• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1156-1167
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• 2010

The constant rate of strain (CRS) consolidation test has been widely used to evaluate consolidation characteristics of soils instead of the standard Incremental Loading Test. In practical problems, after the ground improvement, the condition of the soil is over-consolidated. Therefore, it is important to determine the recompression indices and the coefficient of consolidation(or the coefficient of swelling) of unloading-reloading cycle to predict the settlement behavior. However, since standard testing procedures or studies related with strain rate are insufficient especially in unloading-reloading cycle, it is difficult to predict the settlement field behavior accurately from the CRS consolidation test results in spite of its lots of strengths. The several CRS consolidation tests were performed changing the unloading strain rate from 0.2%/hr to 20%/hr with vertical drainage condition using the reconstituted kaolinite sample. For the reconstituted kaolinite sample in CRS consolidation test, the recompression indices are insensitive to the strain rate. It is revealed that the coefficient of consolidation of reloading is affected by the developed pore pressure during unloading. Additionally, the test should be conducted in the positive pore pressure ratio range (3~15%) to obtain the reasonable coefficient of consolidation in the whole range(loading, unloading and reloading).

• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.99-106
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• 2000

The main advantage of incremental loading consolidation test is the simplicity of equipments that can be used. However, it is known that the incremental loading test has several deficiencies including long testing time, non-uniform stress state, high and variable rates of strain, very soft clay and problem of back pressure saturation. Due to these drawbacks, various testing methods including constant rate of strain consolidation test(CRS) were developed. In this paper, CRS consolidation test was performed with three different strain rate. The results were verified by the modified CRS theory of Wissa et al.(1971). And then the results obtained from the CRS consolidation tests were compared with those from incremental loading test and direct permeability test.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.455-462
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• 2002

There exist several kinds of continuous consolidation tests to analyze the consolidation behavior of soft clay. The constant rate of strain (CRS) test has been adopted as a standard method by several countries, and some researches also have been peformed by domestic researchers. Among those, the constant pressure ratio (CPR) test is peformed with the constant ratio of excess porewater pressure to vertical effective stress. The test has the advantage of considerable reduction of duration time. In the study, the consolidation characteristics are analyzed by performing the CPR test as validate the pressure ratio with undisturbed soft clay and remolded clay, Also, results of the standard consolidation test and CRS test are compared to verify the CPR test can be employed for practical use. As a result, effects of variation of the pressure ratio on consolidation parameter are similar to the strain rate in the CRS test. Therefore, the test can be used to analyze the consolidation behavior of soft clay But the test have some problems such as expensive cost of equipment and highly skilled workmanship.

• Journal of Auto-vehicle Safety Association
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• v.9 no.3
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• pp.31-38
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• 2017

For years, Q1.5 (anthropomorphic test device for 1.5 years old infant) and Q3 (anthropomorphic test device for 3 years old infant) dummy protection has been improved considerably by the effort of EuroNCAP. ISOFIX strength of vehicle structure has increased and many child occupant protection tests have made child restraint system (hereafter CRS) optimized for child safety. However, from 2016, EuroNCAP changed the dummy which is used for the child occupant protection from Q1.5/Q3 to Q6/Q10 and these were also adopted in KNCAP from 2017. Therefore, a new method is required to secure the safety for older children In this research, child dummies were tested by using adult safety systems, and the different results from each adult restraint system were compared. Finally, dummies were tested with the CRS harness belt commonly used for infants, which has yielded significant result. In this research, mid-sized sedan and small SUV were used for the test. The researchers of this paper performed sled tests to correlate between the different adult safety belt system and child injury. Following the sled test, an actual vehicle test was conducted to gather the injury data of Q-dummy with the CRS harness belts. This paper will show the advantages of applying a pre-tensioner in the second row for child protection and the necessity of CRS which has its own harness belts to improve safety for older children.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.311-317
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• 2003

The swelling index of clayey soil was examined by constant rate of strain(CRS) consolidation test. Four kinds of strain rate were applied during unloading. The strain rates are l/l, l/5, 1/10, l/l 5 of loading. The strain rates during loading are 0.05%/min and 0.03%/min. From the test results using standard consolidometer, the swelling indexes were much similar values in case of 1/5 or 1/10 of the strain rate during loading stage. In the relation between effective stress and excess pore water pressure ratio, it was found that the existence of cross point and the stress level can be separated into two zones according to the swelling index.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.335-342
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• 2000

