Downloaded from the Online Library of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE)

INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING

This paper was downloaded from the Online Library of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). The library is available here: https://www.issmge.org/publications/online-library

This is an open-access database that archives thousands of papers published under the Auspices of the ISSMGE and maintained by the Innovation and Development Committee of ISSMGE. 158

And Plasticity Index of soils. A.S.T.M. de 4) Ultra-mechanical analysis of soils: Puri, signation: D.424-39. A.S.T.M. Standards. A.N., and B.R. Puri: 3. Afrlc. Scl., 1941, Part II. Non-metallic materials - Construc ¿I, 171-7. tional. The American Society for Testing 5)T h e Sub-division of the clay fraction in Materials Philadelphia, Pa., 1944 (The So mechanical analysis: Russell, B.W.: J .Agric. ciety). Scl., 1943, 22 (?). 147-54. 3) Classification and Identification of Soils. 6) Electron micrographs of clay minerals: Casagrande, As Proc. Am. Soc. Civ. Eng. 1947. Shaw, B.T., and R.P. Humbert.: Proc. Soil 2 1 , pp. 783-810. Scl. Amer. 1941, 6, 146-9.

-o-o-o-o-o-o-

SUB-SECTION II b IDENTIFICATION TESTS

|| b 1 AN EXPERIMENTAL STUDY OF THE MAXIMUM AND MINIMUM POROSITIES OF SANDS

J.J. KOLBUSZEWSKI DIPL.ING. Imperial College, University of. London

3. Stone Court 52 - 100 B.S.S. INTRODUCTION. 4. Stone Court Medium-Uniform 5. Stone Court Well-graded This, paper presents the results of re 6. Ham River 25 - 52 B.S.S. search to determine limiting porosities for any given sand. Fig. 1 shows grain distribution curves for These limiting porosities (maximum and all of these sands. The roundness and spheric minimum) if obtained by simple and reliable ity of the grains were determined by inspec methods should provide convenient and useful tion of the projected shapes, as outlined by values not only for the description of a sand KRUMBEIN 8) and 9). but should serve as criteria for its expected behaviour, in other words should provide the SAND Mean Mean same sort of comparable values as Atterberg's Sound Spheric limits in case of clays. ness ity

It may, for example, be known that the 1. Leighton Buzzard 18 - 25 0'840 porosity of sand in the field is r$, but by 0*5. itself this value conveys little, and for its 2. Stone Court 18 - 25 0'3 0*803 significance to become apparent it must be re 3. Stone Court 52 - 100 0*3 lated to the maximum and minimum O'787 porosities at which the sand can exist in 4. Stone Court Med.-Unif. 0'3 0*800 stable packing. 0*3 0*786 The main factors which have been consider 5. Stone Court Well-Graded ed in this study include the size of measuring 6. Ham - River 25 - 52 0'4 O'772 vessel, the rate of pouring, the difference between pouring in air and water, the influ Specific gravities of the Sands are: ence of tamping and vibration. Many tests were run to study these factors and the results Leighton Buzzard 2'6 were averaged so as to assure representative Stone Court 2'7 values. Every effort was made to keep all Ham River 2 *7 other minor variables constant (temperature, moisture content). Other Sands have been used for checking the results and techniques. In all experiments special care was taken to repeat exactly the developed techniques. LOOSE PACKING. A limited number of tests have been run to obtain supplementary information. Pouring in Air. It must be clearly recognized that some At an early stage of the research it- was- of the results will require further investig found that quick pouring of the same quantity ation in order to complete the general picture (weight) of sand through air results in higher of the research since this appearB to be a porosities than those obtained by slow pouring. first attempt to deal systematically with this A series of tests thus were carried out problem. and special techniques developed to Investigate the rate of pouring through air. THE SAND SAMPLES. The final technique was as follows: The sands which have been used are as 1. Apparatus (see diagram No. 2) follows s The apparatuB consisted of the following: 1. Leighton Blizzard 18-25 B .S.S. a) A series of p&per funnels perforated to 2. Stone Court 18 - 25 B.S.S. provide an uniform rain of sand partic- 159 thoroughly mixed portion of the air-dried sand Q STONE COURT was poured through the funnels from different 52-100 heights. Time of pouring and volume obtained were recorded. The weight of sample was record ed after the experiment and the porosity calcu © STONE COURT lated. Each test has been repeated not less WELL GRADED. than 10 times and mean value calculated. The results obtained for three of the 6 0 STONE COURT above mentioned sands are represented in this MEDIUM UNIFORM. paper by figures Nr. 3»4,5, where porosities

® STONE COURT 18-2 5.

