Criteria of Acceptance for Constant Rate of Strain Consolidation Test for Tropical Cohesive Soil

Geotech Geol Eng DOI 10.1007/s10706-016-0016-8

ORIGINAL PAPER

Khairul Anuar Kassim . Ahmad Safuan A. Rashid . Ahmad Beng Hong Kueh . Chong Siaw Yah . Lam Chee Siang

Received: 7 October 2015 / Accepted: 15 April 2016 Ó Springer International Publishing Switzerland 2016

Abstract In this study, the rapid consolidation This research has produced a set of criteria for equipment (RACE) was developed as an alternative determining the suitable rate for the rapid consolida- device to the conventional consolidation test using tion test based on the ratio of normalized strain rate, b, Oedometer, consuming merely a few hours for the and proposed a new coefficient in terms of a ratio of b whole precedure to determine the consolidation char- to clay fraction (CF), as a part of new criteria for acteristics of cohesive soil. RACE operates based on testing a fine soil. Four types of sample were tested the constant rate of strain (CRS) consolidation theory, with different rates of strain using the RACE and their which is a continuous loading method of testing, results were compared with those conducted using the requiring a good estimation of the loading rate such Oedometer on the same soil type, from which fairly that it is ideal for the achievement of steady state good agreements were evident in many specimens. It condition during testing. The steady state condition is was found from the study that the minimum value of achieved when the cv values from drained and normalized strain rate, b, for the CRS test is 0.005 and undrained face of CRS converged with the cv from for the ua /rv ratio is suggested as 0.01. Also, the Oedometer test. A slightly modification has been made maximum b/CF for soils with clay friction lower and on the normal constant rate of strain (CRS) test by higher than 50 % are 0.008 and 0.001, respectively. proposing a direct back pressure system to the The minimum b/CF value for both conditions is specimen using a tube to saturate the soil sample. 0.0001.

Keywords Consolidation Á Soft clay Á Strain rate Á Compression characteristics

K. A. Kassim Á A. S. A. Rashid (&) List of symbols Department of Geotechnics and Transportation, Universiti C Compression index Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia c e-mail: [email protected] cv Coefﬁcient of consolidation CF Clay fraction A. B. H. Kueh Ho Sample height Construction Research Centre, Universiti Teknologi r Rate of strain Malaysia, Johor Bahru, Johor, Malaysia ua Excess pore water pressure C. S. Yah Á L. C. Siang rv Applied pressure Universiti Teknologi Malaysia, Johor Bahru, Johor, b Normalized strain rate Malaysia 123 Geotech Geol Eng

