Astm stp 599 1976

SOIL SPECIM EN PREPARATION FOR LABORATORY TESTING A symposium presented at the Seventy-eighth Annual Meeting AMERICAN SOCIETY FOR TESTING AND MATERIALS Montreal, Canada, 22-27 June 1975 ASTM SPECIAL TECHNICAL PUBLICATION 599 D A Sangrey, symposium co-chairman R J Mitchell, symposium co-chairman List Price $35.00 04-599000-38 ,4N~L ~L~/~AMER~CAN SOCIETY FOR TESTING AND MATERIALS 1916 Race Street, Philadelphia, Pa 19103 qi]|lY Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized (~) BY AMERICAN SOCIETY FOR TESTING AND MATERIALS 1976 Library o f Congress Catalog Card Number; 76-704 NOTE The society is not responsible, as a body, for the statements and opinions advanced in this publication Printed in Bahimore, Md June 1976 Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized Foreword The symposium on Soil Specimen Preparation for Laboratory Testing was presented at the Seventy-eighth Annual Meeting of the American Society for Testing and Materials held in Montreal, Canada, 22-27 June 1975 Committee D-18 on Soil and Rock for Engineering Purposes sponsored the symposium D A Sangrey, Cornell University, and R J Mitchell, Queen's University of Kingston, presided as symposium cochairmen Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized Related ASTM Publications Performance Monitoring for Geotechnical Construction, STP 584 (1975), $14.00, 04-584000-38 Field Testing and Instrumentation of Rock, STP 554 (1974), $18.75, 04-554000-38 Analytical Methods Developed for Application to Lunar Sample Analysis, STP 539 (1973), $15.00, 04-539000-38 Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized A Note of Appreciation to Reviewers This publication is made possible by the authors and, also, the unheralded efforts of the reviewers This body of technical experts whose dedication, sacrifice of time and effort, and collective wisdom in reviewing the papers must be acknowledged The quality level of ASTM publications is a direct function of their respected opinions On behalf of ASTM we acknowledge with appreciation their contribution A S T M Committee on Publications Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions aut Editorial Staff Jane B Wheeler, Managing Editor Helen M Hoersch, Associate Editor Charlotte E DeFranco, Senior Assistant Editor Ellen J McGlinchey, Assistant Editor Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized Contents Introduction Effect of Water Saturation History on the Strength of Low-Porosity Rocks G BALLIW, B LADANYI,AND D E GILL Testing Equipment Rock Types Specimen Preparation Testing Procedures Experimental Results Conclusions 11 12 19 Four Factors Influencing Observed Rock Properties-P G CHAMBERLAIN,E M VAN EECKHOUT,AND E R PODNIEKS Discussion of Critical Factors Summary 21 22 34 Trimming Device for Obtaining Direct Shear Specimens from Samples of Stiff Fissured Clay Shale G N DURHAM Residual Shear Test Procedures Waterways Experiment Station Residual Shear Testing WES Direct Shear Trimming Device Specimen Preparation Discussion 37 38 38 39 40 42 Effects of Specimen Type on the Residual Strength of Clays and Clay Shales F C TOWNSENDAND P A GILBERT Previous Investigations Materials and Equipment Specimen Preparation Test Results and Analyses Conclusions 43 44 45 47 49 63 Effects of Storage and Extrusion on Sample Properties-ARA ARMANAND S L MCMANIS Literature Survey Sampling and Field Testing Laboratory Tests and Results Selection of Representative Specimens General Conclusions 66 67 68 69 80 85 Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized Transportation, Preparation, and Storage of Frozen Soil Samples for Laboratory Testing T H W BAKER Factors Affecting Laboratory Tests on Frozen Soils Frozen Soil Samples Machining and Preparation of Specimens for Testing Rough Cutting Methods Finishing Methods Storage and Protection During Laboratory Testing Conclusions 88 89 89 97 98 98 104 111 Temperature-Controlled Humid Storage Room-MICItAEL BOZOZUK Design Closed Flow Conditioning System Handling and Preparation of Samples for Storage Effect of Storage Time on Test Results Summary 113 115 119 122 122 125 Effect of Storage and Reconsolidation on the Properties of Champlain Clays P LA ROCHELLE, J SARRAILH,AND F A TAVENAS Characteristics of the Cemented Clays Water Migration Following Sampling Influence of Reconsolidation Influence of Storage Time Conclusion 126 128 130 137 140 144 Pore Water Extraction