Presentation on theme: "Site Investigation and Field Tests"— Presentation transcript:
1 Site Investigation and Field Tests
2 Site investigation (SI) methods
Surface Grab Sampling Boreholes (and sampling by SPT and tube) Excavation and auger Piezocone Penetration (CPTU) Macintosh Probing Field Density Test Rock and Fracture Mapping Geophysical Methods Others?
3 Why Do We Carry Out Site Investigation
General Assessment and Design Geotechnical Assessment of an EIA Slope Stability Design Foundation Design Fill Assessment and Design Embankment Design Damn Design Rock Slope Design Rock Tunnel Design Landfill Assessment and Design Other reason?
4 In Situ Soil Testing Methods, by popularity in Malaysia
SPT in Boreholes Macintosh Probing Piezocone Penetration (CPTU) Field Vane Shear Field Density Test And many more Can you tell the difference between SI and In-Situ Test?
5 1. SI by Surface Grab Sampling
Advantage - Easy (and cheap) Disadvantage - Not representing sub-surface soils Why? For quick and preliminary information To verify certain probing results
6 2. SI by Bore Hole (and sampling by SPT and tube)
Advantage - Able to retrieve representative samples and test soils at greater depths, directly Disadvantage - Cost and disturbance caused by washing Why? - To have a continuous description of soil with depth, to retrieve samples via SPT and sampling tube, and to carry out SPT and vane shear tests
7 Disturbance caused by washing of a bore hole
Reportedly more than 12 inches (30 cm) in sands but only 3 inches (7.5 cm in clays) Despite of the above, the practice only disregards 6 inches (15 cm) of SPT results in sands and in clays
8 Bore Hole Drilling Equipment: TOHO type for soil and rock drilling
Rotary type but can be converted to percussion type any time Drilling: BS5030(1981) Get soil samples via split spoon sampler SPT(N) Test: BS1337(1975) Normally, can also get 54 mm rock core (NX)
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10 Soil Description vs. Soil Classification
The description of soils as drilling progresses is not a soil classification work (such as USCS) but mere layman’s description of the soils such as: Sand, Yellow Sand, Clay, Clay and Sand, Yellow Clay, Dense Sand, Loose Sand, Stiff Clay, etc. The real soil classification is done when a sample has been subjected to lab tests and the results produced. Examples of classification names are MH, SM, etc., such as used in the USCS method. A piezocone test also describes soils and appoint names but with another and different procedure than used in the USCS method.
11 SPT in a Borehole Names of Test: Standard Penetration Test, SPT Data: Standard Penetration Test Number, SPT(N), Standard Penetration Resistance Hammer Weight: 63.5 kg (140 lb) Hammer Lift: 760 mm (30 in) Dimensions of Sampling Tube: 35 mm inside diameter, 50 mm outside diameter, 650 mm length Procedure: Number of blows per 75 mm advance is recorded for 6 consecutive advances starting at the bottom of a borehole. Numbers of blows of the last 4 advances (300 mm, 12 in, foot) are summed and is called SPT(N). Numbers of blows of the first two advances are discarded due to disturbance of the soil layer by washing and boring. Maximum number of blows per foot to record is 50.
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13 How to get SPT(N) number
5.4 of MS1056 N30 is blows/30 cm N60 is blows/30 cm assuming 60% hammer efficiency Some demand blows/7.5 cm Discard the blows of the first 15 cm (2x7.5) Read blows for every 7.5 cm So readings of 2, 3, 6, 7, 10, 19, 20 will give N30 = 42 Normally taken for every 1.5 m interval
14 SPT(N) versus f correlation for cohesion-less soils (Old JKR Document)
SPT(N) versus f correlation for cohesion-less soils (Coyle and Castello, 1981) SPT(N) versus f correlation for cohesion-less soils (Old JKR Document)
15 SPT(N) versus f correlation for cohesion-less soils (McCarty, David F, 1998)
10 20 30 40 50 60 32 35 38 42
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17 SPT(N) c, kPa 2 4 8 15 30 14 25 50 100 200
18 SPT in Sand Angle of Friction Description 0 – 4 0 – 28 degree Very Loose 4 – 10 20 – 30 Loose 10 – 30 30 – 36 Medium 30 – 50 36 – 41 Dense > 50 > 41 Very Dense
19 SPT in Clay Cohesion (c), kPa Description < 2 0 – 14 Very Soft 2 – 4 14 – 25 Soft 4 – 8 25 – 50 Medium 8 – 15 50 – 100 Stiff 15 – 30 100 – 200 Very Stiff > 30 > 200 Hard
20 N60 Equation (The corrected N due to depth)
Where: N = Measured penetration number A = Hammer Efficiency (Actual, in %) B = Correction for BH diameter C = Sampler Correction D = Correction for Rod Length Tables of correction factors available in book (e.g., Das B M, Fundamentals of Geotechnical Eng) Why ? Because of 60% efficiency
21 Field Vane Shear Names of Test: Field Vane Shear Apparatus to measure in-situ un-drained shear strength Data: In-Situ Shear Strength Maximum Depth: 30 m Dimension of vane: 77 mm outer diameter Procedure: Place shear vanes in cleared bore hole. Up to 30 m deep. Measure up to 100 kPa.
