THESIS T 8992
Trang 2UMI Number: 3229172
INFORMATION TO USERS
The quality of this reproduction is dependent upon the quality of the copy submitted Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction
In the unlikely event that the author did not send a complete manuscript
and there are missing pages, these will be noted Also, if unauthorized
copyright material had to be removed, a note will indicate the deletion ® UMI UMI Microform 3229172 Copyright 2007 by ProQuest Information and Learning Company
All rights reserved This microform edition is protected against unauthorized copying under Title 17, United States Code
ProQuest Information and Learning Company 300 North Zeeb Road
P.O Box 1346
Trang 41H ABSTRACT
The Missouri Department of Transportation (MoDOT) routinely acquires seismic cone penetrometer (SCPT) shear wave velocity control as part of the routine investigation of soils at highway structures or other geotechnical sites within the Mississippi
Embayment In an effort to ensure their geotechnical investigations are as effective and efficient as possible, the SCPT tool and several available alternatives (crosshole: CH; multichannel analysis of surface waves: MASW; and refraction microtremor: ReMi) were evaluated and compared on the basis of the interpretation of processed field data acquired at two test sites in the Poplar Bluff area, southeast Missouri These four methods for determining the shear wave velocity of soils were subsequently ranked in terms of
accuracy, functionality, cost effectiveness, other considerations and overall utility On the basis of the comparative analyses, it is concluded that MASW data are
Trang 5iv
ACKNOWLEDGMENTS
Special thanks go to the Missouri Department of Transportation for supporting the
project I thank Dr Neil Anderson who served as my advisor I would also like to thank Dr David Rogers and Dr Richard Stephenson who served on my dissertation committee I would like to thank Katherine Mattison, the department administrative assistant and
Paula Cochran, the graduate studies assistant Without their help, patience, and
understanding this project would not have been completed without difficulty
My appreciation goes to Dr Richard Rechtien, who served on my committee and as my mentor during a very long journey in my graduate study He gave me invaluable advice in data collection and offered me several possible solutions to my data processing Without him the data collection and processing in this project would have been difficult
I thank Dr Gerald Rupert who served on my committee He provided me with the support and motivation that made the research a success He also helped me solve many problems during the past two years Thank you very much Dr Rupert
Finally, I would like to thank my mother and father for their support and
understanding during my study period I would also like to thank my girlfriend for her
support from a distance I would like to thank my fellow students in B40 McNutt Hall
Trang 6TABLE OF CONTENTS
PAGE
ABSTRACT c1 nh TH Hy Hy nh ng ¬ iii
ACNOWLEDGMENTS .0 cccccccccecscceseecsesseecsesusceceveuereversversesssesrsenseenstens iv LIST OF ILLUSTRATIONS .0.cccccccecesessecseesseeveseeseecssesseeeseetsstinsenteesnass ix
LIST OE TABLES L TH SE E151 1111151 xà kg tà nàng xii L INTRODUCTION, ccccssscssesssesssessesssesssessessessessressessutsetesteseseee ne 1 1.1 STATEMENT OF PROBLEM 2 1 ST HH ng 1 1.2 RESEARCH OBJECTIVES L0 TH TS HT eu 2 1.3 STUDY AREA L L TH ng HT HH HH kg nàng 3 1.4 DISSERTATION OUTLINES - L1 1211121195112 hy rên 4 2 SCOPE OF "1 1 6 2.1.OVERVIEW " ¬ 6
2.2 GEOPHYSICAL FIELD WORK PROGRAM 2c cv 6
2.3 POPLAR BLUEF TEST SITES HH HH HH th 7
3 CROSSHOLE SEISMIC (CH]) - c1 1 21112112111 511 x12 kg 15
3.1, OVERVIEW oecccccccccccsccssccsecseecssecssensevcrecrseesecssecreevesnecsereeesnn 15
3.2 BOREHOLE PREPARA TION óc 1 1E 1112k nàng l6
3.3 BOREHOLE DEVIATION SURVEY cào: He 20
3.4 DATA ACQUISITION c1 21111 11H Hà tàn 20
3.5 DATA PROCESSING L QQ HT HT HH HH ên 23
Trang 7vi
3.7 SUMMARY EVALUATION OF CH SEISMIC METHOD 26 SEISMIC CONE PENETROMETER TEST (SCPT) c 29
n9 2:94: 16 (3+ .Ẽ Ẽ an ey 29
4.2 SCPT: ACQUISTTION, PROCESSING AND INTERPRETATION 30
4.2.1 Acquisition and prOC€SSITE cv nh nhớ 30 4.2.2 ÍnterpretaflO' ST nà kh tà va 34
4.3 SUMMARY EVALUATION OF SCPT METHOD 47 MULTI-CHANNEL ANALYSIS OF SUREACE WAVE(MASW 52
5.1 OVERVIEW icc EEE EEE CEEOL E EEE a Ean ướt 52
5.2 1-D MASW: ACQUISITION, PROCESSING AND
INTERPRETATIƠN centre nett netted rene eee eeeee eee ea eneenaee ed 53
