FABRIC OF CONSOLIDATED KAOLINITE

Transcription

1 Clays and Clay Minerals. Vl. 23. pp. 1%25. Pergamn Press Printed in Great Britain FABRIC OF CONSOLIDATED KAOLINITE R. TORRENCE MARTIN and CHARLES C. LADD Getechnical Divisin, Department f Civil Engineering. M.I.T., Cambridge, Massachusetts 02139, U.S.A. (Received I8 March I974) Abstract--Fabric refers t the spacial arrangement f clay particles in a sample relative t a reference plane. X-ray diffractin data yield an 'amunt f rientatin' (AO) that varies frm zer fr ideal randm t 100 fr ideally riented fabric. The AO has been related t the average angle f inclinatin f clay particles t the reference plane. Fabric data frm 50 samples invlving 2000 determinatins are presented n the effects f: the methd f sample preparatin prir t ne-dimensinal cnslidatin; the magnitude f cnslidatin stress frm 0.1 t ver 1000 kg/cm2; changes in directin f cnslidatin stress; istrpie cnslidatin; and disturbance during remval f samples frm edmeter cells. The single mst imprtant variable was the methd f sample preparatin, as illustrated by the fllwing data n samples cnslidated ne-dimensinally t 1.5 kg/cm 2 :clay initially mist, AO = 27 per cent; air-dry clay, AO = 44 per cent; clay slurries, AO = per cent. The change in fabric with increasing cnslidatin stress was mst prnunced with samples at very lw stresses, the changes in fabric were small fr cnslidatin stress increments usually encuntered in engineering practice. Fabric data prvide a very sensitive measure f sample disturbance. Extrusin causes significant disturbance at the center f a 24 cm dia. sample cylinder. INTRODUCTION PROCEDURE Many aspects f the engineering behavir f chesive sils ha~e been explained by varius authrs (van Olphen, 1951; Lambe, 1960; Seed and Chan, 1961; Olsen, 1960; Mitchell, 1964; Olsn and Mesri, 1970) in terms f the 'structure' f the clay phase. Structure is the cmbinatin f the gemetrical arrangement f particles and the frces perating between them. The gemetrical arrangement f particles and assciated vids is called 'fabric' and is the cmpnent f structure that is mst amenable t measurement. Since the structure cncept has been invked t explain s many features f clay behavir, a reliable quantitative methd fr determining the fabric f clay is extremely imprtant. Martin (1962) described a methd fr quantitative fabric measurement f wet clay samples. The technique is: (1) impregnate the wet clay with plyalchl, (2) grind a flat surface and (3) examine the surface by X- ray diffractin with a diffractmeter equipped with a Schulz ple figure device fr measuring the amunt, directin, and variability in particle rientatin within the clay mass. The bjective f the present discussin is t present sme refinements cncerning the validity f the methd and its quantitative expressin fllwed by bservatins n fabric change resulting frm (1) variatin in initial clay preparatin, (2) sample disturbance and (3) ne-dimensinal cnslidatin. The results reprted herein entailed mre than 50 engineering-sized samples upn which ver 2000 individual fabric measurements were made. The authrs gratetully acknwledge the U.S. Army Engineers Waterways Experiment Statin wh supprted the wrk under Research in Earth Physics. 17 The cmplete methd frm impregnatin thrugh XRD data cllectin has been thrughly treated previusly (Martin, 1966) and is nly briefly reviewed here. Specimens fr XRD examinatin are prepared frm Carbwax 6000 (Unin Carbide Crp.) impregnated samples, fl = 0 specimens have the surface t be examined by XRD cut nrmal t the directin f the first majr stress applicatin. Usually, a fl = 0 specimen means XRD data frm the hrizntal plane. Peak rati, PR, is defined as net peak amplitude f 002 kalinite peak divided by net peak amplitude f 020 kalinite peak bth measured at a fixed tip angle, 05. The peak rati, PR, is a measure f the amunt f rientatin. Figure 1 shws the ple figure device mtins which permit accurate measurement f the angle f maximum rientatin relative t the specimen surface. The angle f maximum rientatin is btained frm a series f tip curves, 05, in which the specimen rtates arund the XX'-axis with the detectr set n the 20 psitin f the 002 kalinite peak. The curve generated, intensity vs tip angle 05 gives the angular distributin f diffracted intensity abut the z-axis fr a selected azimuth angle, ct. Anther measure f the amunt f rientatin is defined by W. which is the width f the tip curve in degrees ~b measured at ne half the maximum amplitude f that particular tip curve. Numerus tests were perfrmed by Martin (1962, 1966) t cnfirm that the prcedure fr impregnating wet clay with Carbwax and grinding a flat surface des nt disturb measurably the fabric f the riginal wet clay mass. The fllwing test further cnfirms the validity f the methd.

