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HomeMy WebLinkAbout258i GOLDEN VIEW ELEMENTARY SCHOOL E3 Subsurface Investigation & Foundation. Recommendation_s Prepared for ECI/HYER 40-40 "B" Anchorage-, NOVEMBE~ ~!~#~ DOWL ' Eng!neers 4040 "B' Stree! Anchorage, Alaska 99503 Phone (907) 278-1551 ( Telecopier (907) 272-5742 ) October 25, 1982 WO ~D50039 Grid: 3237 ECI/Hyer 101 Benson Blvd., Suite 306 Anchorage, Alaska 99503 Re: Golden View Elementary School Site 3 Located Within the NE 1/4, Sec. 3r T. 11N, R. 3W, S.M., AK Gentlemen: Transmitted herein are the results of our subsurface investi- gation consisting of 10 test borings. The subject site is located near the intersection of 162nd and Loretta Street which is west of Golden View Drive. This investigation is a general evaluation of the site for planning purposes. Please call if we may provide additional service. Sincerely, DOWL Engineers Mark Holum Geotechnical Engineer Approved: Melvin R. Nichols, P.E. Partner MH:MRN:kf Kenneth B. Walch Melvin R. Nichols SUBSURFACE INVESTIGATION AND FOUNDATION RECOMMENDATIONS GOLDEN VIEW ELEMENTARY SCHOOL SITE 3 Geotechnical Engineer ~4elvin R. Nichols, P.E. Partner Prepared for: ECI/Hyer Prepared by: DOWL ENGINEERS October, 1982 W.O. #D50033 GOLDEN VIEW ELEMENTARY SCHOOL ' . SITE 3 INTRODUCTION This report presents the results of a preliminary subsurface investigation for the proposed Golden View Elementary School, Site 3. The location shown in Figure 1 is near Golden View Drive and 162nd Avenue. If this site is selected for develop- ment, once a site plan is established, additional exploration will be necessary for final design. The proposed school will consist of an approximately 50,000 square foot single story building. Building loads are assumed to be similar to those listed in our report of August 13, 1982 which addressed another site near Golden View Drive. This investigtion has not described all possible foundation systems in detail, but has focused on evaluating various types of foundations. Ten test borings were placed within and outside the roughly located building area in order to determine foundation systems, allowable soil loads, ground water levels, and the potential for on-site waste water disposal. SITE CONDITIONS The topography of the site, based on the Municipality of A31chorage 1" = 200' scale, four foot contour interval mapping, may be described as moderately sloping to the west. Slopes on the site range from 2° to 22°, but the average slope in the building area is approximately 5°. Approximately 12 feet of vertical relief exists between extreme building points. The 10 test borings indicate, that soils generally consist of a thin surface organic layer underlain by silty gravelly sand which resembles a glacial till. Occasional small lenses of sandy silt and silty gravel were also encountered, but the predominate soil type is medium dense to very dense silty gravelly sand. The silty sand is frost susceptible and is generally classified as F3 material according to t'he U.So Corps of Engineers classification. The silty sand also contains a sufficiently large percentage of silt.to necessi- tate precise moisture control while the material is being excavated or compacted. If allowed to saturate this material will be difficult to handle. -1- Ground water is relatively high at the site. The ground water level was observed at depths of less than three feet in Test Borings 2, 7, 8, and 9, and zones of saturated soil were observed in Test Borings 1, 3, 4, 5, and 6. Test Boring 10 was located above the school and encountered wet, but not saturated, soil. The low permeability of the soils prevented rapid establishment of a stable ground water level and implies that the wet and saturated soil may represent high levels of ground water or zones of perched ground water. We expect that any clean, permeable layers of soil that might be encountered will