5.2.1 Acquisition and DrOC€SSInE con ng n nhe 33 5.2.2 1-D MASW data InfterprefatIOn ence eee eeae eee eeaeeuens 56
5.2.2.1 1-D MASW shear-wave velocity profiles of Site #3 56 5.2.2.2 1-D MASW shear-wave velocity profiles of Site #15 56
5.3, 2-D MASW: ACQUISITION, PROCESSING AND
INTERPRETATION 0 0 ccc cececec teen cent ee ee eee e eens eee e eens bene na seen anes 59
5.3.1 Acquisition and DrOC€SSINE SH nh nh ro 59 5.3.2 2-D MASW data Interpretatlon cà cà như 61
5.4 SUMMARY EVALUATION OE MASW METHOD 69 REFRACTIƠN MICROTREMOR (REMI) che 74
S947: 21 ă aa a eae 74
Trang 8vii
6.3 INTERPRETATION OF 1-D REMI DATA AT SITES #3 AND #15 77
6.3.1 1-D ReMI shear-wave velocIty profile at SIte #3 77
6.3.2 1-D ReMI shear-wave velocity profile at Site #1Š 80
6.4 SUMMARY EVALUATION OF REMI METHOD 83
7 COMPARATIVE ANALYSES OF SHEAR-WAVE METHODS 87
rm9 2:22 EE EEE EEE EE REE HERE n ea 87 7.2 ACCURACY cece cece cnn renee rE EEE CEE E EEE nàn Bà hết 87 7.2.1 NEHRP Quantitative Comparison Method 88
7.2.1.1 NEHRP Quantitative Comparison of S1te #3 89
7.2.1.2 NEHRP Quantitative Comparison of Site #lŠ 90
7.2.2 Predicted ground motion amplification c.Ă- 91 7.2.2.1 Predicted ground motion amplification of Site #3 94
7.2.2.2 Predicted ground motion amplification of Site #1Š 95
7.2.3 Discussion of Accuracy Comp4r1SOnS c cà se 96 7.3 FUNCTIONALTTY (DATA ACQUISTTIƠN) 07
7.4 FUNCTIONALTTY (DATA PROCESSING) ¬ nen eae 98 7.5 COST EFFECTIVENESS LH TH HH nọ BE Hà tt nà 99 7.6 OTHER CONSIDERATIONS LH nh HH kg 100 7.7 QVERALL UTILTTY TO MODOT cĂààà nhe Hưe 101 8 NEHRP SITE-CLASS MAP OEF THE POPLAR BLUFE AREA 106
8.1.OVERVIEW cà TK kh nh kh 106 8.2 OVERVIEW OF NEHRP SITE CLASSIFICATIONS 107
Trang 101X
LIST OF ILLUSTRATIONS
Figure Page
Eigure 1.1: Location map of the sfudy af@a con nh nhu 5
Figure 2.1: Poplar BÏIuf study ar€a cnnn nnn HH nh nh nh nh cà 10 Figure 2.2: Poplar Bluff study area physiographic provinces and
Surficlal maf€r1aÌS - SH TH TT KT nà nà ho hy 11
Figure 2.3: Poplar Bluff study area MASW test sites (2-D MASW shear
wave Velocity profiles were acquired at Sites #3, #10, #13 and #31.) 12 Figure 2.4: Poplar Bluff study area SCPT test SIt€S nen à 13 Figure 2.5: Crosshole seismic test SIf€S SH HH nhe 14
Figure 3.1: Borehole lithologic log at S1fe #3 nh nh nh kh kh re 17
Figure 3.2: Borehole lithologic log at Site #ÏŠ uc nh kh net 18 Figure 3.3: Borehole geometry of Site #3 ¬ entree ren ere nee ree need 19
Figure 3.4: Borehole geometry Of Site #TŠ nh nh nh nhớt 19 Figure 3.5: Shows the crosshole selsmic dafa acqu1S1t1OH 21 Figure 3.6: The borehole s€1SmIC SOUFC€ cọ SH HH nhe kh Hệ 22
Figure 3.7: Three-component downhole receiver with vertical sidewall clamp 22 Figure 3.8: Example of composite CH data from Site #3 e- 23 Figure 3.9: Crosshole data of Site #3 and borehole lithologic log 25 Figure 3.10: CH data Site #15 and borehole lithologic log - 25 Figure 4.1: The SCPT rig used by MoDOTT in the Poplar Bluff area 31
Trang 11Figure 4.4: Site #3 2-D MASW line, SCPT and CHÍ location 34
Figure 4.5: Site #10 2-D MASW survey line and SCPT location 35
Figure 4.6: Site #13 2-D MASW survey line and SCPT location ¬ 35
Figure 4.7: Site #31 2-D MASXW survey line and SCPT location 36
Figure 4.8: Plot of CH and SCPT shear-wave velocity profiles for Site#3 37
Eigure 4.9: Suit of SCPT shear-wave velocity profiles from Site #3 39
Figure 4.10: Suit of SCPT shear-wave veloctty profiles from Site #10 42
Figure 4.11: Suit of SCPT shear-wave velocity profiles from Site #13 44
Figure 4.12: Suit of SCPT shear-wave velocity profiles from Site #31 46
Figure 5.1: MASW field configuration (Park et al, 1999) cu se seo 54 Figure 5.2: General procedure of MASW processing A multichannel record (shot gather) in (a) is transformed into (b) a dispersion image in which the fundamental-mode dispersion is identified and corresponding signal curve is extracted, and then (c) the curve is inverted into a 1-D Vs profile (Park et al, 1999) " cette eee tees tees eee eeeet nae enaeenanens 55 Figure 5.3: Field MASW data and dispersion curve of Site #3 57
Figure 5.4: Plot of MASW and crosshole shear-wave velocity profiles for Site #3 58
Figure 5.5: MASW data and dispersion curve l)(-š:4 h5 Œa - 58
Figure 5.6: Plot of MASW and crosshole shear-wave velocity profiles for Site #15 59
Figure 5.7: Generation of a 2-D MASW shear-wave velocity profile (Park et al, 1999) occ cece nent e teen ence ne eee tne eet e eee neon ene t ees 60 Figure 5.8: 2-D MASW shear-wave velocity profile for Site #2 62