and the Effect of Sample Storage on the Pore Water Chemistry of Leda Ciay J K TORRANCE Soil Material Storage Procedures Pore Water Extraction Results and Discussions Conclusions and Recommendations 147 149 149 150 151 155 Variation in Atterberg Limits of Soils Due to Hydration History and Specimen PreparationmD A SANGREY,D K NOONAN, AND G S WEBB Test Program Conclusions 158 160 167 Effect of Specimen Preparation Method on Grain Arrangement and Compressibility in SandmARsHUD MAHMOOD,J K MITCHELL, AND ULF LINDBLOM Soil Fabric One-Dimensional Compressibility Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized 169 170 171 Experimental Investigation Fabric Results Compression Test Results Conclusions 171 178 180 190 A Technique for the Preparation of Specimens of Loose Layered Silts V A NACCIAND R A D'ANDR~A Soil Description Specimen Preparation Typical Testing Procedure and Result Conclusions 193 195 195 198 200 Shrinkage of Soil Specimens During Preparation for Porosimetry Tests T F ZIMMIEAND L J ALMALEH Equipment Experimental Work Conclusions 202 204 211 214 Compaction and Preparation of Soil Specimens for Oedometer Testing A R BOOTH Choice of Compaction Method Construction of Mold Method of Compaction Adjustment of the Degree of Saturation Comparison of Specimens Effect on Results Conclusions 216 217 218 219 221 223 224 225 Laboratory Preparation of Specimens for Simulating Field Moisture Conditions of Partially Saturated Soils T Y CHH AND S N CHEN Review of Current Methods for Pretesting Treatment Development of Equipment and Procedures for Pretesting Treatment Test Results and Discussion General Conclusion 232 236 243 Scalping and Replacement Effects on the Compaction Characteristics of Earth-Rock MixturesmR T DONAGHE AND F C TOWNSEND Procedure Test Results and Discussion Conclusions 248 249 257 274 Study of Irregular Compaction Curves P Y LEE Laboratory Investigation 278 281 229 230 Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized 327 LADE AND NEJADI-BABADAI ON MICROWAVE OVEN DRYING 200 I I I I I I I q MICROWAVE OVEN: 148.6 % CONVENTIONAL OVEN: 147.3%qi ~ 160 V 121.2 o-~ ~ 120 I'Z bJ t,'oZ,._) 80 hi 4O 0 ~ o I I I0 86., a A zx-" - - ' - o I I A 65.3 % 609% " -~ ~ I 15 20 25 DRYING TIME (rain) I I 50 55 o 40 FIG l Drying curves for lO0-g specimens of Haley clay with different initial water contents be explained as follows: For the same amount of wet soil, the amount of solid material increases with decreasing water content Assuming that the amount of absorbed and hydroxyl water increases with the amount of solid material, the water available for removal by microwave heating (but not for removal by conventional heating at 105 ~ increases with decreasing water content Therefore, the difference between water contents determined from the two different heating processes increases with decreasing water content The data presented in Table indicate that drying of clayey soils in the microwave oven corresponds to drying in a conventional oven at temperatures higher than 105 ~ Increasing the drying temperature results in removal of adsorbed water and some hydroxyl water Highly plastic clays can adsorb more water to the surfaces of the particles than low plastic silts The difference in water contents, as determined by microwave oven and conventional oven, is therefore greater for the highly plastic bentonites than for the low plastic L-soil Sands The results of tests on Antelope Valley sand, with negligible amount of particles smaller than 2/~m and on silty sand with percent clay (< 2/~m) are also shown in Table It may be seen that the differences between the water contents determined by the microwave oven and by the conventional oven were only 0.5 and 0.2 percent, respectively Thus, very little additional water was removed by the microwave heating, and this little water was most likely associated with the clay minerals Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized 328 SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING TABLE Comparison o f water contents for lO0-g specimens with different initial water contents dried in the microwave oven and the conventional oven Type of Soil Water Content Determined Using Microwave Oven, % Difference Water Content Between Determined Using Water Contents, Conventional Oven, % % Black Hills bentonite 926.1 692.7 659.0 906.5 660.8 603.0 19.6 31.9 56.0 Dixie Bond bentonite 138.4 130.3 84.1 127.3 