probably be saturated. CONCLUSIONS AND DISCUSSION Foundations The inorganic soils found at a moderate depth below the surface are sufficiently dense to support a conventional spread footings foundation. If spread footings are used, the site grade will necessitate.the use of either deep fill sections or relatively deep footings. Because of the cross slope to the building site, if a conventional footing depth is used, there will be considerably more fill under one side of the building than the other. This fill difference must, at least for planning purposes, be restricted to no more than five feet unless the fill can be preloaded for a minimum of three months or allowed to set for six months to allow differential settlements to occur prior to placing the footings. Such an approach probably is not practical because of schedule, on this site. Therefore, the footings will have to be deepened, or material on the "cut" side of the building overexcavated from beneath the footings and recom- pacted similar to the fill on the other side of the building to reduce the.potential for differential settlement, if spread footings are to b~ used. Ail footings may be placed on a thin lift of coarse fill over undisturbed soil, but this foundation system will necessitate the use of high footing walls. These walls will be subject to down drag forces created by the fill placed against the wall. Large fill depths will reduce the need for high footing walls, but must be designed to accommodate fill settlement and variable soil stiffness. Footings placed above dense undisturbed soil have a soil bearing capacity of 4000 psf provided all fill beneath the footings is compacted properly. Allowable soil loads may be increased by one-third for wind and seismic load conditions. At least two feet of coarse fill should be placed beneath footings to protect the silty wet soil from disturbance while forming concrete. -2- A pile foundation is also capable of supporting the building, provided the entire building is placed on piles. No other foundation system should be combined with piles, since piles are much stiffer than other types of foundation systems unless joints in the structure separate the two foundation systems. Preliminary estimates for a pile foundation indicate that a dense bearing layer exists at a depth of 10 to 20 feet below grade. This dense layer may be utilized to support end bearing piles consisting of closed end pipe piles or H sections. Closed end pipe piles may have a few feet less penetration into the bearing layer than would H piles, but both types of piles should develop sufficient resistance to support allowable loads of 100 tons/ft2 on the gross pile cross section, which for H piles is the web depth times flange width. Actual pile capacity should be determined by pile load tests. Pile penetration into the bearing layer and driving characteristics should also be determined with test piles. Drainage Ground water is a major design constraint and will affect construction procedures. Ground water in the building area should be controlled with adequate subsurface and surface drainage. Drainage along access roads and parking areas should also be provided to avoid icing conditions. The waste water disposal area will also require ground water control through the use of curtain drains, or mounded systems may be used to keep the treatment area above the ground water level. The dense soil is expected to possess low percolation rates, but no soil percolation test was performed at this site. ~ Although many test borings do not indicate an observed ground water level, the wet and saturated soils are often capable of supplying sufficient water to create a ground water problem with leach fields. Protective measures in the -form of an increased period of observation of ground water levels and curtain drains are recommended. High ground water will create wet conditions while placing