In this study, the swelling characteristics of reconstituted clayey soil were investigated by STD and CRS test. The strain rate during loading was constant i.e. 0.05 %/min, 0.03 %/min and during unloading was varied in proportion to 1/1, 1/5, 1/10 and 1/15 of strain rate during loading. From this study the following conclusions were obtained; (1) There were similar values, especially, during unloading in case of 1/10 or 1/15 of strain rate during loading and the test results between STD and CRS were much to be alike. (2) The cross point of effective stress versus excess pore water pressure ratio curve, was increased during unloading, while the stress level of the cross point was decreased. The stress level can be separated into two zones according to the swelling index named Cs1 and Cs2. From the test results, the values of Cs1 were approximately constant irrespective of strain rate during unloading, but the values of Cs2 were much influenced by strain rate. (3) In CRS consolidation tests, it was found that unloading strain rate did not affect on the existence of zone.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.173-180
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• 2004

In this study, a consolidometer for radially inward drainage under constant rate of strain (CRS) loading was developed. Theoretical solutions for determining the effective vertical stress and the coefficient of consolidation from the test result were also proposed. Reconstituted kaolinite samples which were consolidated up to 130 kPa were used to verify the developed consolidometer and the theory. Comparative experiments with CRS loading and incremental loading (IL) were carried out in radially in ward drainage as well as vertical and radially outward drainage. The results obtained from the developed CRS loading test agreed consistently with those of the conventional incremental loading test according to drainage directions. And the effect of drainage direction and drain diameter to consolidation characteristics was also evaluated. From the test results the applicability and the reliability of the suggested method were verified.

• Proceedings of the KSR Conference
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• 2000.05a
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• pp.399-406
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• 2000

In this study, using the CRS consolidation tests on reconstituted marine clay, the characteristics of C$\sub$v/, k, e and $\varepsilon$, the anisotropic characteristics of specimen according to the rate of strain were estimated. Also, the validity of the Wissa et al.(1971) consolidation theory on CRS(Constant Rate of Strain) consolidation tests were reviewed. From that results, it was shown that the value of C$\sub$v/, k and u$\sub$b/ was increased as the rate of strain was increased. While the difference of the value( C$\sub$v/, k and u$\sub$b/) between vertically reconstituted specimen and horizontally reconstituted specimen became small as the rate of strain was increased. It is known that k is different due to the hydraulic gradient(i) during the CRS consolidation tests. The subject of this study is to distinguish steady state from transient state in CRS consolidation tests. Consequently, the difference of the value(C$\sub$v/ and k) is higher in case of vertically reconstituted specimen than horizontally reconstituted specimen.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.240-247
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• 2005

In order to analyze effects of strain rate on consolidation characteristics on Busan clay, a series of constant rate of strain(CRS) consolidation tests with different strain rate and incremental loading test(ILT) were performed. From experimental test results, it was found that the preconsolidation pressure was dependent on the corresponding strain rate occurred during consolidation process. Also, consolidation curves normalized with respect to preconsolidation pressure gave a unique stress-strain curve. Coefficient of consolidation and permeability estimated from CRS test had a tendancy to converge to a certain value at normally consolidated range regardless of strain rate. An increase in excess pore pressure without change of total stress was noted on the incremental loading test after the end of loading.

• Journal of the Korean Geotechnical Society
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• v.21 no.6
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• pp.127-135
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• 2005

In order to analyze effects of strain rate on consolidation characteristics of Busan clay, a series of constant rate of strain (CRS) consolidation tests with different strain rate and incremental loading tests (ILT) were performed. From experimental test results on Busan clay, it was found that the preconsolidation pressure was dependent on the corresponding strain rate occurring during consolidation process. Also, consolidation curves normalized with respect to preconsolidation pressure gave a unique stress-strain curve. Coefficient of consolidation and permeability estimated from CRS test had a tendency to converge to a certain value at normally consolidated range regardless of strain rate. An increase in excess pore pressure was observed after the end of loading without change of total stress on the incremental loading test, which phenomenon is called Mandel-Cryer effect. It was also found that rapid generation of excess pore pressure took place due to collapse of soil structure as effective stress approached to preconsolidation pressure.