Fall Cone Test Parameters and Their Effects on the Liquid and Plastic Limits of Homogeneous and Non- Homogeneous Soil Samples

Transcription

1 Fall Cone Test Parameters and Their Effects on the Liquid and Plastic Limits of Homogeneous and Non- Homogeneous Soil Samples M. Reza Emami Azadi Assistant Professor, Dept. of Civil Eng., Shahid Madani University of Azarbaijan, Tabriz, Iran; Tel/Fax: S. R. Monfared Dept. of Civil Eng., Shahid Madani University of Azarbaijan, Tabriz, Iran ABSTRACT In this experimental work, we investigated the effects of various fall cone parameters such as cone apex angle, diameter, overload, cone surface roughness on Atterberg Limits of both homogeneous and non-homogenous (layered) type soil samples. The liquid limit of cohesive clayey silt as well as silty-clay soil samples were determined based on fall cone tests with four different cones with 30 o and 60 o apex angles, two different diameters and also different surface roughness. The results showed that the apex angle of cone may play a more important role in determining the Liquid limit of soil. Furthermore, it is found that the dropped cone behavior in soil sample changes from a dynamic to quasi-static by increasing the cone apex angle from 30 o to 60 o. It is also shown that the penetration vs. moisture content response curves in non-homogenous type soil samples have changed rather considerably near the boundary of layers compared to the homogeneous soil counterparts. The results of this study have also shown that this variation would depend on the layering structure of soil. The current study has also shown that for non-homogeneous soils 20mm penetration may not be accurate for determining the liquid limit of soil compared to homogeneous samples. The findings also indicated that fall cone test results may also be applied for determining the plastic limit of clayey and silty soil samples. The obtained results based on different cones might also be used to determine the undrained shear strength (S u ) of clayey or silty soil samples at the lower bound limits of penetration vs. moisture content curves. KEYWORDS: Fall Cone Tests; Moisture Content; Liquid Limit; Plastic Limit, Cone Apex Angle, Homogeneous Soil, Layered Soil

2 Vol. 17 [2012], Bund. K 1616 INTRODUCTION In the past decades, several studies have been conducted on fall cone tests to determine Atterberg Limits of cohesive soils such as works by Karlsson (1961,1977), Wood and Worth (1978), Lawrence(1980), Wood(1985), Wasti and Bezirici (1986), Harison (1988), Koumoto and Houlsby (2001), Brown and Downing (2001), Feng (2004), Rashid(2005), Muntohar and Hashim (2005), Prakash and Sridaharan (2006), Hazell(2008), Landris Lee and Freeman (2009),Sivakumar et al.(2009), Ying and Wang (2009), Saad (2011) and Kayabali (2012). These studies showed that the liquid limit of soil samples may be determined more accurately by fall cone tests or other methods (e.g. Namdar, 2008) in comparison with the test method using Casagrande device. The differences observed may be attributed to the fact that in Casagrande test, the dynamic effects during various blows may exist. Also the nature of test may involve some error due to measurements and rate of blows. Another problem is related to the fact that Casagrande's test method may not applicable for very silty or sandy soils. The previous works by Houlsby (1982) and Koumoto and Houlsby (2001) have also indicated the effects of cones with different weights or apex angles on only homogeneous soils. The most recent works by Muhunthan and Sariosseiri (2008) and Landris and Freeman (2009) have also indicated that using the cones with two different weights, the plastic limit of cohesive soil sample may be determined quite satisfactorily. More recently studies by Muntohar and Hashim (2005) and Hashim (2010) have also shown the influence of cone surface roughness on the penetration depth of the dropped cone during tests. Houlsby (1982) had introduced an adhesion parameter showing the effect of surface roughness on fall cone performance during tests. Koumoto and Houlsby (2001) have shown that this effect may be more significant for a penetrometer cone with an apex angle of 60 o. The works by Lawrence (1980) and Wast i(1987) showed that from fall cone tests for a penetration depth of mm, the plastic limit of clayey soil (PL) may be obtained by extrapolating the penetration depth vs. Liquidity Index Curves. Such works indicated minimum penetration depths achieved during fall cone tests which were usually much greater than 2.0mm. The recent technical report by GEONOR (2010) offers a new automated fall cone device with data acquisition system added and with a different size of mold. This report indicate that this device can determine the un-drained shear strength of cohesive soil specimens as well as their Atterberg Limits based on a calibration K parameter, penetration depth and weight of dropped cone. EXPERIMENTAL WORK Test Procedure This new experimental work was carried out at the soil mechanics Laboratory of Faculty of Eng., Azarbaijan T.M. University from 5 Feb.2011 until 15 Jan The silty clay, clayey silt and sandy soils were obtained from the university site near Azarshahr (see also Emami Azadi, 2008). We first performed a sieve analysis to determine the grain size diagram and to obtain the Cc and Cg parameters. Hydrometer analyses were performed on clayey and silty soil samples to obtain the grain size diagram of the soil used in the subsequent tests. To perform hydrometer analysis of clayey and silty soils, first Specific Gravity (Gs) values of soil samples were

