The effect of silt on claystone strength properties and its predictability utilizing borehole geophysics

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The effect of silt on claystone strength properties and its predictability utilizing borehole geophysics
Davis, Mark Warren
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vii, 72 leaves : illustrations ; 29 cm


Subjects / Keywords:
Clay -- Testing ( lcsh )
Silt -- Testing ( lcsh )
Borehole mining ( lcsh )
Borehole mining ( fast )
Clay -- Testing ( fast )
Silt -- Testing ( fast )
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )


Includes bibliographical references (leaves 40-41).
General Note:
Submitted in partial fulfillment of the requirements for the degree of Master of Science, Department of Civil Engineering.
Statement of Responsibility:
by Mark Warren Davis.

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Source Institution:
University of Colorado Denver
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Auraria Library
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All applicable rights reserved by the source institution and holding location.
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17995282 ( OCLC )
LD1190.E53 1986m .D38 ( lcc )


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THE EFFECT OF SILT ON CLAYSTONE STRENGTH PROPERTIES AND ITS PREDICTABILITY BOREHOLE GEOPHYSICS by Mark Warren Davis B.A., University of Colorado, 1969 M.S., UniVersity of Utah, 1980 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in Denver in partial fulfillment of the requi rement,s for the degree of Master of Sci ence Department of Civil Engineering 1986


This thesis for the Master of Science degree by Mark Warren Davis has been approved for the Department of Ci vi 1 Engi neer.i ng by


Davis, Mark Warren (M.S., Civil Engineering) The Effect of Silt on Claystone Strength Properties and its Predictability Utilizing Borehole Geophysics Thesis directed by Associate Professor Tzong H. Wu iii Plans for a proposed tunneling project in eastern Colorado require strength properties in anisotropic soft claystones be obtained for construction design. This thesis addresses certain strength parameters of the claystones, the effects of silt on claystone strength, and the utility of borehole geophysical methods for the prediction of these properties Direct shear and indirect tensile testing was conducted on drill core, the results of which indicate a correlation between increases in silt content and reduction in claystone tensile and shear strength. Contract geophysical work was conducted at each drill hole location. Information pertinent to engineering was obtained with neutron, gamma-gamma, and sonic logging.


CONTENTS ABSTRACT iii v LIST OF FIGURES Purpose and Scope .. Methods of Investigation SITE DESCRIPTION Geology .. vi 3 4 6 IV. V. VI. VII. Direct Shear Testing Indirect Tensile Testing Clay Mineralogy Determinations. FIELD TESTING ... Borehole Geophysics ......... Sonic Velocity Gamma-Gamma Density .. .. .. .. .. .. .. Neutron Logging ... In Situ Pressure Meter Testing SUMMARY BIBLIOGRAPHY. ............ ......................... 9 19 21 25 25 32 38 40


v TABLES Table 1. Determination of Normal and Maximum Shear Stress ... 11 2. Correlation of Normal Stress and Maximum Shear Stress On Intact Rock ................. 13 3. Linear Regression Analysis Comparing Silt Content to Maximum Shear Stress ........ 15 4. Linear Regression Analysis Comparing Silt Content to Post Peak Shear Stress .. 17 6. Clay Percentages by X-ray Analysis 0 22 7. Non-Clay Percentages by X-ray Analysis .. 23 9. In Situ Pressure Meter Results ........ 31 10. Comparison of Data Obtained by Di fferent Testi ngMethods 0. .. 37 0'


vi FIGURES Figures 1. Geologic Section 6 2. Linear Regression Plot of Holes 6 and 10 ... 14 3. Linear Regression Plotof All Holes 14 4. Linear Regression Plot of 44-48 and 62-65 psi Normal Stress Maximum Shear Stress V5 Silt Content, Intact Rock 16 5. Example Curve for Di1atometer Response ... 30


vii APPENDIX A. 42 B. Sample Location and Description .... 62 C. 68 D. Description of Geophysical Logs Used Primarily for Geologic Correlation ........... 69 .......................... Spontaneous Potential 70 Res is ti vi ty Loggi ng '.' 71 Induced Polarization 71


CHAPTER I INTRODUCTION A site in eastern Colorado is under consideration for the construction ofa large underground proton accelerator. This Superconducting Super Collider (SSC) is designed be installed in a shallow tunnel, circular in plan view and over 50 miles in length. The geologic requirements for the proposed SSC project include suitability for rapid excavation with a tunnel boring machine and low hydraulic conductivity. The Colorado Geological Survey selected a site for further study based on an extensive review of the geologic literature. Purpose and Scope The purpose of this study is to further the understanding of rock strength properties in material which is intermediate in strength between soil and rock. Unpublished results by Amadei and testing of Pierre Formation in South Dakota by Nichols, 1983, have yielded unconfined compression strengths in the neighborhood of 600 psi. This is one-tenth the unconfined compression values usually assigned to shales (Goodman, 1980).


The other important and more specific aspect of this study is the fact that there are two major rock types which have been encountered in the drilling for the project notwithstanding the insignificant amounts of limestone. These are siltstones and claystones. These two rock types can be gradational, thus the terminology silty claystone and clayey siltstone. These terms, however, do not distinguish between rocks with alternating bands of each end member versus a homogeneous mixture favoring whichever composition the adjective suggests. Since the siting criteria for the include homogeneous rocks with similar properties it is fundamental that tests should be performed which would identify and quantify any differences which might affect tunnel design. The main objective of this study, therefore, is to examine the effects (if any) on rock strength properties caused by silt lenses in the more prevalent claystone to assure that this proposed site fits within the design criteria. Borehole geophysics may playa useful role in future determinations of site suitability. Because these are often cheaper and quicker than laboratory techniques, it would be expedient to determine the applicability of borehole geophysics to the identification and solution of geotechnical engineering problems.


Numerous advances have been made in the sophistication of these techniques (McCain, 1984) and an opportunity presents itself during this testing to compare many of these techniques and help establish their utility to the engineering community. Methods of Investigation Following the general site selection, five drill sites were located on approximately four mile centers. NX core holes were drilled to a depth of twenty-five feet below the plane of the -tunnel invert. The core from this drilling was protected from desiccation and then tested later in the laboratory. Laboratory tests were selected which would identify the weakest characteristics in both the silt-rich and silt-poor claystones. These tests include direct shear and indirect tension. Moisture contents were taken at the time of testing and silt-shale ratios were ascertained on the plane of failure. Borehole geophysical methods were employed in each hole and the logs were analyzed at the specific depths from which the laboratory samples were taken. The borehole logs included gamma, spontaneous potential, single-point resistance, 1611 normal resistivity, gamma-gamma density, caliper, neutron, and sonic logs. Borehole SSC-7 was tested with a dilatometer to determine elastic moduli and in situ compressive strength. 3


CHAPTER II SITE DESCRIPTION Criteria for site selection for the Superconducting Super Collider was imposed by the SSC Committee. These criteria inclUded geologic, hydrologic, and demographic considerations. The geologic considerations for this installation included uniformity of material and the ability to be excavated with rapid tunnel boring machines. Site groundwater hydrology considerations were mainly limited to low hydraulic transmissivity in and near the plane of the tunnel. Demographic considerations included proximi ty to a compl ete trans'portation network and other factors pertinent to a large, scientific installation. The site. in eastern Colorado was selected for its geologic attributes based on studies conducted by the Colorado Geological Survey with assistance from several other organizations. Information utilized in these studies was obtained from published geologic maps, and from oil and gas log information obtained through exploration conducted by private companies.