Trang 12XI
Figure 5.10: 2-D MASW shear-wave velocity profile for Site #13 66 Eigure 5.11: 2-D MASW shear-wave velocity profile for Site #31 68 Figure 6.1: Shows ReMi data processing steps (Modified from Louis (2001)) 76 Figure 6.2: ReMi data from SIfe #Â LH ene ene e kh kh nà khu 78 Figure 6.3: Plot of CH, SCPT, MASW, and ReMi shear-wave velocity profiles
50) GSA oe cự 79
Figure 6.4: ReMi data of Site #15 HH TT nh nh kh và 81
Figure 6.5: Plot of CH, MASW, and ReMi shear-wave velocity profiles for
Site BLS EE Erne nen rte 82
Figure 7.1: Amplification ratios of Site #3 00 cece cence eee ee entree e neta ene ne enens 95
Figure 7.2: Amplification ratiOS Of S1t€ #ÏŠ HH nh kh va 96 Figure 8.1: Poplar Bluff study area shear-wave velocity test values and surficial
Materials UNITS occ cece eee ne een rene EEE EEE EEE SEE EES EE ee EE ERE 111 Figure 8.2: Values of Vs(100) vs soil units found in Poplar Bluff area (Table 9.1) 112
Trang 13xi
LIST OF TABLES
Table Page
Table 2.1: Summary of geophysical field work pian cà 7 Table 3.1: Tabularized sunmary ofthe CH method - 26 ˆ Table 4.1: Tabularized summary of the SCPT method - 48 Table 5.1: Tabularized sunmary of the MASW Method 70
Table 6.1: Summary ofthe ReMI method con nen 84
Table 7.1: NEHRP site classes - Gà Hy HH kho in 89 Table 7.2: Site #3 Vsio0) , WSs) and site class " 90 Table 7.3: Site #15 s(iooy and site claSS - cu HH HH nh nen ho 91 Table 7.4: Ranking of accuracy of MASW, CH, ReMI, and SCPT 103
Table 7.5: Functionality (acquisition) of MASW, CH, ReMi,
and SCPT methods - - con HH HH HH nh nh ng kh nhu 103 Table 7.6: Functionality (processing) of MASW, CH, ReMi,
and SCPT methods HH HH HH nh ng 104 Table 7.7: Cost-effectiveness of MASW, CH, ReMi, and SCPT
shear-wave methods - co HH HH HH nh nà nà hen kế 104 Table 7.8: Ranking of other considerations of MASW, CH, ReMi,
and SCPT shear-wave velocity profile methods 105
Table 7.9: Overall ranking of CH, MASW, SCPT, and ReMi methods
Trang 141 INTRODUCTION
1.1 STATEMENT OF PROBLEM
In situ shear-wave velocity profiles are used in a variety of earthquake
engineering applications, including site response studies, liquefaction analyses, and soil structure interaction evaluations (Woods and Stokoe, 1985; Stoke et al., 1988: Stoke et al., 1994) Borehole seismic methods such as crosshole and downhole methods normally have been employed to measure shear-wave velocity since they are direct measurements More recently, a suspension logger has been used for this purpose However, the borehole methods are normally expensive because borehole needs to be drilled for data
acquisitions Until recently, there are many new techniques have been developed
including seismic surface-wave methods and seismic cone penetrometer method These
methods are increasingly used by many engineering geophysicist and geotechnical engineer to determine in situ shear-wave velocity However their reliability needs to be
established by comparison with more direct methods
Missouri Department of Transportation (MoDOT) is always acquired shear-wave velocity data for their geotechnical site characterization programs For the above reason, MoDOT wanted to evaluate the relative utility of the conventional and newly developed methods in order to ensure their geotechnical site characterization programs are as effective and efficient as possible MoDOT asked UMR to evaluate four geophysical field methods used to determine the shear-wave velocity of soils to depths of 100 ft The proposed geophysical methods to be evaluated include:
Trang 152 Seismic Cone Penetrometer Test (SCPT)
3 Multi-channel Analysis of Surface Wave (MASW)
4, Refraction Microtremor (ReMi)
The CH method was selected because CH data is generally accepted as more
reliable than shear-wave velocity data derived from other geophysical methods (Kramer,
1996) Consequently, the CH shear-wave velocity data were used as a yard stick for determining the reasonableness of other selected geophysical methods The SCPT was selected for evaluation because it is the current method that MoDOT uses for determining
shear-wave velocity of soil MASW and ReM1 methods were selected because they are
newly developed surface acquisition methods for determining shear-wave velocity
These four geophysical methods were evaluated individually and comparatively
in terms of accuracy, functionality, cost-effectiveness and overall utility This
comparative evaluation of available shear-wave technologies was conducted in Poplar
