Use of shallow seismic measurements what information can analysis of surface waves (MASW) provide?

Size: px

Start display at page:

Download "Use of shallow seismic measurements what information can analysis of surface waves (MASW) provide?"

Madeline Pitts
7 years ago
Views:

1 NGF Grunnundersøkelskomiteen - 15 th Oktober 2013 Use of shallow seismic measurements what information can analysis of surface waves (MASW) provide? Mike Long UCD (Shane Donohue, ex UCD / Peter O Connor APEX Geoservices) UCD School of Civil, Structural and Environmental Engineering.

2 Presentation Outline Introduce techniques in general MASW MASW work in Norway Correlations with soil properties Link with CPTU Other applications 2/40

3 Seismic Waves P-wave Fastest ;compressional Particle motion parallel to direction of propagation S-wave Shearing and rotation Particle motion perpendicular to direction of propagation 3/40

4 Some common techniques Intrusive / active methods Seismic cone (SCPT) Cross hole (or down hole) Campanella et al. (1986) 4/40

5 Surface waves Seismic wave propagating along the surface Elliptical particle motion Wave used is the Rayleigh wave (largest amplitude) Use dispersive properties of soil velocity of propagation depends on frequency. High frequency near surface Low frequency affects deeper layers 5/40

6 Surface wave techniques CSW: Continuous surface wave GDS Ltd. 6/40

7 Surface wave techniques SASW: Spectral analysis of surface waves NTNU quick clay research site Tiller (Kvenild) 7/40

8 SASW in Sweden 8/40

9 MASW MASW (multi-channel analysis of surface waves) MASW The wave of the future (Crice, 2005) Similar equipment and acquisition procedures as used in conventional seismic reflection surveys Multiple receivers allow easier isolation of noise NGI research site Museumparken, Drammen 9/40

10 General methodology for MASW 1. Generate vertical ground motions 2. Detection and measurement of surface wave 3. Record the surface wave 4. Produce a dispersion curve 5. Inversion of the dispersion curve 6. Derive a stiffness-depth profile 10/40

11 (1) Generation of surface wave (2) Measure & (3) Record surface wave Low Frequency Geophones (4.5Hz)

12 (4) Surface wave dispersion Low frequency (Long wavelength) waves travel deeper than higher frequency (short wavelength) surface waves 12/40

13 (4) Dispersion curve Typical shot record and dispersion curve from Onsøy Plot of surface wave velocity and frequency (dispersion curve) 13/40

14 (5) Inversion of surface wave dispersion curve 1. Converting dispersion curve into a shear wave velocity (V s ) depth profile 2. Software Surfseis 3. Assumed soil model (layer thickness, V s,, ) is inputted and a synthetic dispersion curve is generated 4. Synthetic curve compared to field dispersion curve. 5. V s is updated after each iteration until the synthetic dispersion curve closely matches the field curve 14/40

15 (6) Shear wave velocity to stiffness G max may then be calculated from: G max = V s 2 Use in deformation analyses (seismic, dynamic, machine, wind, wave, liquefaction potential etc. 15/40

16 Research sites in Norway Approach was: Initially investigate sites where V s profiles already known to give confidence Later then study other sites To date 22 sites studied MASW (20)/ SASW (5) + 2 Swedish Long and Donohue (2007, 2010) Can. Geo. Jnl. 16/40

17 Onsøy: G max from SCPT Depth (m) Crust Soft Clay Compared with 5 MASW profiles Gmax (MPa) SCPT 1 SCPT 2 SCPT 3 MASW 1 MASW 2 MASW 3 MASW 4 MASW Bender Element (Slightly lower Gmax) /40

18 Drammen clay sites: Danviksgata & Museumpark 18/40

Berg - Trondheim Depth (m) Vs (m/s) 0 50 100 150 200 250

19 Berg - Trondheim Depth (m) Vs (m/s) Site1 Cross hole Barnehage site 19/40

Depth (m) Holmen Drammen - sand site Vs (m/s) 0 25 50 75 100 125 150 175 200

20 Depth (m) Holmen Drammen - sand site Vs (m/s) MASW Raleigh wave SCPT1 SCPT2 SCPT3 Cross hole avg. 20/40

21 All sites 21/40

22 Correlations between V s and soil properties 22/40

23 Correlations for clays - I V s or G max depends on, e, OCR (Hardin, 1978) G max / ' v0 should vary with e Janbu / Langø g max max ` a m Use high quality (block) samples only G 23/40

24 Correlations - II 24/40

25 s u versus V s correlation Irish till 25/40

26 Link to CPTU 26/40

27 Mayne and Rix correlation G max not V s q c not q t Log scales Worldwide database Norwegian soils? 27/40

28 Norwegian clays Best quality data only Each point refers to a block sample 28/40

29 Use of CPTU B q 29/40

30 Subsequent trial - Fredrikstad 30/40

31 Combined use of MASW and CPTU 31/40

32 Other applications 32/40

33 Continuous MASW 33/40

34 O Connell St Central Dublin 34/40

35 Can create 2d stiffness profiles Onsøy little variation, highly uniform 35/40

36 Canal embankment Chester, UK 36/40

37 Passive MASW Nödinge 37/40

Depth (m) Assessment of ground improvement Vs (m/s) 0 100 200 300 400 0 2 Shallow wet till improved by lime / cement

38 Depth (m) Assessment of ground improvement Vs (m/s) Shallow wet till improved by lime / cement stabilisation and assessed using MASW Zone 1 Zone 2 Zone 3 Untreated Zone 3 Treated Zone 4 Zone 5 Zone 6 38/40

Depth (m) Assessment of sample disturbance V s (m/s) 0 20 40 60 80 100 120 140 160 0 54 2 76 Blocks 4

39 Depth (m) Assessment of sample disturbance V s (m/s) Blocks 4 MASW 1 MASW 2 6 MASW 3 MASW 4 8 MASW MASW 5 Remoulded Remoulded Air (After extrustion)

40 Conclusion MASW now well proven mature technique Scope for further work on link between V s and parameters of Norwegian clays (s u, p c ', M 0 etc.) Scope for similar work in other Nordic countries Industry / University collaboration essential Thank You For Listening 40/40

Satish Pullammanappallil and Bill Honjas. Optim LLC, Reno, Nevada, USA. John N. Louie. J. Andrew Siemens. Siemens & Associates, Bend, Oregon, USA

Comparative Study of the Refraction Microtremor (ReMi) Method: Using Seismic noise and standard P-wave refraction equipment for deriving 1-D S-wave profiles Satish Pullammanappallil and Bill Honjas Optim