Geology The study area is composed of clastic sedimentary rocks, Cretaceous to Tertiary in age with some Quaternary sands and gravels in stream beds and eolian silts and clays overlying many of the formations. The formations of importance to this study include in ascending stratigraphic order, the Pierre Formation, the Fox Hills Formation, the Laramie Formation, and the Ogallala Formation shown in Figure 1. The Pierre Formation of Cretaceous age is the most important to be considered in this study. The Pierre Shale can be divided into three members. Each of these members, the Lower, Middle, and Upper Member were deposited in an extensive, shallow Cretaceous sea. These marine sediments display different energy regimes as shown by the variations in 1 i tho1 ogi es. The Up'per is composed predomi nant1y of claystones, silty claystones'and siltstones with minor amounts of limestone. The Middle Member is represented by a series of sandstone and siltstone layers interlayered with claystone and silty claystone. The Lower is composed principally of claystone. Overlying the Pierre Formation to the west is a sequence of sandstone, siltstone, and shale comprising what is commonly termed the Fox Hills-Pierre transition zone. This is aptly named as it represents the interface between marine and continental clastics. The Fox Hills Formation is a coarse grained delta front and beach deposit. The sandstones of the Fox Hills Formation are 5


Geologic Cross Section WOlf Fo" t cs : c u" -8OO

massive and form an important aquifer in various parts of Colorado. Overlying the Fox Hills Formation are claystones and siltstones of the Laramie Formation The study area itself is composed of an outcropping of Upper Member Pierre Formation from which the overlying Fox Hills and Laramie Formations have been eroded. The eastern portion of the study area is covered by sands and gravels of the fluvial Ogallala Formation which form an important aquifer in northeastern Colorado. Unconsolidated Quaternary age sediments including sand and gravel deposits mostly confined to stream beds are localized throughout the study area as are eolian deposits of silt and silty sand. The Pierre Formation is directly overlain in many areas of this study by up to one hundred feet of this wind-blown material The study area lies on the eastern flank of the Denver-Julesburg which is a prominent structural feature generally considered to extend from south central Colorado, into southern Wyoming. Beds on the east flank dip to the west at rather flat angles amounting to only afew tens of feet per .mi1e. There are some minor folds within the area and some minor growth faults have been reported. Jointing is prevalent within the weathered zone of the Upper Member of the Pierre Formation but is rare in the unweathered zone (Rogers, 1985).


CHAPTER II I LABORATORY TESTING Thirty-nine direct shear and eight indirect tensile tests were conducted in this program. These tests were utilized to identify characteristics in the silt-rich and silt-poor claystones as these characteristics pertain to strength anisotropies associated with the horizontal bedding planes. Fourteen of the core samples were carefully trimmed, measured, and wei ghed for densi ty determi nati on and water content according to standard laboratory procedures. The failure surfaces were examined to quantify the silt-clay ratio by-reproducing the compositional layers on gridded tracing paper. A sharp color contrast between the light-gray silt and the medium-to-dark gray clay facilitated this evaluation. Each surface was also examined under magnification. Thirteen samples were subjected to x-ray analysis by USGS investigators. Silt-clay ratios were also determined by USGS investigators using the hydrometer method for grain size di stribution. The s11 t-cl ay rati os obtai ned by USGS were based on


a larger sample than those obtained by failure surface examination and therefore are more appropriate to use for total sil t rather than the silt directly affecting sample strength. Direct Shear Testing The method of direct shear testing was selected for this project principally because'the material appears extremely anisotropic in strength. Due to the horizontal nature of the sedimentary bedding, the individual bedding planes are perpendicular to the core axis. The location of high angle joints in the project area was concentrated in the upper fi fty feet so joint contributions to strength anisotropy is minimal within the area of interest. This naturally leads to a of testing which addresses the condition of minimum strength. Since direct shear testing is satisfactory when utilized in soil strength evaluation it has been considered here due to the very weak nature of these rocks. This author is also aware of the difficulties encountered when stronger'rocks are direct shear tested with respect to data replication and the continued reliance on triaxial testing held by many investigators. Direct shear testing was performed on the sample core to assure that the individual laminae of silt and claystone could be tested without generating the antithetic failure planes which would be obtained in a triaxial test. 9


In order to conduct these it was necessary to modify the Wykeham-Farrance direct shear apparatus located at the University of Colorado at Denver. The direct shear testing apparatus required that a shear box be designed in which the slightly undersized NX core could be tested. In order to accomplish this, inserts were machined which could be placed in the shear box to hold the core vertically. Metal shims were used to assure that the core fit tightly into the adapted shear box an9 that the individual lamina could be oriented at the shear surface between the upper and lower shear box block. These individual silt laminae were selected by visual methods to assure that some silt-rich samples were tested. -Howeve-r, most of the samples were tested by random placement in the apparatus and evaluated for silt after testing. This would minimize any bias caused by a visual pre-test placement. 10 The normal force was supplied conventionally on a specially machined block to allow for the smaller sample diameter of approximately 1.8 inches. The range of applied normal force was selected to match existing overburden pressures from just below the surface to the plane-of the tunnel invert.


11 Determinations of normal stress and maximum shear stress are shown in Appendix B and the results of direct shear testing are listed below in Table 1. TABLE 1 Determination of Normal and Maximum Shear Stress Sample Water Dens.ity Sil t Normal Maximum Shear Number Content (%) (gm/ee) 0.!l. Stress (2si) Stress (psi) lA NO NO 13 48.0 124 2A NO NO 17 104.8 272 3A 15.9 NO 5 26.7 142 4A 15.9 NO 5 26.7 196 5A 15.9 NO 21 129.9 156 6A 15.7 NO 0 100.9 147 7A 17.1 NO 0 100.9 151 8A 15.0 NO 12 121.4 195 9A 17.5 "NO 10" 21.3 92 lOA 17.8 NO 10 209.6 230 llA 19.4 NO 5 104.8 225 12 14.4 NO 18 24.9 67 13 17.1 NO 20 24.9 98 14 17.0 NO 19 44.7 126 15 14.3 NO 34 62.6 149 16 14.3 NO 37 97.7 85 17 14.8 NO 45 97.7 171 18 15.7 NO 36 24.9 109


12 Determination of Normal and Maximum Shear Stress (Continued) Sample Water Densi ty Sil t Normal Maximum Shear Number Content (%) (gm/cc) Stress (Esi) Stress (Esi) 19 14.5 NO 50 44.7 177 20 14.5 NO 50 200 21 16.0 NO 13 97.7 140 22 17.0 NO 50 122.2 197 23 16.2 NO 38 24.9 91 24 16.0 NO 36 44.7 113 25 14.9 NO 29 62.6 167 26 15.3 NO 21 97.7 183 28 16.1 2.35 16 26.7 109 29 15.6 2.25 8 46.2 174 30 15.9 2.15 4 66.5 184 31 15.5 2.24 6 100.9 151 32 16.0 2.27 14 129.9 175 33 15.6 2.21 1 24.9 92 34 16.1 2.22 6 44.7 145 35 15.8 2.21 10 64.5 113 36 16.1 2.20 0 97.6 220 37 16.0 2.28 31 125.7 215 39 16.2 2.23 23 24.0 62 40 16.4 2.22 1 62.3 111 41 16.5 2.18 4 121.3 184


A statistical approach was employed with the data from Table even though the sample population was small and contained the added parameters of water content, dens.i ty, and percent sil t. A linear regression analysis was performed on the total sample field, and also on the individual holes. The results of this analysis are shown in Table 2. Correlation of Normal Stress and Maximum Shear Stress on Intact Rock 13 Hole r 159 Y Slope s Number of Samples No. 1 .48 No. 6 .58 No. 7 1.00 No.8.82 No. 10 .55 All Holes .65 62 69 83 90 74 138 119 173 176 152 109 30 91 370 510 73 510 128 280 98 Where: r = correlation coefficient x = Mean normal stress (psi) y = Mean shear stress '(psi) Y = Y intercept (psi) s = standard deviation (psi) 41 5 33 15 36 5 57 11 43 39 A plot of the data for the most sampled holes, 6 and 10, and from the total field are shown in Figure 2 and Figure 3.