fill both in the building and parking areas. Fill which contains appreciable amounts of fines or fine sand will be extremely difficult to compact and handle while wet. Construc- tion procedures for wet conditions may require use of additional sumps or drains to control water in excavations. -3- Subdrains should be placed around the perimeter of the building at a depth at least below the deepest footing. Interior drainage for crawl spaces should also be provided with additional subdrains. Drains should be constructed on the uphill side of the parking areas to intercept ground water. These drains should be reviewed during site design to determine their required depth and location. Fill and footings require a firm base for support. Peat must be stripped from beneath all structural fill for the building and footings. Peat depths were observed to vary from approximately 1 to 5 feet. Small amounts of organic material were occasionally found at much greater depths but these occurrences involved only trace amounts of organics and are not anticipated to affect building design and may be left in place. The difference in elevation between the highest and lowest ground level points in the building area is approximately 12 feet. The surface of the inorganic soil was observed to have a maximum elevation difference of approximately 16 feet. However, the large scale contour (4' contour intervals) map used to determine test boring elevations implies that actual elevations may vary by several feet. The maximum differences in elevation roughly indicate the maximum fill depths, and influence the amount of fill beneath the footings. The large amounts of fill will require the earthwork design to accomodate the differences in stiffness between the fill and undisturbed inorganic soil. Different amounts of fill beneath the footings will contribute to non-uniform settle- ment, but the total and differential amounts of settlement can be controlled ~y designing the fill depths beneath the footings to be similar, or by preloading as previously described. General site conditions are wet and will require the contractor to control the ground water while placing fill. Fill with little or no fines (gravel or coarse sand) will be required for fill in wet areas. This type of fill is recommended for use for the initial lifts to help provide drainage. Siltier material such as F1 or F2 soil may be used for fill where frost heave protection is not a concern and provided the moisture in the fill and on the site can be closely controlled at near optimum as determined by test method ASTM D1557. Filter fabric should also be used beneath the fill to help prevent contamination of the coarse fill by the underlying silty soil. -4- SUBSURFACE INVESTIGATION Subsurface exploration for this study was conducted on October 12-15, 1982, and consisted of 10 test borings. Depth of borings varied from 15 to 28 feet. All drilling was accomplished by Denali Drilling, Inc., employing a Mobile B-50 drill equipped with a hollow stem auger. Test holes were logged by Alaska Testlab geologist, Mr. Terry Barber. Test hole locations were measured from access roads by cloth tape and have not been surveyed. Test boring locations shown on Figure 1 may be inaccurate. Penetration samples were taken by driving a standard 2-inch O.D. split spoon sampler into the soil by the action of a 140 pound hammer, free falling a distance of 30 inches. The number of blows to drive the sampler the last 12 inches of an 18 inch penetration is recorded on the logs. A large diameter, 2.5" I.D., splitspoon driver by a 340 lb. hammer dropped 30 inches'was also used. Ail laboratory testing was performed by Alaska Testlab and. involved visual classification, moisture tests, and grain size analysis. The results of the tests are shown on the boring logs and on the grain size distribution sheets. -5- ACCESS RD, KEY: I~1 TEST LORETTA STREET SCALE 1"=200' BORINGS TEST BORING LOCATION MAP GOLDEN VIEW ELEMENTARY W.O. D 500:39 FIGURE SCHOOL SITE 3.6 HA 1.5 0.4 MA BORING 1 TEST LOCATION: DEPTH ELEVAT ON:. . ~BROWN PEAT, SOFT 0.