(?) LEIGHTON fcUZZARD.

Sands used in the experiments. FIG.1 Leighton Buzzard 18/25 B.S.S. FIG.3

STONECOURT 52/IOC \ n w

-S T» ,n, \ \ i ¡/// s IOOO CCS. CL. CTL. H«i f t 2000 CCS. CL. CTL. M■ 2 FT. •X«, V 2000 CCS CL. CTL. N» 1 Ft >s, w v ,\ \ V

Ar \ © \

STANO

FIG. 2 TIME MINUTES. les and permitting control of the time of Ham river sands 25/52 B.S.S. pouring. b) Glass graduates. FIG. 5 i) volume lOOOccs. having 2" in diameter ii) volume 2000ccs. having 3" in diameter have been plotted against time of pouring for c) Laboratory stand with funnel support, each height of pouring. suitable for changing height of pouring Undoubtedly the Leighton Buzzard Sand from 0 to 6 feet. showed the greatest response to small changes 2. Procedure. of time of pouring and was the most difficult material from the point of view of repeating A sample weighing lOOOgms. taken from the results. This seems to be very important as Leighton Buzzard Sand is being used as a Standard for field volume and other measure ments. The more angular Stone Court and Ham Hiver sands were more satisfactory from this point of view and generally speaking sands possessing high roundness and high sphericity appear to be more sensitive than those with both values of lower degree. As has been montioned it is very impor tant that the technique should be exactly re peated. Any slight disturbances during the test - for example when taking readings of volume-mey disturb sand structure and give inaccurate results. It will at once be seen from Figs 3»4 and 5 that the rate of pouring and the height of drop have a profound influence on the porosity* For any given height of drop the porosity de creases with time of pouring, to some limiting value, and this limiting value itself tends to decrease with increasing height of drop, at least up to 6 ft. Indications were obtained that further increase in height produced little or even negative effects. These phenomena appear to be of consider able importance, especially in laboratory work on sands, and they are at present being more fully investigated. The porosities obtained in lOOOccs. glass cylinder (2ndia) are in general slightly higher than those obtained in 2000css glass cylinder (3"dia). This was investigated separately and is reported below. Since it had been shown that the porosity increased with decreasing time of pouring it was decided after discussion with Prof.Skempton to try a very simple technique involving the FIG. 6 following procedure:

a FIG. 7 b 161

Place lOOOgms. of sand In a 2000ccs. cy linder (3"dia) and place a stopper in the top of the cylinder. Tip the cylinder upside down, and then quickly tilt it hack to its original vertical position. The porosities obtained in this way corresponded reasonably closely to the limit towards which the curves in Figs 3,4 and 5 are tending for zero time of pouring The test can be easily repeated many times and it ie therefore suggested that it could be adopted as a standard method for obtaining the loosest packing. As will be seen later very slightly greater porosities can be obtained by depositing the sand through water, but the differences are not important from a practical point of view.