2 18 R.T. MARTIN and C. C. LADD ~,xis f rt~in Vertical t silt X-ray beam Hrizntal slit ~a**n ~y Axis f ~ rtatin Fig. 1. Mvements fr ple figure diffractmeter. Thin sectins acrss shear znes when viewed with plarized light shw the same rientatin bands whether the thin sectin is 50 r 10#m thick. The PR n specimens with unifrm fabric remains unchanged frm a specimen thickness f 7 mm dwn t a specimen thickness f 20 #m (the abslute intensities prgressively decrease when the thickness becmes less than 100 gin, but nt the PR). The abve X-ray data indicate that any surface smearing resulting frm the preparatin technique is insignificant fr tw prepared surfaces mre than 20#m apart. The micrscpe bservatins indicate that surface smearing is insignificant fr tw smeared surfaces 10/~m apart. All tests were dne with kalinite clay (Peerless N. 2, R. T. Vanderbilt C.). The grain size distributin f the clay was 90 per cent finer than 10, 60 per cent finer than 2 and 45 per cent finer than 1 #m. The Atterberg limits were: liquid limit = 58 per cent, plastic limit = 28 per cent, plasticity index = 30 per cent. The s.g. equalled Unless therwise specified the clay was used withut any pretreatment. A generalized cnslidatin curve cvering the stress range f interest is given in Fig. 4(B). PHYSICAL MEANING OF PEAK RATIO The peak rati (PR) is a quantitative numerical measure f rientatin fr the tip angle gb at which the measurement is made. Fr ne-dimensinally cnslidated samples, the maximum bserved PR cnsistently ccurs at a tip angle very clse t the directin in which the majr stress was applied. An index fr the amunt f rientatin (AO) is given in terms f the bserved PR at the tip angle which gives the maximum 002 amplitude f the ~b curve and the bserved PR fr a truly randm sample: AO = I er~ ---- PRrand~ PRb~ J'~m~x X 100. [1] The AO is defined in such a way that the amunt f rientatin in a randm sample is numerically zer and in an ideally riented sample appraches 100 per cent. It has been shwn (Martin, 1966) that a PR = 2.0 is truly ideal randm fr kalinite and that this can be achieved experimentally; thus PR randm in equatin (1) equals 2-0. The maximum PR btained experimentally has been 400, which crrespnds t an AO = 99.5 per cent. Ideally, randm fabric is usually visualized as the situatin where the average rientatin f the basal planes f ne particle relative t its neighbrs is at an angle f 45 ~ which implies that all pssible rientatins are present in equal abundance. Ideal rientatin, at the ther extreme, is where the angle between the basal plane f ne particle and its neighbrs is zer. With the aid f the ple figure device, this distributin f particles abut the ple f the maximum rientatin directin is measurable experimentally. Martin (1966) defined a functin Wwhich is a measure f the distributin f particles abut the ple f maximum rientatin. This functin W is the width f the tip curve in degrees measured at the ne half maximum amplitude psitin. Experimentally, W varies frm 105~ ~ fr randm samples and frm 21~ ~ fr the maximum rientatin pssible t achieve with Peerless N. 2 kalinite. Based upn X-ray diffractin data btained n single flakes f muscvite and chlrite (assumed t have 'ideal' rientatin) Martin (1966) shwed that the theretical Wfr ideal rientatin f kalinite wuld be 20 ~. With this infrmatin, it is nw pssible t set up an expressin in terms f Wthat will give an average inclinatin angle f 45 ~ fr randm and 0 ~ fr ideal rientatin. The expressin is: Wb, - 20 Average inclinatin angle = - - [2] 2 The 20 cmes frm the theretical ideal rientatin calculated fr kalinite emplying experimental data fr ideal riented single flakes f muscvite and chlrite. Since the experimental width f tip curve VCbs includes bth plus and minus ~b angles, the expressin is divided by 2 t give the average inclinatin angle. The upper limit f experimental Wbs fr randm kalinite is 110 ~ which upn substitutin in equatin (2) gives an angle f 45 ~ fr randm. The minimum value f W experimentally btained n the best riented samples was 21 ~ qs, yielding an average inclinatin angle f nly 0'5 ~. Figure 2 shws a plt f AO vs average inclinatin angle fr 24 different kalinite samples cvering a wide range f cnslidatin pressures and preparatin techniques. It wuld appear that a linear scale fr AO frm per cent is a reasnable apprximatin fr expressing rientatin that is cnsistent with the physical cncept f particle arrangement as described abve. General EFFECT OF PREPARATION AND HANDLING Befre discussing fabric data fr different amunts and types f cnslidatin, the sensitivity f fabric t changes in sample preparatin and handling is examined. Tw specific variables are cnsidered: placement