$ F~~, BROWN SILTY GRAVELLY SAND, DAMP, MEDIUM DENSE URAT'ED/ F-3, 8ROAN SILTY GRAVELLY SAND, DA~ ~' SAT DENSE ( .... ~ ~ ~ 15.0 TEST BORING COMPLETED 10/12/82 KEY M~ = MECHANICAL ANALYSIS LL : LIOUID LIMIT Pi = PLASTlC INDEX [] : GRAB SAMPLE [] : SPT SAHPLE [] : SHELBY TUBE-PUSHED [] ~ 2.5" I.D. SPOON SAMPLE ~40# WEIGHT, ~0" FALL DOWL ENGINEERS LOG OF BORING] LOGGED BY~fB W,O. NO-: 050039 FIGURE 10.2 MA ~2.0 BORING.2 DEPTH --~.~BROWN PEAT, SOFT 0.5 ~Z F-3, GREY SILTY GRAVELLY SAND, MEDIUM DENSE F-2, BROWN SILTY SAND YIfH TRACE GRAVEL, DAMP. DENSE 11.5 _ TEST BORING COMPLETED 10/12/82 KEY MA = MECHANICAL ANALYSIS LL = LIOUID LIMIT PI = PLASTIC INDEX [] = GRAB SAMPLE [] = SPT SAMPLE [] : SHELBY TUBE-PUSHED [] = 2.5",l.D. SPOON SAMPLE 340# WEIGHT, ~0" FALL L DOWL ENGINEERS LOG OF BORING LOGGED BY~TB W.O. NO-~ 0500~9 FIGURE TEST LOCATION= ELEVATION= BORING 3 DEPTH BROWN PEAT, SOFT O.s F-3. BROWN GRAVELLY SILTY SAND, DAMP, MEDIUM DENSE 3-5 ~ ~WN GRAVELLY SANDY SILT, PLASTIC. DAMP, STIFF TO HARD / ....... [Z7:r:'< ........ ~,7-5 F-2. BROWN S]--"~'~-Y ~RAVELLY SA~D, WET TO SATURATED? TEST BORING COMPLETED 10/12/82 KEY MA : MECHANICAL ANALYSIS LL = LIOUID LIMIT PI = PLASTIC INDEX [] : GRAB SAMPLE [] = SPT SAMPLE [] = SHELBY TUBE-PUSHED [] : 2.5" I,D- SPOON SAHPLE 340# WEIGHT, JO" FALL DOWL ENGINEERS LOG OF BORING LOGGED BY: TB W.O- NO.: 050039 F I CURE 8,6 ,.~ "-. ,~'" TEST BORING 4 ~ z~ ~ LOCATION= L ELEVATION= DEPTH 39.0 m ms~ ---~BROWN PEAT, SOFT F-2 ~B~ROWN SJLT~ GRAVELLY SAND, DAMP. DENSE, ~ SATURATED ZONE AT S,O',~ VERY DENSE BELOW 39.0 43.0 GM 0.5 23.0 GREY SILTY SANDY GRAVEL WiTH TRACE VERY DENSE TEST BORING COMPLETED 10/13/82 $0.0 KEY MA = MECHANICAL ANALYSIS LL = LIOUID LIMIT P1 = PLASTIC INDEX [] : GRAB SAMPLE [] : SPT SAMPLE [] = SHELBY TUBE-PUSHED [] = 2.5~ I.D. SPOON SAMPLE 340# WEIGHT, 30" FALL DOWL ENGINEERS LOG OF BORING LOGGED BY~TB W.O. NO.: DS0039 F 1 OUR E ~9 kEY MA : MECHANICAL ANALYSIS LL = LIOUID LIMIT Pi = PLASTIC INDEX [] = GRAB SAMPLE [] = SPT SAMPLE [] = SHELBY TUBE-PUSHED [] = 2.5" I.D. SPOON SAHPLE 340# WEIGHT, 30" FALL TEST BORING LOCATION= ELEVAT I 5 DEPTH BROWN PEAT, SOFT ' 0.8 F-3; BROWN S1LTY GRAVELLY SAND, DAMP TO WET, DENSE F-3. BROWN S LTY SANQY.~GR, AV. EL.,J41TH OCCASIONAL COBBLES~?~gET T~. SATURATED,, ~'ERY DENSE B.O TEST BORING COMPLETED 10/14/82 16.7 DOWL ENGINEERS LOG OF BORING LOGGED BY~TB W-O. NO-: D50039 FIGURE 35 lA IA 7,9 KEY NA : HECHAN]CAL ANALYSIS LL : LIOU1D LIHIT P1 : PLASTIC iNDEX [] = GRAD SAMPLE ~] = SPT SAHPLE [] = SHELBY TUBE-PUSHED [] = 2.5" I.D. SPOON SAHPLE ~40~ WEIGHT, 30" FALL TEST BORING LOCATION: ELEVATION: 6 DEPTH BROWN PEAT. SOFT F-3. GREY TO BROWN GRAVELLY SILTY SAND. SAtURatED, HEDIUH DENSE, TRACE OF ORGANIC HATERIAL ,,~ _ _ _ 23-0 TEST BORING COMPLETED 10/13/82 DOWL ENGINEERS LOG OF BORING LOGGED BY~TB W-O. NO.: 050039 FIGURE j7.9 KEY MA = MECHANICAL ANALYSIS LL = LIQUID LIMIT Pi = PLASTIC INDEX [] = GRAB SAHPLE [] = SPT SAHPLE [] = SHELBY TUBE-PUSHED [] ~ 2.5",I.D. SPOON SAHPLE 340# WEIGHT, 30" FALL TEST LOCATION= ELEVAT ! ON= BORING 7 DEPTH BROWN PEAT, SATURATED, SOFT F~$, GREY GRAVELLY SILTY SAND. SATURATED, .MEDIUM DENSE TO'VERY DENSE 4.0 F-) BROWN SAND¥~JG~R~VEJ-~!41TH OCCASIONAL COBBLE~;~T URATED ~J~,... ~ -._MEDi UM DENSE 8.5 BROKEN ROC~R~COMER~D--AI 19.0' ....................... 27.5 TEST BORING COMPLETED 10/14/82 AUGER REFUSAL AT 27.5' DOWL ENGINEERS LOG OF BORING LOGGED BY~TB W.O- NO.