• Journal of the Korean Geotechnical Society
• /
• v.29 no.4
• /
• pp.13-22
• /
• 2013

To simulate the soft ground improved by vertical drain method and to investigate the effect of overlapping smear on subsequent consolidation behavior, a series of consolidation tests with a large consolidation chamber and mandrel insertion device were conducted. Based on the test result, numerical analysis was also performed to analyze the efficiency of the vertical drain method. Laboratory test and numerical analysis results showed that the effect of smear zone increased consolidation settlement but the overlapping smear zone decreased the consolidation settlement. In addition, vertical drain accelerated consolidation rate but narrowing the drain spacing did not affect the consolidation rate because of the effect of smear. The efficiency of consolidation rather decreased substantially when the smear zone was overlapped.

• Geomechanics and Engineering
• /
• v.13 no.6
• /
• pp.963-975
• /
• 2017

Improvement of soft clay deposit by preloading with vertical drains is one of the most popular techniques followed worldwide. These drains accelerate the rate of consolidation by shortening the drainage path. Although the analytical and numerical solutions available are mostly based on equal strain hypothesis, the adoption of free strain analysis is more realistic because of the flexible nature of the imposed surcharge loading, especially for the embankment loading used for transport infrastructure. In this paper, a numerical model has been developed based on free strain hypothesis for understanding the behaviour of soft ground improvement by vertical drain with preloading. The unit cell analogy is used and the effect of smear has been incorporated. The model has been validated by comparing with available field test results and thereafter, a hypothetical case study is done using the available field data for soft clay deposit existing in the eastern part of Australia and important conclusions are drawn therefrom.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.54 no.5
• /
• pp.103-111
• /
• 2012

In this study, the full-scale laboratory model test on utilization of recycled aggregates and crushed stone as vertical drains to use an alternative material of sand in soft ground is performed. The settlement and pore water pressure were measured to evaluate the discharge capacity and filed application, and the results were compared and analyzed through the finite element method. The measured and estimated settlement in all vertical drain materials decreases gradually with the load increase. The measured settlement 6.55~8.63 mm, and the estimated by the Hyperbolic model was 7.45~7.92 mm. So the model used for the analysis can be applied to the settlement estimation of the actual field. The variations of pore water pressure with time showed constantly regardless of the load in all vertical drainage materials. The pore water pressure was similarity to that of sand after rapid drawdown. Therefore, it was applicable to the field because discharge capacity was enough to be an alternative material to the sand which had been being used as the vertical drains.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.4
• /
• pp.69-77
• /
• 2007

In this study, the consolidation behavior of clayey ground improved by vertical drain method was analyzed by the finite difference method based on the three-dimensional elasto-viscous consolidation theory, which can express the behavior of the secondary consolidation without considering the distinction of the normally consolidated and overconsolidated states. And the applicability of the elasto-viscous consolidation theory was discussed by comparing with the test results obtained from the model test of ground improved by vertical drain system. From these results, it is found that the amount of the settlement when the excess pore water pressure almost dissipated in the clay ground with vertical drains became smaller than that of the one-dimensional condition, and then the amount and rate of the residual settlement at secondary consolidation process became larger than those of the one-dimensional condition. finally, the effect of soil parameter on behavior of consolidation process was investigated by the results of a series of numerical analysis for the normalized and overconsoldiated states.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.14 no.5
• /
• pp.1243-1251
• /
• 1994

The implicit finite difference program was developed to evaluate the relationship between time and consolidation ratio within the zone of vertical drain effective radius. In the evaluation, the excess pore water pressure was considered to dissipate in two directions, namely, vertical and radial flow direction. To calculate subsoil stress increments in the soil due to multi-step embanking, the foundation soil was assumed to be an isotropic and homogeneous elastic medium and the initial excess pore water pressure was estimated by using Skempton's parameters whose condition is plane strain and elastic phase of pore pressure response within the soft ground. Regarding to the settlement estimation, immediate and primary consolidation settlements were calculated. The secondary or delayed consolidation settlement was not considered. Numerically calculated excess pore water pressure and settlements were similar to the measured data in situ. Thus, this method can be used to predict the time-consolidation ratio of each layer treated by vertical drain method.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2009.03a
• /
• pp.720-728
• /
• 2009