3 Fabric f cnslidated kalinite ~.40 - c 20?, E /! O, "idea I rlen'r'tin" \ I 0 0 Average inclina't'in angle e'~ parl"ieles "idea I randm" Fig. 2. Amunt f rientatin vs average angle f inclinatin between particles. cnditin and amunt f sample disturbance. The latter includes a discussin f sample hetergeneity. The placement cnditin is determined by the cmbinatin f the water cntent, w, f the clay and the methd f placement f the clay in the cnslidatin cylinder. A 'slurry' is a mixture f saturated clay at any water cntent, abve the liquid limit, which has been mechanically mixed. Slurries with a wide range f water cntents were placed by puring int the cnslidatin cylinder. The slurry water cntent at which a demarcatin line frms between sediment vlume and supernatant liquid depended upn the water cntent f the slurry and als the mechanical mixing energy and : any chemical pretreatment. At the ther extreme, 'air dry' clay was carefully placed in successive I in. layers until the cylinder cntained the desired weight f clay. Air dried kalinite had a water cntent f abut 0.7 per cent. An intermediate cnditin, designated 'wet-up', was btained in the fllwing manner. A air dry preparatin, as just described, was allwed t imbibe water very gradually thrugh the bttm prus stne until the entire clay mass appeared mist. At this time the water level was very slwly raised (5 mm/hr) until free water appeared ver the tp f the clay. This wet-up prcedure gave an initial water cntent between 1130 and 120 per cent. The edmeter cylinders fr slurry and wet-up samples had diam. f 7.62 and 24.1 cm with sample heights, after initial cnslidatin, f cm and cm respectively. Air dry samples were prepared in the small edmeter. Preparatin cnditin The majr influence f preparatin prcedure n fabric was the initial water cntent. Figure 3 shws a wide range in the peak: rati r amunt f rientatin fr different water cntents at the time f preparatin. The decrease in vid rati, e, fr each cnditin was prduced by increasing the cnslidatin stress. The w = 5600 per cent slurry curve f Fig. 3 cntains differences in cnslidatin stress and in chemical treatment. All the w = 5600 per cent slurries were strngly flcculated slurries prduced by washing the clay with acidified NaCI and then remving the free salt. The slurry which gave e = 5"6 had a plyelectrlyte aggregate added t increase further the flcculatin while the slurries which gave e = 1"0 and 1.55 had a sdium chlride slutin (0'5 N) added t reduce flcculatin slightly. In Fig. 3, fr a cnstant amunt f rientatin, AO f 73 per cent (PR = 7.4) the vid rati range is 0.18 t 5.6. Fr a cnstant vid rati 1.2, the AO range is frm per cent (PR = 4-44). Obviusly, there is n unique relatin between the amunt f rientatin and vid rati. Althugh the angle f rientatin was nt measured in every case, it shuld be nted that all measurements were n/~ = 0 surfaces at ~b = 0, which is fr all practical purpses identical t the angle f maximum rientatin fr ne-dimensinally cnslidated samples. Table 1 shws fabric variatins fr different initial cnditins where all samples were cnslidated ne dimensinally t 1.5kg/cm z. The mst significant pint shwn by the data in Table 1 is that the water cntent at the time f initial placement is very imprtant. This is evident by cmparing the fabric f the wetup and air-dried samples which had the same water cntent as initially placed and that adding water (wetup sample) had n effect n AO upn subsequent cnslidatin t 1.5 kg/cm 2. Als, fr slurries, the water cntent f the slurry influences AO t a larger degree than the chemical treatment used. Sample hetergeneity and disturbance Sample hetergenity represents scatter in the data abve the variatin due t the ttal experimental errr 50 /96 Symbl PreprTlOn Wter ] 45 Wet-u IO0 },s I r i Slur,ft / rg I 9 / ~ I Slurry ~liuurrrr~ /! cj ~ N Ct 05 N 5600 Slurry~ ply- ~3 30- \ "C, ~ ej,~ IC \\ 80 e { I 1 I { t , Vid retie, e Fig. 3. Peak rati and amunt f rientatin fr different kalinite samples cnslidated t different vid ratis. 60

