Geotechnical laboratory ( )

Transcription

1 VŠB TECHNICAL UNIVERSITY OF OSTRAVA Faculty of Civil Engineering Department of Geotechnics and Underground Engineering Geotechnical laboratory ( ) Study support for combined form of bachelor study Geotechnics and Underground structures Subject guarantor: Ing. Barbara Luňáčková, Ph.D.

2 Aims of course By completing the Geotechnical Laboratory, the student will be able to determine the basic soil features (which are essential for geotechnical calculations) or the parameters essential for assessing the extent of the rock mass treatment, based on laboratory and field tests. Summary The course deals with practical measurements which are most often used in exploratory works for determination of soil properties in laboratory and in situ. The subject follows the laboratory practice gained by the students in the subject Soils and Rocks Mechanics. The aim of this subject is to extend the acquired experience and practical skills in the field of geotechnical characterization of soils by field tests and other advanced laboratory measurements. Exercises are devoted not only to testing and measurement itself, but also to the evaluation and interpretation of the measured data. Syllabus of practical exercises: - Preparation of reconstituted samples - Index and descriptive soil tests - Modified Proctor Exam - IBI - CBR - Triaxial test - Soil permeability test - Light dynamic plate - Light dynamic penetration - Static load plate - Membrane densitometer Compulsory literature: KNAPPETT, Jonathan. a R. F. CRAIG, Craig's soil mechanics. 8th ed. New York: Spon Press. ISBN TERZAGHI, K., PECK, R. B., MESRI, G. Soil Mechanics in Engineering Practice. John Wiley & Sons, 3rd edition, ISBN Recommended literature: BS EN ISO :2016. Geotechnical investigation and testing. Laboratory testing of soil. Determination of particle size distribution BS EN ISO Geotechnical investigation and testing. Laboratory testing of soil. Part 11. Permeability tests 2

3 ASTM D e2 Standard Test Method for Density of Soil in Place by the Drive-Cylinder Method ASTM D Standard Test Method for California Bearing Ratio (CBR) of Laboratory- Compacted Soils BS EN :2010 Unbound and hydraulically bound mixtures. Test methods for laboratory reference density and water content. Proctor compaction BS EN ISO :2005+A1:2011 Geotechnical investigation and testing. Field testing. Dynamic probing ASTM D1196/D1196M - 12(2016) Standard Test Method for Nonrepetitive Static Plate Load Tests of Soils and Flexible Pavement Components, for Use in Evaluation and Design of Airport and Highway Pavements 3

4 Particle size analysis Determination of soil grain is aa important soil test. The grain analysis consists of a sieving and sedimentation test (in our case, hydrometer analysis). The sieving test is used to divide sandy and gravely grains by size using standard sieves. The hydrometer test is used to determine the granularity of the silty and clayey grains, based on the rate of grain settling in water suspension. An important fact is that for soils (not rare cases) dry sieve analysis is fundamentally inappropriate. Furthermore, if circumstances do not require, it is clearly better to not dry the sample in advance and prefer to leave it in the natural state. As noted, for the most perfect separation of the fine fraction from the coarse it is necessary to perform a wet sieving analysis to separate the fine fraction that is captured on the bowl. Care must be taken to avoid overloading the smallest sieve (0.063 mm). Sieve residues can be dry, and a sample of this sample is run through a set of standard sieves and a percentage amount is recorded on individual sieves. Fine grains obtained from the wet and dry sieves test is subjected to a hydrometer test. The recommended amount of soil required for the test is listed in the following table. In principle, this procedure is applicable to all coarse-grained and fine-grained soils. Table: Minimum amount of soil required for the sieve test (CSN EN ISO ) Grain diameter D 90 (mm) Minimum amount of soil required for the sieve test (g) 0,5 50 1, , , , , , , , , ,

5 (ČSN ) (Knappett, 2012) 5

6 (BS EN ISO 14688) 6

7 CBR, California bearing ratio ASTM D Standard Test Method for California Bearing Ratio (CBR) of Laboratory- Compacted Soils BS EN :2010 Unbound and hydraulically bound mixtures. Test methods for laboratory reference density and water content. Proctor compaction The California Bearing Ratio test, or CBR test, is an empirical test to estimate the bearing value of sub-base. The CBR test is a constant rate of penetration shear test in which a standard plunger is pushed into the soil at a constant rate and the force required to maintain that rate is measured at suitable intervals. The load penetration relationship is drawn as a graph from which the loads corresponding to standard penetrations are read off and expressed as ratios (percent) of standard loads. The accepted percentage is known as the CBR value of the soil in the CBR = F F s 100 % F Fs measured force (kn), standard force (kn). The soil is prepared using the Proctor test. 7