Bluff area
1.2 RESEARCH OBJECTIVES
The objective of this research consists of two main purposes The first objective was to evaluate four geophysical methods with a view to comparing and contrasting their
accuracy, functionality, cost effective, and overall utility The ultimate goal is to find
Trang 16The second objective of this research was to determine the NEHRP (National
Earthquake Hazards Reduction Program) site classification map of the Poplar Bluff area by acquiring a large number of shear-wave velocities to 100 ft depth (Vsv100)) VS100) is the shear-wave velocity averaged to 100 ft depth and is one predictor of earthquake ground motion amplification and potential hazard in similar alluviaum-filled basins in California Under NEHRP-UBC provisions (BSSC, 1998) sites are categorized for
shaking hazard using Vsv109) To accomplish the second objective, several shear-wave
velocities within Poplar Bluff area were acquired using MASW method Sufficient shear- wave velocity data was collected to obtain a realistic view of the variation in shear wave velocity All shear wave velocity data were used to generate the NERHP soil
classification map (BSSC, 1998)
1.3 STUDY AREA
The study area for this research is the Poplar Bluff area, Butler County Missouri
(Figure 1.1) It includes the area within the four standard 7.5' topographic quadrangles of
Poplar Bluff, Rombauer, Harviell and Hanleyville (Figure 2.1) The city of Poplar Bluff is centrally located near where these four quadrangles meet The Poplar Bluff area was selected for study because significant basic geologic and earthquake data already exists for the area and the area is currently being investigated for earthquake soil amplification by the Missouri Department of Natural Resources (MoDNR), Geological Survey as part of an Association of Central United States Earthquake Consortium State Geologists project Exchange of data between that project and the research here should provide a
Trang 171.4 DISSERTATION OUTLINES
The dissertation is organized into 9 chapters Chapter | is an introduction to the research, objectives, significance, and overview of the study area Chapter 2 provides the scope of field work program and the detail of the test-site locations The overview of data acquisitions and data processing of individual geophysical methods were discussed in Chapters 3 to 6 These chapters also cover the advantage and disadvantage of the individual geophysical methods Chapter 7 covers the comparative analysis and ranking of all four geophysical methods base on their accuracy, reliability, functionality, cost,
utility, and over utility to MoDOT The NEHRP site-class map of the Poplar Bluff area
was discussed in Chapter 8 Chapter 9 is the conclusions of this research and
Trang 18^
Trang 192 SCOPE OF WORK
2.1 OVERVIEW
The four field methods were tested at selected sites in the Poplar Bluff study area
during summer and fall 2004 Geophysical data collected for this study consists of CH data, MASW data, SCPT data, and ReMi data All geophysical data were acquired within
the MoDOT right-of-way in order to facilitate accessibility for all geophysics equipments
2.2 GEOPHYSICAL FIELD WORK PROGRAM
Table 2.1 summarizes the geophysical field work plan A total of 40 sites were
selected in the Poplar Bluff study area 1-D MASW data were acquired at all 40 test sites; 2-D MASW data were acquired at 4 test sites Crosshole (CH) shear wave velocity data were acquired at two test sites SCPT data were acquired at 15 test sites (including the
four 2-D MASW test sites) In this study SCPT data were acquired by MoDOT The field
Trang 20Table 2.1: Summary of geophysical field work plan Field Method Number of Sites Tested with Field Methods 1-D MASW 40 Crosshole Seismic 2 SCPT 10 ReMi 2 2-D MASW 4 2-D SCPT 4
2.3 POPLAR BLUFF TEST SITES
The Poplar Bluff study area was selected to include four USGS 7.5’ topographic quadrangle maps with the City of Poplar Bluff located near where the four maps join The four maps are the Poplar Bluff, Rombauer, Harviell and Hanleyville quadrangles The
study area is about 17 miles north-south and 14 miles east-west
The northwest portion of the study area is within the Ozarks uplands province and
the southeast portion is in the Mississippi Embayment lowlands province (Figure 2.1) The soils, or surficial materials (Figure 2.2), the topography and the groundwater level in these two areas are quite different The lowland are almost flat and have stream deposited alluvial soils composed mostly of sand with some silt, clay and gravel The alluvial soils are 100 to 200 feet thick, except adjacent to the uplands The groundwater level is very shallow in the lowlands, commonly 5 to 15 feet deep In the Ozarks uplands the