3 Vol. 17 [2012], Bund. K 1617 determined using standard ASTM procedures. To determine more accurate values of Gs, initially PPM of lab water used in Gs testss were evaluated in the chemical synthesis lab. of Azarbaijan S.M. University as shown in Fig.1. PPM of soil has been determined ass 220mg/lit in terms of Ca2+ and Mg.2+. Then ph test of tab water sample was conducted indicating This means that water used has no harmful effect on Gs tests etc. To evaluate the plasticity index of soil samples, we further conductedd liquid limit tests using Casagrande device for clayey silt and silty clay soil samples. Then plastic limit tests were performed according to ASTM method to determine the PL of soil samples. After these initial tests, fall cone tests were performedd on homogeneous clayeyy and silty soils in a standard mold according to BS.1377, using a standard steel alloy cone of 80gr with an apex angle of 30 o and smooth surface. Then a new round of fall cone tests performed using a new cone with different surface roughness and the same apex angle as 30 o on uniform samples of clayeyy and silty soils in a standard mold. Subsequently a new series of fall cone tests were performed on uniform clayeyy and silty samples this time in a new larger glass container with 15cmx30cmx20cmm dimensionss as shown in Fig.8b below, using first a smooth cone with an apex angle of 30 o, then a cone with rough surface with an apex angle of 30 o, subsequently a smooth cone with an apex angle of 60 o and finally using a cone with rough surface with an apex angle off 60 o. In the last part of this study, a series of fall cone tests were performed with the latter four types of cones on specimens of clayey and silty and sandy soils (Fig.2) overlain in three different layers with 4cm thickness each inside the new large glass mold. Figure 1:a Test set up for determining lab. water ph (Azauniv. Chemical Lab.)

4 Vol. 17 [2012], Bund. K 1618 Figure 1b: Ultrasonic test equipment for determining Gs of Soil (Azaruniv. Chemical Lab.) Figure 2: Three Different Soil Types Soil-1: Clayeyy Silt Soil-2: Silty Clay Soil-3: Sand SOIL SAMPLES CLASSI FICATION Figs..1a and b show the test equipment and set-up for determining the PPM of lab. water used during the tests. From test results in Chemical Lab.,, PPM of Lab. water 220mg/Lit of (Ca2+, Mg2+) and the ph of water 8.33 has been determined which indicates no acidic condition

5 Vol. 17 [2012], Bund. K 1619 Table 1: G s data from pycnometer tests for sand, clay and silt samples Table 1 shows the specific gravity (G s ) values obtained from pycnometer tests at Azaruniv. Chemical Lab. for sand, silty clay and clayey silt soil samples. G s values range from 2.58 to 2.64 for sand to clayey silt and silty clay soils. The results have been used in Hydrometer tests to determine the fine grain size distribution of the silty clay and clayey silt samples of university site near the Azarshahr and the Urmieh Lake. Figure 3: Grain size curve of the sand sample used in one of the layers

6 Vol. 17 [2012], Bund. K 1620 Table 2: Grain sizes/percentage data from sieve analysis for sand sample used in one of the layers. The sieve analysis results on the fine grain samples used in our tests have been shown on Fig.3. As seen in the grain size diagram, the sample contains about 100% particles finer than sieve size 1.18mm and 61.5% finer than sieve size 0.6mm, about 46% finer that sieve size 0.425mmm and about 31.5% less than sieve 0.212mm and about 5% less than sieve size 0.075mm. Hence, the corresponding uniformity and conformity coefficients are computed as follows: (1) Hence, according to Unified Soil Classification System, this soil is considered as poorly graded sand with small proportion of silt fines (SP-SM). The initial tests which carried out on these sand soil samples in Casagrande apparatus and also ELE fall cone penetrometer test as will be described in the following sections which showed that this soil may not be suitable in either test method. Thus this had verified the fact thatt LL or PL off such soil samples cannot be known even if they contain some small part of silty soil. The main reason for failure of LL tests may be the liquefying behavior of the silty sand soil samples at small water content levels due to loss of shear strength whichh is mainly due to internal friction between soil particles rather than cohesion. This geotechnical property of sandy soil may often be exposed in nature when the underground water table is at or above such layers so when they experience rapid shear loading due to earthquakes or explosion shocks etc. tend to liquefy and not be able to carry the effective stress required to bear such shock or dynamic loads. Ying and Wang (2009) have also recently indicatedd similar findings. According to their results the fall cone tests may not so suitable for silty sand soils and as well as clayey silt or sand with less than 13% clay particle size content

7 Vol. 17 [2012], Bund. K 1621 Figure 4: Grain size curve of the clayey silt sample used in one of the layers. Table 3: Hydrometer test data for clayey silt sample Fig.4 shows the grain size diagram of the clayey silt obtained from hydrometer test (see Table 3 below). It can be seen that the percentage finer than the particle size of 0.002mm (i.e. clay particle size) are less than 20%. The diagram of grain size distribution in Fig.4 indicates that slightly more than 75% of the soil is finer than 0.075mm that is silt and clay fines. This means that about 75% of soil particles are clayey silt and about 25% are very fine sand with size less than 0.425mm