FIGURE 2 Linear Regression Plot of Holes 6 and 10 0 LO 0 /// 0 / 0.. "-" 0 OJ / ..-4 -+-l V') Hole 6 10 OJ V') / 0 Hole 10 0 ",-..-4 a 50 100 150 200 250 Normal Stress (psi) ,',:-' FIGURE 3 Linear Regression Plot of All Hal es 0 LO 0 0 ..... 0.. OJ a LO -+-l ..-4 V') IO OJ V') 0 0 ..-4 a 50 100 150 200 250 Normal Stress (psi)


A linear regression analysis was also performed comparing silt content to maximum shear stress. The samples were grouped according to the normal stress such that for a given narrow range of normal stress, variations in shear stress could be evaluated with respect to si1tcontent. The results of this analysis are displayed in Table 3. TABLE 3 Linear Regression Analysis Comparing Silt Content to Maximum 'Shear Stress Stati sti cal 1 Stress Range (psi) Parameter 24-27 44-48 62-65 97-105 105 r -.45 -.73 +.61 -.26 +.09 s (psi) 40.8 24.0 37.6 53.0 27.0 x (psi) 107.3 136.4 148.0 174.5 .192.8 y (psi) 18.1 16.4 24.8 14.4 21.7 Y (psi) 33.7 66.8 -48.4 28.0 10.6 slope _8.3 -20.30 26.3 _4.5 3.30 Number of Samples 10 6 5 10 7 15


16 The data listed in Table 3 show a correlation in the 44-48 psi normal load category between reduction in shear strength and silt content. The 24-27 psi and 97-105 psi ranges show limited correlation. The 62-65 psi range show a correlation between increased shear strength and an increase in silt content. The load range greater than 105 psi shows no correlation. The 44-48 psi and the 62-65 psi data are shown in figure 4. +-J ...rFIGURE 4 Linear Regression P1ot"of 44-48 and 62-65 psi Normal Stress Maximum Shear Stress vs Silt Content, Intact Rock Maximum Shear Stress (psi) 0 50 100 150 20 250 +-J 20 62-65 44-48 s:::: s... a... 40 \


A post peak shear strength was determined by allowing continued shearing of the failed sample in the shear test apparatus. The lowest value shown by the stress ring was then taken as the post peak shear strength. Difficulties with respect to the recognition of residual stress in Pierre Formation testing by previous investigators (Fleming, 1970) led to this modified approach. The values obtained do not represent the residual strength. More acceptable values would have very flat friction angles (Nichols, 1983). However, the fact that each sample was tested in the same manner with approximately the same travel distance lends some credibility to this testing procedure. The results of this modified residual shear strength testing are listed in Appendix B. 17 Normal loads were not sufficient to cause any observable shearing of the asperities on the failure plane. The shear displacement was also insufficient to abrade noticeable quantities of clay material but silty detritus was present. The failure surfaces consist of a combination of undulations and asperities which make calculation of an asperity angle extremely difficult. If it were possible to calculate this angle, determination of an internal angle of friction on the failure surface could be approximated by assuming that the normal load range is below the asperity shearing normal load value in the bilinear plot proposed by Patton (Goodman, 1980). Consideration was given to the calculation of this angle by noting the magnitude of the shear


18 displacement as taken from the position of maximum shear strength of the intact rock to the position relating to the particular post. peak shear strength. This horizontal displacement could then be compared to the vertical displacement of the normal load platen. This method proved inappropriate because accurate measurement of the vertical displacement was questionable. The hor;'zontal measurement from the point of failure of the intact rock was also questionable due to the violence of the failure. The statistical application utilized in maximum shear stress was also employed for this modified residual stress. The results of these studies indicate the expected good correlation between residual stress and normal stress (r = .92). Comparisons were also drawn between residual stress and silt content within the five categories of normal stress. The results of these studies are shown in Table 4. TABLE 4 Linear Regression Analysis Comparing Silt Content to Post Peak Shear Stress. Stat; sti cal Normal Stress Range (psi) Parameter 24-27 44-48 62-65 9T-105 105 r -.51 -.79 -.60 -.04 -.26 s (psi) 13.8 19.5 13.4 17 .3 l6.9 x (psi) 53 70 81 109 120


Linear Regression Analysis Comparing Silt Content to Post Peak Shear Stress (Continued) Statistical Normal Stress Range (psi) Parameter 24-27 44-48 62-65 97-105 105 y (psi) 17.2 22.0 24.8 15.3 22 Y (psi) 41.9 71. 7 95.1 19.1 52.6 Number of Samples 10 6 5 7 6 Indirect Tensile Testing Indirect tensile testing employed flexure testing for modulus of rupture to determine tensile strength. Because the is horizontal, the individual silt laminae are perpendicular to the core axis and parallel to the imposed force. This represents what is suspected to be a weak orientation which would lead to failure along the weakest plane. The failure plane was evaluated for silt-clay ratio. Knife edges fabricated to fit the core were placed at the one-third positions of the sample. Vertical force was applied by means of a manually turned screw seated against a platen in series with a calibrated stress ring. Stress in the extreme fibre designated as Tmr was calculated by: Where: Tmr = p = L = d = Tmr = 16 PL modulus of rupture (psi) (Goodman, 1980) applied maximum load at failure bs. ) sample length between the load reactions the lower surface (in.) sample diameter (in.) on 19


20 The results of this testing are displayed in Table S. TABLE 5 Modulus of Rupture Sample Hole Depth Load Length Diameter Percent Tmr Number Number (ft.) bs. ) (i n. ) (in.) Silt Rl 10 114.0 2.6 5.13 1.81 0 3.8 R2 10 114.5 8.6 5.13 1 .81 0 12.6 R3 6 151.6 5.8 4.75 1.81 24 7.9 R4 6 152.0 5.4 6.38 1.81 10 9.8 R5 10 251.5 .9.6 6.00 1.81 81 16.5 R6 10 252.0 11.5 5.00 1.81 79 16.4 30 1 102.7 1.9 4.88 1. 75 0 0.6 33 8 158.0 1.5 4.88 1. 75 5 0.5 These results suggest that there may be a correlation with respect to silt and reduction in tensile strength within an'individua1 hole at a certain depth. Deeper test samples, however, within the same hole are stronger than the shallow samples even though possessing higher silt content. The value Tmr relating to tensile strength is two to three times greater than the value obtained by direct testing methods (Goodman, 1980). Because the failure takes place in the weak pl anes perpendi cu1 ar to the core axi,s, Tmr values are one-tenth of the values obtained by the Brazilian method on core from the same holes (Amadei, 1986).


Clay Mineralogy Determinations Thirteen samples from hole SSC-7 and SSC-10 were analyzed by x-ray methods for clay mineralogy by USGS. The general procedure for x-ray determinations include the separation of the sample into size fractions and disaggregation. This is accomplished by means of Stoke's law and by centrifugation for specific time periods. Samples are ethylene.glycolated to affect the swelling. The glycolation facilitates the identification of smectites from other clays. These are then x-rayed from oriented mounts which emphasize the peak obtained from the basal 001 face. Peaks are then compared with known peaks to identify and quantify the particular clay mineral suite. The results from the x-ray analysis (Brownfield, personal communication, 1986) show the clay types as a percentage of the 21 total clay and the total clay as a percent of the sample. The mixed layer smectite-illite in samples 50, 51 and 53 which were taken in close proximity show consistency. The smectite percent as indicated in table 6 suggests that, on the average, swelling clays represent 20% of the material in the vicinity of holes SSC-7 and SSC-10.


