Licture_3 - Subsurface Exploration Subsurface 2.1. Purpose...

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Unformatted text preview: Subsurface Exploration Subsurface 2.1. Purpose of Subsurface Exploration. 2.2. Subsurface Exploration Program.. 2.3. Exploratory Boring in the Field. 2.3. 2.4. Procedures of soil sampling and SPT. 2.5. Observation of Water Table 2.6. Vane Shear test. 2.7. Cone penetration Test (CPT). 2.8. Coring of Rocks. 2.9. Preparation of Boring Logs. Subsurface Exploration (Con’t) 2.3 Exploratory boring in the Field Methods of soil Borings Methods 1- Auger Boring 2- Wash Boring 3- Rotary Drilling 4- Percussion Drilling 1. Auger Boring Solid and hollow stem augers Drilling configuration Continuous Flight Auger Drilling Systems 1 Finger and Fishtail bits • The fights of the auger bring the loose soil the bottom of the hole to the surface . • Any changes in the type of soil can be detected by the changes in the speed and sound of drilling. • Hollow-stem auger does not have to be removed Hollowfrequently for sampling or other tests. • The most common and simplest method used for borehole . • Boreholes up to 60 m can be easily made using this method. • Augers are available in sections 1 to 2 m with outside diameter up to 114 mm (solid) and 228 mm (hollow), and 76 mm inside diameter (hollow). 2. Wash Boring 2 • The casing is derived into the ground, and the chopped by a chopping bit attached to the drilling rod. • Water is pressurized through the drilling rod and reach the soil at the bottom of the chopping bit. • The water and the chopped soil rise up trough the casing and collected in a container at the ground surface. • Wash borings are rarely used in USA and other developed country. 3. Rotary Drilling • In rotary drilling the bore hole is advanced by rapid rotation of the drilling bit. • The drilling bit cuts and grinds the material at the bottom of the hole into small particles. • Soil is removed by pumping slurry of water and bentonite down through the drilling rod, forcing the grinded soil to the ground surface. • Rotary drilling with a diamond bit can be used efficiently through Simi-hard rock. Simi• The drilling rod is raised and the drilling bit is replaced by a sampler to get a soil sample. 4. Percussion Drilling • It used through hard rocks such as granite. • A down-hole Hammer downis used to crush the rock. • Compressed air or mud is used to flush the cuttings and dust from the hole. • Rotation speed of 10-30 10RPM ensures a straight and circular cross-section. crossTruck-mounted Rotary drilling rig. Truck- Diamond drill bit. 3 Stages of Percussion Drilling 2.4 Procedures of Soil Sampling 1. Disturbed Samples Those obtained using equipment that destroy the macro structure of the soil but do not alter its minerals or composition. They are used for the following Laboratory tests: • Grain-size Distribution, Grain• Atterberg limits, • compaction characteristics of soils, • Specific gravity, and • Soil Classification. 2. Undisturbed Samples Obtained in clay soil for use in laboratory testing to determine the engineering properties of soils such as: • Consolidation, • Shear strength tests, and • Hydraulic conductivity. For granular soils (Sand & Gravel) Undisturbed samples can be obtained using specialized procedures such as freezing. Undisturbed Samples (Cont’d) (Cont’ It should be noted that the term “undisturbed” soil undisturbed” sample refers to the relative degree of disturbance to the soil’s in-situ properties. soil’ inThe Degree of sample disturbance is expressed as area ratio AR 2 Do − Di2 AR = Di2 Do & Di = outer and inner Diameters 4 Split Spoon Sampler and SPT D2 − D2 AR = o 2 i Di AR = 112% a) Split Spoon sampler Split Spoon with Undisturbed Sample. Split Spoon with Disturbed Sample. b) Spring core catcher Start of the next Lecture • It is a steel tube that split longitudinally into half. • At a selected depth the sampler is lowered to the bottom of the hole with the drilling rod. • Then it driven into the soil by a hammer which has standard weight and falls from standard height. • The number of blows required to penetrate 3 intervals of 6 in each are recorded. • Standard Penetration Number is the summation of the number of blows required for the last two intervals. • It referred to as N. • This tests is called Standard Penetration Test Standard 5 ...
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