8 Vol. 17 [2012], Bund. K 1622 Figure 5: Grain size curve of the silty clay sample used in one of the layers. Table 4: Hydrometer test data for silty clay sample Fig. 5 also shows the grain size diagram of silty clay soil obtained from Hydrometer test(see Table.4). The diagram of grain size distribution in Fig.4 indicates that slightly more than 80% of the soil is finer than 0.075mm that is silt and clay fines. It can be seen that the percentage finer than the particle size of 0.002mm (i.e. clay particle size) is about 23%. The soil mainly consisted of about 82% particles with size less than 0.075mm and according to the Atterberg limits obtained here and using a plasticity chart the soil is classified as (CL)

9 Vol. 17 [2012], Bund. K 1623 Figure 6: Casagrande Device used for determining the LL of Soil samples according to ASTM D4218 test method Figure 7: Diagram of Moisture Content vs. blow numbers (Liquid Limit Test) obtained using Casagrande Device according to ASTM D4218 test method Fig. 6 shows the Casagrande Apparatus during tests and Fig.7 indicates the Liquid Limit test results using the Casagrande device. The best fitted linear curve to the test data here indicates a liquid limit (LL) value of around 38.5% and 27% at 25 blow counts for silty clay and clayey silt samples. Casagrande test has also proved that for silty sand (containing only 5% silt fines) sample of taken from near Azaruniv. Lab. the liquid limit cannot be determined so it has LL near 0.0. The same observation was made subsequently using falll cone test device, the silty sand with a very little amount of moisture has begun to liquefy and fail. Such observations during our tests were coherent with our initial understanding of this type of soil

10 Vol. 17 [2012], Bund. K 1624 Figure 8a: ELE Fall Cone Test Apparatus (with standard cone) used for determining LL and PL of soil samples Figure 8b: ELE Fall Cone Test Apparatus (with modified cone & new container) used for determining LL and PL of soil samples

11 Vol. 17 [2012], Bund. K 1625 Figure 8c: Standard ELE and Modified Cones used for determining LL and PL of soil samples Figure 8d: Standard ELE and Modified Holding Bars for Fall Cone Test Apparatus Figure 8e: ELE Fall Cone Test with Modified Cone In Homogeneous Soil for determining LL and PL of soil samples

12 Vol. 17 [2012], Bund. K 1626 SUMMARY OF THE RESULTS STANDARD FALL CONE TESTS Fig.8a and b shows ELE fall cone test apparatus used for determining the Liquid Limit and Plastic Limit of silty clay and clayey silt samples with standard and modified cones and a standard mold with size of 55mm in diameter and 40mm in depth and also a modified container with 15cmx30cmx20cm dimensions. Cones 1,2,3 and 4 and the holding bars (see Figs.8c and d) with a small attached pin together weigh 80.33gr, 80.01gr, gr and gr, respectively. Cone 1 was the standard ELE cone with 1.81cm diameter and an apex angle of 30 o and smooth surface while cone 2 had the same diameter and apex angle but with rough surface. Cones 3 had diameter twice as standard cone 1 with apex angles of 60 o and smooth surface. Cone 4 had the same dimensions of cone 3 but with rough surface. The test procedure used in this part of study was according to BS1377. Penetration of each cone is measured within 5sec from its release into the mold. Fig.8e shows a fall cone test using modified cone on in homogeneous soil sample with 12cm thickness in the modified container of 15cmx30cmx15cm dimensions. Figure 9: The test results from standard fall cone tests on clayey silt samples (cone.1) Table 5: Fall cone tests results for clayey silt soil as a uniform layer using standard cone and a mold size of 55mm x 40mm

13 Vol. 17 [2012], Bund. K 1627 Fig. 9 shows the liquid limit test data obtained from fall cone tests on clayey silt soil samples. It can be seen that the moisture vs. cone penetration curve has a rather non-linear form and at 20mm penetration depth of the standard 80.33gr cone, LL is obtained to be about 28.2%. If the curve is extrapolated by a non-linear curve fitting technique, then at a penetration depth of about 2.0mm, the plastic limit of this clayey silt sample is found to be about 20.9%. Table.5 indicates the corresponding data obtained during the tests by standard cone for determining LL, PL and Su of soil. Undrained shear strength of the clayey silt samples are determined here using formula given initially by Hansbo(1957) as: /h (2) where Wc is the weight of the steel cone itself plus the steel bar holding the cone with a small pin, K is a calibration factor which is obtained as for standard ELE cone with apex angle of 30 o and weight of about 0.78N and hi is the penetration depth of cone into the soil specimen in the standard mold. The fall cone factor K may be obtained based on Hansbo s method as: (3) Here ξ can be computed based on the shear strain rate during the fall cone tests as 0.74 for cone with apex angle of 30 o. The calibration factor K may be given as 1.52 for standard cone 1 with apex angle of 30 o rather smooth surface and for cone 2 with the same apex angle but with a rough surface. K is obtained to be about for cone 3 with smooth surface. For cone 4, K is computed as It can be seen that the undrained shear strength (SU) range of cohesive soil samples can be determined easily using the Eq.2 based on Hansbo's calibration approach. The results might give an approximate indication of Su and can be compared with the most expensive and accurate direct shear tests results. Similarly, we have calibrated Eq.2 for the modified cones (2,3,and 4) with different apex angles, weights and also varying surface roughness. Karlsson (1977) states that a 10-mm penetration of a 60 cone of mass 60 g corresponds to a soil shear strength of 1.7 kpa. This value corresponds to the mean value of fall cone factor K as obtained above for smooth and rough surfaces (cones 3 and 4) as which then gives Su as 1.73kPa which is in very good agreement with his findings and also with the most recent findings by Hazell (2009). For simplicity and sake of comparison, we adopted lower-bound values: K=1.013 for cones 1 and 2 (with apex angles of 30 o ) and K=0.25 for cones 3 and 4 (with apex angles of 60 ) based on GEONOR report, respectively. Plastic Limit value may be obtained based on Lawrence (1980) and Wasti & Bezirci (1987) as follows: (4) where w 1,w 2, M 1 and M 2 denote the moisture contents corresponding to 20mm penetration obtained from fall cone tests using two different cones and the weights of these two cones, respectively. S u for the liquid condition of clayey silt sample is computed from fall cone test data to be around 2.0kPa. While for Su>23.2kPa the clayey silt sample is near its plastic range. At a