Trang 21nearly level on the upland drainage divides The residual soils are derived from prolonged weathering of the bedrock upper surface Intense weathering has dissolved the soluble
portions of the bedrock units leaving behind thick deposits of insoluble clay and large
amounts of chert gravel The residuum varies in thickness from about 40 feet to over 200 feet, commonly being about 100 feet thick The groundwater level is usually below the base of the residuum in the bedrock although small perched groundwater zones
occasionally exist in the residuum Alluvial valleys within the Ozarks have some
characteristics similar to the Mississippi Embayment except the alluvial soils are less extensive, more gravelly and usually thinner One unusual area of sand dune soils exists within the Mississippi Embayment area
Test sites for measuring shear wave velocity were selected based on three criteria: 1) sample the range of soil types and conditions in the study area, 2) achieve a relatively
uniform aerial distribution of sites throughout the study area and 3) test locations at or
near where soil borings and geotechnical data already exist, preferably at MoDOT bridge sites with multiple borings Some consideration was also given to how easy it would be for test equipment to access the sites and site ownership Most sites selected are on
MoDOT right-of-way Of the four shear wave velocity testing techniques used in this
study the MASW testing method is the most versatile because it could be used in all
geologic settings Forty sites were selected for MASW 1-D testing with about half in the uplands and half in the lowlands (Figure 2.3 and Table 2.1)
Trang 22could be compared to the similar SCPT profiles which were only available in the lowland
setting
The SCPT method was not usable in the uplands area because the rocky, gravelly
nature of the residual soils could not be penetrated by the cone Therefore, all of the SCPT tests were sited in the lowlands or in the alluvial valleys within the uplands area Ten sites were selected for the SCPT method in this study Some of the SCPT had been tested during the previous CUSEC-SG study which shown as existing in Figure 2.4 A subset of 4 test sites had profiles of 5 SCPT run at them (Site #3, #10, #13, and #31)
The CH technique is usable in either the upland or lowland setting but it requires the installation of twin boreholes at each site with casings installed in the holes Two CH sites were selected, one in the uplands and one in the lowlands (Figure 2.5 and Table 2:1)
The lowland site was selected to be the same location as one of the sites with MASW and
Trang 23
Poplar Bluff Study Area
Trang 2411 Poplar Bluff Study Area Surficial Materials Rombauer Quadrangle Tư « a ` =
Harviell Quadrangle $$ Hanleyville Quadrangle
Trang 2512
Poplar Bluff Study Area
MASW Test Sites
Poplar Bluff Quadran Rombauer Quadrangle — +
Harviell Quadrangle — Hanleyville Quadrangle owen aor j2, U8 se 6UB47 Co] Peper ci #erfailil Mlsterlale La Ea
MAW 4.0 Tost Ste 3 Afuons Hmmmase Ll] Faywegrephte Provinces Si GE ach nào Soi Khu > a wk
4 t 4 z 3 4 5 a 7 5 5 Miles BHYT m ntwdr+ ch lớn 8 nem 21L, hot mớc 2 ê nh nh recive #L, Raksmtc Ằ - sạn soalbo@uc
Figure 2.3: Poplar Bluff study area MASW test sites (2-D MASW shear wave
Trang 26
Poplar Bluff Study Area
Poplar Bluff Quadrangle Rombauer Quadrangle
Harviell Quadrangie Hanieyviile Quadrangle
Trang 2714 @ Crosshole Test Site Quadrangles ff wo 33 4
Poplar Bluff Quad
Poplar Bluff Study Area
Crosshole Test Sites
rangle Rombauer Quadrangle Cara TS oe
Harviell Quadrangle Hanleyville Quadrangle
wl TO Poptsr Bintt Sutficio) Materials Unies
A us 60 8 Us 67
[ ¬ = Aurela
i a ‘i Resk Hall - gravel
[HJ Physiegraphic Provinces ga Set lecss & reskdoum
5 10 Miles BH & Reborte 0 geared, lence 6 ra ddnns)
Trang 2815 3 CROSSHOLE SEISMIC (CH)
3.1 OVERVIEW
Crosshole (CH) seismic shear-wave velocity data were acquired at two sites, site
#3 and #15, in the Poplar Bluff study area (Figure 2.5) Good quality CH data is generally accepted as more reliable than shear-wave velocity data derived from other methods (Kramer, 1996) Consequently, the CH data set were used as a yard stick for determining the reasonableness of the acquired MASW, ReMi, and SCPT shear-wave velocity data