~ 050039 FIGURE .0 .6 .7 .2 TEST LOCATION= ELEVATION= BORING 8 DEPTH .BROWNPEAT, SATURATED, SOFT F-3, BROtJNvERy DENSE SILTY GRAVELLY SAND. SATURATED,~..] ] TEST BORING COMPLETED I0/15/82 .0 15.0 KEY MA = MECHANICAL ANALYSIS LL = LIOU1D LIMIT P! = PLASTlC iNDEX [] = GRAB SAMPLE [] = SPT SAMPLE [] = SHELBY TUBE-PUSHED [] = 2.5" I.D, SPOON SAMPLE 340~ WE]GHI, 30" FALL DOWL ENGINEERS LOG OF BORING LOGGED BY,TO ~.0. NO.: 050039 FIGURE 9.6 ~0 TEST BORING 9 DEPTH ~BROWN PEAT, SOFT 0.5 ~ F-3, BROWN SILTY GRAVELLY SAND, ANGULAR GRAVEL. BECOMES MORE GRAVELL'Y AT ........................... ~5.0 TEST BORING COMPLETED 10/12/82 KEY MA : MECHANICAL ANALYSIS LL : LIQUID LIM1T P1 = PLASTIC iNDEX [] = GRAB SAMPLE [] = SPT SAMPLE [] : SHELBY TUBE-PUSHED [] = 2.S" I,D. SPOON SAMPLE ~40# WEIGHT, JO" FALL DOWL ENGINEERS LOG OF BORING LOGGED BY:TB W,O. NO.~ 050039 FIGURE 25 ~5 MA MA TEST LOCATI ON: ELEVATION-- BORING 10 DEPTH FBROWN PEAT~ SOFT ] 0.5 F-3, BROWN SILTY GRAVELLY SAND, WET. DENSE 8.0 -3, BROWN SILTY SANDY GRAVEL, DENSE 8.5 _ '_F-2, BROWN GRAVELLY SAND. DAMP, MEDIUM DENSE TEST BORING COMPLETED 10/12/82 KEY MA = MECHANICAL ANALYSIS LL = LIQUID LIMIT P1 =PLASTIC INDEX [] : GRAB SAMPLE [] = SPT SAMPLE [] = SHELBY TUBE-PUSHED [] = 2,5" I,O, SPOON SAMPLE ~40# WEIGHT, 30" FALL DOWL ENGINEERS LOG OF BORING LOGGED BY~TB ~4.0. NO-~ 050039 F I GUR E o o o ~ o R ~ ~o o ~ I-~'qq'lqqqFFl-l-T'llllllllllll Illlllllllll Iltlltllllllllllll Illlllll!ll, 'llllllllllilllll~llllll~l IlllllI~liili , o ~ O0 IIII ]}lllt~l II[IJl~lllllllllf Illl[llll[ '~'~'"" IIIIIIIIII IIIIIIIII IIIIIIIIl~llllll!lll III Illllllllllll~ IIIIIIIIII llllllllllll!llllllll II illl, !!11!11111 II IIIIIIIII , ,,,,,,~,,,,,,,,,,,,,111~," Illlllllllllll IIIIlllllllllll IIIII!1 II!llllllll ~ ~o ~o o ~o o ~ o ~o R o ~o ~ ~o ~o ~ IIIIIl~ll ~ 111111 I II I ,,,, ,I,, ]4 IIIllllllll II IIII II ~ IIIIIIllll Itll Illll iii!1 ~ Illlllllilll I Ill II II II Test Hole Lo~l - DeSCription Guide The soil descriptions shown on the Ings are the best estimate of the soaps characteristics at the time of field examination and as such do not achieve the precision of a laboratory testing procedure. If the lug includes soils samples, those samples receive an independent textural classification in the laboratory to verity the field examination. 'The logs often include the follow, aug items: Depth Interval - usually shown to 0.1 foot, within that zone no significant change in soil type was observed through drill action, direct observation or sampling. Frost Classification - NFS, Fl. F2. F3. F4, see "Soil Classification Texture of Soil - An engineering classification of the soils by particle size and proportion, sec "Soil Classification Chart". note the proportions are approximate attd modifications to the soil group due to dry. no or little apparent surface moisture, damp. moisture forms portion of color, less than plastic limit. sand. (The moisture content is further defined by reference to. PI, LW. NP. M% or ddatency.) Density - refers to more.or-less non.cohesive soils, such as sand gravel mixtures with or without a fine fraction, derived from drilling action and/or sample data: usually described as: very loose, loose, medium dense, very dense. Genera] intent is to portray earthwork characteristics. Stiffness - refers to more-or-]ess cohesive soils and fine grained silts of the clay-silt groups. Derived from drill action and/or sample data. Very loft, soft, stiff, very stiff and hard are commonly used terms. , Particle size -- Thc largest particle recovered by the split spoon is 1-3/8", Shelby tube y', auger flights (minute-man) 2', Auger flights {B-SO hollow stem) 6"-8'. Larger particles are described indirectly by action of the drdliug and are referred to as cobbles, 3" to 8", or boulders 8"+. Therefore when reviewing the gradation sheets, if any, the description on the hole log must be considered for an'indication of larger particles. Unified Soil Classification - This is a two letter code. See Unified Classification sheet {'or further definition. In some cases AASHO and/or FAA soil classifications may be shown as well as the unified. Atterberg Limits - useful for fine grained and other plastic soils. natural moisture content believed to be less than plastic