1 Introduction

The Oedometer test is commonly used to determine the soil consolidation characteristics in which a step loading is applied based on Terzaghi’s theory, the procedure of which that normally takes around 1 week for the completion of one test (loading and unloading stages) (Znidarcic et al. 1986; Head 1986). In addition to such a time-consuming procedure, the test is limited to low and medium loading for a sample size of 75 mm diameter. Besides that, the pore pressure at the bottom of the soil sample cannot be measured. To remedy these issues, the hydraulic consolidation equipment, which is capable of measuring pore pressure, the Rowe cell was therefore introduced, noting however that the testing procedure is also based on a step loading method (Head 1986). Due to several limitations given above, a rapid consolidation equipment abbreviated simply as RACE, as shown in Fig. 1, has been introduced and developed in this paper to conduct the consolidation test based on the constant rate of strain (CRS) theory, which could accelerate the consolidation process for cohesive soil, shortening the time consumption from 1 week (when using Oedometer and Rowe cell tests) to only a few hours. Some modification has been made based on the standard CRS equipment, allowing for a back pressure system to directly saturate the sample before the test is conducted (Head 1986). It is well known that the main problem with Fig. 1 a Schematic and b Photogrammetric of the Rapid continuous loading consolidation is to determine a Consolidation Cell Equipment (RACE) proper strain rate for the consolidation test (Ozer et al. 2012). The selection of the test rate remains as a major (1981), and the maximum ua /rv ratio, which is varied hurdle in the conduct of the CRS test although many between 0.03 and 0.7, as reported in previous studies attempts had been carried out to address this issue. (Gorman et al. 1978; Larsson and Sallfors 1985; Many recommendations had been offered from the Sandbaekken et al. 1986; Sheahan and Watters 1997; previous researchers for the selection of practically ASTM 2008). The value of cv can be determined from acceptable test rate, based on several criteria of several equations and charts as demonstrated in acceptance (Gorman et al. 1978; ASTM 2008; Larsson numerous studies done previously for a normally and Sallfors 1985; Sandbaekken et al. 1986; Lee et al. consolidated clay (Carrier 1985; Raju et al. 1995; 1993; Sheahan and Watters 1997; Ozer et al. 2012). Sridharan and Nagaraj 2004). It is however somewhat These criteria of acceptance were determined based on practically unsatisfactory that so far the minimum the following characteristics; the relationship of the limits for both values have not been suggested by void ratio, e, against effective stress, r0, coefficient of previous researchers, to produce a better and accept- consolidation, cv, liquid limit value, normalized strain able CRS test result. rate, b, and ratio of excess pore pressure to applied Ozer et al. (2012) reported that a problem may arise total stress, ua/rv. Well received criteria include the in determining the consolidation properties if the maximum limit for b, which is 0.1 as proposed by Lee strain rate test is conducted at a very small rate. Lee 123 Geotech Geol Eng et al. (1993) also confirmed that the lowest feasible only to the top of the specimen. By proposing this rate depends on the accuracy of the pore pressure modification, the saturation process will be faster and transducer and suggested that further research is could be monitor precisely. needed to address this. Although Ozer et al. (2012) This equipment allows also the pore water pressure proposed a new semi-empirical method to calculate to be observed during the test. O-rings are used to the proper strain rate for CRS testing of soils based on avoid any leakage in the system. The friction between the changes of strain and void ratio, e, of sample the loading piston and the top cell is reduced using ball during the test, this method requires the user to bearings. The main loading machine for the CRS test conduct the incremental loading consolidation proce- consists of a loading frame with a multi-speed drive dure to determine the void ratio of the sample. unit. In this study, the CRS tests were conducted in Therefore, in this study, a series of laboratory works various strain rates. 50 mm linear variable displace- was conducted employing RACE to determine a ment transducer (LVDT), 1500 kPa pressure trans- suitable criterion for the strain rate used in the CRS ducer and 1 kN S type load cell were used to measure test for various types of clay obtained in Malaysia. The the deformation, pore water pressure and the loading, strain rate, r was determined based on Lee (1981) respectively. All the inputs were read and stored approach of normalized strain rate, b where the systemically using the data acquisition unit. maximum limit for b is 0.1. Modification on the available strain rate selection method and hence a set 2.2 Sample Preparation of lower bound values for CRS test was then recommended. The soil samples were collected from Air Papan, Gemas and Kluang, which are located in the southern part of West Malaysia. The locations of the site were 2 Experimental Description displayed in the Fig. 2. Also, Kaolin clay was used as the control material in the investigation. The classi- 2.1 RACE Equipment fication properties of the soil samples are presented in Table 1. This study is conducted on the typical For convenience, a description of RACE is given tropical soil within a range of the Liquid Limit (LL) herein (see Fig. 1). The major components of RACE and Plasticity Index (PI) was between 40–53 and are the base, cell top, cell chamber and the stainless 23–26 respectively. Further investigation is required steel ring (Kassim et al. 2014). The soil specimen for in order to different range of LL and PI of soil. For this equipment comes in a cylindrical form with a each test, a remoulded sample was prepared in a slurry diameter of 100 mm that is placed at the bottom of condition using 1 kg of oven dried soil sample that stainless steel ring with a height of 25 mm. In addition, was mixed with the distilled water at 1.4 times the porous stones are placed at the top and bottom of the liquid limit to produce a homogeneous sample (Rashid soil specimen. A modification has been made on the et al. 2015a, b). In addition, a specially designed back pressure system where the back pressure is remould sampler with an internal diameter of 150 mm applied directly through the sample by using a tube. In was used to prepare the sample under different order to ensure accurate measurement on the back maximum pre-consolidation pressures (100, 200 and pressure applied on the sample, two rubber O-rings 300 kPa). For each maximum pressure, a step loading were used between load platen and stainless steel ring method was applied to ensure the sample was to seal the specimen. The friction between the rings uniformly consolidated. A soil cake with a height of and load platen and stainless steel ring was assumed 100 mm was produced at the completion of the insignificance by applying grease between both mate- consolidation process. Steel rings with internal diam- rials. It is also possible to either apply the same back eters of 50 and 100 mm were pressed on the pressure to the base of the specimen or prevent compressed soil cake to obtain samples for Oedometer drainage from the base and measure the pore pressure and RACE tests, respectively. Each sample was then at the base. During the saturation stage the back trimmed and placed inside the cell. RACE tests were pressure is applied to both top and bottom of the conducted such that the resulting compression curves specimen; during the consolidation stage it is applied can be compared with those from Oedometer tests. 123 Geotech Geol Eng