22 TABLE 6 Clay Percentages by X-ray Analysis Mixed Layer 5ample Hole Mixed Layer Chlorite Total Depth Number Number 5mectite III ite III i te Kaolinite (ft.) 50 55C-1O 20 45 21 14 78 95.7 51 55C-10 "40 17 25 18 73 95".7 52 55C-10 28 34 20 18 84 106.4 53 55C-10 24 41 18 17 80 99.9 54 55C-10 35 23 21 21 87 115.0 55 5SC-10 29 30 22 19 27 144.5 56 55C-10 18 47 20 15 64 195.0 57 S5C-10 26 51 9 14 74 61.9 58 55C-10 27 40 16 17 34 28.0 59 5SC-7 38 9 29 25 60 277 .4 60 55C-7 25 55 9 11 58 201.0 61 55C-7 35 45 10 11 30 14.0 62 55C-7. 41 16 23 20 73 24.4 Average 30 35 19 17 63 The non-clay fraction is represented by a suite of minerals shown as percent of the total in Table 7. The total non-cl ay fracti on is shown as the percentage of the total sampl e."


23 TABLE 7 Non-Clay Percentages by X-ray Analysis Sample Depth Total Number Quartz Plagioclase K-spar Dolomite Calcite (ft) Non-clay 50 50 20 10 20 95.7 22 51 59 15 11 15 T 95.7 27 52 50 10 10 30 106.4 16 53 50 10 10 30 99.9 20 54 54 8 8 24 115.0 13 55 60 15 10 15 T 144.5 73 56 50 15 5 30 195.0 36 57 50 10 10 20 8 61.9 26 58 50 20 10 20 28.0 66 59 55 11 7 33 4 277.4 40 60 52 15 5 30 -201 .0 42 61 60 15 10 10 14.0 70 62 10 7 20 24.4 27 Average 54 13 9 23 37 The quartz and feldspar percentages are in the expected range, however, the dolomite is higher than expected. Mica and gypsum were identified in trace amounts. More abundant quantities of gypsum were located in the near surface environment and have probably been concentrated along joints.


CHAPTER IV FIELD TESTING Five test holes were drilled in the Pierre Formation at the proposed SSC These holes were spaced several miles apart along the western one-half of what would be the surface trace of the tunnel path. The objective of this drilling waS to gain information regarding the geologic and engineering properties of this proposed site. The holes were drilled with ,6 1/2 inch hollow stem auger through the soil horizons and into the weathered zone. The augering depth was controlled by a predetermination that coring would begin at fifty blpw-count material utilizing the standard falling hammer penetration test. The augers were left in the hole throughout the testing and the core drilling and removed immediately prior to hole reclamation. Standard penetration tests utilizing a California split spoon sampler were taken at five foot intervals and twenty pound grab samples were taken from the cuttings during each five foot interval. The soil samples and penetration tests were logged for each hole. Core drilling with a 3 1/8 inch diameter bit proceeded from the bottom of the auger hole to twenty-five feet below the plane of the tunnel invert. A geologic log was compiled


25 immediately upon retrieval of the 1 7/8 inch NX core from the wireline core barrel. This log included a geologic evaluation for rock type, joints, and faults and a visual examination for silt content. The core was also tested with dilute hydrochloric acid for calcium carbonate. Rock quality data using the Rock Quality Designation (RQD) was also compiled for all core recovered. The core was protected against dessication immediately following the logging and stored until testing at a humidity controlled facility. Each of the holes was probed with a suite of geophysical devices following completion to total depth. The results from the geophysical probing were used for lithology correlation and to evaluate index properties for engineering design studies. Hole SSC-7 was tested by in situ stress methods with a dilatometer. Borehole Geophysics Borehole geophysical studies were conducted in each drill hole to evaluate geologic and engineering parameters. The most useful tests from an engineering standpoint are discussed below. Those most useful for geologic interpretation but of possible engineering use are discussed in Appendix D. Sonic Velocity Sonic velocity was determined in hole SSC-7 from the bottom of the hole at 314 feet to the bottom of the hollow stem at 12 feet. The velocities ranged from 6757 feet per second to 7353 feet per second within the claystone and silty claystone. From


26 these velocity studies it is possible to determine important engineering parameters of dynamic Young's modulus and Poisson's ratio. The equations are shown in Appendix C. The results of the sonic studies are shown in Table 8 taken at specific depths within the hole. TABLE 8 Sonic Velocity Young's Oepth Oensity Velocity Modulus Poisson's (ft.) 9,!!!/cc (fps) (psi) Ratio 14.0 2.05 NO NO NO 24.4 .00 NO NO NO 182.9 2.15 6849 1.07x10 6 .28 183.0 2.15 6849 1.07x10 6 .28 183.2 2.1.5 6849 1. 07x1 0 6 .28 201.0 2.20 6944 1.13x10 6 .28 265.0 2.20 7692 1. 38x1 0 6 .28 276.3 2.18 7353 1.24x10 6 .28 The sonic probe utilized in this study is constructed wlth a transmitter isolated from two receivers. by a 2 foot rubber connector. This assures that transmitted frequencies do not short circuit through the tool to the receivers but travel through the surrounding r6ck. The first receiver is positioned 3 from the transmitter and the second receiver is 4 feet from the


27 transmitter. The difference in the arrival times is then a function of the receiver spacing and the rock properties. The arriving signals can be observed on an oscilloscope and on the log printout of sonic transit time and wave amplitude. Both the pressure wave and the shear wave velocities are for the calculation of dynamic Young's modulus and Poisson's ratio. However, the shear wave arrival is difficult to differentiate from the pressure wave arrival (McCain, 1984). One test was successfully conducted by USGS utilizing ultrasonic pulse measuring apparatus (Swo1fs, personal communication, 1986). The results of this test yielded a pressure \ wave velocity of 6017 fps and a shear wave velocity of 3349 fps. This yields Vp = 1.8 Vs' This ratio was used to approximate the velocity of the shear wave which is not obtainable from the sonic log. Dynamic tests for Young's modulus usually produce higher results than those obtained utilizing static tests. This is a result of strain levels. The static tests yield strain levels measured in percent while the dynamic tests yield strain levels measured in parts per million. Ultrasonic tests yield different results from either static tests or from dynamic low frequency tests. These ultrasonic tests are performed at very high frequencies.


Gamma-Gamma Density Gamma-gamma density logs were run on all holes within the program. Formation density can be obtained accurately from this technique so long as proper corrections are made. The gamma tool utilizes a radioactive material which can bombard the area around the probe with gamma rays generated by an Americium 241 source. These gamma rays interact with electrons, are scattered, and are then detected by scinti11 ometry. The degree of is a function of the electron density of the formation (McCain, 1980). Counts per second are read directly from the log and converted to density from a logarithmic calibration curve. The results of gamma-gamma density studies yield a range of values from 2.22 gm/cc at 319 feet to 1.87 gm/cc at 22 feet with an average of approximately 2.18 gm/cc. Limestone lenses within the study area are displayed very well on the density logs. Neutron Logging 28 Neutron logging was conducted in all holes. Fast moving neutrons generated from cesium 137 bombard the formation losing energy with each collision. The energy loss is maximized by collisions with hydrogen atoms. When the neutron has reached a slow enough velocity it is captured by the nucleus of an atom with the consequent release of gannna radiation. The emitted gamma is measured by a detector in the down hole probe. Because hydrogen is most effective in dissipating the neutron energy, liquid filled pore spaces cause the primary responses. The tool is calibrated


in apparent 1 imestone porosity all owing the count per second direct reading to be correlated to the percent porosities located at the bottom of the log sheet. Values of porosity in hole SSC-7 range from approximately 50% at 21 feet in the eolian material to 25% at 266 feet in the claystone. In Situ Pressure Meter Testing 29 A dilatometer Probex-l was used in hole SSC-7 to determine in situ stress parameters and moduli. Dilatometers became available in 1966 (Dixon, 1970) and have been used considerably in foundation design in stiff soils (Davidson, 1986). An expandable cylinder is pressurized against the borehole wall at the depth to be tested. This pressuring is done with a hand .operated hydraulic pump. The volume change is measured with a displacement transducer, a linear variable differential transformer (lVDT), and plotted verses pressure The following terminology is used in the example curve shown in Figure 5 and with the results listed in Table 9 (Woodward-Clyde Consultants, personal communication, 1986). aho = In situ horizontal total stress Po from test curve ahO (Tv Ko Po Pc = Pore pressure Effective horizontal stress = Effective vertical stress = Coefficient of lateral earth pressure = Seating pressure, beginning of the elastic range = Creep pressure, end of-the elastic stress range