116.6 70.1 11.1 13.7 14.0 Haley clay 148.6 121.2 88.3 63.3 147.3 119.8 86.1 60.9 1.3 1.4 2.2 2.4 Grundite clay 97.8 61.5 54.1 40.8 96.3 59.8 52.2 38.4 1.5 1.7 1.9 2.4 H-soil 56.2 50.4 41.6 55.1 49.0 40.1 1.1 1.4 1.5 M-soil 43.0 31.2 30.4 42.7 30.5 29.3 0.3 0.7 1.1 L-soil 41.6 33.5 27.9 40.7 32.4 26.5 0.9 I 1.4 Antelope Valley sand 11.6 11.1 0.5 Silty sand 15.3 15.1 0.2 8.0 8.0 0.0 Ottawa sand present in the soils Tests on clean Ottawa sand, consisting o f quartz grains, resulted in exactly the same water content determined by the two methods of heating, which also supports the hypothesis that only clay minerals are sensitive to the drying process in the microwave oven Effects of Amount of Soil and Soil Type Batches o f soil with uniform water content were prepared as follows Air-dry powder was mixed with water to produce a uniform lean mix, with water content above the liquid limit This liquid soil was then consolidated in a large double draining consolidometer to produce a cylinder of soil with uniform water content Specimens ranging in weight from 10 to 500 g were cut from the soil cylinder and dried in the microwave oven, Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized LADE AND NEJADI-BABADAI ON MICROWAVE OVEN DRYING 329 according to the procedure outlined previously Control specimens were dried for 24 h in the conventional oven at 105 ~ for comparison of water contents Typical drying curves are shown in Fig for soil specimens of different sizes The same characteristic shape was observed in all cases, regardless of the weight of soil The larger specimens required longer drying times This increase in drying time with increasing amount of wet soil may be explained as follows: the initial microwave penetration is impeded because a portion of the waves is reflected from the wet surface of the soil, and the penetration depth of the microwaves is limited, as explained previously The loss in weight from equally wet specimens is therefore initially proportional to the surface area of the specimens For specimens with the same shape, the ratio between volume and surface area is proportional to the linear dimensions of the specimens Therefore, the amount of water being driven off, relative to the volume of the specimen, is smaller for a large specimen than for a small specimen, and the initial slopes of the drying curves consequently decrease with increasing amount of wet soil The time required for complete drying of the soil specimens in the microwave oven increased with amount of wet soil Complete drying of the small specimens (10 g) was accomplished within 10 to 20 The highly plastic clays with high initial water content tended to require longer time for complete drying than less plastic soils with low water content The difference is drying time between the high and low plastic soils was more pronounced for the large specimens (500 g), for which the drying times ranged from about 20 to h The water contents obtained from the two different drying methods and the differences in water content are listed in Table for the seven types of clay soil tested The difference in water content for each type of soil is seen to decrease with increasing amount of wet soil This may be explained by the limited penetration depth of the microwaves Thus, for large volumes of soil, the microwaves may not reach the interior of the specimen, and the drying of the soil in the middle is accomplished through heat transfer from the surface It was noticed that a specimen, which was first dried in the microwave oven, then cooled down in the desiccator, and again heated by microwaves, does not heat up to the same high temperature as the initially wet specimen Therefore, after the outer shell of a specimen had dried, the heat generation by microwaves and the heat transfer to the interior of the specimen decreased Some of the more strongly held water molecules, which could not be reached by the microwaves, may therefore not have evaporated from the large specimens The difference between the two water contents therefore decreased with increasing specimen size However, this effect is somewhat obscured by a tendency of the large specimens to crack, due to high vapor pressures generated inside the specimens by the rapid heating process in the microwave oven Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized 330 SOIL SPECIMEN 70 I t PREPARATION oE/ I FOR I LABORATORY , TESTING r g f L / g ~ 3o ~ 20 0 I I I L I I I0 15 20 25 30 35 40 DRYING TIME (mi n) FIG Drying curves for specimens o f Haley clay showing influence of amount o f soil Effects of Microwave Heating on Soil Characteristics Due to the nature of the microwave heating process, the temperature to which the soil is heated in the microwave oven is difficult to measure However, the change in the soil classification according to the Atterberg limits may be taken as a measure of the effects of heating by microwaves Liquid limit, plastic limit, and shrinkage limit tests were performed on clays and clayey silts which, in powder form, first had been either (1) dried in the microwave oven for 20 min, (2) dried in the conventional oven at 105 ~ for 24 h, or (3) left in initial air-dry condition before testing All water content determinations, subsequent to these treatments, were made using the conventional oven The results from the liquid limit and plastic limit tests are presented on plasticity charts in Fig for soils of low plasticity and in Fig for highly plastic clays Liquid limits, plastic limits, and plasticity indices all decreased Clay soils predried in the microwave oven gave the greatest changes, and those predried in the conventional oven gave intermediate changes, as compared to the values obtained from only air-dried soil This sequence is referred to hereafter as M-C-A The most extreme reductions in plasticity occurred for the highly plastic Black Hills bentonite, and the smallest reductions occurred for the low plastic L-soil The general trend indicated on the plasticity charts is to change the soil classification in the order M-C-A along the A-line towards the silt region The same trend has Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized LADE AND NEJADI-BABADAI ON MICROWAVE OVEN DRYING 331 TABLE Comparison o f water contents f o r specimens with the s a m e initial water content and different wet weights dried in the m i c r o w a v e oven and the conventional oven Water Content Determined Using Micro- Type of Soil Initial Amount of Wet Soil, g wave Oven, e/0 Water Content Determined Using Con- Difference ventional Oven, Between Water 07o Contents, % 10 746.3 50 200 500 735.6 728.4 709.0 702.0 33.6 26.4 7.0 Dixie Bond bentonite 10 50 200 500 81.4 80.7 80.5 80.1 73.8 7.6 6.9 6.7 6.3 Haley clay 10 50 250 500 66.7 64.5 64.0 64.0 63.1 3.6 1.4 0.9 0.9 Black Hills bentonite 44.3 10 41.1 50 200 500 40.2 40.0 40.0 H-soil 10 50 200 500 35.4 34.8 34.3 34.0 33.7 1.7 1.1 0.6 0.3 M-soil 10 50 250 500 27.3 26.9 26.5 26.4 26.0 1.3 0.9 0.5 0.4 L-soil 10 50 200 500 27.7 27.4 27.5 26.9 26.5 1.2 0.9 1.0 0.4 Grundite clay 1.4 39.7 0.5 0.3 0.3 been observed for soils being heated conventionally to increasingly high temperatures, [4, 6-10] These observations indicate that drying of clayey soils in a microwave oven corresponds to drying in a conventional oven at temperatures higher than 105 ~ However, the temperature corresponding to the microwave heating is most likely different for different types of clay mineral The loss of plasticity has been attributed to irreversible loss of adsorbed water and to breakdown of the crystalline structure of the clay minerals, due to loss of hydroxyl water [4] and fusion of the flat surfaces of the clay mineral particles [10] This produces larger soil particles, with properties closer to those of silt Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized 332 SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING [ i I I I I I l I 50 60 70 o AIR-DRY SOIL z~ SOIL HEATED IN CONVENTIONAL OVEN a SOIL HEATED IN MICROWAVE OVEN 40 x 30 la.i t:3 >.- 20 o_ io M- o t /~ I0 L- SOIL 20 I 30 40 LIQUID L.IMIT F I G Plasticity chart showing reduction in plasticity after heat treatment in conventional oven and microwave oven f o r soils o f low plasticity 6O x t 40- i sO0 4oo I I I BLACKHILLS BENTON,TE I / / zo | E /0 / /- / / [ I I I I o AIR-DRY SOIL //o A SOIL HEATED IN CONVENTIONAL / , , ~ OVEN ///A-, [] SOIL HEATED IN M I C R O W A V E / / OVEN _ BOND ~ GRUNDITE ///- BENTONITE I I I I I ~ 3oBoo I0- 0 J ~ I0 20 I 30 I 40 50 60 LIQUID LIMIT I I I 70 80 90 I O0 FIG Plasticity chart showing reduction in plasticity after heat treatment in conventional oven and microwave oven f o r highly plastic clays Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized LADE AND NEJADI-BABADAI ON MICROWAVE OVEN DRYING 333 The shrinkage limits were found to increase in the order