CH testing in this research was conducted according to ASTM standard: D
4428/D 4428-00 CH seismic testing is a valuable technique for site investigations, since
it can be used to produce detailed compression (P) and shear (S)-wave velocity profiles (Butler and Curro, 1981) Seismic CH tests use two or more boreholes to measure wave
propagation velocities along horizontal paths The simplest CH test configuration consists
of two boreholes, one of which contains an impulse energy source and the other a
receiver By fixing both source and receiver at the same depth in each borehole, the wave
propagation velocity of the material between the boreholes at that depth is measured By
Trang 2916
3.2 BOREHOLE PREPARATION
In this research, twin boreholes were drilled at two sites (Sites #3 and #15) by MoDOT during summer 2004 Each borehole was cased with 4-inch D PVC pipe, grouted to the host medium, sealed, and evaluated The borehole lithologic logs of these two sites were shown in Figure 3.1 for Site #3 and Figure 3.2 for site #15 The soil at
Site #3 consists almost exclusively of sand, silt and clay The limestone bedrock at Site #3 was encounter at a depth of ~113 ft The soil at Site #15 consists almost exclusively of residium (gravel, sand, silt, and clay) The bedrock was not encountered at this site
The borehole remained evacuated during all seismic data acquisition activity
Trang 30Depth (ft) Site#3 0 Tan silty clay 22 Brown clean fine to medium sand 30
Mostly gravelly sand with some fine sand and stiff clayey sand 50
Light gray fine clean sand
Trang 31Depth (ft) 10 30 50 75 80 100 130 140 150 Site #15 Dark orangish red clayey fine sand Orange to red silty clay with some fine sand
Mostly light yellow clayey silt with some redish orange silty clayey sand
Red clayey gravel with some red fine to medium sand
Light yellow silty clay
Coarse sand and fine gravel with some
red silty clay
Mostly tan to light yellow very stiff silty clay and red clayey sand with some fine gravel
Red clayey sand
Brownish red sandy clay with small amount of course
sand fine gravel
Figure 3.2: Borehole lithologic log at Site #15
Trang 3320 3.3 BOREHOLE DEVIATION SURVEY
The borehole deviation survey was conducted for each borehole at two sites The objective was to determine accurately the horizontal distance between two boreholes The borehole deviation tool employs a combination of precision magnetometers and
inclinometers to measure its orientation with respect to the earth’s magnetic and
gravitational fields This information was transmitted continually to the surface data
acquisition system, as tool was raised from bottom to top inside the borehole
At each point in the borehole, two measurements were taken, normally referred to as northing or inclination, and easting or declination Inclination refers to the deviation angle of the boreholes with the vertical Declination refers to the orientation of the borehole relative to azimuth Inclination and declination measurements are used to calculate the distance between the two boreholes at each station
From the result of borehole deviation survey at both sites, the boreholes at each
site were quite vertical The maximum deviation did not excess 1 ft at both two sites
3.4 DATA ACQUISITION
The acquisition of the CH shear-wave velocity data was relatively
straightforward Figure 3.5 illustrated the CH seismic data acquisition used in this study
Trang 3421
station, the borehole mechanical source was discharged twice in the upward and
Trang 3623 3.5 DATA PROCESSING
The seismic data acquired at each depth were gathered together to form the
composite seismic record (Figure 3.8) At each depth the forward and reverse polarity seismic records were plotted on the same depth In Figure 3.8, although the downhole hammer is suitable for generating vertical polarized shear-wave, observable
compressional wave (p-wave) can also be seen on the composite seismic record The transit time of the shear wave, form source to receiver, was determined for each test depth on the basis of the cross-over time of the reverse polarity seismic records The transit time and borehole separation data were then used to determine the in-situ shear-wave velocity of the soil at each depth tested CH shear-wave velocity profiles for
Trang 3724
3.6 DATA INTERPRETATION
Figure 3.9 shows the shear-wave velocity profile determined from CH testing at site #3 and also accompanied by borehole lithologic log The twinned borehole at this site