OJ en t: ...c:::: OJ o P f = Yield pressure PL = Limit pressure OCR = Over consolidation ratio El = Elastic modulus E2 = Reload modulus S = Undrained Shear Strength, based on E2 value C = Cohesion = Internal friction angle FIGURE 5 Example Curve for Dilatometer Response (Dixon, 1970) Elastic Behavior Reload Cell Pressure Plastic Behavior --/ / / 30


31 TABLE 9 In Situ Pressure Meter Results {Woodward-Clyde Consul tants, 1986}. Depth (ft) Parameter 200 210 274 293 O'ho (psi) 187 195 225 243 u (psi) 81 86 113 122 O'ho {psi} 106 109 112 121 (psi) 100 105 136 145 -Ko (psi) 1.05 1.03 0.82 0.84 Pc {psi} 502 513 285 583 P f (psi) 973 1074 1388 1250 PL (psi) 2153 2181 2777 2500 OCR (psi) 4.0 3.9 4.2 3.5 El (l04 psi ) 7.63 6.45 8.09 6.05 E2 (l05psi) 3.27 3.05 2.77 3.12 S (psi) 300 308 385 350 C (psi) 275 160 degrees 35 35


32 SUMMARY As set forth in the introduction there have been two main focuses to this study. The first has been to further the understanding of strength properties in material which is intermediate in strength between soil and rock and specifically to ascertain the effects of silt content on claystone strength. The second aim of this study has been to use borehole geophysics for the characterization of this site and to determine the applicability of downhole logging to the identification and solution of engineering problems. LABORATORY TESTING Direct Shear Testing The data obtained by shear testing shows considerable scatter. Plots of normal stress versus maximum shear stress were drawn using linear regression functions. The results of this analysis yielded the line shown in Figure 2 which is a "best fit" line within the data points. The standard deviation of S = 43 is a measure of dispersion around the mean. The correlation coefficient describes how well the data fits a straight line. The correlation coefficient for the total sample is .'65. This indicates that there is a correlation between normal stress and shear stress but it does not indicate a particularly good correlation. The slope of the calculator generated line represents the angle of internal friction. The y-intercept


represents the cohesive strength or more appropriately, the shear strength intercept. For the total sample field the angle of internal friction is 36 and the cohesive strength is 98 psi. 33 Because the holes are far apart each hole was individually analyzed. The most scatter was associated with SSC-l where r = .48, and the best linearity was associated with SSC-7, r = 1.00. The average shear stresses for each hole and for all holes are less than 200 psi. These results when applied through standard soils engineering equations in Mohr Coulomb failure criterion yield results similar to those obtained by other investigators (Nichols, 1983, Amadei, 1986). A linear regression analysis was also performed comparing maximum shear stress to silt content. The normal _stress ranges were grouped as shown in Table 3 to determine if shear stress is a function of silt content. The analysis showed that there is no direct and simple correlation. In the low normal stress ranges (24-48 psi) increased silt in the plane of failure caused the sample to fail at a lower shear stress level. The same is true for the 97-105 psi range. The correlation coefficients for the three pressure ranges are -.45, -.73 and -.26 with increasing normal load. The intermediate range (62-65 psi) is correlative but opposite in sense to the previously discussed ranges. The 61-65 psi range with a correlation coefficient of .61 suggests that silt on the fracture plane increases shear strength. The


normal load range greater than 105 psi showed no correlation whatsoever. The correlation coefficient for this range was .09. Residual shear strength, more appropriately called a "post peak" shear strength was determined by continued travel of the shear box block after failure. The results when subjected to the same linear regression analysis as the maximum shear stress show considerably more uniform correlation. The normal pressure ranges of 24-65 psi and the range greater than 105 psi show a decrease in shear strength with increase in silt content. The 97-105 psi range shows no correlation. If these tests were conducted under higher normal loads and were repositioned and repeated a number of times a much lower set of values would have been obtained as more of the asperities would have been obliterated. Indirect Tensile Testing The beam method of indirect tensile testing was employed instead of the Brazilian method because failure in any plane except the horizontal bedding would produce artificially high tensile strengths. The results of this testing as shown in Table 5 indicate that a correlation may exist between increased silt content and a reduction in tensile strength. In order to derive this conclusion each hole and each location within a given hole should be examined individually. Samples Rl and R2 in hole SSC-10 were taken from 114.0 and 114.5 feet. Both have no silt on the failure planes. The range in strength varies by a factor of three


35 and the low value is weaker than siltier samples taken at a depth of 251 feet. The reason that there is such a diversity may be due to lithologic parameters. The densities at 114 feet and 251 feet are 2.00 gm/cc and 2.20 gm/cc respectively. The porosities are 43% at 114 feet and 34% at 251 feet. These differences in rock properties may contribute to the greater strength at the deeper 1 ocati on. FIELD TESTING Borehole Geophysics Sonic Velocity Sonic velocities were determined in hole SSC-7 and range between 6757 feet per second to 7353 feet per second for the compressional wave. These a Young's modulus of 1 x 106 psi and Poisson's ratio of .28. The USGS laboratory analyzed one sample from 265 feet in hole SSC-7 by ultrasound methods and obtained a P-wave velocity of 6017 fps and an S-wave velocity of 3349 fps. These yield a Young's modulus of 8.2 x 105 psi and a Poisson's ratio of .28. The difference. in modulus can be attributed to the large difference in,ve10city of approximate1yVp = 900 fps attained by the borehole method over that obtained by the ultrasound method. Either of these methods can be used so long as the investigator does.not use the methods interchangeably without a correction factor.