This thesis is results of numerical analyses about test results of discharge capacity apparatus using penetration method. Applicability of numerical approach with FEM technique, using Cam-clay model, was confirmed by analyzing the results of standard consolidation test before analyzing test results of discharge capacity apparatus using penetration method. Thus, input parameters for the model was convinced to be appropriate. For numerical analyses about test results of discharge capacity apparatus using penetration method, identical initial and loading conditions during tests were applied to simulate test results correctly. Effects of ground disturbance resulted from installment of vertical drains on the behaviors of consolidation were also simulated. Applicability of numerical approach was investigated by comparing test results with numerical ones. As results of them, both of consolidation settlement were found to be in good agreements so that its applicability was confirmed. As results of numerical estimation, degree of consolidation with the condition of considering smear zone was found to be delayed, compared with results without smear zone. On the other hands, parametric numerical analyses of changing parameters related to smear zone such as permeability and size of smear zone and permeability of vertical drain were also carried out.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.48 no.6
• /
• pp.69-77
• /
• 2006

In this study, the large scaled model test improved by sand drain was carried out to clarify the internal behavior of the three-dimensional consolidation under different secondary consolidation periods. From the results of model test, the void ratio in the undrained side was lager than in the drained side. In addition, the unconfined compressive strength in the long-term consolidated specimen was larger than that in the short-term consolidated one. It was also found that the unconfined compressive strength was larger in the drained side than in the undrained side. These reasons are considered to be due to the large effective stress by quick pore water pressure dissipation by the short drainage distance in the drained side. Furthermore, in order to investigate the three-dimensional consolidation behavior of clay ground improved by the vertical drain method, the numerical analysis obtained from the three-dimensional elasto-viscous consolidation theory proposed by author (2006) were compared with the test results. It was found that during the three-dimensional consolidation process not only vertical displacement but also radial displacement occurs inside the specimen.

• Proceedings of the KSR Conference
• /
• 2001.10a
• /
• pp.552-557
• /
• 2001

Copper slag is the by-producted material on the proceeding of refining the copper. To verify applications of copper slag to vertical drain material can substitute for the sands in ground improvement, laboratory soil tests and consolidation model tests were conducted. The results of consolidation model test was analyzed as the hyperbolic method. The hyperbolic method assumes that the settlement(s) versus time(t) behavior approaches a straight line describes a hyperbolic reaction. The inverse of the slope of the line would then yield the ultimate settlement. Through in this study, copper slag is compatible with vertical drain material as like sands. Copper slag compaction pile promote the consolidation settlement.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.49 no.6
• /
• pp.93-101
• /
• 2007

In general, geotechnical properties have many uncertain aspects, thus probabilistic analysis have been used to consider these aspects. It is, however, quite difficult to select an appropriate target probability for a certain structure or construction process. In this study, minimum expected cost design method based on probabilistic analysis is suggested for design of vertical drains generally used to accelerate consolidation in soft clayey soils. A sensitivity analysis is performed to select the most important uncertain parameters for the design of vertical drains. Monte Carlo simulation is used in sensitivity analysis and probabilistic analysis. Total expected cost, defined as the sum of initial cost and expected additive cost, varies widely with variation of input parameters used in design of vertical drain systems. And probability of failure to get the minimum total expected cost varies under the different design conditions. A minimum value of total expected cost is suggested as a design value in this study. The proposed design concept is applicable to unit construction process because this approach is to consider the uncertainties using probabilistic analysis and uncertainties of geotechnical properties.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.4
• /
• pp.125-132
• /
• 2007

The oedometer, radial CRS and Rowe cell tests, composite discharge capacity tests and smear effect tests are carried out to estimate the parameters for the reliability-based design of vertical drain method. Also the sensitivity analysis, the probabilistic and deterministic solutions of radial consolidation theory are presented. The result of probabilistic analysis was compared to that of deterministic analysis using the tested and estimated parameters. The results indicated that the drain spacing in the deterministic method is larger than that in the probabilistic method because the former does not consider the uncertainties in the geotechnical property. The divergence of two methods is dependent on the probability of achieving target degree of consolidation by a given time and the coefficient of variation (COV) of the coefficient of horizontal consolidation ($c_h$).