was encountered bedrock at a depth of ~113 ft However, either because of obstructions or the shortness of the PVC casing, CH shear-wave seismic data were obtained only to a
depth of 110 ft The visual inspection of CH profile indicates that the shear-wave velocity
of soil, with minor fluctuations (on the order of + 100 ft/sec), increases gradually with depth of burial (from a low of about 600 ft/sec to a high of about 1000 ft/sec) The soil at
site #3 consists almost exclusively of sand, silt and clay The observed minor fluctuations in shear-wave velocity are attributed to minor changes in lithology (sand, silt, clay
concentrations) and grain size
CH shear-wave velocity of site #15 is plotted in Figure 3.10 The twinned
borehole at this site did not encounter bedrock The visual inspection of the CH data at
this site indicates that the shear-wave velocity of soil, with minor fluctuations (on the
order of + 50 ft/sec), increases gradually with depth of burial (from a low of about 850
Trang 38Depth (ft) 20 40 60 80 100 120 S-wave velocity (ft/sec) 9 600 1000 1800 | @ _® _* .ò® :*® — bee Q en eee beeen oe | e e ¬— NMMWWWWWgw â : âđ | ._ L _ đ Teen em ®- : e i e : - Eseerrreeeee ee ị e: ®
Tan silty clay
Brown clean fine to medium sand
Mostly clean brown chert gravel with some tan and light gray sand
Mostly light gray stiff clayey sand
Tan/brown gravelly sand Gray and tan clean sandy fine gravel
Light gray fine clean sand
Light gray medium to fine clean sand with some gravel Light gray fine clean sand
Light gray medium to fine clean sand with some gravel Dolomite Figure 3.9: Crosshole data of Site #3 and borehole lithologic log Depth (ft) 20 40 60 80 100 120 140 160 S-wave velocity (ft/sec) 9 500 1000 1500 2000 Dark orangish red clayey fine sand Orange to red silty clay with some fine sand
Mostly light yellow clayey silt with some redish orange silty clayey sand
Red clayey gravel with some red fine to medium sand
Light yellow silty clay
Coarse sand and fine gravel with some red silty clay
Mostly tan to light yellow very stiff silty clay and red clayey sand with some fine gravel
Red clayey sand
Brownish red sandy clay with small amount of course
sand fine gravel
Figure 3.10: CH data Site #15 and borehole lithologic log
Trang 3926
3.7 SUMMARY EVALUATION OF CH SEISMIC METHOD
The CH method can be used to generate a very accurate shear-wave velocity
profile of the subsurface (Indeed CH shear-wave velocity profiles are generally
considered to be more accurate than MASW, SCPT or ReMi shear-wave velocity profiles.) The CH method works particularly well in fairly uniform soils and in
reasonably quiet (acoustically) environments The main problem with the method is that it is very expensive, as twinned (or tripled) PVC-cased, air-filled boreholes are required (Borehole deviation data must also be acquired.) A tabularized summary of the CH method is presented as Table 3.1
Table 3.1: Tabularized summary of the CH method 1, ACQUISITION 1.1 Brief overview of field procedure
Twinned boreholes (PVC-cased, air-filled) were drilled with a separation of
15 ft A shear-wave acoustic source was lowered to the base of one borehole; a shear-wave acoustic receiver was lowered to the same depth in the adjacent
borehole The source and receiver were locked inplace The borehole source was discharged (in an upward direction); the receiver recorded the arrival time and amplitude of the acoustic shear-wave energy that traveled directly
from the source to the receiver (cross-hole seismic field record) The source
was then discharged in a downward direction thereby generating an opposite
polarity field record The source and receiver were raised to the surface at 5 ft increments Each time the source/receiver pair was raised, the source was
discharged twice (in opposite directions), and cross-hole seismic field records
were recorded A borehole deviation tool was used to meter accurately determine the separation between the twinned boreholes at every depth tested
The transit time and borehole separation data were ultimately used to
determine the in-situ shear-wave velocity assigned to the soil at each test depth
1,2 Field equipment The borehole acoustic data were acquired using a portable equipment consisting of a borehole shear-wave acoustic source, a borehole receiver (triaxial geophone), source and receiver cables, a source control unit (with trigger switch cable), an engineering seismograph, 12-V battery, and laptop The borehole deviation tool (rental) consisted of a borehole inclinometer, a winch and a control unit 1.3 Field crew Minimum of 2 persons Three is the optimum number 1.4 Other considerations e = Size of test site CH data can be acquired anywhere twinned boreholes can be drilled and completed
