A STUDY OF A LABORATORY COMPACTION TEST USING A SWEDISH VIBRATORY APPARATUS

Transcription

1 ROAD RESEARCH LABORATORY Ministry of Transport RRL REPORT LR 129 A STUDY OF A LABORATORY COMPACTION TEST USING A SWEDISH VIBRATORY APPARATUS by T.O. Odubanjo ROAD RESEARCH LABORATORY CROWTHORNE BERKSHIRE 1968 t

2 CONTENTS Page Abstract 1. Introduction 2. Materials used in the investigation 3. The Swedish vibratory compaction apparatus 4. The vibrating-hammer compaction test 5. Experimental procedure 5.1 General 5.2 Determination of the effect of using the same procedure with the Swedish apparatus as that used in the B.S. vibrating hammer compaction test 5.3 Determination of the effect of using the Swedish apparatus without mounting the mould on a concrete block 6. Discussion of results 7. Conclusions 8. Acknowledgements 9. References ~) CROWN COPYRIGHT 1968 Extracts from the text may be reproduced provided the source is acknowledged

3 Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on I st April This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

4 A STUDY OF A LABORATORY COMPACTION TEST USING A SWEDISH VIBRATORY APPARATUS ABSTRACT This Report describes a study of a Swedish vibratory compaction apparatus for the laboratory compaction of soil and base materials. The results are compared with those obtained with a B.S. laboratory compaction test, using a vibrating hammer, which has been developed at the Laboratory. The materials used in the study were a heavy clay, a uniformly graded fine sand, a well-graded sand and a crushed limestone. With all four materials tested the Swedish Vibratory compac, tion apparatus produced densities which ~vere either similar to or somewhat lower than those obtained using the B.S. vibrating hammer compaction test. Optimum moisture contents were similar or very slightly higher. The differences in maximum dry density with some materials are such that the two tests cannot be regarded as alternatives for specifying compaction standards. The purpose in developing the vibrating hammer compaction test in the United Kingdom is to indicate the ranges of moisture content within which granular materials should be compacted. For this purpose the Swedish apparatus is as effective as the new B.S. test. The availability in this country of vibrating hammers of the appropriate size is likely to make the vibrating hammer test more acceptable.. TTVI"I"~D('~T'~T'II"~'-I"TC'~X'I, :~, " ~,], JLl ~i JL 1%, 1L,.J 1,.,/I,,,J w,.,.., 1 II ~LJ 1 'N This Report describes a study of a Swedis h vibratory compaction apparatus for th e labora- " tory compaction of soils and base materials. The results are compared with those obtained. with a new ~.S. laboratory compaction test, using a vibrating hammer, developed at the,. Laboratory.. The British Standard laboratory compaction tests, using free-falling rammers 2, provide a poor guide to both the optimum moisture content for compaction and the state of compaction which can be achieved by plant with many types of granular material 3. With such material modem vibratory compaction plant is capable of producing much higher states of compaction than even the B.S. 1-1b-rammer compaction test 4,5. For this reason a laboratory compaction test, using a vibrating hammer, was de~)eloped at the Laboratory 1. The test makes use of apparatus, apart from the tamping foot, which is already in widespread use in this country. This test method was shown to produce values of maximum dry density and optimum moisture content similar to those of full-scale compaction plant over a wide range of materials. In particular, it produced values of maximum dry density higher than those produced by the B.S. 1-1b-rammer 1

5 compaction test with earse granular materials, with which the latter test has been shown to be relatively inefficient. At the same time as the vibrating hammer compaction test was being developed, an apparatus for the same purpose was produced in Sweden 6. This apparatus consists of an electrically-powered vibrator unit which is widely used in that country, together with a special tamping foot and mould. It was considered that it would be of interest to compare the results produced by the two methods over a range of materials.. MATERIALS USED IN THE INVESTIGATION Four materialswere used in this study. These were a heavy clay, a uniformly graded fine sand, a well-graded sand and a crushed limestone. The particle-size distributions of these materials and the results of plasticity and specific gravity tests, determined according to B.S , are shown in Fig THE SWEDISH VIBRATORY COMPACTION APPARATUS The apparatus is shown in Plates 1 and 2 and details of the apparatus are given in Table 1. The apparatusconsists of a 3-phase electric motor integral with an eccentric unit, a tamping foot to which the motor is clamped, a mould and a collar. The tamping foot has a circular compacting face 15 cm in diameter and is also fitted with a circular guide-plate which operates within the collar. The collar is attached to the mould by a pair of rubber lugs and, in normal use, the mould is clamped rigidly to a concrete block weighing at least 4 kg. It is recommended by the manufacturer of the apparatus that material should be compacted in the mould in two layers, with two minutes of vibration per layer. To determine the bulk density of the compacted specimen it is necessary to know the depth of the compacted soil in the mould as well as the weight of material. There was no special provision with the apparatus for measuring the depth of specimen and this value was determined, during the study of the apparatus, by laying a datum bar across the top of the mould and measuring the height of the datum bar above the surface of the compacted material to the nearest 1--~" in. (.25 mm), by means of a depth gauge.