Fig. 2 Location map of the Air Papan, Gemas and Kluang site

Gemas

Air Papan

Kluang

Table 1 Classiﬁcation Soil characteristics Soil types properties of soil samples Kaolin clay Gemas clay Air Papan clay Kluang clay

Liquid limit (%) 51.40 47.02 40.47 53.19 Plastic limit (%) 28.40 24.53 19.53 26.87 Plastic index (%) 23.00 22.49 20.95 26.32

Speciﬁc gravity, Gs 2.64 2.60 2.59 2.55 Soil classiﬁcation CH CL CL CH

The result from the RACE tests is considered accept- undrained and drained conditions were employed able if a similar shape of curve is obtained. In this from the top and bottom of the soil sample in the CRS study, the Oedemeter tests were conducted in seven test. In this study, the strain rate, r was determined stages of loading (maximum 1200 kPa) and four based on Lee (1981) approach. For the determination stages of unloading (minimum 25 kPa). of normalized strain rate, b, Eq. 1 is commonly used to estimate the rate of strain, r. 2.3 Testing Procedures rH b ¼ o ð1Þ c In total, 12 major tests had been conducted for four v samples of soil. Three different intensities of pre- where Ho is the sample’s height and cv is the average consolidation were applied. A simple notation was coefficient of consolidation. The average coefficient of used to label the soil samples under different pre- consolidation, cv from conventional oedometer test consolidation pressures as shown in Table 2 e.g. Air were used to estimate the strain rate before the CRS Papan 100 denotes Air Papan soil with a pre-consol- test. The values of the normalized strain rate, b, and idation pressure of 100 kPa. For the Oedometer test, strain rate, r for all samples are listed in Table 2 based two tests were conducted on each sample to provide on Eq. 1. All the tests were conducted within the confidence as to the repeatability of the test prepara- maximum b value of 0.1 except for three tests on tion methods. Meanwhile, for the CRS test, the Kluang clay in order study the effect of higher b value. 123 Geotech Geol Eng

Table 2 Summary of measured consolidation characteristic from CRS and Oedometer tests

Soil types with different Average cv from Cc from ß value Strain rate for Cc pre-consolidation pressures Oedometer test Oedometer CRS test (mm/ from test min) CRS test

Air Papan 100 12.09 0.2345 0.025 0.0125 0.2329 0.05 0.025 0.2348 Air Papan 200 10.62 0.1875 0.05 0.02125 0.1914 0.075 0.0325 0.1923 Air Papan 300 16.08 0.1875 0.025 0.015 0.1873 0.05 0.0325 0.1884 Gemas 100 30.44 0.2090 0.025 0.3 0.2108 0.05 0.061 0.2134 Gemas 200 27.72 0.20800 0.01 0.01 0.2076 0.025 0.0275 0.2081 Gemas 300 32.41 0.2160 0.01 0.0125 0.2063 0.025 0.0325 0.2063 Kaolin 100 45.00 0.2850 0.01 0.0175 0.3159 Kaolin 200 47.16 0.3050 0.025 0.047 0.3068 0.05 0.094 0.3071 Kaolin 300 50.22 0.2700 0.025 0.05 0.2549 0.05 0.1 0.2583 Kluang 100 3.05 0.3586 0.10 0.01225 0.3584 0.26 0.03225 0.3589 Kluang 200 3.59 0.2877 0.1 0.01425 0.2867 0.15 0.0216 0.2738 Kluang 300 3.09 0.2325 0.1 0.01225 0.2327 0.15 0.0185 0.2320

3 Measured Consolidation Characteristics tests. For all four types of soil under different pre-

consolidation pressures, the compression indices, Cc, 3.1 Compression Index, Cc obtained from the compression curve based on the normalized void ratio, match closely those obtained Due to inconsistency of the initial void ratio, the void from the conventional Oedometer test, ensuring ratio had been normalized with that of initial, e/eo. therefore the acceptability of Cc produced by the Figure 3 shows the curve of e/eo against effective CRS test. stress for Gemas 100 sample from Oedometer and