14 Vol. 17 [2012], Bund. K 1628 penetration depth of close to mm the soil is at plastic limit (PL) this may correspond to Su about 100 times that of LL. Figure 10: The test results from standard fall cone tests on silty clay samples (cone.1) Table 6: Plastic Limit test Data of Clayey Silt Sample Fig.10 shows the standard fall cone test results as plotted in dotted lines and best fitted parabolic curve to the data. As seen the fall cone penetration vs. moisture content of the silty clay soil samples of Azarshahr has a non-linear relationship. The liquid limit obtained in this case corresponding to hi=20mm is about 36%. Plastic Limit of silty clayey soil may be obtained in this case by extrapolating the fall cone data up to a hi=2mm to 3mm as PL=18-21% compared to PL value obtained as 21.22% obtained from plastic limit tests. Table.6 shows the plastic limit tests data of clayey silt according to ASTM D4218. The plastic limit of silty clay soil sample (of 20gr in weight) is obtained as PL=23.59% of three different specimens each divided and converted into four threads of diameter of 3.2mm. This

15 Vol. 17 [2012], Bund. K 1629 value can be compared with PL=21-23% range obtained from standard fall cone tests for hi=2-3mm. In verification tests for PL of silty clay as performed later in March,2012 using the BS1377 method, the authors obtained average PL value of 22.53% which had shown variations of about 5-6% compared to the average values of the initial tests. These discrepancies are well in the range of expected margin as obtained by Brown and Downing (2001) and Sherwood (1975), Stone and Phan(1995) and Sivakumar et al. (2009). For Clayey Silt soil specimens the initial tests did not yield a proper PL value due to early shrinkage of the threads during rolling process and higher sensitivity of silt compared to clay, but later more careful verification tests gave average values of PL as 23.59% for such soil samples. The latter might also indicate that a more accurate procedure as discussed by Koumoto and Houlsby (2001), Sivakumar et al.(2009) and Rashid (2010) might be adopted based on fall cone tests. Figure 11: The test results from modified fall cone tests on clayey silt samples (cone.2)

16 Vol. 17 [2012], Bund. K 1630 Figure 12: The test results from modified fall cone tests on silty clay samples (cone.2) MODIFIED FALL CONE TESTS WITH OVERLOAD Figs.11 and 12 show the results of fall cone test using modified cone with a rough surface but the same apex angle as 30 o and the same diameter on clayey silt and silty clay soil samples, respectively. These fall cone test were also performed using a standard mold size 55mm x 40mm. The weight of this modified steel cone (cone.2) was 83.2gr. The test procedure used was the same as standard cone (cone.1) according to BS As seen, the penetration depth vs. moisture content curve for clayey silt soil sample has almost linear form with a LL=28.57% at hi=20mm. Plastic limit value of this soil may be determined in the range of PL= % by extrapolating this curve to a penetration depth of hi= mm. Fig.14 shows a nonlinear relationship of hi-w curve for silty clay soil sample. Test results are indicated with dashed blue line and the fitted parabolic curve has been shown in this graph with a solid dark line. It can be seen that LL=36.81% may be determined for silty clay soil sample at hi=20mm while PL range for this soil type may be obtained in the range of 17-20% from extrapolating the hi-w curve for hi= mm. Again this silty clay soil has exhibited a semi-plastic condition at hi=5mm

17 Vol. 17 [2012], Bund. K 1631 Figure 13: The test results from modified fall cone tests on clayey silt samples (cone.1+50gr overload) Fig.13 shows the fall cone test results on clayey silt soil sample using a standard cone of ELE with an overload of 50gr. For this cone.2 test, the liquid limit at hi=20mm can be obtained as 27.4%. The corresponding undrained shear strength can be found as 30kPa from Fig.16. It can be seen that Su again in this cone tests decreases exponentially from around 200kPa at hi=8mm to about 10.kPa at hi=34.5mm. Plastic Limit of this clayey silt from extrapolation of hi-w curve in Fig.13 can be obtained in the range of % at hi= mm range. This is in close agreement with the results obtained from the standard fall cone.1 tests as described above. From the plastic limit tests, it is hence found that PL values obtained for the clayey silt soil samples may correspond to hi= mm. Figure 14: The test results from modified fall cone tests on silty clay samples (cone.1+50gr overload)