4 20 R.T. MARTIN and C. C. LADD Table 1. Initial water cntent and fabric after cnslidatin t 1.5 kg/cm 2 Water cntent Vid PR (~) befre rati n Preparatin* cnslidatin e # = 0 AO %t Slurry Slurry Slurry$ Wet-up Wet-up Air-dry * See text fr details. t Amunt f rientatin as defined by equatin (1). Slurry dispersed by adding Na2CO3 slutin t give an equilibrium ph f 7'3 t the slurry. in data reprducibility. The reprducibility f data is influenced by instrument factrs and sample preparatin prcedures. A check n the instrument, including alignment f an impregnated clay specimen, was established frm data n PR variatins measured n identical surfaces f fur different specimens ver a perid f ne year. The results shwed that the cefficient f variatin (100SD/PR) never exceeded 10 per cent. Therefre cefficients f variatin exceeding I0 per cent are a measure f sample hetergeneity. Initial studies shwed that the vertical variatin in PR thrugh the 3'8 cm height f a 7.6 cm dia. sample cnslidated ne-dimensinally t 1 kg/cm 2 was extremely variable. The tp sectin f Table 2 cntains data fr samples that were all prepared frm slurries with w = 190 per cent and cnslidated t 1 kg/cm 2. Fllwing cnslidatin, the bttm platen was remved and the clay sample extruded by frcing the cnslidatin pistn thrugh the cylinder. The PR value fr each sample given in Table 2 represents separate surfaces taken at different vertical lcatins alng the vertical eenterline f the cylinder. The cefficient f variatin is s large that there is a twfld change in the mean value fpr, PR, between sampies. Even the samples with the least percent variatin shw a hetergeneity that is statistically significant at better than the 95 per cent cnfidence level. Martin (1966) suggested that the variatin arse, in part at least, frm sample disturbance during extrusin frm the 7.6 cm alia. cylinder. The remainder f Table 2 prvides data fr examining the effects f sample disturbance. All samples extruded frm the 24 cm dia. cylinder (I, II, IV, and VI) are hetergeneus, shwing cefficients f variatin frm per cent. It is t be nted that there is n statistical difference in cefficient f variatin between the slurry and wet-up preparatins. Therefre, all ther things being equal, ne wuld nt expect any difference in hetergeneity between slurry and wet-up preparatins in a 7'6 cm dia. cylinder, By cntrast with sample VI, which is very definitely hetergeneus at the level f measurement, sample V, which was carefully cut frm the 24 cm dia. cylinder, has a very hmgeneus fabric at the level f measure- Table 2. Effect f remval methd n fabric N. Preparatin PR"f Cylinder Remval ~c n dia. methd* (kg/cm z) # = 0 Amunt f rientatin (AO) Cefficient f variatins 1 Slurry, w = 190~ 7.6 E 3 Slurry, w = 190% 7.6 E 4 Slurry, w = 190~ 7.6 E 5 Slurry, w = 190~ 7.6 E 6 Slurry, w = 190~ 7"6 E 7 Slurry, w = 190~ 7-6 E 8 Slurry, w = 190~ 7-6 E 20 Slurry, w = 190~/O 76 C I Slurry, w = 190~ 24 E II Slurry, w = 190~ 24 E IV Wet-up 24 E VI Wet-up 24 E V Wet-up 24 C 25 Wet-up, under vac, 7.6 C 26 Wet-up, under vac. 7.6 C 27 Wet-up, air 7.6 C 28 Wet-up, air 7.6 C * E = extruded, C = cut frm cylinder. See text fr details. t PR n fl = 0 surfaces at vertical centerline f cylinders. :~ Cefficient f variatin = 10O SD/PR " " '0 11'1 82"0 O'O l'4 1'5 ll "5 11" " '0 3' " " " ' '0 9.l