CRS tests. For Gemas 100, two rates of strain, which 3.2 Coefﬁcient of Consolidation, cv are 0.03 mm/min (b = 0.025) and 0.061 mm/min

(b = 0.05), were applied in the CRS test. It can be It should be noted that a convergence of cv against log 0 0 observed that the relationships of e/eo versus log rv rv curves derived from the drained and undrained produced from both the CRS test and the standard faces of a specimen was observed in the conventional Oedometer test are in good agreement. Also, a slower Oedoemeter result (Lee 1981). The steady state strain rate of CRS test produces a better result with condition is achieved when the cv values from drained respect to that of Oedometer. and undrained face of CRS converged with the cv from Table 2 summarizes all measured consolidation Oedometer test. Undrained and drained coefﬁcient of properties obtained from the Oedometer and CRS consolidation values were derived from the top and

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Fig. 3 e/eo versus effective 1.0 stress relationship for Gemas 100 sample 0.9

0.8 o 0.7 e/e

0.6

Oedometer 1 0.5 Oedometer 2 CRS 0.03mm/min CRS 0.061mm/min 0.4 10 100 1000 10000 Effective Stress (kPa) bottom of the soil sample in the CRS test. This Oedometer test results compared to those with the comparison is important because one of the main strain rate of 0.0325 mm/min, as shown in Fig. 4b. The purposes of running the conventional Oedometer test results from the latter show signiﬁcant difference with is to ﬁnd out the rate of the compression process for the those of Oedometer. In the presence of higher pre- soil specimen. A good agreement of cv decreases the consolidation pressure, cv values for Air Papan 300 soil testing time from around 2 weeks to a few hours. samples that were conducted with a strain rate of

The coefﬁcient of consolidation, cv, for drained and 0.015 mm/min follow closely those obtained from the undrained soil of CRS test can be calculated from the Oedometer (Fig. 4c). CRS test with 0.0325 mm/min following expression (Wissa et al. 1971): strain rate produces somewhat scattered cv values 2 under both the undrained and drained conditions. H rv; doru0 cv; doru ¼ ð2Þ Although, there slightly exists convergence in the 2ua Dt 2 range of effective stress of 150–200 kN/m , cv values 2 where H is the current thickness of the specimen, ua is increase continuously after 200 kN/m . the excess pore pressure derived from the difference of The comparisons of cv against effective stress pore water, u and back pressures, ub and rv; doru0 /Dt is curves for Gemas 100, Gemas 200 and Gemas 300 the rate of change of effective stress at the drained or samples are shown in Fig. 5. Both undrained and undrained face. drained cv obtained from the CRS test for Gemas 100 Figure 4 shows the curves for coefﬁcient of con- (Fig. 5a) with a strain rate of 0.061 mm/min agree solidation, cv, against effective stress for Air Papan practically well with those from the Oedometer test 100, Air Papan 200 and Air Papan 300 samples. It can compared with those conducted with a strain rate of be observed that for both undrained and drained Air 0.03 mm/min. Meanwhile, both of the strain rates used

Papan 100 samples, cv obtained from the CRS test in the CRS tests for Gemas 200 (Fig. 5b) and Gemas (Fig. 4a) with a strain rate of 0.025 mm/min converge 300 (Fig. 5c) samples had produced compatible to those from Oedometer test. However, for CRS test results with those conducted with Oedometer. Both that was conducted with a strain rate of 0.0125 mm/ CRS curves indicate that the steady state condition has min, there exists a sharp increase in cv after an effective been achieved. In comparison, slower strain rate stress of 250 kN/m2 for both conditions. For Air Papan (0.01 mm/min for Gemas 200 and 0.0125 mm/min

200, the cv curves obtained from the CRS test with a for Gemas 300) produce somewhat better CRS test strain rate of 0.02125 mm/min are fairly close to the results.