limit ppe; natuxal moisture content believed to be between plastic and liquid ~-lmits natural moisture content believed to be greater than liquid limit NP; non-p/esot, uteful as a modifying description of some tilty rnat ~ria L~, Dilltency - is the abdity of water to migrate to the lurface of a ~turated or nearly saturated loll sample when vibrated or jolted - uled as In aid to determine if a fine grained tod i~ a shghtly or non-plastic silt or a volcanic a~h. Rock flour - finely ground soil that is not plastic but otherwise appears similar to a clayey silt. Organic Content - usually described as Peat, PT. sotnetimes includes discrete particles such as wood, coal, etc. as a modifier to an inorganic soil. Quantity described as; trace, or an estimate of volume, or, in case of all organic, - as Peat. This may include tundra, muskeg and bog material. Muck .- a modifier used tn describe very soft, semi-organic deposits usually occuriug below a peat deposit. Amorphus peat -. organic particles nearly or fully disintegrated. Fibrous Peat -- organic particles more-ordess intact. Bottom of Testhole - includes last sample interval. Frost Line - seasonal frost depth as described by drilling action and/or samples at the time of drilling. Frozen Ground - other than frost line. described by samples, usually includes description of ice content, often will include modified Unified Classification for frozen soils - this is a special case related to permafrost studies. Free Water Level - The free water level noted during drilling. This is not necessarily the static water table at the time of drilling or at other seasons. Static water table determination in other than very permeable soils requires observation wells or piezomcter installations, used only in special cases. Blow/6" - The nulnber of blows of a 140 weight free falling 30" to advance a 2" split spoon 6"; the number of blows for a 12" advance is, by definition, thc standard penetration. ,,,1% -- natural moisture content of the soil sample, usually not pe--~fr ormed on clean sands or gravels below the water table. Type of Sample - ~, refers to 2" split spoon driven into the soil by 140 pound weight, a disturbed sample. S. thin wall tube, "Shelby" used to obtain undisturbed samples of fine grained soil, ~, "grab" disturbed sample from auger flights or wall of trench, C, cut sample, undisturbed sample from wall of trench. Dry Stren6th - a useful indicator of a soil's clayey fraction, N=None, L=Low, M=Mediu m, H=High Group - The samples are placed into apparently similar groups based on color ~nd texture and are arbitrarily assigned a group '.citer. Further disturbed tests including Atterberg Limirs, grain size, moisturedensiry relationship, etc. nlay be performed on the group and are assumed to reflect the general distrubed characteristics of the soils assigned to the group. This is an important phase of the soil analysis and is u~ed to ~tandardize the various qualitative determinations and to reduce the number of quantitative tests necessary to describe the soil mass. TEXTURAL SOIL CLASSIFICATION CHART GRAVEL 30% CLAY CLAYE ;LAYE~ OR SAND SILT GRAVEL GRAVEL GRAVELLY 20 30 GRAVEL SAND 40 · 50 60 70 + ~ 4 SCREEN) % BY WEIGHT ' 0 I0 80 90 I00 FROST CLASSIFICATION SYSTEM NONFROST SUSCEPTIBLE SOILS ARE INORGANIC SOILS CONTAINING LESS THAN 3% FINER THAN 0.02 mm. GROUPS OF FROST-SUSCEPTIBLE SOILS: F1 GRAVELLY SOILS CONTAINING BETWEEN 3 AND 20% FINER THAN 0.02 mm. F2 SANDY SOILS CONTAINING BETWEEN 3 AND 15% FINER THAN 0,02 mm. F3 a. GRAVELLY SOILS CONTAINING MORE THAN 20% FINER THAN 0.02 mm, AND SANDY SOILS (EXCEPT FINE SILTY, SANDS) CONTAINING MORE THAN 15% FINER THAN 0.02 mm. b. CLAYS WITH PLASTICITY INDEXES OF MORE THAN 12. EXCEPT VARVED CLAYS, F4 a. ALL SILTS INCLUDING SANOY SILTS, b. FINE SILTY SANDS CONTAINING MORE THAN 15% FINER THAN 0,02 mm, c, LEAN C.LAYS WITH PLASTICITY INDEXES OF LESS THAN 12. d. VARVED CLAYS,