5 Fabric f cnslidated kalinite 21 ment. Samples cut frm the 7-6 cm dia. cylinder (Ns. 2%28) are als hmgeneus within the level f measurement. Sample N. 20 cut frm a 7,6 cm dia. cylinder after cnslidatin t nly 0-06 kg/cm 2 shws abut half as much variatin in PR as the least hetergeneus sample cnslidated t a much higher cnslidatin stress, but extruded frm the 7-6 cm alia. cylinder. In fact, sample N. 20 shws less variatin in PR than slurry samples extruded frm a 24cm din. cylinder. This is particularly significant when ne realizes that all fabric data frm the 24 cm dia. samples given in Table 2 were taken frm the axial center f the sample. In summary, all the evidence strngly suggests that kalinite cnslidated t as much as 1.5 kg/cm 2 is severely disturbed thrughut the clay mass during extrusin frm a cylinder as large as 24cm in din. EFFECT OF CONSOLIDATION The effect f ne-dimensinal cnslidatin n fabric was implied by the data already presented in Fig. 3. In the present sectin, the effect f ne-dimensinal cmpressin where there is n change in directin f majr stress applicatin thrughut the sample histry will first be presented. Then the effect n fabric f a change in directin f cnslidatin will be discussed. Finally, the fabric prduced by anistrpic stresses due t ne-dimensinal cmpressin will be cmpared t that prduced by an istrpic state f stress. One-dimensinal cnslidatin with n change in directin f majr stress applicatin (-6 c perpendicular t fl = 0 surface) crrespnds t a nrmally cnslidated sediment prir t any tilting r flding f the sediment frmatin. Under these cnditins, cnslidatin wuld be expected t prduce rientatin because f the highly anistrpic shape f clay particles. Figure 4(A) shws the increase in amunt f rientatin (AO) as a functin f cnslidatin stress, ~c, fr varius preparatin cnditins. Every pint in Fig. ~A) represents the mean PR fr between 8 and 40 different surfaces all nrmal t ~c; i.e. ]~ = 0 surfaces, n the particular sample under investigatin. The data in Fig. 4(A) again pint ut the great imprtance f sample preparatin n fabric. The pltted vid rati pints in Fig. 4(B) are fr the identical samples n which the fabric data f Fig. 4(A) were btained. Unfrtunately, vid rati data fr many f the fabric samples are nt available. 8 -G J5 3OI 3l (A)..~"..~ 9 -~'-I-" 9 x~x--x ~ =~ 2 25 c 3 -G c ~55 ~5 -- g ~ E < sl 20 I s mbl Prepar- WaTer 0 I O0 r O. 0 J 01 ~ I ~ 0 ~ O0 ~ 0 O0 Cnslidatin s1"ress,~ kg/cm 2 ~(%)= J ( PR-2 )/PR AveIinclinTin ngle frm "figure (B) 2"0 1"6 1.2 > 0-8 0,4 x I l I I I I %.%, "I" 0,0001 0, ( I I0 I00 I000 Cnsnslidtin sl"ress,~, kg/cm 2 Fig. 4. Effect f ne-dimensinal cnslidatin f kalinite n: (A) Fabric; (B) Vid rati.

6 22 R.T. MARTIN and C. C. LADD Table 3. Mean peak rati fr wet-up kalinite cnslidated nrmal and parallel t the riginal stress directin Sample Stress directin Cnslidatin relative t stress, ~,, = 0 surfaces (kg/cm 2) Fabric n surfaces nrmal t directin f final cnslidatin stress~" PR SD CV 1. Initial Nrmal --* Oedmeter Nrmal Oedmeter Nrmal Initial Parallel --* Oedmeter Parallel '0 6. Oedmeter Parallel 512 5" 12 0; * Ba tch ~+ = l kg/cm 2. + PR = mean peak rati, SD = standard deviatin, CV = cefficient f variatin (%). The effect f changing the directin f majr stress applicatin was investigated by preparing tw edmeter samples frm the same unifrm batch f clay cnslidated ne-dimensinally t 1 kg/cm 2. One sample was prepared s that additinal cnslidatin wuld be parallel t the/3 = 0 surface; i.e. a 90 ~ shift in directin f the majr stress applicatin. A cmparisn f the mean peak ratis, PR, fr these samples cnslidated nrmal and parallel t the /3 = 0 surface given in Table 3 shw that a very large cnslidatin stress is required t change the directin f preferred rientatin. That the preferred rientatin directin has been cmpletely reversed is clearly evident frm a cmparisn f the ple figures in Fig. 5 fr samples 3 and 6 f Table 3. The ple figure represents the steregraphic prjectin f amplitude cnturs btained frm 002 kalinite diffractin peak data n a series f ~ curves at many ~ angles. The ple figure gives the statistical distributin f kalinite particle rientatin with respect t the majr ple f rientatin, 05,,,~, marked by X in the ple figures. The asymmetry abut the zenith is just as large in Figure 5(B) where bth initial and final cnslidatin stresses were nrmal t the plane f the figure, as in Fig. 5(A), where nly the final cnslidatin stress was nrmal t the plane f the figure. Only half f eachple figure is shwn because the ther half f each ple figure shws the same asymmetry, The fact that 4~,, fr cnslidatin nrmal and parallel t the fi = 0 surface is the same prvides further cnfirmatin that the directin f preferred rientatin n sample 6 (Fig. 5B) has been changed cmpletely s that the preferred rientatin n bth samples (3 