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Fig. 4 a Comparison of the relationship of cv and effective stress for Air Papan 100 sample. b Comparison of the relationship of cv and effective stress for Air Papan 200 sample. c Comparison of the relationship of cv and effective stress for Air Papan 300 sample

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Fig. 5 a Comparison of the relationship of cv and effective stress for Gemas 100 sample. b Comparison of the relationship of cv and effective stress for Gemas 200 sample. c Comparison of the relationship of cv and effective stress for Gemas 300 sample

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2 Figure 6a shows the relationships of cv against effective stress of 500 to 800 kN/m for Air Papan 100 effective stress for Kaolin 100 samples. The results for sample. An extensive excess pore pressure increases

CRS test with a strain rate of 0.0175 mm/min are the cv value, as shown in Fig. 4a. A similar condition acceptable as they are compatible with the results from can be observed for Gemas 100 sample under the the Oedometer test. With higher pre-consolidation strain rate of 0.03 mm/min as shown in Fig. 5a where pressure, the results from Kaolin 200 (Fig. 6b) sample extremely high cv values were achieved. This is conducted with a strain rate of 0.047 mm/min are resulted by the small excess pore pressure produced at considered satisfactory as they converge with the the bottom of the specimen as shown in Fig. 8b. High

Oedometer test results and reach a steady state after an and unstable cv values on both undrained and drained effective stress of 300 kN/m2. However, disagreement faces are due to small excess pore pressure and in can be noticed when samples were tested with a higher practice such samples are normally rejected. Figure 8b strain rate (0.094 mm/min). From Fig. 6c, it is shows the unstable excess pore pressure for Air Papan observed that all cv curves from CRS tests do not 100 and 200 samples performed with the strain rates of agree with those of Oedometer tests because the CRS 0.0125 and 0.0325 mm/min. It can be seen that the test results at both strain rate (0.05 and 0.1 mm/min) excess pore pressures for both strain rates have not did not converged and far from the Oedometer test achieved steady condition and are still increasing at result. The different might be contributed from a the end of the CRS test especially for the strain rate of higher rate of strain as compared to the Kaolin 100. 0.0325 mm/min. As a result, the cv values under strain For Kluang soil samples, all curves produced from rate of 0.0325 mm/min is higher compared to the CRS tests are in good agreement with those of results from that of Oedometer and the test conducted Oedometer tests (see Fig. 7) although results from with the strain rate of 0.0125 mm/min produced CRS tests with a strain rate of 0.0185 mm/min diverging outcome beginning at an effective stress of demonstrate a constant difference of 20 m2/year in 300 kPa (Fig. 4a). cv from Oedometer’s results. Generally, the coefﬁcient Note that a rapid increase in excess pore pressure of consolidation, cv, for samples with higher pre- creates a transient condition, which is unacceptable as consolidation is relatively smaller because voids it is not compatible with Oedometer results that between the soil particles are smaller when the pre- maintain a steady state condition in the pore pressure consolidation pressure is increased, resulting in a development. Similar trend was observed by Youn and longer consolidation time. Chung (2005), Ahmadi et al. (2011), Raftari et al. (2014) where the pore water pressure increases rapidly 3.3 Pore Water Pressure corresponding with an increase in the strain rate, due to the drainage condition, soil structure and hydraulic During the tests, the pore water pressure was moni- gradation. Also, an extremely low excess pore pres- tored at the bottom of the specimen to determine the sure gives unreasonably high cv values. Hence, it is stability condition in the presence of the load appli- important to have a limiting lower bound for the strain cation since it constitutes one of the factors affecting rate, in particular, that of the normalized, b. the resulting consolidation coefﬁcient obtained from the CRS test. Stability condition is achieved when the pore pressure becomes slightly stable in term of 4 Post-Processing magnitude after the increment of load. Figure 8 shows the excess pore pressure in relation to applied total 4.1 Normalized Strain Rate (b) vertical stress for CRS tests. Figure 8a shows the stable excess pore pressure for A range of strain rates adopted for the CRS test was

Air Papan 200, Air Papan 300 and Gemas 200 under calculated from cv values obtained from the Oedome- strain rate range from 0.015 to 0.0275 mm/min. It is ter test based on the upper limit of normalized strain clear that the stable condition contributed to similar rate (b = 0.1) suggested by Lee (1981) (see Table 2). pattern with the Oedometer and converged well as In general, extremely high or low normalized strain shown in Figs. 4b, c and 5b. Figure 8b shows that rates, b, produce unacceptable cv values. Therefore, it unstable excess pore pressure was produced under the is important that the acceptable normalized strain 123 Geotech Geol Eng