36 Gamma -Gamma Density Density determinations from the log appear to be extremely accurate and compare very well with densities calculated by USGS investigators (Collins, personal communication, 1986). The USGS used the buoyancy method in the field on samples as they were retrieved from the core barrel. This investigator trimmed samples into right circular cylinders, averaged several length measurements and diameter measurements and then weighed the samples. A comparison between log determined density and volume determined density showed the latter to be overestimated by two percent. Neutron Logging Porosity values appear to range around 30 percent which is the expected value for the Pierre Shale. An interesting relationship can be obtained by utilizing the values obtained through borehole logging and applying them to phase equations. The results can be-a check on log accuracy. For example: SSC-7 at 227.4 ft. from the porosity log since e _1_ l-n from the x-ray scan n = 33% e .49 specific gravity-of the solids G = 2.9 Find the water content w assuming S 90% 100% (Braddock, 1979) The average w for samples taken from SSC-7 is w = Se G w = 15.2 to 16.9% w = 16.3%


Miscellaneous Logging The suite of logs listed in Appendix D were useful in locating gross lithologic changes such as the thin limestone lenses encountered in the drilling. They might also be used to identify the siltstones and the claystones but identification of the thin laminae of silt or the gradational silty claystones and clayey siltstones is speculative. Therefore using these logs for predicting engineering parameters within the silty claystones would be impractical In Situ Pressure Meter Testing Results obtained with the dilatometer give a Young's modulus of 7.6 x 10 pSi, a shear strength of 159 psi to 275 psi, and an angle of internal friction of 35. The shear strength intercept and the friction angle are similar to those obtained by other methods but the modulus is considerably lower. Laboratory and field generated data are listed in Table 10. TABLE 10 Comparison of Data Obtained by Different Testing Methods Mean" Shear 37 Strength Intercept Range Angle Method Investigator (Esi) (Est) (degrees) Direct Shear Davis 98 32-128 28-37 Triaxial Amadei, 1986 200 100-240 13-32 Dilatometer Woodward-Clyde 159-275 30-35 Consultants


CONCLUSIONS The objectives of this work included the gaining of knowledge within the unique field of soft claystones, the effects of silt on claystone strength, and the application, of borehole geophysics to these studies. The conclusions to this work are listed below. 1. The soft claystones show extremely low shear strength valves parallel to bedding planes and low tensile strength valves perpendicular to bedding planes. 2. These laminated claystones have distinct strength anisotropies which are sensitive to the type of laboratory testing and to the orientation of samples within the testing apparatus. 3. Mean cohesive strengths obtained by three different methods of testing show considerable variation. The potential significance of this variation becomes apparent during the calculation of safety factors for slope stability. It is suggested that consideration be given to the proper selection of a cohesive strength depending on the respective orientations of the assumed failure plane and the bedding planes. 4. Silt has a minor weakening affect on claystone shear strength, and no consistently observed affect on tensile strength. This is enigmatic in that silt has no demonstratable cohesion and


might be considered to have a higher angle of internal friction than an assemblage of clay minerals. 39 The main reason proposed by this investigator is that no water has flowed through the silt partings with enough volume to alter, transpose, or dissolve the interstitial cementing material. This is suggested because none of the silt appears friable. It is likely that the silt and the clay are codepositional and that no matter how silty a particular laminae appears, there may be enough clay to offer some cohesion. Another alternative which could be confirmed by thin section petrographic studies would be authigenic dolomitization due to preferential fluid invasion of the silts. The large percentages of dolomite in the rock as determined by x-ray have not been explained. 5. The borehole geophysical techniques of neutron logging, gamma-gamma density, and sonic logging and the down-hole pressure meter testing obtain valuable information for the engineer. Other borehole geophysical information is helpful in the determination of gross lithologic sequences for geologic correlations, but of limited use for the identification of engineering parameters.


BIBLIOGRAPHY Amadei, B., 1986, Geotechnical Characterization Colorado SSC Project: Unpublished report. Braddock, William A. and Machette, Michael, 1974, Experimental Deformation of Pierre Shale, [abs]: Eos(American Geophysical Union Trans.) v. 55, no. 4, p. 420. Davidson, Richard R. and Bodine, Daniel G., 1986, Analysis and Verification of Louisiana Pile Foundation Design Based on Pressure Meter Results; The Pressure Meter and its Marine Applications: Second International Symposium, ASTM STP 950, J.L. Briand and.J.M.E. Audibert, Eds., American Society for Testing and Materials. Dixon, S.J., Pressure Meter Testing of Soft Bedrock; Determination of the In Situ Modulus of Deformation of Rock: American Society for Testing and Materials, ASTM STP 477. Fleming, R.W., Spencer, G.S. and Banks, D.C., 1970, Empirical Study of Behavior of Clay Shale Slopes: U.s. Army Engineer Nuclear Cratering Group, NCG Technical Report No. 15, Livermore, CA. Goodman, R.E., 1980, Introduction to Rock Mechanics: John Wiley and Sons. Hoffman, G. L., Jordan, G.R., and Wallis, G.R., 1982, Geophysical Borehole Logging Handbook for Coal Exploration: The Coal Mining Research Center, Edmonton, Alberta, Canada. McCain, R.C., 1984, Applications of Geophysical Well Logs in Geotechnical Engineering: Master of Science Thesis, University of Colorado, Boulder, CO.


41 Nichols, T.C. Jr., Collins, D.S. and Davidson, R.R., 1986, In situ and laboratory geotechnical tests of the Pierre Shale near Hayes, South Dakota --A characterization of engineering behavior: Canadian Geotechnical Journal 23. Rogers, William P., Kirkham, Robert M., Collins, Donna B., and Crouch, K., 1985, Suitability of the Pierre Shale in eastern Colorado as a tunneled bedrock site for the SSC research facility: Unpublished Colorado Geological Survey report. Sch1umberger, 1972, Log Interpretation, Volume I Principles: Schlumberger Limited, 277 Park Avenue, New York. Seigel, Harold 0.,1967, The Induced Polarization Method; Mining and Groundwater Geophysics: Economic Geology Report No. 26.


20 % NA -NA o. 00 -APPENDIX A Adams 158' M.Davis Light brown silty sand Light to medium brown silty sand Some clay at 14' Medium to dark brown, silty sandy clay NA Medium dark gray clay 42 No silt, no reaction to RCL Very wet, difficult recovery 100 Medium to dark gray claystone, Machine induced fractures 100 --Medium to dark gray claystone No joints or fractures No reaction to RCL 100 Medium to dark gray claystone No joints or fractures


1 2 70 % 100 Medium to dark gray claystone minor silt, 100 --no fractures or joints machine fractures Medium. to dark gray silty claystone no joints or fractures some horizontal vugs, slight fissility 80 ---90 100 110 -120 130 100 Medium dark gray silty claystone some fissility 1" pyrite nodules at 82.5' machine fractures 100 dark gray claystone no natural frac.tures 100 dark gray claystone no natural fractures 100 no reaction to HCL dark gray claystone minor silt 100 Medium gray silty claystone to clayey siltstone possible natural joint or fradUre 60 to core axis


% 1 100 Medium gray silty claystone 140 --150 --160 TD 159' -100 100 l' limestone bed 133' to 135' medium to dark gray silty-claystone no fractures or joints no reaction to HCL medium to dark gray silty claystone machine induced fractures 44 3


GWF --: -/ 20 / 30 -; ---40 --50 NA NA 90 45 Light Brown Clayey Silt Top of weathered zone, silty clay Light to medium brown silty clay Many thin gypsum beds 1/4" in weathered zone Light to medium brown silty clay 1.5' limestone bed 26.5'-28' Light to medium brown silty clay very weak in tension 90 31-31.5 0.5' limestone bed 100 100 at 34' changes from brown to medium to dark gra). claystone, no gypsum beds Medium to dark gray claystone no joints or fractures Medium to dark gray claystone Minor silt bands 0.2' limestone bed 55.0-55.2 0.5' limestone bed 55.5-56.0


46 2 60 70 80 90 100 110 100 100 -100 --lOO -Medium to dark gray claystone minor silt no joints or fractures Medium to dark gray claystone minor silt 76.7-80' not wrapped Medium gray silty claystone no joints or fractures Medium gray silty claystone Possible horizontal fracture upper contact of limestone bed Medium gray silty shale No natural fractures 100 Medium gray silty shale No joints or fractures 100 Medium gray silty shaley claystone -no reaction toHCL


130 100 140 100 -150 100 160 100 170 100 180 TD 180' 6 Medium gray silty claystone some fissility 143.5-144' limestone medium gray silty claystone Medium gray silty claystone to clayey 'siltstone 3 Thin limestone in core but may be location for recovery problem No faults or fractures Medium to dark gray silty' claystone 176.4'-176.7' Limestone bed Light to medium gray silty limey claystone