6 TABLE 1 Details of the Swedish vibratory compaction apparatus Manufacturer Vibrator motor:- Type Serial number Power consumption Nominal frequency of vibration Centrifugal force at nominal frequency Dimensions Diameter of tamping foot Area of tamping foot Diameter of mould Depth of mould Depth of collar Weights Weight of tamper and motor Static pressure under tamping foot A.B. Vibro Verken, Sweden ER W 3 vib/min 55 lbs (25 kg) 5.91 in (15 cm) in 2 (177 cm 2) 6 in (15.2 cm) 5.43 in (13.8 cm) 9.56 in (24.3 cm) 78 lb (35.4 kg) 2.84 lb/in 2 (2 gm/cm 2) 4, THE VIBRATING-HAMMER COMPACTION TEST This test, developed at the Laboratory1,: has now been accepted as a British Standard laboratory compaction test. The apparatus consists of a vibrating hammer having a power consumption of 6-75 watts and an operating frequency of c/rain, a circular tamping foot of 5¾ in (14.6 cm) diameter, and a mould of the type used in the CBR test, i.e. 6 in (15.2 cm) diameter, 5 in (12.7 cm) deep, and with a 2-in (5.1 cm) high collar. The material to be tested is compacted in three layers, with one minute of vibration per layer. During compaction, pressure is applied to the vibrating hammer, by the operator, so that the total static load on the tamping foot is between 7 and 9 lb (32 and 41 kg). The depth of the compacted specimen is determined by laying a datum bar across the collar of the mould and measuring the height of the datum bar above the surface of the compacted specimen, to the nearest _!.1 in ( 5 mm), by means of a depth gauge; the final 5 total thickness of the sample should be between 5 and 5¼ in. (12.7 and 13.3 cm) for the test to be valid. The bulk density is determined from the weight of the compacted specimen and its calculated volume. 5. EXPERIMENTAL PROCEDURE 5.1 General Most of the tests with the Swedish apparatus were carried out according to the recommendations of the manufacturer. Thus the mould was bolted to a concrete block weighing about 11 cwt (56 kg), and the test material compacted using the procedure recommended by the manufacturer (see Section 3). The quantity of material to be compacted in each layer was not stipulated but, as the apparatus was being compared with the B.S, vibrating hammer compaction test and the diameters of the moulds were the same, the same total weight of material was used in each method.

7 ) With each of the four materials (Fig. 1), tests were carried out over a range of moisture contents. Sufficient material was prepared at each moisture content so that each method could be used on a separate sub-sample. The results are shown in Figs. 2 to 4, and are summarised in Table 2. TABLE 2 Values of maximum dry density and optimum moisture content obtained with the two laboratory compaction methods Material B.S. vibrating hammer compaction test Maximum dry density (Ib/ft 3) (t/m 3) Optimum moisture conten) (per cent) Swedish vibratory compaction Maxlmuma~Pr~ aratus (Iblft 3) density (t/m 3) Optimum' moisture content (per cent) Heavy clay Uniformly graded fine sand Well-graded sand Crushed lime stone Determination of the effect of using the same procedure with the Swedish apparatus as -that used in the B.S. vibrating hammer compaction test An additional series of tests was carried out with the Swedish apparatus on limestone in which the material was compacted in three layers, with one minute of vibration per layer, i.e. as in the B.S. vibrating hammer compaction test. The results are included in Fig Determination of the effect of using the Swedish apparatus without mounting the mould on a concrete block In addition to the tests described above, a comparison was made between the results obtained using the Swedish vibratory compaction apparatus bolted to the concrete block {normal procedure) and free-standing on a concrete floor. In the free-standing tests it was found necessary to support the motor and tamper by hand to prevent the apparatus toppling over. The tests were carried out using well-graded sand and the results are included in Fig DISCUSSION OF RESULTS The results obtained with both the Swedish vibratory compaction apparatus and the B.S. vibrating hammer compaction test were very similar for heavy clay over most of the range of moisture contents tested (Fig. 2) and for well-graded sand (Fig. 3). With uniformly graded fine sand (Fig. 2) and crushed limestone (Fig. 4), however, the B.S. vibrating hammer compaction test produced a higher value of dry density at any given moisture content than did the Swedish apparatus. 4