Fig. 6 a Comparison of the relationship of cv and effective stress for Kaolin 100 sample. b Comparison of the relationship of cv and effective stress for Kaolin 200 sample. c Comparison of the relationship of cv and effective stress for Kaolin 300 sample

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Fig. 7 a Comparison of the relationship of cv and effective stress for Kluang 100 sample. b Comparison of the relationship of cv and effective stress for Kluang 200 sample. c Comparison of the relationship of cv and effective stress for Kluang 300 sample

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Fig. 8 a Excess pore (a) 20 pressure for Air Papan and Gemas in the presence of effective stress. b Excess pore pressure for Air Papan and Gemas in the presence 15 of effective stress

Excess Pore Pressure (kPa) Pressure Excess Pore 5

Gemas 200 (CRS 0.0275mm/min) Air Papan 300 (0.015mm/min) Air Papan 200 (0.02125 mm/min) 0 0 200 400 600 800 1000 1200 Effective Stress (kPa)

(b) 25 Air Papan 100 (0.0125mm/mm) Gemas 100 (0.03mm/min) Air Papan 200 (0.0325 mm/min) 20 Kluang 200 (0.01425mm/min) Kluang 200 (0.0216mm/min)

10 Excess Pore Pressure (kPa) Pressure Excess Pore 5

0 0 200 400 600 800 1000 1200 EffectiveStress (kPa) rates, b, can be determined from the convergence of the determined b values are less than the upper limit the undrained and drained cv values of the CRS tests as (b \ 0.1) suggested by Lee (1981). It is found that low well as from the compatibility of cv values with the normalized strain rates produce extremely high cv conventional Oedometer test results. In the present values, which are not acceptable, resulting in dis- study, the actual normalized strain rates, b, were agreement of behaviour as shown in Fig. 4a for Gemas calculated based on the cv values from the CRS test 100 kPa samples with a strain rate of 0.03 mm/min results. (b = 0.0003). A similar behaviour is observed from Table 3 shows the tabulation of actual and accept- the CRS test for the Kaolin samples under 200 kPa able b limits for soil samples under pre-consolidation (Fig. 6b) and 300 kPa (Fig. 6c) pre-consolidation pressures of 100, 200 and 300 kPa. Generally, most of pressures.

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Table 3 Tabulation of acceptable b limits for different soil samples Soil types with different pre-consolidation pressures Actual b range Acceptable b range and strain rates (mm/min) Lower limit Upper limit Lower limit Upper limit

Air Papan 100 (0.0125) 0.000270 0.120000 0.006000 0.121000 Air Papan 100 (0.025) 0.006500 0.209000 0.014900 0.097000 Air Papan 200 (0.2125) 0.005100 0.256000 0.011700 0.255700 Air Papan 200 (0.0325) 0.004000 0.145000 0.005000 0.013000 Air Papan 300 (0.015) 0.006000 0.082000 0.008800 0.082000 Air Papan 300 (0.0325) 0.002600 0.333000 0.009400 0.021000 Gemas 100 (0.03) 0.000300 0.004400 – – Gemas 100 (0.061) 0.007600 0.033000 0.021000 0.033000 Gemas 200 (0.01) 0.000356 0.033600 0.005200 0.034000 Gemas 200 (0.0275) 0.007700 0.028000 0.008000 0.028000 Gemas 300 (0.0125) 0.000700 0.009800 0.005400 0.098000 Gemas 300 (0.0325) 0.004700 0.048400 0.012000 0.048400 Kaolin 100 (0.0175) 0.006000 0.090500 0.006000 0.090000 Kaolin 200 (0.047) 0.006400 0.055000 0.014000 0.049000 Kaolin 200 (0.094) 0.016800 0.029800 0.020000 0.029000 Kaolin 300 (0.05) 0.006000 0.011400 0.007600 0.011000 Kaolin 300 (0.1) 0.001000 0.023000 0.015000 0.017000 Kluang 100 (0.01225) 0.003000 0.073000 0.006000 0.047900 Kluang 100 (0.03225) 0.008000 0.450000 0.008000 0.069000 Kluang 200 (0.01425) 0.004800 0.018000 0.007600 0.018000 Kluang 200 (0.0216) 0.010000 0.037000 0.013200 0.037000 Kluang 300 (0.01225) 0.002800 0.048000 0.005000 0.048000 Kluang 300 (0.0185) 0.003500 0.033000 0.007700 0.033000