7 270 -277 .4 280 -286.8 290 100 medium to dark gray claystone minor silt 100 100 no fracutes medium gray silty claystone no reaction to HCL medium gray silty claystone no fractures 3.0' limestone at 294.5' 5 may be suitable for testing (flagged) 300 ---100 medium gray silty claystone -no faults or fractures 307 medium gray silty claystone 310 100 slight reaction to HCL -medium gray silty claystone 320 100 no faults or fractures -+----+----1 TD 325'


49 7 4 200 100 200.7 medium gray silty claystone -no reaction to HCL -207.7 no fractures 210 100 -light to medium gray silty claystone NA 220 lost penetration rate and cutting indicate. -no charige in geology for lost interval -100 230 100 Limey zone 231' -medium gray claystone -no faults, fractures 238.1 240 100 light to medium gray silty"" claystone slight fissility no fractures 247.9 250 lUU medium gray claystone minor silt --"no reaction to HCL 257.3 260 light to medium gray claystone -no faults 267.3 270


131. 7 140 141.4 150 151 160 160.8 170 172 180 181.6 190 19L2 100 --100 100 --100 --100 100 100 50 7 3 dark gray claystone minor silt no fractures no reaction to Het dark gray claystone minor silt Light gray silty claystone to clayey siltstqne 150'-157' slight reaction to HCL medium to dark gr.ay silty claystone slight reaction to HCL thin liinestone 169' pqssible core loss medium to dark gray silty claystone no fractures, no reaction to HCL machine fractures dark gray claystone no fractures medium to dark. gray claystone minor silt


51 7 2 % 100 :lledium to dark gray claystone no fractures some fissility 70 100 medium to dark gray claystone -74.4 minor silt 80 100 medium to dark gray claystone 84 -minor silt 90 -100 dark gray claystone 93.5minor silt -some fissility 100 102laC dark gray claystone faults or fractures no 110 100 dark gray claystone 111.8 no fractures 1" limey zone @ 111.5' & 112' 120 121.4 100 dark gray claystone core diameter 1.8" ---


52 7 Arapahoe 4/8/86 nv. 4920' 4/14/86 325' M. Davis % 50 Light brown silty claystone gypsum l' limestone at l' Light brown silty claystone gypsum coated fracture 45 to core many machine induced fractures _______ --26' medium to dark gray 22' lost bands of dark gray and medium claystone many machine fractures 100 horizo.ntal fissures in brown have gypsum crystals -36.8' 37' medium gray no fissures 40 100. medium gray claystone no faults or fractures 45.9'_0 50 100 medium gray claystone no reaction to ReL 55' --


53 8 Adam: 3/13/86 3/18/86 4730 210' M. Davi NA Dry light brown sil::: .' sand sand Light brown silty 10 NA Light brown silty cl.?.yey sand -Light brown clayey gravel GWT 20 0 NA 0 0 Light to medium :. clayey gravel (1" ) --" 0 30 100 Medium dark gray .clc"stone many machine frac tUi:: s Auger to 35' -40 100 -. Medium gray silty cl.?.ystone -No faults or fractu:::: .!s 50 100


54 8 2 60 100 Medium gray claystone -Minor silt -No fractures 70 100 Medium gray claystone Minor silt no fractures 80 100 0.5' limestone bed 82'-82.5' -Medium gray claystone --Minor silt 90 100 -Medium gray claystone' -no joints, no fractures minor silt 100 100 Medium gray claystone ----Some silt 110 -lOU Medium gray silty claystone No fractures --No reaction to HCL 120 -lUU -Light to medium gray silty claystone -light gray banding -No reaction to HCL 130


55 8 3 100 -Medium ;ray silty claystone -No fra : :ures 140. -100 Medium .ray silty claystone -150 100 Medium dark gray claystone 160 -100 Medium silty claystone };r9-Y --No frac.:ures -170 100 Light to medium gray silty claystone No fractures 180 100 Light tu medium gray silty claystone --Carbonj_'::ed plant remains 186' -No frac.:ures or joints 190 100 -Light to medium gray silty claystone 1 limf"stone bed 198'-199' 2.'JO I--


56 8 4 --200 100 Medium gray silty claystone slight reaction to HCL, -no faults or fractures 210 TD 210' -


10 Adams 3/5/86 ROD NA 3/12/86 4750' M.Davis Weathered Zone, brown to dark brown silty clay, minor gypsum, dry 10 Moist light brown to brown silty clay, thin arkosic silty sand, clay contact in liner 19' encounted stiff drilling 20 ... __-_-+----+l--m-e-d'l., u-m--d'a-r-;k--g-r-a-y--c'l;-a-y-s-=t--o-n-e-,--m'"';i-n-o-r--s"":-i'l-=t---------f 100 Some machine induced fractures Medium dark gray to dark gray silty claystone 100 --no natural fractures 100 Medium dark gray to dark gray claystone 0.5' bentonite bed 44' slight reaction to HCL 100 -60 -Medium dark gray claystone No joints or fractures


58 10 70 80 90 100 110 120 l30 % -100 100 91...,. 100 medium gray claystone no bedding no joints or fractures 0.01' light gray material reactive to HCL medium gray claystone minor silt, fossil fragments and worm bores minor fissility 0.5' limestone at 84' 100 several 0.01' bentonite beds medium gray claystone some limey zones 100! minor fault at 106.5' dip 55 medium gray silty claystone some fossil shards 100 light to medium gray claystone minor silt 100 medium gray shaley claystone no joints at faults machine induced fractures


59 10 3 100 Q -Medium to dark gray claystone -Fossils, minor silt Slight' reaction to RCL 140 100 Medium to dark gray claystone --No faults or fractu!'es 150 100 Medium to dark gray claystone -0.4' limestone 153' --Mino!' silt 160 100 Medium to dark gray claystone -Minor silt -Worm 'bores No fractures 170. 100 Medium to dark gray claystone Minor silt -No reaction to RCL 180 100 0.5' limestone bed Medium dark gray claystone -Minor silt no faults or joints 190 100 Medium gray shaley claystone minor silt No faults 200 -


10 210 220 230 240 250 260 270 -100 Medium gray shaley claystone Minor s-ilt ; No faults or fractures -100 Medium gray shaley claystone Minor no No reaction to HCL 100 Dark gray claystorie Minor silt, no fractures 100 Medium gray silty claystone some light gray banding 100 l' limestone 242' vug in limestone 100 Medium dark gray silty claystone to clayey siltstone -No reaction to HCL 100 Medium to dark gray silty claystone No joints or fractures 60


61 10 5 % 270 100 3 'Limestone Medium dark gray silty claystone -TD 277' -


APPENDIX B Sample Location and Description Sample Hole Depth Geologic Number Number feet Description lA 10 112.5 silty claystone 2A 10 112.9 si1 ty cl aystone 3A 10 113.3 sil ty cl ayston.e 4A 10 114.5 silty claystone SA 10 110.0 si1 ty cl aystone 6A 10 110.3 claystone 7A 10 110.5 claystone 8A 10 111 .0 claystone, minor silt 9A 10. 114.S claystone, minor silt lOA 10 114.8 claystone, minor silt llA 10 115.0 claystone 12 6 155.6 sil ty c1 aystone 13 6 155.8 sil ty cl aystone 14 6 156.0 clayey siltstone 15 6 156.2 clayey siltstone 16 6 156.4 clayey siltstone 17 6 156.6 clayey siltstone 18 6 147.6 clayey siltstone 19 6 147.8 clayey siltstone