22 Field Vane Shear Apparatus
23 3. Excavation and auger Advantage - Able to retrieve representative samples and directly test soils at depths up to 6 m, cost effective Disadvantage - Depth limited by reach of bucket or length of auger Why? - To gain a quick information of soil to 6 m depth
24 Auger
25 4. Piezocone Penetration (CPTU)
Advantage - Able to carry out tests at depths and unlike in boring, on relatively undisturbed soils, cost effective Disadvantage - No samples retrieved, cannot penetrate hard layer or rock like boring can Why? - To gain a relatively quick information of soil to 30 m depth
26 Piezocone Machine
27 Piezocone Penetration
Names of Test: Piezocone, CPTU, Cone Penetration Test with Pore Water Acquisition Data: Tip Resistance, Skin Friction, SPT(N) Equivalence, Soil Type, Pore Water Pressure, Dissipation of Pore Water Pressure Advance Rate: 2 cm/second Maximum Depth: 30 m Dimension of cone: 35 mm diameter, 10 cm square of cross sectional area Procedure: Cone advanced via rods to maximum depth of 30 m, data acquired automatically and continuously via computer
28 Piezocone - CPTU Observe how soil changes with depth
Observe how soil resistances (skin and end) change with depth Observe how water pressure changes with depth Cannot get samples Cannot do field tests (other than those done by the cone)
29 Specific Cone Results Tip Resistance in MPa
Sleeve (skin) Friction in kPa Pore Water Pressure (u) in kPa These three values decide soil type according to table and N60 equivalent
30 Piezocone Probe
31 5. Macintosh Probing Advantage - Light, simple, fast, and cost effective Disadvantage - Cannot go very deep (10 m limit), less accurate interpretation Why? - To gain a relatively quick information of soil to 10 m depth, at the same time, cost effective
32 Macintosh Probing Names of Tool: Macintosh Probe, Dynamic Probe, JKR Probe, Portable Penetrometer Data: Macintosh Probe Number, JKR Probe Number, Macintosh M-Value Hammer Weight: 5 kg (11 lb) Hammer Lift: 300 mm (12 in, foot) Dimensions of steel driving rod: 16 mm diameter, 120 cm length Dimension of coupling: 22 mm diameter x 52 mm length Dimensions of probes: JKR Probe (25.5 mm x 100 mm), Macintosh Probe (27.5 x 152 mm) Procedure: Number of blows per foot advance is recorded. Maximum blow per foot to record is 400
33 Operating Macintosh Probe
34 Portable probe SI can be carried out manually JKR probe versus (old) McIntosh probe In Malaysia, we use JKR probe always JKR gives same reading as McIntosh JP (JKR probe); MP (McIntosh probe) JP# =30 is equivalent to SPT(N) = 6 (medium) in clays JP# =30 is equivalent to SPT(N) = 10 (loose-medium) in sands
35 6. Field Density Test Sand replacement method
Main result is % of dry density achieved in the field as compared to dry density from lab compaction
36 6. Rock and Fracture Mapping
Why? - To gain information for determining stability against sliding and toppling for slopes - To estimate cost of excavation for tunnels
37 Rock and Fracture Mapping involves:
Scan Line Survey Collection of Joint Data Stereographic Projection Method
38 7. Geophysical Investigation
Resistivity, Seismic, and Microgravity Advantage - Fast and can cover large areas Disadvantage - Less accurate and has to be supplemented with boreholes Why? - To gain a relatively quick but rough information covering large area of site
39 tomography with borehole correlation
A resistivity survey result of an area over old landfill Waste refuse + leachate contamination Bedrock A pseudo section of the subsurface imaging tomography with borehole correlation
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41 End of Lecture Session Questions?
42 SI OF VARIOUS PURPOSES/PROJECTS
Aim Grab Sampling BH with SPT BH with sampling tube BH with vane shear Excavate Auger CPTU Mac-kintosh Rock Mapping General Assessment x Geotechnical Assessment in an EIA Slope Stability Design Foundation Design Embankment Design Dam Design Rock Slope Design Rock Tunnel Design Note: The required SI will depend on the actual project. This table is indication only, while geophysical methods are not included in the table.
43 Ready for Quiz?
44 The three Major Physical Properties of a Geotechnical Material required for design are:
Compressibility Permeability Shear strength Which of the major physical properties is measured by the following tests? - SPT in Boreholes - Macintosh Probing - CPTU Penetration - Field Vane Shear - Plate Bearing - Consolidation test - Permeability test
45 Which soil property would you be concerned with?
If you come across any of the following cases: - Settlement of a raft foundation - Bearing failure of a pad foundation - Failure of a pile foundation - Water loss through a bund - Failure of a slope - Soft Ground Which soil property would you be concerned with? compressibility permeability shear strength
46 The design of which of the following structures require shear strength information?
Slope Shallow foundation Pile (deep) foundation Embankment foundation Ground improvement Coast protection
47 How Deep should an SI (or assessment) go for the following purposes?
Embankment/Road Foundation Pile Foundation Settlement Investigation Slope Assessment /Design Landfill Assessment/Design Rock Slope Assessment/Design EIA/Geotechnical Assessment
48 EMBANKMENT/ROAD FOUNDATION
49 Stress Bulb underneath a road embankment
50 Stress reduction with depth
51 End
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