A-C-M, thus indicating a reduction in swelling potential of the soils having initially been heated in the two ovens Similar reductions in swelling potential have been observed for soils which have been heated to high temperatures [4, 10 121 Liquid limit and plastic limit tests were performed on the two marine days, designated NBC-1 and NBC-23 These soils were only available in wet condition and were not predried Half of each specimen tested was dried in the microwave oven, and the other half was dried in the conventional oven The results of the Atterberg limit tests are listed in Table Both liquid limits and plastic limits were found to be higher for the specimens dried in the microwave oven than those obtained from soil drying in the conventional oven These results are in agreement with the other data described herein Thus, it is concluded that, if the microwave oven is used for soil drying, values of liquid and plastic limits will be determined to be too high Summary and Conclusions This paper presents the results of an investigation of the usefulness of the microwave oven for water content determination and soil drying before testing Twelve different soils, ranging from highly plastic clays to clean sand, were used in the investigation All soils were inorganic, and the main effort was concentrated on drying of different clay types The influences of initial water content, amount of soil, and soil type on the drying time were investigated Typically, the time for complete drying varied from about 10 for 10 g to about 45 for 500 g of wet soil Highly plastic clays with high water content tended to require longer time, whereas low plastic soils with low water content dried completely in shorter time The water contents determined using the microwave oven were higher for all soils containing clay minerals than those determined for the same soils, using the conventional oven at 105~ The greatest difference in these water contents was observed for small volumes of highly plastic clays The difference decreased with increasing volume, increasing initial water content, and decreasing plasticity Typically, the difference in water content varied from 0.3 to 1.5 percent for low to medium plastic soils to 14 percent for very highly plastic clays Negligible or no difference was observed for silty sand and clean sand The change in soil classification, according to the Atterberg limits, was taken as a measure of the effects of heating by microwaves The liquid limit, the plastic limit, and the plasticity index were found to decrease for all the soils when they had been preheated in the microwave oven The largest reductions in these limits occurred for the highly plastic days, and the Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized 334 SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING TABLE Liquid and plastic limits for marine clays determined using the microwave oven and the conventional oven Limit Determined Using Microwave Oven Determined Using Conventional Oven NBC-I LL PL 165 46 147 41 NBC-23 LL PL 173 55 151 48 Type of Soil smallest reductions were observed for the low plastic soils The shrinkage limits tended to increase after preheating in the microwave oven, thus indicating a reduction in swelling potential of the soils The effects of preheating a plastic soil in the microwave oven are comparable to the effects of drying the soil in a conventional oven at high temperatures It may be concluded that the microwave oven can be used for quick drying of soil, but the characteristics of plastic soils will change Although accurate determinations of water content may only be achieved for nonplastic soils such as coarse silts, sands, and gravels, the error encountered for plastic soils may be acceptable for many purposes Thus, the microwave oven may be useful for rapid determinations of approximate water content of clay soils and for research purposes, when control specimens show no difference in water content However, it is not recommended to use this oven on a routine basis until the magnitude of the possible error has been established for the type of soil to be dried Acknowledgment The writers express their appreciation to the National Science Foundation which provided support for this study under Grant GK 37445 K L Lee of the University of California at Los Angeles provided valuable advice for the preparation of the manuscript References [1] Piischner, H., Heating