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9 Record CBR Sample identification Location: Laborer: Date: water content Swelling time: Type of Proctor mould: Weight: Weight with soil: Weight of soil: Penetration Standard force [kn] [mm] 0,5 1,0 1,5 2,0 2,5 13,2 3,0 3,5 4,0 4,5 5,0 20,0 5,5 6,0 6,5 7,0 7,5 8,0 8,5 9,0 9,5 10,0 Notes: Height: Diameter: Volume of soil: Dry unit weight: Test n. 1 Test n. 2 Force [kn] CBR [%] Force [kn] CBR [%] Average CBR [%] 9

10 SOIL MEMBRANE DENZITOMETER The soil densitometer serves for: Determination of the density of soil in the natural state ρ (kg / m 3 ), Determination of the dry soil density d (kg / m 3 ) of the construction or natural soil layers insitu. The instrument further demonstrates the degree of compaction of the assessed layer by comparing the bulk density determined by in-situ densitometer and the laboratory test by Proctor standard. 10

11 Record soil density determination Sample identification Soil description Date Laborer Piston surface: date: Point Note. L1 [cm] measurement moisture box Soil sample [g] L2.1 [cm] L2.2 [cm] n. m(tára) [g] mwet mdry1 mdry2 mdry2 Notes: 11

12 Static plate load test of soils ASTM D1196/D1196M - 12(2016) Standard Test Method for Nonrepetitive Static Plate Load Tests of Soils and Flexible Pavement Components, for Use in Evaluation and Design of Airport and Highway Pavements (The Static Plate Load Tester supports the following standards: ASTM D1194, ASTM D1195, ASTM D1196; DIN1834; BS1377) ADAM, Christoph et al., Computational validation of static and dynamic plate load testing. Acta Geotechnica. 4(1), DOI: /s ISSN A circular load plate made of steel with a radius r is placed on the planar subsoil to be tested. If required, a thin layer of sand can be used to smoothen the surface of the subgrade in order to ensure proper force transmission across the entire plate. The plate is loaded vertically in welldefined load steps, and the vertical displacements are recorded simultaneously. Subsequently, the load is stepwise reduced until the applied force is nearly zero. This procedure is repeated consecutively. The displacement of the load plate, which corresponds to the settlement of the subsoil, is recorded by means of a dial gauge relative to a frame, which is positioned in a prescribed distance to the plate. The static load plate test is evaluated by assuming that the assessed subsoil can be characterized by a linear elastic, homogeneous, isotropic half space. From the settlement s of the rigid circular plate, which is loaded by a concentrated force P the Young s modulus E can be determined according to the theory of elasticity E = 1 ν2 the subsoil, and r denotes the radius of the plate Used equipment: 2 P rs, where ν is Poisson s ratio of ECM-Static (ECM Electronic Control & Measurement) - a device for semi-automatic measurement of deformation parameters and control of the static load capacity of compacted soil. Selection of technical parameters: Minimum height of the supper surface: 520 mm, Maximum allowed force: 50 kn, Maximum load pressure: 0,530 MPa, Maximum settlement: 24 mm, Pressure measurement error: +/- (1 % + 1kPa), Settlement measurement error: +/- 0,005 mm, Operating temperature: ( ) C. The soil is loaded with a circular plate in at least 5 steps. The increase in load from one stage to the other is to be gradual and at each stage the load is maintained without any fluctuations until the compression is stabilized. The load is then increased to the next stage. The load plate then releases smoothly to zero. 12

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14 Record Static plate load test Site name: Location (x, y, z; GPS): Test date: Static plate load diameter: Sketch (scale / without scale) with a direct geotechnical survey: point n. phase of the test contact stress [MPa] plate settlement [mm] ground water level: 14