8 To obtain a more exact comparison between the performance of the Swedish apparatus and that of the B.S. vibrating hammer compaction test, tests were carried out using limestone in Which the compaction procedures were the same for the two methods, i.e. three layers of material were compacted using one minute of vibration per layer (Fig. 4). However, the amended procedure caused a reduction in the values of dry density obtained at any given moisture content with the Swedish apparatus, and thus further increased the divergence from the results obtained with the B.S. yibrating hammer compaction test. These results indicate that the compactive energy provided by the Swedish vibratory compactio n apparatus is less than that provided in the vibrating hammer test. During compaction, the tamping foot of the Swedish apparatus was observed to bounce erratically, and it might well be that the introduction of some form of retaining pressure to prevent the apparatus bouncing, as is present in the vibrating hammer test, would enhance its performance. The use of the Swedish apparatus in the compaction'of wel'l-graded sand without. bolting the mould to a concrete block (Fig. 3) had little or no effect on the results as compared with those obtained with the normal procedure. Although further study would be required to show conclusively whether or not the apparatus requires bolting to a concrete block, the results suggest that such a measure may not, in fact, be necessary, i~owever, it should be noted that the "free-standing" tests were carried out with the mould standing on a concrete floor and different results might be obtained v~ith other test conditions. 7. CONCLUSIONS With all four materials tested the Swedish vibratory compaction apparatus produced densities which were either similar to or somewhat lower than those obtained using the B.S. vibrating hammer compaction test. Optimum moisture contents were similar or very slightly higher. The differences in maximum dry density with some materials are such that the two tests cannot be regarded as alternatives for specifying compaction standards. The purpose in developing the vibrating hammer compaction test in the United Kingdom is to indicate the ranges of moisture content within which granular materials should be compacted. For this purpose the Swedish apparatus is as effective as the new B.S. test. The availability in this country of vibrating hammers of the appropriate size is likely to make the vibrating hammer test more acceptable. The Swedish apparatus, using a standard vibrating unit can be more strictly specified than the vibrating hammer test. Should future experience show that this stricter specification is necessary, it may well be worth considering apparatus of the Swedish type as standard..8. ACKNOWLEDGEMENTS Thanks are due to AB Vibro Verken of Sweden, and to Dr. Lars Forssblad of that Company, for the loan of the apparatus. The work was carried out in the" Earthworks and Foundations Section under the direction of W.A. Lewis and A.W. Parsons. 5

9 9. REFERENCES.... Q 6. PARSONS, A.W. An investigation of a laboratory vibratory compaction test for soils and base materials. Department of Scientific and Industrial Research, Road Research Laboratory. Note No. LN/612/AWP, (Unpublished). BRITISH STANDARDS INSTITUTION. Methods of testing soils for civil engineering purposes. British Standard 1377:1961. London, 1961 (British Standards Institution}. WILLIAMS, F.H.P. and D.J. MACLEAN. The compaction of soil: a study of the performance of plant. Department of Scientific and Industrial Research, Road Research Technical Paper No. 17. London, 195 (H.M. Stationery Office). LEWIS, W.A. and A.W. PARSONS. The performance of compaction plant in the compaction of two types of granular base material. Department of Scientific and Industrial Research, Road Research Technical Paper No. 53. London, (H,M. Stationery Office). LEWIS, W.A. Recent research into the compaction of soil by vibratory compaction equipment. Prec. 5th internat. Soil Mech. Conf. Paris, 1961, 2, FORSSBLAD, L. investigations of soil compaction by vibration. Acta Polytechnica Scandinavica, Civil Engineering and Building Construction series No. 34, Stockholm, Sweden, 1965 (The Royal Swedish Academy of Engineering Sciences). I 6