and 6) is nrmal t the final Re, althugh sample 6 initially had its preferred rientatin parallel t the final -~,. The effect f additinal cnslidatin at 90 ~ t the riginal cnslidatin directin als was examined fr a mre riented riginal clay fabric. Since it has been shwn that initial preparatin frequently dminates the final bserved fabric, great care was taken in these tests. Tw identical samples were trimmed frm a 24 cm dia. slurry batch with axes perpendicular t the riginal cnslidatin pressure, placed in standard edmeters, and prepared fr lading. Sample B was laded t 2 kg/cm 2 and the lad dubled every day until a final lad f 32 kg/cm 2 was applied. The final lad was left n 3 days, at which time the sample was care- fully cut frm the cell and impregnated. Sample A was nt laded but was carefully cut frm the edmeter cell and impregnated. Therefre, samples A and B have had identical treatment except that sample A nly had the initial cnslidatin, ~, f 1 kg/cm 2 applied nrmal t the fi = 0 surface while sample B had a final cnslidatin, #f, f 32 kg/cm z applied parallel t the = 0 surface. Remember that the/3 = 0 surface is by definitin taken as nrmal t the initially applied majr stress. Table 4 summarizes the results f fabric measurements, Additinal cnslidatin parallel t the/3 = 0 surface definitely changed the fabric f this mderately riented kalinite and increased the fabric hetergeneity as shwn by the large percent increase in the cefficient f variatin n bth ~ = 0 and ~ = 90 surfaces. Hwever, Table 4 shws that 32 kg/cm 2 is nt adequate t reverse the directin f the initial rientatin. A graphical picture f the fabric change is revealed in the ple figures f Fig. 6, where the fabric detail f samples A and B can be directly cmpared. Cmplete?,b.z"f~ ~I ~- 'B m Grid interv]s C ncenl-r ic, ~- 5 ~ Rdil, a~30 ~ Fig. 5, (002) Ple figures fr kalinite surfaces nrmal t final cnslidatin f 512 kg/cm2: (A) Sample n, 6, ~y directin at 90 + t ~+ directin; AO = 67.2 at 4~m,~ = (B) Sample n. 3, ~y directin = t ~ directin; AO = 77.3 at 4~ma, = --1.

7 Fabric f cnslidated kalinite 23 Table 4. Fabric f mderately riented kalinite resulting frm additinal cnslidatin nrmal t the initial cnslidatin Sample A. Reference, initial cnslidatin f 1 kg/cm-' perpendicular t the fl = 0 surface. B. Additinal cnslidatin f 32 kg/em 2 parallel t the fl = 0 surface. Fabric = 0 Surfaces.fl = 90 Surfaces PR* CVt PR CV "3 * PR = mean value f average peak ratis determined n ten surfaces in directin stated. "~ CV = Cefficient f Variatin, 100 SD/PR. ple figure data were btained n fur separate surfaces at 1 mm vertical intervals frm Sample B with essentially the same result. Als, the entire experiment was repeated with the same results. The sketch in the lwer left t Fig. 6 shws the relatin f the surface frm which the ple figure data were btained. The effect f additinal cnslidatin parallel t the/~ = 0 surface prduced a definite shift in preferred rientatin directin because Fig. 6 shws a 45~ ~ spin (~ rtatin) and a 25 ~ tip (q~ rtatin). The sketch in the lwer right f Fig. 6 is an idealized presentatin f the preferred rientatin as interpreted frm the ple figures. The rientatin f clay particles relative t the rectangular blck is shwn by dts fr particle faces and by dashes fr clay particle edges; therefre, Grid inl"ervals Cncentric, ~b=5* 120 Radial,r =~0" i Spin axis [~) ~25"r Fig. 6. (002) Ple figures lbr fl = 0 surfaces f kalinite: --- (A) Surface nrmal t a~ := I kg/cm ; AO = 75'9 at = - 1 ; (B) Surface parallel t ~I 2 = 32 kg/cm 2 ~A,~ 70.1 at q~ma~= preferred rientatin is apprximately parallel t the plahe ABCD. Fur measurements f small area peak rati n the fl=0 surface f sample B at ~b=25 ~ and fr c~ between 45 ~ and 60 ~ gave a mean f 6.7 (AO = 70.1) with a maximum deviatin frm the mean f 0-2; hwever a 5 ~ change in either ~b r ~ utside this range reduced the spt peak rati t 5'3 r less. Clearly changing the directin f applied stress frm nrmal t parallel t the directin f preferred rientatin primarily rtates the directin f preferred rientatin tward being nrmal t the applied stress. A very large increase in applied stress wuld be required t cmpletely shift the directin f preferred rientatin when