18 Vol. 17 [2012], Bund. K 1632 Fig.14 shows the modified fall cone tests on silty clay soil samples using a standard cone plus an overload of 50gr in a standard mold of size 55mm x40mm. As shown, for hi=20mm the liquid limit from the tests results plotted here is obtained as about 35% for this soil type. The corresponding undrained shear strength value can be found from about 3.4kPa. Figure 15: The test results from modified fall cone tests on clayey silt samples (cone.2+50gr overload) Figure 16: The test results from modified fall cone tests on silty clay samples (cone.2+50gr overload) Figs.15 and 16 show the results of the modified fall cone tests using cone.2 plus a 50gr overload on clayey silt and silty clay soil samples in a standard mold size 55mm x40mm, respectively. The liquid limit values for clayey silt and silty clay soil types from Figs.15 and 16 can be obtained at hi=20mm as LL=27.61% and LL=35.27%, respectively. These results are also in very good agreements with the LL values obtained from the tests using cone.1 plus the same 50gr overload. However, there is a slight discrepancy due to more roughness of the steel cone

19 Vol. 17 [2012], Bund. K 1633 compared to cone.1. The plastic limit range values can also be obtained approximately by extrapolating the Figs.15 and 16 as % and 16-20% for hi= mm range. Table.7 compares the LL values obtained from various fall cone test using cones.1 and 2 with extra overload of 50gr and without it. It can be seen that with extra 50gr overload the LL values have shown about 2-3% reduction in clayey silt soil and about 4-5% reduction in silty clay soil samples. Table 7: Comparison of LL values from Various Fall Cone Tests Figure 17: Comparison of the test results from modified fall cone tests on clayey silt samples using 4 different cones

20 Vol. 17 [2012], Bund. K 1634 Figure 18: Comparison of the test results from modified fall cone tests on silty clay samples using 4 different cones MODIFIED FALL CONE TESTS WITH DIFFERENT APEX ANGLE AND ROUGHNESS IN HOMOGENEOUS SOILS Fig.17 compares the tests results on clayey silt samples using the cones 1,2,3 and 4 Cone-1 is standard ELE cone made of stainless steel with 30 o apex angle and smooth surface. While cone-2 had the same apex angle and the same diameter as cone-1 but with a rather rough surface.cone-3 had a diameter as twice the cone-1 with an apex angle of 60 o and cone-4 with the same dimensions as cone-3 but with a rough surface. The modified cones were also manufactured of stainless steels with different grades in Tabriz. As shown in Fig.17, the fall cone penetration vs. soil moisture curves for the cones 1 and 2 with 30 o apex angle have nonlinear form in general but are quite close. This might indicate that the effect of surface roughness is not so dominant in this case. Whereas the fall cone penetration vs. soil moisture curves using the modified cones 3 and 4 differ considerably from the previous fall cone test results as shown in Fig.17. For the same amount of soil moisture the penetration depth of falling cones 3 and 4 are much less than cones 1 and 2. This would indicate that the apex angle of cone may have more pronounced effect on the fall cone test results. Fig.17 also indicates that the effect of roughness of the fall cone surface for cones 3 and 4 is more significant than cones 1 and 2. This can be due to larger area and also the different friction and end bearing effects of the cones 3 and 4 with 60 o apex angle compared to cones 1 and 2 with 30 o apex angle. Similar trends can be seen in Fig.18 for silty clay soil samples. While the cones 3 and 4 (with larger diameters and weights but with apex angles of 60 o ) have shown completely different behavior compared to the cones 1 and 2 with 50gr overload disks. The findings in this case endorse the inherent fact that the weight of cone has opposite effect compared to apex angle of falling cone on penetration response curve. In all the test results shown in Figs.17 and 18, near end of curves (i.e. at moisture content values far above LL) the cone penetrates rapidly into soil

21 Vol. 17 [2012], Bund. K 1635 layer indicating a punch-through type failure mechanism. At the failure point, for clayey silt samples w values range from 33% to 37% and for silty clayy soil samples, w values range from 38.5% to 49.5%. Figure 19: Comparison of the test results from modified fall cone tests on Non- Homogeneou us & Layered Soil using 3 different cones(after H. Vazifeh, 2011) Figure 20: Fall Cone Testing of A Non-Homogen neous Soil Sample with 3 Layers (Profile-1)

22 Vol. 17 [2012], Bund. K 1636 Figure 21: A Non-Homogeneous Soil Sample with 3 Layers (Profile-1) Figure 22: Comparison of the test results from modified fall cone tests on Non-Homogeneous Soil using 4 different cones (Profile-1)