e Vehicular access All CH test equipment can be transported by hand Usually, the equipment
Trang 4027
completed
e Background noise Acoustic noise can degrade the quality of the recorded data, particularly at
shallow test depths If the boreholes are located adjacent to a roadway, the
source should be discharged multiple times (in both directions at each test
depth) and the records should be stacked The source should also be discharged when traffic noise is relatively low
e Anchoring requirements The equipment does not need to be physically anchored or coupled to the ground surface; however the winch needs to be set firmly on the ground surface e Nature of ground surface CH data can be acquired anywhere twinned boreholes can be drilled and completed e Subsurface lithology or material CH data can be acquired anywhere twinned boreholes can be drilled and completed se Depth of investigation CH data can be acquired anywhere twinned boreholes can be drilled and
completed The acoustic source and receiver can be lowered to the base of any
ait-filled cased borehole
e Proximity to structures and utilities (buried)
CH data can be acquired anywhere twinned boreholes can be drilled and completed However, background acoustic noise can be a problem particularly at shallow test depths
e - Proximity to built structures and utilities
CH data can be acquired anywhere twinned boreholes can be drilled and completed However, background acoustic noise can be a problem e Permitting Permits may be required to drill the twinned boreholes e Notiñcation Permission drill may be required (from the surface rights holder and others)
1.5 Brief description of field data The field data (one record for each depth tested), consisting of unfiltered cross-hole seismic field records, are recorded digitally and stored on the laptop coupled to the seismograph Borehole deviation data are also recorded
digitally
1.6 Time required to acquired to acquire field data at one test site
One set of cross-hole data (twinned boreholes) and associated borehole deviation data can generally be acquired less than six hours (assuming: crew
and equipment are on-site)
1.7 Estimated cost to acquire field
data at one test site
Basic field costs include: a) 6 hours of crew time plus travel time; b)
equipment rental and/or depreciation; c) vehicle rental and/or depreciation
plus fuel Note: the cost of drilling and completing the twinned boreholes is not included in this estimate
1.8 Potential for errors
e Human The only critical non-automated process is the placement of the geophone and
source If the geophone and source are accurately placed (and coupled to the
casing) each time the source is discharged, there is little possibility for human error leading to significant misinterpretation Inasmuch as the source and
receiver are separated laterally by 10 ft, errors in the vertical placement the
source and receiver on the order of less than 6 inches will not be significant However, accurate borehole deviation data must be acquired
e Equipment Equipment problems are unlikely to generate errors that will lead to
misinterpretation
1.9 Reproducibility of field tests Field results are reproducible This is one of the reasons that CH shear-wave velocity data are generally assumed to be more reliable than SCPT, MASW,
and ReMi data
2 DATA PROCESSING
2.1 Brief overview of data
processing Each pair of opposite polarity cross-hole field records is analyzed visually The transit time of the acoustic shear-wave energy (from source to receiver)
and the physical source-receiver separation (from deviation data) at each test
depth is used to calculate the shear-wave velocity assigned to that test depth The output is a 1-D shear-wave velocity profile of the subsurface (with velocity values at vertical depth intervals of 5 ft)
2.2 Output of data processing The output is a 1-D shear-wave velocity profile of the subsurface with values at depth intervals of 5 ft (Poplar Bluff data set) This shear-wave velocity
profile constitutes the final deliverable
2.3 Estimated cost to process field
data from one test site Basic processing costs include: a) 2 hours of interpreter’s time; b) hardware/software renta! and/or depreciation