the clay has been mderately riented initially. It has been previusly shwn by Martin (1966) that istrpic stress up t 1 kg/cm 2 prduced n measurable change in fabric. Kalinite slurry at w = 190 per cent under a very small stress (a slurry 3 cm deep in a beaker) gave a PR = 2.7. This is the same PR btained n kalinite slurry at w = 190 per cent Cnslidated istrpically t 1 kg/cm 2. In cntrast, ne-dimensinal cnslidatin f a w = 190 per cent slurry t I kg/cm 2 prduces a P---R f abut 9 (see Fig. 4A). Cnsequently, the anistrpic stresses in ne-dimensinal cnslidatin are the cause f the rientatin rather than the average cnslidatin stress per se. Fr nrmally cnslidated kalinite, the hrizntal stress is abut ne-half f the vertical stress since the cefficient f earth pressure at rest K is abut ne-half. DISCUSSION The ease with which clay particles are riented by an anistrpic stress depends upn the bnd strength between particles and upn stearic hindrances. In ther wrds, the ease f changing sil fabric is determined by sil structure which includes the initial fabric and the frces perating between and within the fabric units. Fabric changes bserved as a result f stress changes are then the net effect prduced by the stress increment applied t the riginal sil structure. Hence,

8 24 R.T. MARTIN and C. C. LADD it is very unlikely that ne wuld bserve a unique relatin between particle rientatin and either vid rati r applied anistrpic stress, This statement is brne ut by the data presented in Figs. 3 and 4. All f the data shw that the initial placement cnditin determines the general level f rientatin that can be achieved by ne-dimensinal cnslidatin. This imprtance f the initial cnditin n the fabric develped has been repeatedly bserved (Martin, 1962; Quigley, 1962; O'Brien, 1964; Thiem, 1967; Mrgenstern and Tchalenk, 1967). The imprtance f initial cnditin and the changes in fabric with ne-dimensinal cnslidatin are summarized in Fig. 4(A). Several pints are wrth emphasizing. The slurry samples start ut with a much mre riented fabric than air-dry, mist, and wet-up samples. They als underg much smaller changes in fabric as a result f ne-dimensinal cnslidatin at stresses abve 0.1 kg/cm z. In cntrast, the anistrpic stress f ne-dimensinal cnslidatin changed the fabric f air-dry and mist kalinite frm essentially randm t an amunt f rientatin (AO) f abut 90 per cent. Hwever, extremely large stresses were required t prduce this change. The maximum bserved AO f 92 per cent with cnslidated slurry samples is belw the 99.5 per cent achieved by slw sedimentatin and drying f a thrughly dispersed w = 750 per cent slurry. The AO f 92 per cent crrespnds t an average angle f inclinatin amng particles f 8 ~ While this is indeed a high degree f rientatin, it is still a lng way frm the 0'5 ~ btained with the AO = 99.5 per cent samples. Increased rientatin with increased ne-dimensinal cnslidatin is nt limited t"kalinite. It has been bserved n illitic clays (Quigley, 1962; O'Brien, 1964; Quigley and Thmpsn, 1966) and n mntmrillnite (Englehardt and Gaida, 1963; Theim, 1967). Mrgenstern and Tchalenk (1967) state that 'fr flcculated kalin prepared by sedimentatin the develpment f intense rientatin in this test is virtually cmplete at a stress level f 0'1 tn/ft, z, ( ~ cm2). Their wn data n slurried kalin are qualitatively very similar t the data given in Fig. 4(A). O'Brien (1964) bserved analgus behavir fr Pennsylvanian age underclays in Illinis. Reviewing the literature fr natural sils, Meade (1966) culd find n unequivcal evidence fr increase in rientatin with depth f burial. Data presented herein suggest several pssibilities fr the lack f crrelatin between rientatin and depth. These include the fllwing: (1) the changes in fabric with increasing cnslidatin stress can be very small if the degree f rientatin is high t start with (2), changes in fabric with cnslidatin appear t be related t the lgarithm f stress, thus very large stress increments prduce slight changes in fabric when the stress level is high, (3) sample disturbance may cmpletely mask fabric changes with depth, especially since the amunt f disturbance might increase with depth. In additin, varying depsitinal envirnments and/r