10 - I L--~ /- E, 2,.J I" - o ~ I U),x,, LL* l.a-- U') > od /. L "/L gl S~ N,., In "" la..l.i 9 zs, E I m m E U 9o : ~ t U / m U UI::::.-~_ I..r) D '~ ~ ~ >,,, "~ X ~c_ C~ I u -- U i i ~'. e- N ~ U 1 (.) r- om LL ~L I'".if O~ l.a.l " X O I m ILl I.LI m 1 C fl d~.j '1" 8-_E...J~ 8 o E~ -~ O O N I.9 C) :) ~ C) C) C) "r o)! I: / I.-,I I o. O ebo~,ue3jed U!~,OUJLUnS Rood R ~ h L ~ M o.t. 7

11 [HEAVY CLAYJ 1% air voids I ero lair voids 't ) E >s.,4,,a I/I Q 1 95 L /. B:S. vibrating- hammer., compaction test Swedish vibratory compaction apparatus Moisture content (per cent) J~,.. Ill '1 r-s I UNIFORMLY GRADED FINE SAND D ~ e----- j 2 % air voids...---~,% _N 1% air voids "-,/ ~_...---~ O B.S.vibrating-hemmer compact ion test Swedish vibratory ompqction opporat us 95 J /, 16 Moisture content (per cent) ~ m ?.m =r,- "1 Q Fig. 2. RELATIONS BETWEEN DRY OENSITY ANO MOISTURE CONTENT OF HEAVY CLAY ANO UNIFORMLY-GRAOED FINE SANO OBTAINEO WITH THE SWEOISH VIBRATORY COMPACTION APPARATUS ANO THE B.S. VIBRATING-HAMME R COMPACTION TEST 8

12 1/. air voids WELL- GRADED SAND % ojr voids 2.. E >., 12 4-* I/! a C o/ /. ll O B.S, vibroting-hammer.compaction test Swedish vibratory compaction opparotus ( norrno[ use) A Swedish vibratory compaction apparatus ( moul.d not bol.ted to concrete bl.ock) Moisture content ( per cent) Fig. 3. RELATIONS BETWEEN DRY OENSITY ANU MOISTURE CONTENT OF WELL-GRAOEO SANO OBTAINEO WITH THE SWEDISH VIBRATORY COMPACTION APPARATUS ANO THE B.S. VIBRATING-HAMMER COMPACTION TEST. RESULTS OBTAINEO USING THE SWEOISH VIBRATORY COMPACTION APPARATUS WITHOUT BOLTING THE MOULD TO THE CONCRETE BLOCK ARE ALSO SHOWN 9

13 CRUSHED LIMESTONE] I T T - 2.s 15 2.~ i voi~ - ) !.,~,o% a,r vi~ ~ P- 2.2 ~ B.S. vibrating- hammer compaction test Swedish vibratory compaction apparatus ( normat use- 2 tayers, 2 minutes per tayer) L~ Swedish vibratory compaction apparatus ( 3tayers, 1 minute per tayer) Moisture content (per cent) "~x Fig. t,. RELATIONS BETWEEN ORY OENSITY AND MOISTURE CONTENT OF CRUSHEO LIMESTONE OBTAINED WITH THE SWEOISH VIBRATORY COMPACTION APPARATUS ANO THE BS VIBRATING-HAMMER COMPACTION TEST. RESULTS OBTAINEO WHEN COMPACTING THREE LAYERS OF MATERIAL WITH ONE MINUTE OF VIBRATION PER LAYER USING THE SWEOISH VIBRATORY COMPACTION APPARATUS ARE ALSO SHOWN I

14 PLATE 1 The Swedish vibratory compaction apparatus 1!

15 i iii ~ i :iii: jill i i, i t - - ~ i i~! ~ ~ ~ ~:i~i i~i~,: '. : /iiiiii~i~i v~i~ : ;~ i;i~ii~ ii ~ ~,/. ~ v,!!~iii:i~ ;~ i "!..e ta., ~... PLATE 2 The components of the Swedish vibratory compaction apparatus 12 M.P.Ltd /68