15 Dynamic load plate test ASTM E (2015) Standard Test Method for Measuring Deflections with a Light Weight Deflectometer (LWD) TAWFIK, Mohamed M. a Yasser M. EL-MOSSALLAMY, Application of the finite element method for investigating the dynamic plate loading test. Ain Shams Engineering Journal. 8(1), DOI: /j.asej ISSN The Light Falling Weight Deflectometer (LFWD) is the testing device of the technique of dynamic plate loading test (DPLT) used for compaction control of constructed subgrades and compacted soils. The apparatus is easy to handle because of its light total weight (about 30 kg) and it can be easily operated. When being released, the 10 kg falling weight freely falls from a height of 72 cm, along the guide rod, to hit an installed dashpot unit in the middle of the loading plate. The loading steel plate has a diameter of 30 cm and a thickness of 20 mm and its weight is 15 kg. The steel plate is configured such that it is sufficiently rigid to settle with the soil under the impact of the falling weight. A centering sphere is positioned in the middle of the loading plate to entitle for transmitting only the compressive forces. The apparatus is calibrated to deliver a maximum pulse force of 7.07 kn with an impact duration of about ms and a corresponding frequency of Hz. In the standardized testing procedure of the LFWD [1], the loading steel plate is firmly rested onto the surface of the tested soil. Three initial seating drops are to be performed to create full contact between the plate and the tested soil. Three further working drops are subsequently performed, for which the plate deflections are recorded by means of the deflectometer. From the records of the three working drops, the mean value of the peak plate deflection is electronically estimated to be employed in evaluating the Mvd modulus. Used equipment ECM-LDD 100 (ECM Electronic Control & Measurement) - device used to perform rapid control of dynamic parameters of compacted soil. Selection of technical parameters: Measurement of Mvd in range MPa, Weight of the measuring plate 15 kg, Diameter of the circular loading plate 300 mm, Weight of impact weight 10 kg, Pulse force 7,1 kn, Impact duration ms. 15

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17 Record Light Weight Deflectometer Site name: Location (x, y, z; GPS): Soil type: Soil temperature: Date: Sketch (scale 1: / without scale) *) with other type of test (static load test): Notes: 17

18 Lightweight dynamic penetrometer DIN Subsoil - Field investigations - Part 1: Cone penetration tests ASTM D Standard Test Method for Mechanical Cone Penetration Testing of Soils. Penetrometers are used to establish the thickness of different stratifications when investigating the suitability of a site for bridge, road or other construction works. In general, if the ground is not too compact, penetration tests with this apparatus can be carried out to depths of about 8 to 12 m. The objective of dynamic penetration tests is to determine the resistance of soil and semi-rock in-situ against the penetration of the cone. A "constant force" is applied to the cone by a ram of known weight and a constant height of fall. The penetration resistance is then defined as the number of strokes required to kick the cone at a specified depth. Dynamic penetration tests are indirect and serve as a complement to direct geotechnical exploration, most often as a complement to geological boreholes. From the results of the penetration tests in comparison with another source of information (e.g. geological drilling), the following conclusions can be drawn: determination of interfaces of individual geological layers to a depth of about 10 m, strength and deformation properties of soils, density index (non-cohesive soil) consistency index (cohesive soil), location of very stiff layers of the subsoil finding critical positions of soils with weakened strength, localization of sites affected by internal erosion, control of compaction. 18

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20 Record Lightweight dynamic penetrometer Site name: Location (x, y, z; GPS): Date: Type of dynamic penetrometer test: Sketch (scale 1: / without scale) with a direct geotechnical survey: Notes: 20

21 Lightweight dynamic penetrometer Lightweight dynamic penetrometer n.: Type: DPL date: Location (x, y, z; GPS): Depth N 10 Depth N 10 Depth N 10 Depth N 10 Depth N 10 0,1 2,1 4,1 6,1 8,1 0,2 2,2 4,2 6,2 8,2 0,3 2,3 4,3 6,3 8,3 0,4 2,4 4,4 6,4 8,4 0,5 2,5 4,5 6,5 8,5 0,6 2,6 4,6 6,6 8,6 0,7 2,7 4,7 6,7 8,7 0,8 2,8 4,8 6,8 8,8 0,9 2,9 4,9 6,9 8,9 1,0 3,0 5,0 7,0 9,0 M [Nm] M [Nm] M [Nm] M [Nm] M [Nm] 1,1 3,1 5,1 7,1 9,1 1,2 3,2 5,2 7,2 9,2 1,3 3,3 5,3 7,3 9,3 1,4 3,4 5,4 7,4 9,4 1,5 3,5 5,5 7,5 9,5 1,6 3,6 5,6 7,6 9,6 1,7 3,7 5,7 7,7 9,7 1,8 3,8 5,8 7,8 9,8 1,9 3,9 5,9 7,9 9,9 2,0 4,0 6,0 8,0 10,0 M [Nm] M [Nm] M [Nm] M [Nm] M [Nm] Notes: GWL: 21