natural cementatin as bserved by Quigley and Ogunbadej (1972) might prduce fabrics that wuld nt necessarily be related t depth f burial, Hwever, it is difficult t explain the essentially randm fabric fund by Meade (1966) fr burial depths up t 600m by this mechanism, An istrpic in situ stress cnditin during cnslidatin culd, in thery, explain such a randm fabric with depth. But abundant labratry data (e.g. Brker and Ireland, 1965) and sme field measurements (e.g. Kenney, 1967) shw that the in situ stresses are anistrpic during virgin cmpressin since K fr nrmally cnslidated clays typically equals "1. The greater the preferred rientatin the mre imprtant it is t knw that the measurement is at the angle f maximum rientatin. Fr this reasn, every specimen fr which PR data are given in Tables 1 and 2 and Figs. 2-4 was checked using the universal stage diffractmeter t verify that the PR measurements were being made at the angle f maximum rientatin. The very small fabric change bserved by Mrgenstern and Tchalenk (1967) when the directin f cnslidatin stress was shifted 90 ~ may be due t a lack f knwledge regarding the directin f maximum rientatin. In the present investigatin the precise angle f maximum rientatin, as well as the statistical distributin f particles abut the axis f maximum rientatin, was determined with the universal stage diffractmeter, Thiem (1967) with X-ray diffractin and Lafeber (1967) with light micrscpy als have emplyed the universal stage fr lcating the angle f maximum rientatin. Changing the directin f the ne-dimensinal cnslidatin stress by 90 ~ appears t change the fabric by a fairly unifrm rtatin f the riginal fabric tward alignment nrmal t the new applied stress directin, The stress increment required t cmpletely rtate the riginal fabric int alignment nrmal t the new stress directin again depends upn the initial sil structure, as shwn by the data in Tables 3 and 4 and in Figs. 5 and 6. REFERENCES : Brker, E. W. and Ireland, H. O. (1965) Earth Pressure at Rest Related t Stress Histry: Can. Getech. J. 2, Engelhardt, W. and Gaida, K. H. (1963) Cncentratin Changes f Pre Slutins During Cmpactin f Clay Sediments: J. sedim. Petrl. 33, Kenney, T. C. (1967) Measurements f In Situ Stresses in Quick Clays: Prc. Getech. Cnf. Osl. 1, Lambe, T. W. (1960) Cmpacted Clay: Trans. Am. Sc. Cir. Engrs. 125, (Part I) Martin R. T, (1962) Research n the Physical Prperties f Marine Sils: M.I.T. Department f Civil Engineering: Sils Divisin Publicatin Number 127, Martin, R. T. (1966) Quantitative Fabric f Wet Kalinite: Clays and Clay Minerals. 14, Meade, R. H. (1966) Factrs Influencing the Early Stages f the Cmpactin f Clays and Sands--Review: d. sedim. Petrl, 36, , Mitchell, J. K. (1964) Shearing Resistance f Sils as a Rate Prcess: d. Sil Mech. Fdns., Am. Sc. cir. Enrs. 90, Mrgenstern, N. R. and Tchalenk, J. S. (1967) The Optical Determinatin f Preferred Orientatin in Clays and its Applicatin t the Study f Micrstructure in Cnslidated Kalin: Pre. R. Sc. (A) 300,

9 Fabric f cnslidated kalinite 25 O'Brien, N. R. (1964) Origin f Pennsylvanian Underlays in the Illinis Basin: Bull. Gelg. Sc. Am. 75, Olsen, H. W. (1960) Hydraulic Flw Thrugh Saturated Clays: Prc. 9th Cnf., Clays and Clay Minerals. 9, Olsen, R. E. and Mesri, G. (1970) Mechanisms Cntrlling Cmpressibility f Clays: J. Sil Mech. Fdns. Div. Am. Sc. cir. Engrs. 96, Quigley, R. M. (1962) The Engineering Prperties f lllite Related t Fabric and Pre Water Cmpsitin: 16th Can. Sil Mech. Cnf. Quigley, R, M. and Orunbadej, T. A. (1972) Clay Layer Fabric and Oedmeter Cnslidatin f Sft Clay: Can. Getech. J. 9, Quigley, R. M. and Thmpsn, C. D. (1966) The Fabric f Anistrpically Cnslidated Sensitive Marine Clay: Can. Getech. J. 3, Seed, H. B. and Chan, C. K. (1961) Structure and Strength Characteristics f Cmpacted Clay: Trans. Am. Sc. cir. Engrs. Part I, 126, Thiem, H. K. (1967) Quantitative Textaranalyze Durch Rntgenintensitatsrnessungen und ihre Anwerdung auf experimentell verdichtete kalinit-und mntmrillnit- Tne: Dktrs Dissertatin Eberhard-Karls-Universitat za Tub ing e n. Van Olphen, H. (1951) Rhelgical Phenmena f Clay Sils in Cnnectin with the Charge Distributin n the Micelles: Discussin Faraday Sc. 11,