with Microwaves, Centrex Publishing Co., Eindhoven, The Netherlands, 1966 [2] Waite, W P., Cook, K R., and Bryan, B B., "Broad Spectrum Microwave Systems for Remotely Measuring Soil Moisture Content," Publication No 18, Water Resources Research Center, University of Arkansas, Fayetteville, 1973 [3] Arulanandan, K., Basu, R., and Scharlin, R J., Highway Research Record, No 426, 1973, pp 23-32 [4] Grim, R E., Applied Clay Minerology, McGraw-Hill, New York, 1962 Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized LADE AND NEJADI-BABADAI ON MICROWAVE OVEN DRYING 335 [5] Lambe, T W., "How Dry is a 'Dry' Soil?", Proceedings, Highway Research Board, 1949, pp 491-496 [6] Casagrande, A., Public Roads, Vol 13, 1939, pp 121-130 [7] Chandrasekharan, E C., Boominathan, S., Sadayan, E., and Narayanaswamy Setty, K R., Proceedings, International Conference on Effects of Temperature and Heat on Engineering Behavior of Soils, Special Report 103, Highway Research Board, 1969, pp 161-172 [8] Laguros, J G., Proceedings, International Conference on Effects of Temperature and Heat on Engineering Behavior of Soils, Special Report 103, Highway Research Board, 1969, pp 186-193 [9] Lambe, T W., and Martin, R T., Proceedings, Highway Research Board, Vol 34, 1955, pp 566-582 [10] Radhakrishnan, N., Katti, R K., and Hussain, M., Proceedings, Third Asian Regional Conference on Soil Mechanics and Foundation Engineering, Vol I, Haifa, 1967, pp 111-115 [11] Aylmore, L A G., Quirk, J P., and Sills, I D., Proceedings, International Conference on Effects of Temperature and Heat on Engineering Behavior of Soils, Special Report 103, Highway Research Board, 1969, pp 31-38 [12] Leonards, G A., Foundation Engineering, McGraw-Hill, New York, 1962 [13] Ryley, M D., "The Use of a Microwave Oven for the Rapid Determination of Moisture Content of Soils," Report LR 280, Road Research Laboratory, Berkshire, England, 1969 [14] Lade, P V., and Nejadi-Babadai, H., "Characteristics of Soil Drying by Microwave Oven," Report No UCLA-ENG-7476, School of Engineering and Applied Science, University of California, Los Angeles, Oct 1974 [15] Lambe, T W., Soil Testing for Engineers, Wiley, New York, 1951 [16] "Laboratory Soils Testing," Engineer Manual EM 1110-2-1906, Office of the Chief of Engineers, Department of the Army, Washington, D C., 1970 DISCUSSION P A Gilbert ~ a n d M M A l - H u s s a i n i I (written d i s c u s s i o n ) - - T h e aut h o r s have p r e s e n t e d v a l u a b l e a n d interesting i n f o r m a t i o n o n soil d r y i n g in a m i c r o w a v e oven I n a r e c e n t study, t h e W a t e r w a y s E x p e r i m e n t Station (WES) conducted a number of water content determinations on vario u s t y p e s o f soil, o f which t h e p e r t i n e n t characteristics a r e p r e s e n t e d in T a b l e B o t h c o n v e n t i o n a l a n d m i c r o w a v e ovens were u s e d in the test p r o g r a m , a n d the results are p r e s e n t e d in T a b l e T h e s t u d y shows t h a t , while m i c r o w a v e e n e r g y o f f e r s a r a p i d m e t h o d f o r d r y i n g soil, it s h o u l d b e used with c a u t i o n since m i c r o w a v e e x p o s u r e t i m e g r e a t l y influences t h e r e s u l t i n g water c o n t e n t I n all tests c o n d u c t e d , the s t a n d a r d d e v i a t i o n in water c o n t e n t , as o b t a i n e d b y the t w o m e t h o d s , was less t h a n 0.5 p e r c e n t T h e c o n s i s t e n c y a n d r e l i a b i l i t y o f the results d e p e n d o n a c c u r a t e k n o w ~Civil engineer and research civil engineer, respectively, Soils and Pavements Laboratory, U.S Army Engineer Waterways Experiment Station, Vicksburg, Miss 39180 2Gilbert, P A., "Feasibility Study Microwave Oven Used for Rapid Determination of Soil Water Contents," WES MP 3-478, U.S Army Engineer Waterways Experiment Station, Vicksburg, Miss 39180 Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized 336 SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING TABLE Description o f materials tested Atterberg Limits, % Identification LL b pL c PI d Description Long Lake clay (CH) 71 23 48 fat dark brown, alluvial soil composed of silt and clay-size partides of montmorillonite with some quartz and illite; extremely sticky and plastic when wet Vicksburg buckshot clay (CH) 56 22 34 similar to Long Lake clay Vicksburg silty clay (CH) 34 22 12 fine-grained