Pouring in Water. Ordinary tap water was used for this part of experiments, having room temperature. The range of temperature in the laboratory was very small and could not have any effect in the re sults. It is necessary to point out that the effect of comparatively big changes in temper ature, in this part of tests, was not inves tigated. Attention was given to the effect of en trapped air when pouring sand through water and a special device was developped for pour ing without air (see Fig. 6). The results obtained by pouring sand through water with (Fig. 7) and without en trapped air are shown on Fig. 8. In all cases

POURED IN WATER

WITH & WITHOUT

A R ENT R>kPPED FIG. 9

in water with and without entrapped air has been investigated. Results obtained showed: SANDS: a) water moving slowly downwards in the con + ST- CT. 3 2-100 tainer, after the sample has been settled, does not affect structure of the sample at A ...... A ST CT. 18-25 all and leaves porosity unchanged, and that • ST. CT. M. UN. b) slight movements of the water upwards caused a decreasing of porosity to a cer 0„ o L- 8. 18-2 5 tain constant value for each sand. , ______That was investigated in the device re * H. R. 2 5-52 presented in Fig. 10. ^ 0 X ST CT W. C" The effect described under b) the author explains as in Fig. 11 which shows how arches formed by sand grains are being destroyed by water moving upwards. FIG. 8 The author feels that the porosities ob tained with entrapped air are to some extent the porosities are lower when no air has been "artificially" high, and that the more funda trapped, but the differences were not great mental result is that obtained by depositing except for Leighton Buzzard Sand, possessing the sand without this air. Although the differ high roundness end high sphericity which shows ence between the results obtained by this again "sensitiveness". technique and by rapid pouring in air are not It has been noted that in case of Leigh very large, the former gives somewhat higher ton Buzzard Sand the air bubbles (see Fig. 9) porosities and the results are probably the are being formed not only at the surface of closest approximation to the loosest packing the water, where the surface tension in broken so far obtained, but this does not alter the by grains, but some of the grains are adsorb suggestion, made above, that the "tipping" ing air from water when at comparatively big test should be used as a standard for the loo6e depth in the vessel. Tha't phenomen was not state, since the differences are not large and noted in the case of other sands and the the tipping test is so very simple. author is of the opinion, that this may be A limited number of tests were run to explained by assuming that the more equal dis study the porosities of sands poured through tribution of surface molecular forces, in the a solution of bentonite (1.2 gms/lOOccs) and case of gains with high sphericity, enables the results obtained showed no essential dif the air disolved in water to form bubbles ference in comparison with pouring through around sand grains. ordinary water. This should not be regarded as The stability of sand structure formed a final result and further investigations 162 the above described experiments: l"dia glass tube 2"dia lOOOccs glass cylinder 3"dia 2000ccs glass cylinder 3"dia glass tube 8"dia glass vessel It was found that in all techniques, wether dry or wet, the porosity decreases when the diameter of the container increases and that changes are bigger in case of con tainers having the diameter smaller than 3 inches. In case of diameters bigger than 3 inches changes are very small and it can be, in the authors opinion , assumed for practical purpos es that for sand work the vessels 3" in diame ter can be used and the influence of the con tainer neglected. Fig.12 shows the influence of the con tainers' diameter in the case of pouring sands through water without air.

FIG. 10 Influence of size of the container. FIG.12

The influence of the container has been mentioned by other investigators and is usually explained by the wall friction 14-). Observing the sand grains falling through water in vessels of 1,2 and 3 inches in diame ter the author was not convinced that comparat ively big changes in porosity could be caused by wall friction: firstly because the experi ment can be carried out in such a way that practically no grains will touch the walls of the container. Yet in all cases influence of the container was distinctly noted. At the beginning of the research an expe riment with packing of ideal spherical grains showed that large empty spaces may be establish ed, tridimensional arching supported by the walls occuring. That sort of arching is easier in case of smaller containers and therefore gives higher porosities. That explanation, in case of grains with i inch diameters and 1,2 & 3" dia containers is easy to understand, but in case of small sand grains also appeared to be insufficient. Finally when powdered mica has been introduced to the experiments it was noted that during the settlement of particles in the water some very characteristic vertical chan nels were formed, through which water from the Pouring in water. bottom of the container moved upwards, being replaced by the settling material. The amount FIG.11 of the channels is always bigger in case of a should be made in future, especially with fine smaller container when the same quantity of sands. material is settling and in case of a large container only a few of those channels occur. Influence of the size of the Container. It was also found that these channels remain Tiie following containers were used in in the settled material after the end of the 163 settling proces. It was observed that In case of very fine sand (100 — 150 B.S.S.) the same sort of channels are in operation but cannot be clearly seen after the end of settling pro cess. The author suggests that different amounts of those vertical channels are affecting poro sities in different container«. Pig. 13 dia- gramaticaly shows the described process.