when the b used for the strain rate estimation are[0.1 Table 4 Maximum and minimum modiﬁed normalized strain rates, b/CF (see Table 2) where they are from 0.0028 to 0.08. For Kluang 100 sample, CRS test conducted with a Soil type Clay fraction (%) Maximum Minimum 0.03225 mm/min strain rate produces b that is [0.1. Air Papan 35 0.00071 0.00014 This is due to an extremely high b value during the Gemas 57 0.0009 0.00009 CRS test. Although the b values adopted for strain rate Kaolin 11 0.0082 0.00055 estimation are [0.1, the normalized strain rates Kluang 68 0.0010 0.00007 produced at the end of the CRS test are much lower compared to the b values adopted for the strain rate estimation at the early stage of the CRS test. For the Kaolin samples, although the b values are Upper limit value (b = 0.1) suggested by Lee below the upper limit suggested by Lee (1981), the (1981) provides a reasonably useful guidance to the produced cv values are higher than the Oedometer test researchers on conducting the CRS test. From our results, as shown in Figs 6b, c. Here, the acceptable b observation, the CRS test with an extremely low for Kaolin 200 and Kaolin 300 were determined from normalized strain rate normally produces poor results. the convergence of undrained and drained cv values This is evident in the test results of the Gemas 100 from the CRS tests range from 0.076 to 0.029 (see remoulded sample that was conducted with a strain Table 3). Normalized strain rates for Kluang rate of 0.03 mm/min, which produced extremely high remoulded samples of CRS test are acceptable even and unstable cv values corresponding to a very low

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Fig. 9 e/eo versus effective stress relationship for UTM laterite soil

normalized strain rate (\0.005). Therefore, it is where the maximum suggested b of 0.1 is not recommended based on the finding of the present applicable for Kluang soil, it is suggested that the measurement that the lower limit of normalized strain clay fraction, CF, should be considered as a factor in rate is 0.005. the establishment of the strain rate. A modified normalized strain rate, b/CF, is hence introduced. 4.2 Modified Normalized Strain Rate, b/CF The values of CF were used as the magnitude in percentage to obtain the ratio between b/CF. From the current study, it has been demonstrated that Table 4 shows the summary of the maximum and the upper limit of the normalized strain rate suggested minimum modified normalized strain rates for all by Lee (1981) is not suitable for a very fine soil currently considered soil types. From the tabulated specimen. This is because excess pore pressure values, soil samples with a clay fraction [50 % have produced at the bottom of the specimen is very small low maximum modified normalized strain rate values, or very hard to measure when very fine soils are tested. which are around 0.001. For the samples with a clay In this regard, the Kluang soil presents the best fraction lower than 50 %, the maximum modified example. CRS tests on the Kluang soil samples that normalized strain rates have higher b/CF values, were carried out at the first stage with a slow strain rate which are around 0.008. For the minimum normalized do not give good results due to insignificant pore strain rate, soils with a higher clay fraction produce pressure at the bottom of the soil sample. As a result, lower modified normalized strain rate compared to the normalized strain rates, b, used for the Kluang those with a lower clay fraction. As a result, the soil’s strain rate estimation at the early stage were minimum b/CF value for both conditions is recom- increased to be[0.1. Considering the arisen problem, mended to be 0.0001.

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Fig. 10 Comparison of the relationship of cv and effective stress for UTM laterite soil

4.3 Validation of b/CF 4.4 Maximum Ratio of Excess Pore Pressure

to Applied Pressure (ua/rv) To check the practicality of the modiﬁed normalized strain rate, a validation of b/CF was conducted on the Table 5 shows the ratios and the acceptable ratios of

