor that matters is the thickness of the sampler tube. Larger the thickness, more is the disturbance and vice versa. The reason is that more thickness provides more area of resistance for the sampler penetration in the soil and therefore a term called Area Ratio is used to demarkate the line of disturbed and undisturbed sampling.

Area ratio is tha ratio of the solid area(that of solid section) with that of the hollow inside area of the sampler. An undisturbed sample has 10% or less than 10% of the area ratio.

Examples: Drill rigs are used by Engineers to collect undisturbed soil samples at depths of soil. Most commonly used samplers are

1.long split-spoon samplers,

2.piston samplers and

3. a pitcher barrel sampler.

Piston samplers are thin-walled tube samplers that collectundisturbed samples in soft soil.

Prob. 17

Standard Penetration Number for a soil is counted at different depths in layers of 30 cm or 300 mm. The number of blow of the standard hammer needed to penetrate a 300 mm layer is known as the N count. Generally values are ignored for the top layer. Also a number of correction are needed such as, overburden correction, hammer efficiency, type of hammer and dimeter corrections.