TECHN.I TECHN.2

TECHN.3 TECHN.4

Stone court well-graded. FIG.14

FIG.13

Influence of the Inclination of the Container. It was found that the inclination of the container affects porosity in the following way: 1) Pouring in Water inclined. All sands formed lower porosities. In case of Well Graded Stone Court differences obtained were comparatively big. 2) Pouring in Air inclined. Generally gives very slightly higher poro sities than when poured vertically. Increased speed of pouring increase porosity in all sands except in case of Well Graded sand where distinct lowering of porosity has been observed when the sand was poured quickly. The different behaviour of Well Graded sand is explained by diagram No.14, where four techniques of producing porosity are represen ted. No. 1 shows structure of sand sample built by pouring vertically in water. Ho. 2 shows how sand poured in water into the inclined contain er forms a comparatively denser structure be cause smaller floating particles are filling small gaps formed by bigger grains sliding on sample's surface. Structures caused by different techniques. No 3 shows how a moving part of quickly poured sand presses the stable part of sample FIG. 15 and causes bigger density. Slowly poured Well Graded san& in tech Fig. No. 15 explains generally how loose nique No. 4 builds itself into a looser struct structures of sands are produced by: 1) slow ure. In case of uniform sands inclination is, pouring in air, 2) quick pouring in air, 3) in contrast, very much less important. pouring inclined and 4) pouring in water. 164

DENSE PACKING, 3. Results obtained by vibrations in steel com For obtaining dense packing following paction Cylinder (Proctors'type) on the vi techniques were used: brating table a) pouring dry sand quickly into the con 1. Hand tamping and vibrating tainer during vibration, 2. Proctors compaction cylinder b) pouring dry sand slowly into the contain 3* Vibrating table er during vibration, 4. Pneumatic and electric hammers. c) tamping during vibration with 5 lbs ram 1. Results obtained in glass cylinder by mer in 3 layers 25 times each layer, a) tamping dry sand with hand tamper in d) vibrating with 25 lbs load at the top of 100 ccs layers, 100 times each layer, the sample, b) tamping dry sand by hand tamper as under are represented on Fig. 18. a), and vibrating by hand each layer 10 times, c) tamping by hand in water each 100 ccs layer 100 times are shown on Fig. 16 0 m i owh 41-4

TAMPED & VIBRATED TAMPED TAMPED IN WATER. IOOO CCS. CL. CYUINDER 0 KAM •„«• .11.

0 IIONC COJ*T M -Jl 0 JIO'.« C€U*t MU. c««ace 0 HAM fi m» »1-11 0 1 TOWl COURT 11-100

0 h id uHir. iio w c coj»t

0 trOME COURT *CU. CPAOCO Vibrating table FIG. 18

FIG.16

2. Results obtained in Proctors' Compaction Cylinder by tamping with 5 lbs. rammer hav ing 12" drop a) applying 25 blows of the ranmer at the top of the dry sample, b) applying 50 blows of the rammer at the top of the dry sample, c) applying Proctors' Standard procedure, varying water content obtain maximum dens ity, are shown on Fig. 1?.

