Marine clayey deposits are widely distributed at the seashore regions in Korea. When multi-stage embankments for the civil engineering works such as harbors, roads and etc. are conducted, the short term stability on each stage embankment should be checked. Incremental strength ratios of marine claye...
Marine clayey deposits are widely distributed at the seashore regions in Korea. When multi-stage embankments for the civil engineering works such as harbors, roads and etc. are conducted, the short term stability on each stage embankment should be checked. Incremental strength ratios of marine clayey deposits which can be evaluated through the consolidated undrained test(CU) will be needed to check the stability. It is composed of saturation, consolidation and undrained shear(compression) on a specimen to do the consolidated undrained test by means of triaxial equipments. This study consists of the consolidated undrained tests and theirs analyses.
Since last glacial maximum(LGM) duration, which was about 15,000~18,000 years ago, the sea level ranging of 132m~140m below present sea level had gradually ascended and it reached the current sea level 5,000~6,000 years ago. For this study, the marine clay which had been deposited from early to late Holocene duration was sampled at the seashore regions of Busan New Port, Pyeongtaek Port and reclaimed land in Mokpo. Using these samples with 5cm diameter and 10cm height, triaxial compression(CU) tests were conducted and test results were analyzed as follow.(The symbol,【】, indicates results of finite difference analysis for the sample with 3.5cm diameter and 7.0cm height)
1. Back pressure saturation test results:
1) The pore pressure parameter B, which is more than 0.97, can be obtained by back pressure saturation in marine clay having the liquid limit, which is more than 0.6 or the preconsolidation pressure less than 100 kPa.
2) According to the increase of preconsolidation pressure of the sample from 30 kPa to 250 kPa, it took 50 minutes to 240 minutes in linear pattern for the sample to be saturated.
3) According to the increase of liquid index of the sample from 0.45 to 0.9, back pressure for saturation decreases from 310 kPa to 160 kPa. In a similar manner, as the preconsolidation pressure of sample became high, back pressure for saturation was increased.
2. Stress ratio in rest as results of Ko consolidation in triaxial cell:
1) According to the increase of plastic index of the sample, stress ratio in rest was increased in a similar manner of previous studies. On the contrary, test results showed lower value than Alpan's proposal value.
2) In relationship between friction angle and stress ratio at rest, test results showed that the stress ratio using friction angles which was estimated in criteria of max. deviator stress for failure were in better agreement with Jaky's relationship than Brooker & Ireland's one.
3) Delayed consolidation after primary consolidation caused Ko value to be reduced slightly. Especially, this tendency is apparent in the clay having high plastic index.
3. Consolidation analysis using isotropic and Ko consolation test results and numerical analysis using finite difference scheme for governing equation of consolidation:
1) As isotropic consolidation has been made using the clay having liquid limit of 43~53%(plastic index of 22~32) sampled at the seashore regions of Pyeongtaek Port, the time for primary consolidation ranged from 16 to 120 min.【9~47 min.】. Using the gradual loading with the rate of 10~20 kPa/min. for Ko consolidation, primary consolidation was made completely in about 30 min.【10 min.】after loading. Numerical results of governing equation of consolidation showed the relationship of in this marine clay.
2) As isotropic consolidation has been made using the clay having liquid limit of 76~110%(plastic index of 44~72) sampled at the seashore regions of Busan New Port, the time for primary consolidation ranged from 80 to 184 min.【43~83 min.】. Using the gradual loading with the rate of 1~2 kPa/min. for Ko consolidation, primary consolidation was made completely in about 110 min.【50 min.】after loading. Numerical results of governing equation of consolidation showed the relationship of in this marine clay.
4. Incremental strength ratio of normally consolidated clay:
1) The relations between the undrained shear strength at a maximum stress ratio and the normal consolidation pressure(isotropic or Ko states) are almost constant in the marine clay with the plasticity index more than 40, which were and respectively. The ratio of to was about 1.1. However, the marine clay with the plasticity index less than 40(or with the liquid limit less than about 60%) showed the tendency to increase with the decrease of plasticity index(or liquid limit).
2) The relations between the undrained shear strength at a maximum deviator stress and the normal consolidation pressure(isotropic or Ko states) was almost constant in the marine clay with the plasticity index more than 40, which were . However the marine clay with the plasticity index less than 40(or with the liquid limit less than about 60%) showed the tendency to increase with the decrease of plasticity index(or liquid limit).