23 Vol. 17 [2012], Bund. K 1637 Figure 23: A Non-Homogeneous Soil Sample with 3 Layers (Profile-2) Figure 24: Comparison of the test results from modified fall cone tests on Non- Homogeneous Soil using 4 different cones(profile-2) MODIFIEDD FALL CONE TESTS WITH DIFFERENT APEX ANGLE AND ROUGHNESSS IN NON-HOMOGENEOUS SOILS Figs..20 and 21 show the fall cone test on a non-homogeneous soil sample with 3-layers of clayey silt, silty clay and sand, respectively. Each layer of soil sample has a thickness of 4cm

24 Vol. 17 [2012], Bund. K 1638 placed in a 15cm x 20cm x 15cm container. Fig.22 compares the cone penetration vs. moisture content curves for cones 1,2,3 and 4 from our lab test results. Similar to homogeneous soil samples tests, the cone apex angle might be seen to affectt the results more tangible than any other parameters such as roughness, weight or overload. The cone penetration depth hi varies from about mm at w=26% to near 60mm at w=34% %-36.5%. Forr the cones 3 and 4, the hi-w curve has shifted significantly indicating a varying effect of end-bearing and interface friction and adhesion with changing the apex angle of the cone. Fig.23 shows the non-homogeneous soil sample soil (profile-2) with clayey silt, silty clay and sand layers, respectively. Fig..24 compares the fall conee test results for this soil profile for cones 1,2,3 and 4, respectively. Fig.24 shows that hi varies from 11-16mmm at w=33.2% to about hi=30-62mm at w=42%. The effect of apex angle of cone on penetration response of fall cone near failure is absolutely significant. While the roughnesss of the cone plays a minor role in comparison with apex angle and also weight. Figure 25: Comparison of the test results from fall cone.1 tests on Homogenous vs. Non-Homogeneous Soil Sampless (Profile-1)

25 Vol. 17 [2012], Bund. K 1639 Figure 26: Comparison of the test results from fall cone.2 tests on Homogenous vs. Non-Homogeneous Soil Sampless (Profile-1) Figure 27: Comparison of the test results from fall cone.3 tests on Homogenous vs. Non-Homogeneous Soil Sampless (Profile-1)

26 Vol. 17 [2012], Bund. K 1640 Figure 28: Comparison of the test results from fall cone.4 tests on Homogenous vs. Non-Homogeneous Soil Sampless (Profile-1) Figs..25 to 28 compare the fall cone tests results for homogeneous and non-homogeneous soil samples using cones 1,2,3 and 4. It can be seen that the non-homogenous soil effect is more apparent for higher values of hi or w and also for cones.3 and 4 compared to other cones. The reason may be sought as the cone falls near to the boundaryy of the second layer after hi>40mm in non-homogenous (layered) soil then the effect of the second layer alters the hi-w curves as the cone penetrates more into that layer. It can be seen that for non-homogeneous soil profile-1, cones 1 and 2 at hi>40mm, the penetration rate is slower thann that of homogeneous soil-1. While using cones 3 and 4 with the same profile-2 samples, the trend hass changed with higher penetration rates compared to the homogeneous soil-1. This may be due to decreased end- to its bearing or friction in the second layer of the non-homogen neous soil profile-1 compared first layer for cones with 60 o apex angle. In contrast, cones 1 and 2 with sharper apex angle of 30 o would tend to penetrate faster into the first layer of soil profile-1 samples which is clayey silt compared to their second layer as silty clay. This might be due to the decreased end-bearing in the case of cones 1 and 2 with sharper apex angles comparedd to the cones 3 and

27 Vol. 17 [2012], Bund. K 1641 Figure 29: Comparison of the test results from fall cone.1 tests on Homogenous vs. Non-Homogeneous Soil Sampless (Profile-2) Figure 30: Comparison of the test results from fall cone.2 tests on Homogenous vs. Non-Homogeneous Soil Sampless (Profile-2)

28 Vol. 17 [2012], Bund. K 1642 Figure 31: Comparison of the test results from fall cone.3 tests on Homogenous vs. Non-Homogeneous Soil Sampless (Profile-2) Figure 32: Comparison of the test results from fall cone.4 tests on Homogenous vs. Non-Homogeneous Soil Sampless (Profile-2) As shown in Figs.29 to 32, for profile-2 type non-homogeneous soil samples, initially the cone.1 and 2 penetration is lower compared to the homogeneous soil-2 changes after penetration depth of but with increase of moisture content w somewhat above Liquid limit, this trendd