loessial deposits Minus fraction is about percent of total specimen and is predominately montmorillonite 79 26 53 inorganic gray clay from Atchafalaya River Basin, La 679 36 643 commercial bentonite drilling mud, approximately 95 percent montmor_illonite Brazilian clay (CH) 96 38 58 dark red clay whitish clay, percent iron gravity G, = DeGray Dam fines (GC) 37 14 23 clayey sandy gravel; only minus No material tested NP e NP NP fine, uniform quartz sand with some feldspar from Mississippi River near Vicksburz Miss EABPL a gray clay (CH) Aquagel(CH) Reid Bedford sand (SP) EABPL a peat (Pt) with mottles of approximately 17 oxides, specific 3.12 fibrous organic material from Atchafalaya River Basin, La QEABPL = East Atchafalaya Basin Protection Levee bLL = liquid limit cpL = plastic limit dpI = plasticity index eNp = nonplastic Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized 17.13 16.48 14.21 141.35 58.39 274.32 373.04 47.22 44.74 10.60 5.13 5.54 Vicksburg silty clay EABPL a gray clay Aquagel Brazilian clay DeGray Dam fines Reid Bedford sand ignited 5.08 5.53 10.55 47.05 44.21 275.06 374.16 142.09 59.79 17.09 16.54 14.19 49.33 52.09 Microwave b (predicted) 0.05 0.01 0.05 0.17 0.53 - 0.74 - 1.12 - 0.74 - 1.40 0.04 - 0.06 0.02 - 0.14 0.11 Difference 1551 620 754 795 913 1225 1302 1451 980 1247 1054 682 600 966 1240 Time in Microwave Oven, s c 470.53 471.20 733.50 709.28 387.86 599.00 349.88 346.60 282.53 653.95 989.28 501.36 357.60 463.14 574.69 Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized - Wet Weight of Microwave Oven Specimen, g aEABPL = East Atchafalaya Basin Protection Levee bWater content determined from Eq 11 using conventional oven water contents and experimental water tent-drying time data c Time required for water loss equivalent to water loss in conventional oven 220.25 49.19 Vicksburg buckshot clay EABPL a peat 52.20 Long Lake clay Material Conventional (actual) Water Content, Percent oven drying times for various soils TABLE Summary o f water contents measured by conventional and microwave ovens and microwave I'- < m O < m z ID -n < O O Z o z z o O m 338 SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING ledge o f exposure time The exposure time required in the microwave oven to produce water contents comparable to those obtained in a conventional oven can be expressed as follows T= 4.2Mw[(0.2/w + 1)(100 - to) + 539] P where T Mw w to P = = = = = time in microwave oven, s, mass o f water present in soil-water mixture, g, water content of soil specimen, initial temperature o f soil-water mixture, and power output of oven, W This governing equation indicates that an estimate o f the specimen water content is required This is not a serious limitation since a duplicate specimen can be incrementally dried in the microwave oven to obtain a water content estimate as input into the equation The results o f the investigation indicate that microwave ovens are not suitable for drying soils with high organic content or soils containing gypsum In addition, microwave energy must be used with care when drying soils with high metallic content, such as iron ore and bauxite The WES study also pointed up the difficulties involved in the simultaneous drying o f multiple specimens These difficulties were grave enough that this procedure is not recommended The use of metallic tare cans or plates should be avoided, as they shield their contents from microwaves Glass vessels should be used as specimen containers since they are transparent to microwaves The study showed that drying time in a microwave oven is influenced by the amount of water present in a soil-water mixture and is not significantly affected by the amount, type, or plasticity of the soil The WES study did not show any evidence o f the effect o f wet surface on drying time; therefore, it is doubtful that there is any significant reflection of microwave from wet surfaces The authors have shown that the water content reached a constant value after about 20 of drying time On the other hand, tests at WES show that, while this is indeed the case for sand and silt (Fig 5), it is not true with clay (Fig 6), for which water content continued to increase with increasing drying time The authors indicated correctly that, the larger the volume o f specimen, the closer the value o f water content obtained by the conventional and microwave ovens For this reason, WES tests have been conducted