Universiti Teknologi Malaysia (UTM) laterite soil, the excess pore pressure to applied pressure (ua/rv) for consisting 10 % of clay. From the conventional Air Papan, Gemas, Kluang and Kaolin samples. The 2 Oedometer test, the average cv value is 30 m /year. acceptable ua/rv can be determined from the conver- Based on the clay fraction of the UTM laterite soil, the gence of the undrained and drained cv values, obtained normalized strain rate used for the strain rate estima- from the CRS tests and the compatibility of cv values tion was 0.008. The strain rate estimated for the CRS to the conventional Oedometer test results. For Air test based on the clay fraction was therefore Papan samples, the cv values from CRS tests 0.2425 mm/min. (Fig. 4b—Air Papan 200–0.0325 mm/min) are some- The resulting normalized void ratio curves are what higher compared to the Oedometer test results shown in Fig. 9. The curves from the CRS test agree since the ratios of ua/rv are too small (\ua/rv = 0.01). very well with the Oedometer test results. Also, it is Similar observation is found in the Gemas 100 observed that the undrained and drained cv values from (0.03 mm/min) samples (see Fig. 5a). Thus, it is the CRS tests are perfectly converged as shown in suggested from Fig. 4a (Air Papan 100–0.025 mm/

Fig. 10. Besides that, CRS curves converge with the min) that the acceptable ua/rv ratios for Air Papan soil 2 Oedometer test result after 600 kN/m . Therefore, it is range from 0.01 to 0.142 where within this range the cv evident that the CRS test produces an acceptable result values obtained from the top and bottom faces based on the modiﬁed normalized strain rate, b/CF. converge and compatible with those from Oedometer.

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Table 5 Maximum and minimum ratios of ua/rv

Soil types with different pre-consolidation pressures Ratio of ua/rv Acceptable ratio of ua/rv and strain rates (mm/min) Lower limit Upper limit Lower limit Upper limit

Air Papan 100 (0.0125) 0.0008 0.063 0.033 0.063 Air Papan 100 (0.025) 0.0049 0.2300 0.0280 0.115 Air Papan 200 (0.2125) 0.0095 0.206 0.010 0.142 Air Papan 200 (0.0325) 0.0058 0.047 0.013 0.042 Air Papan 300 (0.015) 0.009 0.11 0.026 0.084 Air Papan 300 (0.0325) 0.003 0.093 0.025 0.061 Gemas 100 (0.03) 0.001 0.01 – – Gemas 100 (0.061) 0.005 0.099 0.08 0.99 Gemas 200 (0.01) 0.007 0.063 0.01 0.063 Gemas 200 (0.0275) 0.007 0.115 0.029 0.115 Gemas 300 (0.0125) 0.006 0.043 0.019 0.043 Gemas 300 (0.0325) 0.02 0.11 0.03 0.108 Kaolin 100 (0.0175) 0.012 0.0567 0.012 0.0567 Kaolin 200 (0.047) 0.0045 0.08 0.038 0.055 Kaolin 200 (0.094) 0.0016 0.1 0.032 0.065 Kaolin 300 (0.05) 0.013 0.048 0.022 0.048 Kaolin 300 (0.1) 0.027 0.061 0.037 0.052 Kluang 100 (0.01225) 0.0067 0.073 0.019 0.073 Kluang 100 (0.03225) 0.0028 0.084 0.025 0.084 Kluang 200 (0.01425) 0.004 0.05 0.021 0.049 Kluang 200 (0.0216) 0.0044 0.077 0.022 0.077 Kluang 300 (0.01225) 0.0044 0.048 0.026 0.048 Kluang 300 (0.0185) 0.005 0.03 0.0158 0.027

Similar ﬁnding is observed for Gemas (Fig. 5b) and reducing testing time from 1 week to merely a

Kluang (Fig. 7b) samples where the acceptable ua/rv few hours. values range between 0.01 to 0.115. Generally, most 2. The Cc values produced by the CRS test are within of the ua/rv values are less than the limits suggested by the maximum and minimum limits of the standard ASTM (2008), Lee (1981). Therefore, based on the Oedometer test results. current finding, the minimum value for the ua/rv ratio 3. The coefficient of consolidations, cv, from CRS in general can be hereby suggested as 0.01. tests are compatible with the conventional Oedometer test results when the strain rates are within the limiting values based on the normalized 5 Conclusions strain rate, b. 4. It is found that the minimum value of normalized From the current study, several conclusions based on strain rate, b, for the CRS test is 0.005. four investigated soil types using Oedometer and CRS 5. A new criterion of acceptance known as the tests are listed below. modified normalized strain rate, b/CF, is proposed. From this study, the suggested maximum 1. A new rapid consolidation cell equipment modified normalized strain rate, b/CF, for soils (RACE) has been developed adopting CRS with CF [ 50 % and lower than 50 % are 0.001 method for cohesive soil consolidation test,

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