29 Vol. 17 [2012], Bund. K 1643 hi=40mm again the penetration is greater in non-homogeneous soil profile-2 compared to homogeneous uniform soil-2. Whereas for cones 3 and 4, a different response is observed during the tests which indicate that after hi>40mm the penetration in homogeneous soil-2 is faster and larger compared to non-homogeneous soil-2. This may be due to the increase end-bearing and skin friction resistance in the case of cones with apex angle of 60 o in the second layer of profile- 2 compared to its first layer. DISCUSSION Based on dynamics of fall cone tests, it may be perceived that as the moisture content of the soil varies (say from just above PL to far above LL values), the penetration response of cone into soil changes from a quasi-static to dynamic behavior. At lower water content of soil sample, the cone penetrates less and so its speed and acceleration during plunge is less than the case of soil with higher moisture content say w>ll. At the upper limit of w, the soil sample has liquefied and hence the cone penetrates more rapidly to greater depths say hi>=60mm. Koumoto and Houlsby (2001) have modeled this behavior in terms of dynamic equation of motion. The water's viscosity damps out a part of energy of the plunging cone. However, for the case of plastic soil or semi-solid state of soil, the falling cone impacts with the soil surface and due to considerable stiffness of soil layer in this case slows down quickly while it penetrates just few mm into the upper layer. Most of the kinetic energy of the falling cone in this case is dissipated in the form of soil's elastic and plastic strain energy. A small part may be transferred into heat energy due to skin friction between the penetrating cone and the interface soil particles. CONCLUSION The present experimental work has shed more light into fall cone test approach and increased our knowledge to some extent on this particular subject. In particular, for the first time we conducted successfully the fall cone tests on non-homogeneous soil samples with three layers. We also used four different types of cones with different apex angle and surface roughness and also extra overloads to evaluate the effects of these important parameters on determining the soil's Liquid and Plastic Limits. The results of the tests conducted here showed that the effect of apex angle of the cone on LL of soil sample may be quite considerable. The cone penetration vs. moisture content of soil response curves are significantly influenced by the apex angle of the cone. For cones 1 and 2 with apex angel of 30 o, higher penetration depths are usually observed in the same soil samples tested here compared to cones with apex angle of 60 o in The amount of discrepancies in terms of penetration depth hi increased with an increase of water content of soil samples for different cones used in this study. The influence of the surface roughness of cone seems to be less for the cones (1, 2) with apex angle of 30 o compared to the cones (3,4) with apex angel of 60 o. The influence of an overload disk on hi-w curves or LL or PL seems to be rather more than the roughness effect as tested for cones with the same diameter. But for cones with diameter the influence of cone's weight may overwhelms the surface roughness effect. It is observed that the effect of cone's weight or overload on LL of silty clay soil samples was in fact more than that for clayey silt soil samples. The effect of cone surface roughness is seen to be somewhat higher for silty clay samples compared to the clayey silt samples. It is also found that for cone with twice diameter and larger weight or overload, the surface roughness may increase LL more than that for standard cone

30 Vol. 17 [2012], Bund. K 1644 For both homogeneous and non-homogeneous soil samples, the results of fall cone tests conducted during course of this work showed that the penetration depth hi usually varies nonlinearly with increase of moisture content of soil. It is shown that PL values of soil samples can be determined rather accurately by extrapolating the hi-w curves from fall cone test for a penetration depth in the range of mm. It is also verified that using a method established earlier by Lawrence (1980) and Wasti et al.(1987) we could determine the plasticity index and so plastic limit of soil samples tested by means of two different cones (1,3) or (2,4). It is also shown that the undrained shear strength (SU) range of cohesive soil samples can be determined easily using the Eq.2 based on Hansbo's calibration approach. The results might give an approximate indication of Su and can be compared with the most expensive and accurate direct shear tests results. The results of fall cone tests on homogeneous soil samples with depth 12cm compared to standard cylindrical ELE container of 4cm depth which was also used showed an increase in effective depth corresponding to LL from 20mm to mm. It is concluded that for non-homogeneous and layered soil samples, the penetration depth of cone (hi) depends on moisture content of soil (w), the type of soil in the first and the second layer and the boundary conditions or the layers of soil. It is generally observed that after hi=40mm due to changes in the boundaries the trend of hi-w curve might change. It is observed that for considerable variations in water content or weight of cone or apex angle the fall cone response in test soil samples might change from quasi-static to dynamic. It may be verified that dynamic equations given by Koumoto and Houlsby (2001) can be applied for varying weight and apex angle conditions for homogeneous soils in the above tests. However, for layered soil profiles 1 and 2, this computational approach might be rather approximate due to changes in the soil layers. ACKNOWLEDGMENT This research work was carried out at Azarbaijan T.M. University Soil Mechanics Lab. Assistance of Mr. Ziayee at Soil Mechanics Laboratory and Chemical Laboratory of Azarbaijan T.M. University are greatly appreciated. Gratitude is also given to Dr. H. Soltani for his support by providing the geotechnical laboratory room and also for his useful comments. REFERENCES 1. Brown, P. J. and Downing, M. C. (2001) "Discussion of Fall Cone Penetration and Water Content Relationship of Clays", Geotechnique 51, No.2, pp BS1377 (1990) "Methods of Testing of Soils for Civil Engineering Purposes", Milton Keneys, British Standards Institutions. 3. Casagrande, A. (1958) "Note on the Design of Liquid Limit Device", Geotechnique 8, No.2, pp Emami Azadi, M.R., Sadein, M., Jafari, K. and Jajani, S.(2008) "The