Marine clayey deposits are widely distributed at the seashore regions in Korea. When multi-stage embankments for the civil engineering works such as harbors, roads and etc. are conducted, the short term stability on each stage embankment should be checked. Incremental strength ratios of marine clayey deposits which can be evaluated through the consolidated undrained test(CU) will be needed to check the stability. It is composed of saturation, consolidation and undrained shear(compression) on a specimen to do the consolidated undrained test by means of triaxial equipments. This study consists of the consolidated undrained tests and theirs analyses.
Since last glacial maximum(LGM) duration, which was about 15,000~18,000 years ago, the sea level ranging of 132m~140m below present sea level had gradually ascended and it reached the current sea level 5,000~6,000 years ago. For this study, the marine clay which had been deposited from early to late Holocene duration was sampled at the seashore regions of Busan New Port, Pyeongtaek Port and reclaimed land in Mokpo. Using these samples with 5cm diameter and 10cm height, triaxial compression(CU) tests were conducted and test results were analyzed as follow.(The symbol,【】, indicates results of finite difference analysis for the sample with 3.5cm diameter and 7.0cm height)
1. Back pressure saturation test results:
1) The pore pressure parameter B, which is more than 0.97, can be obtained by back pressure saturation in marine clay having the liquid limit, which is more than 0.6 or the preconsolidation pressure less than 100 kPa.
2) According to the increase of preconsolidation pressure of the sample from 30 kPa to 250 kPa, it took 50 minutes to 240 minutes in linear pattern for the sample to be saturated.
3) According to the increase of liquid index of the sample from 0.45 to 0.9, back pressure for saturation decreases from 310 kPa to 160 kPa. In a similar manner, as the preconsolidation pressure of sample became high, back pressure for saturation was increased.
2. Stress ratio in rest as results of Ko consolidation in triaxial cell:
1) According to the increase of plastic index of the sample, stress ratio in rest was increased in a similar manner of previous studies. On the contrary, test results showed lower value than Alpan's proposal value.
2) In relationship between friction angle and stress ratio at rest, test results showed that the stress ratio using friction angles which was estimated in criteria of max. deviator stress for failure were in better agreement with Jaky's relationship than Brooker & Ireland's one.
3) Delayed consolidation after primary consolidation caused Ko value to be reduced slightly. Especially, this tendency is apparent in the clay having high plastic index.
3. Consolidation analysis using isotropic and Ko consolation test results and numerical analysis using finite difference scheme for governing equation of consolidation:
1) As isotropic consolidation has been made using the clay having liquid limit of 43~53%(plastic index of 22~32) sampled at the seashore regions of Pyeongtaek Port, the time for primary consolidation ranged from 16 to 120 min.【9~47 min.】. Using the gradual loading with the rate of 10~20 kPa/min. for Ko consolidation, primary consolidation was made completely in about 30 min.【10 min.】after loading. Numerical results of governing equation of consolidation showed the relationship of in this marine clay.
2) As isotropic consolidation has been made using the clay having liquid limit of 76~110%(plastic index of 44~72) sampled at the seashore regions of Busan New Port, the time for primary consolidation ranged from 80 to 184 min.【43~83 min.】. Using the gradual loading with the rate of 1~2 kPa/min. for Ko consolidation, primary consolidation was made completely in about 110 min.【50 min.】after loading. Numerical results of governing equation of consolidation showed the relationship of in this marine clay.
4. Incremental strength ratio of normally consolidated clay:
1) The relations between the undrained shear strength at a maximum stress ratio and the normal consolidation pressure(isotropic or Ko states) are almost constant in the marine clay with the plasticity index more than 40, which were and respectively. The ratio of to was about 1.1. However, the marine clay with the plasticity index less than 40(or with the liquid limit less than about 60%) showed the tendency to increase with the decrease of plasticity index(or liquid limit).
2) The relations between the undrained shear strength at a maximum deviator stress and the normal consolidation pressure(isotropic or Ko states) was almost constant in the marine clay with the plasticity index more than 40, which were . However the marine clay with the plasticity index less than 40(or with the liquid limit less than about 60%) showed the tendency to increase with the decrease of plasticity index(or liquid limit).
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