on specimens o f not less than 250 g, which should be the lower limit for any successful water content determination in the microwave oven A difference in water content of 14 to 56 percent for certain plastic soils, as indicated by the authors, is unusually high, which may indicate that the soils may have been overheated by the microwave oven Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized 339 LADE AND NEJADI-BABADAI ON MICROWAVE OVEN DRYING 50 ~.o -.o IZ 40 El O n" El n 30 Z El IZ 2.0 O nr" I.i.I L EGEN D OB R A Z I L I A N CLAY ix V I C K S B U R G B U C K S H O T C L A Y I1~, C O N V E N T I O N A L OVEN WATER C O N T E N T I0 200 400 600 800 1000 1200 1400 l iO0 T I M E IN OVEN;, S FIG - - T i m e in microwave oven versus water content o f clay z o z ~ Z LEGEND # ~ o 200 400 OREIDBEDFORDS A N D [] REID BEDFORD S A N D C O N V E N T I O N A L OVEN WATER C O N T E N T 600 800 I DO0 T I M E IN OVEN~ S 1200 1400 1600 FIG - - T i m e in microwave oven versus water content o f sand It is vital that normal safety precautions be observed when using microwave ovens, since microwaves are a form of radiation energy and should be treated as such; also, microwaves affect heart pacers and other sustaining devices at substantial distances P V Lade and H Nejadi-Babadai (authors" closure) The authors appreciate the discussion and the additional information provided by Gilbert and AI-Hussaini The authors agree that the exposure time required in the microwave oven is critical for correct determination of water content of plastic soils due to the sensitivity of clay minerals to drying ternCopyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized 340 SOIL SPECIMEN PREPARATION FOR LABORATORY TESTING perature Since the temperatures generated by the microwaves in the soil specimen are difficult if not impossible to control, a fairly precise estimate of microwave exposure time may substitute the condition used for the conventional oven that drying should continue until no further weight loss occurs An estimate of exposure time is complicated by nonuniform temperature distribution in the specimen and, therefore, by influence of most of the factors mentioned in the paper Gilbert and A1-Hussaini present a formula for estimating the microwave exposure time on the basis of the mass of water present in the soil water mixture, the initial water content, the initial temperature of the specimen, and the power output of the oven The microwave oven used for the present study had a power output of 400 W Whereas the trend indicated by this formula appears to be correct, the drying times calculated for the clays tested in the present study are 30 to 40 percent too short, resulting in water contents which are too small compared to those obtained from the conventional oven However, it is possible that only part of the power output is effective in heating the soil specimen, and the formula for exposure time, therefore, may be better than indicated by the calculations Microwave reflection from wet soil surfaces has been studied previously ([2] of the paper), and it is influenced by the complex dielectric constant and, therefore, the water content of the wet soil The microwave reflection was offered as an explanation for the shape of the initial parts of the drying curves However, the reflection may not have significant effects on the time for complete drying, as pointed up by Gilbert and AI-Hussaini The ability of clays to adsorb water increases with increasing plasticity Since the clays in the present study were dried until no further weight loss occurred, the adsorbed water and some of the hydroxyl water was removed due to temperatures higher than 105 ~ generated by the microwaves Thus, the clays were overheated in the microwave oven, as suggested by Gilbert and AI-Hussaini, and this resulted in the rather high differences in water content for the highly plastic clays The results of the studies performed at the U.S Army Engineer Waterways Experiment Station and at the University of California at Los Angeles serve to indicate the problems and the complexity involved in using a microwave oven for water content determination Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized Copyright by ASTM Int'l (all rights reserved); Wed Dec 22 14:00:00 EST 2010 Downloaded/printed by University of British Columbia Library pursuant to License Agreement No further reproductions authorized