31 Vol. 17 [2012], Bund. K 1645 Effects of Urmieh Salt Water on the CBR Test Results of GSCW and GSBW Soil Samples ", Electronic Journal of Geotechnical Engineering (EJGE), 5. Feng, T. W.(2000) "Fall Cone Penetration and Water Content Relationships of Clays", Geotechnique 50, No.2, pp Feng, T. W.(2004) "Using Small Ring and Fall Cone to Determine the Plastic Limit ", Journal of Geotechnical and Geo-Environmental Eng., Vol.130, No.6, pp GEONOR (2010) "Fall Cone Apparatus- New Model Designed by Norwegian Geotechnical Institute NGI", Oslo, Norway. 8. Hansbo, S. (1957) "A New Approach to the Determination of the Shear Strength of Clay by Fall Cone Test ", Proc. No.14, Royal Swedish Geotechnical Society, Stockholm, Sweden. 9. Harrison, J. A. (1988) "Using the BS Cone Penetrometer for the Determination of the Plastic Limits of Soils", Geotechnique 38, No.3, pp Hazell Edmund (2008) " Numerical and Experimental Studies of Shallow Cone Penetration in Clay", Ph.D. Thesis, Oxford University, UK. 11. Houlsby, G.T. (1982) "Theoretical Analysis Of Fall Cone Tests", Geotechnique 32, No.2, pp Karlsson, R. (1961) "Suggested Improvements in the Liquid Limit Test with Reference to Flow Properties of Remolded Clays", 5th Int. Conf. On Soil Mechanics and Foundation Eng., Vol.1, p.171, Paris, France. 13. Karlsson, R. (1977) "Consistency Limits", In Cooperation with Laboratory Committee of the Swedish Geotechnical Society), Document D6: Landris, T. L. and Freeman R. B. (2009) "Dual Weight Fall Cone Method for Simultaneous Liquid and Plastic Limit Determination", J. of Geotech. & Geoenviron. Eng., ASCE, Vol.135, No.1, pp Kayabali, K. (2011) "Assessment of Shear Strength at Consistency Limits - A Reappraisal", Electronic Journal of Geotechnical Engineering (EJGE), Koumoto, T. and Houlsby, G.T. (2001) "Theory and Practice of the Fall Cone Test ", Geotechnique 51, No.8, pp Lawrence, D. M. (1980) "Some properties associated with Kaolinite soils", M.Sc. Thesis, Cambridge University, UK. 18. Muhunthan, B. and Sariosseiri, F. (2008) "Interpretation of Geotechnical Properties of Cement Treated Soils", Research Report FHWA-DTFH C-00008, Compaction Control of Marginal Soils in Fills, Washington State Transportation Center (TRAC), Washington State University, USA. 19. Muntohar A.S. and Hashim (2005) " Determination of Plastic Limits of Soils Using Cone Penetrometer: Re-Appraisal", J. Teknik Sipil, Vol.11, No

32 Vol. 17 [2012], Bund. K Namdar, A. (2008) "Identification of Mixed Soil Characteristics by Application of Laboratory Tests", Electronic Journal of Geotechnical Engineering (EJGE), Prakash, K. and Sridharan, A (2006) "Critical Appraisal of the Cone Penetration Method of Determining Soil Plasticity", Canadian Geotechnical Journal, 2006, Vol.43, No.8, pp Rashid, A. S. B. A. (2005) "Determination of Plastic Limit of Soil using Modified Cone Penetration Method", M.Sc. Thesis, Univ. of Malaysia. 23. Saad, R. (2012) "The Atterberg Limits Resolution Using Seismic Refraction Method", Electronic Journal of Geotechnical Engineering (EJGE), Sherwood, P. T. (1970) " The Reproducibility of the Results of Soil Classification and Compaction Tests ",Report LR 339, Crowthorne, Road Research Lab., USA. 25. Sivakumar, V., Glynn, D., Cairns, P. and Black, J.P.(2009) "A New Method of Measuring Plastic Limit of Fine Materials", Geotech. 59, No.10, pp Stone, K.J.L. and Phan, K.D. (1995): " Cone Penetration Tests near the Plastic Limit", Geotechnique 45, No.1, pp Vazifeh H. (2011)" Comparison of Fall Cone Test Results on Various Soil Profiles", Project Report, Azarbaijan T.M. University. 28. Wasti, Y.(1987) "Liquid and Plastic Limits as Determined from the Fall Cone and Casagrande Methods", Geotechnical Testing Journal, ASTM, Vol.10,No.1, pp Wasti, Y. and Bezirci, M. H. (1986) "Determination of the Consistency Limits of Soils by the Fall Cone Test", Canadian Geotech. J. 23, No.2, pp Wasti, Y. (1987) "Liquid and plastic limits as determined from the fall cone and Casagrande methods", Geotechnical Testing Journal, Vol. 10, No1, pp Wood, D. M. and Worth, C. P. (1978) "The use of Cone Penetrometer to Determine the Plastic Limit of Soils", J. of Ground Eng., Vol.11, No.3, p Wood D.M. (1985) "Some Fall Cone Tests", Geotechnique 35, No.1, pp Guo Ying and Qi. Wang (2009) "Experimental Research on Fall Cone Test to Determine Liquid Limit and Plastic Limit of Silts", J. of Rock and Soil Mechanics, Vol.30, No.9, pp ejge