63 Sample and Description (Continued) Sample Hole Depth Geologic Number Number feet Description 20 6 148.0 clayey siltstone 21 6 148.3 silty claystone 22 6 148.6 clayey siltstone 23 6 146.2 clayey siltstone 24 6 146.4 clayey siltstone 25 6 146.6' clayey siltstone 26 6 146.8 silty claystone 28 1 103.0 s11 ty c1 aystone 29 1 103.1 silty claystone 30 1 102.7 claystone 31 1 102.8 claystone 32 1 1.02.9 sil ty c1 aystone 33 8 158.0 claystone 34 8 157.9 cl aystone 35 8 157.8 silty c1 ays tone 36 8 157.7 claystone 37 8 157.6 sil ty c1 aystone 39 7 182.9 si1 ty cl aystone 40 7 183.0 claystone 41 7 183.2 claystone


64 Shear Testing Determination of Normal Stress Moment Equation: Machine load X 9.8125 = Normal load. Normal load= Normal stress Area Sample Diameter Area Normal Load Normal Stress Number ( in. ) (59. in.) (1 bs. ) ) lA 1.719 2.32 111.3 48.0 2A 1.719 2.32 243.2 104.8 3A 1.719 2.32 61.9 26.7 4A 1.719 2.32 61.9 26.7 5A 1.750 2.41 313.0 129.9 6A 1.750 2.41 243.2 100.9 7A 1.750 2.41 243.2 100.9 8A 1.750 2.41 292.5 121.4 9A 1.719 2.32 49.4 21.3 lOA 1.719 2.32 486.3 209.6 11A 1.719 2.32 243'.2 104.8 12 1 .781 2.49 61.9 24.9 13 1.781 2.49 61.9 24.9 14 1 .781 2.49 111 .3 44.7 15 1.781 2.49 155.8 62.6 16 1.781 2.49 243.2 97.7 17 1.781 2.49 243.2 97.7 18 1.781 2.49 61.9 24.9 19 1.781 2.49 111 .3 44.7


65 Determination of Normal Stress (Continued) Sample Diameter Area Normal Load Normal Stress Number (i n. ) (sg. in.) bs. ) (Esi) 20 1.781 2.49 155.8 62.6 21 1.781 2.49 243.2 97.7 22 1.781 2.49 304.2 122.2 23 1.781 2.49 61.9 24.9 24 1.781 2.49 111.3 44.7 25 1.781 2.49 155.8 62.6 26 1.781 2.49 243.2 97.7 28 1.719 2.32 61.9 26.7 29 1.750 2.41 111.3 46.2 30 1.750 2.41 160.3 66.5 31 1.750 2.41 243.2 100.9 32 1.750 2.41 313.0 129.9 33 1.781 2.49 61.9 24.9 34 1.781 2.49 111 .3 44.7 35 1 .781 2.49 160.7 64.5 36 1.781 2.49 243.2 97.6 37 1.781 2.-49 313.0 125.7 39 1.813 2.58 61.9 24.0 40 1.813 2.58 160.7 62.3 41 1.813 2.58 313.0 121.3


66 Post Peak Stress Sample Normal Stress Post Peak Stress Number (2s;) (25;) 1A 48 82 2A 104.8 182 3A 26.7 32 4A 26.7 74 5A 129.9 147 6A 100.9 NO 7A 100.9 NO 8A 121.4 112 9A 21.3 60 lOA 209.6 NO 11A 104.8 105 12 24.9 45 13 24.9 56 14 44.7 54 15 62.6 76 16 97.7 NO 17 97.7 120 18 24.9 48 19 44.7 54 20 62.6 81 21 97.7 94 22 122.2 100 23 24.9 39


67 Post Peak Stress (Continued) Sample Normal Stress Post Peak Stress Number (psi) (psi) 24 44.7 52 25 62.6 64 26 97.7 114 '28 26.7 59 29 46.2 79 30 66.5 NO 31 100.9 116 32 129.9 130. 33 24.9 72 34 44.7 99 35 64.5 ,83 36 97.6 134 37 125.7 123 39 24.0 43 40 62.3 101 4'1 121.3 104


APPENDIX C Sonic Log Calculations 2 2. 1. Ed = PVS{3 Vp -4 Vs} : {Vp Vs} 2. :a. a 2-2,vd = {Vp -2 Vs} : 2 (Vp -'Vs) Where: Ed = Dynamic Young's Modulus P = Densi ty gm/cc Vs = Shear wave velocity in km/sec Vp = Pressure waVe velocity in km/sec vd = Poisson's ratio


APPENDIXD Description of Geophysical Logs Used 'Primarily for Geologic Correlation Gamma Logs The gamma log is used to measure natural radioactivity in the formation. This radioactivity is the result of the decay of potassium-40, ,uranium or thorium. The gamma log usually is a measure of clay in a formation because clay -minerals have an affinity for uranium. Certain formation contacts can be picked with the aid of this Ca 1 i per Lo"g The caliper log is a mechanical device with several swinging arms which contact the sides of the borehole and generate a signal proportional to the arm extension. The caliper log is extremely accurate and is therefore used determine if there are any "trouble spots" in the hole. These may be partially bridged portions of the hole or areas where lateral pressures have caused an inward radial strain. These also aid in the identification of incompetent rocks either due-to the hole caving or being "washed out by the drilling fluid.


Spontaneous Potential This is an "electric log" which measures a current generated in the formation by the interaction of fluids of different salinities. An example would be a sodium chloride rich borehole fluid. The Na ions move from the more Na concentrated fluid to the less concentrated fluid. This movement of charged ,ions creates a current. The driving force for these ions represents a measurable voltage potential, the membrane 70 potential. Shales are selective in this process and pass only the cations (Schlumberger, 1972). Another potential is created, the liquid junction potential, when the mobile chlorine ions flow across solution boundaries. This liquid junction potential is only a small fraction of the membrane potential. The SP curve can identify permeable beds as long as there is enough' permeability to allow invasion of borehole fluids. There is, however, no correlation between magnitude of the millivolt reading and permeability. There is no "zero" with respect to SP therefore a "shale line" is established from which to compare more permeable formations. The SP curve is deflected to the left as these more permeable beds are encountered as long as the drilling fluid is less saline than the formation fluid. Even in porous beds, however, the SP curve can be depressed by the presence of clay minerals.


Resistivity Logging Resisti'vity logs show how a formation may affect an induced current. Since minerals are generally very poor conductors of electricity a current may be resisted by the formation. If, however, pore spaces are filled with water and the water has dissolved sodium chloride or other electrolytes an induced current can be conducted through the formation. ResiStivity and resistance are two terms with similar but not interchangeable meanings. The resistivity unit in logging is the ohm-meter2 /meter which is the electrical resistance of a material when a current of one ampere is applied to a one meter length of material with a cross-sectional area of one square meter (Hoffman, 1982). The resistance is an absolute measure depending on the volume and characteristics of the material. The reciprocal to the resistivity is the conductivity and its units are the mho or mi1limho. Formation resistivity is usually measured by short normal and 64 inch resistiVity. These are a function of the distance the current can invade the formation and return to the sonde. Clean' sandstone with non-saline pore fluid would have a high resistivity and claystone would have a high conductivity. Induced Polarization Induced polarization logging is an logging technique extensively in the mining industry for the determination of sulfide The principle is a separation of charge to form a dipolar situation. An applied electric field


can separate charges on a metallic particle such that when the current is abruptly cut off a current decay will be observed. This decay which lasts for seconds is called the "Time-domain" method. -Another method is the "frequency-domain" technique which utilizes sine wave currents at low but discrete frequencies. The polarization effects can be best seen in the low frequency currents as a resistance between the current circuit and the measuring circuit is altered by the polarization phenomenon. Induced polarization signatures may be caused by certain clay minerals related to electrodialysis of the clay particles (Seigel, 1969) but much work is needed to quantitatively utilize this technique. 72