FIG. 17 FIG. 19 165

4. Results obtained by vibrations in steel com 2. Dense. Compaction Cylinder (Proctors'type) paction cylinder with Pneumatic and Electric should be placed in the water tank and sand hammers sample should be vibrated in 3 layers (15 minut a) vibrating in 5 layers dry sample for es each layer) with pneumatic or electric ham about 15 minutes each layer, mer ("Kango hanmer" type). b) vibrating dry sand with load (250 lbs) 1/30 cu.ft. sample should be thus obtained and at the top for about 15 minutes (Fig. 19)» porosity calculated (Pmin). c) vibrating sample in 3 layers for 15 mi Porosity of sand found in the field be nutes each layer and repeating test with expressed in terms of Maximum and Minimum Po different moisture contents, rosities and be called Relative Porosity. d) vibrating sample in 3 layers, 15 minutes each layer, submerged in water, ACKNOWLEDGEMENTS. are shown on Fig 20 (No crushing of grains The work described has been carried out ocourred in any of those tests). during the years 1945 - 1947 in the Soils La Graphs No. 16, 17» 18 and 20 show that lowest porosities were obtained by vibrations boratory of the Imperial College, University of London. under water. The author would like to express his This procedure is here suggested tentativ gratitude to Prof. A.J.S. Pippard D.Sc.,M.I.C.E. ely for obtaining lower limiting state of sands porosity. Head of Civil Engineering Department for per mission granted in 1944 to start research in the College. The work has been directed by Asst. Prof.A.W.Skempton M.Sc.,A.M.I.C.E. to whom the author is indebted for his most valuable suggestions, encouragement and constant help. ® LIICM1UIU» TON © »*“ '"*■ BIBLIOGRAPHY. 0 c, 1) Bagnold R.A., The Physics of Blown Sand and © ( c«l*t Ulb Desert Dunes, London 1941. © 2) Burminster D.M., A Study of the Physical Characteristics of Soils - with special Re ference to Earth Structures, Columbia Uni versity, 1938. 3) Fraser H.J. Experimental Study of the Poro sity and Permeability of Clasic Sediments, Journal of Geology, V0I.XLIII.N0.8.P.I. Nov. Dec.1935- P*P. 910 - 1010. 4) Harper H.J. &. Volk G.W., A method for Mi croscopic Examination of the natural struct ure and Pore space in Soil, Proc.Soil.Sci. Soc.Am., 1936 - 39 - 42. FIG.20 5) Hatch T. & Choate S.P., Statistical descrip tion of the size properties of non-uniform CONCLUSION. particulate substances, I.Frank Inst., 1929, It is tentatively suggested that following 207, 369 - 87. procedures be used for obtaining limiting poro 6) Glossop R. & Skempton A.W., Particle Size sities of sands: in Silts and Sands, Inst, of Civil Eng. 1. Loose.1000 gms of dry and thouroughly mixed London, 1945. sand should be placed in 2000 ccs glass cy 7) Green H., The effect of non-uniformity and linder and a rubber stopper should be put on article Shape on "Average Particle Size", the cylinder. .Frank Inst., 1927, 204, 713-29. 8) ?Krumbein W.C., Measurement and Geological The cylinder with the sample should be shaken a few times and turned upside down, then very Significance of Shape and Roundness of Sedi quickly turned over again. Volume of the sample mentary Particles, Journ. of Sed.Petrol.Vol. should be read and porosity calculated (Pmax). II, No.2, 64-72, 1941. Experiments have shown that porosities 9) Krumbein & Pettijohn, Manuel of Sedimentary thus obtained are not very different from Petrology, The Century Earth Science Series, those obtained by pouring in water without en Appleton Century. trapped air (see Fig. 21 and Figs 3*4,5»). 10) Loos, Comparative Studies of the Effective ness of Different Methods for compacting cohesionless Soils, Proc. of the Int.Conf. on Soil Mech.June 22-26, 1936. TEa-/ 11) Martin G., Research on the theory of fine grinding. Law governing the connection be tween the number of particles and their dia meters in grinding crushed sand, Fr.Brlt. Ceram.Soc. 1923, 23, 61 - 109. 12) Rittenhouse G., A Visual Method of Estima ting Two Dimensional Sphericity, Journ. of Sed.Petrology, Vol.13, No.2,pp. 79 - 81. 13) Terzaghi Karl, Theoretical Soil Mechanics, 1943. 14) Tschebotariof G.P., Effect of Vibrations on the Bearing Properties of Soils, Highway Re search Board, Proc. of the 24th annual meet ing, Washington 1944. p.404 - 425. 15) Graton L.C. & Fraser H.J., Systematic Pach- ing of Spheres with particular Relation to Porosity and Permeability, Journal of Geology Vol.XLIII. N0.8.P.I. Nov.Dec.1935» p.p.785-909.