• Journal of the Korean Geotechnical Society
• /
• v.25 no.9
• /
• pp.67-76
• /
• 2009

The problems of bearing capacity, settlement and shear deformation occur when constructing a structure such as harbor, airport and bridge on soft ground of marine clay, silty clay or sandy soil. Various ground improvement methods are applied to obtain preceding settlement of soft ground and strength increase. In this study, to analyze the applicability of PBD method in deep soft ground, the compound drainage capacity test was operated in comparison with SD. As a result of the test, a minimum drainage capacity of drain material was estimated to be more than $10\;cm^3/sec$ at a more than $400\;kN/m^2$ and less than $5\;cm^3/sec$ at a more than $500\;kN/m^2$ confining pressure in case of single core PBD. In case of double core PBD, it was estimated to be more than $10\;cm^3/sec$ at a more than $500\;kN/m^2$ confining pressure.

• Geotechnical Engineering
• /
• v.13 no.6
• /
• pp.25-36
• /
• 1997

A degree of consolidation at any time can be evaluated by using cone penetration test after soil improvement. In this case, after stopping the penetration of a piezocone, pore pressure dissipation(PPD) best is carried out until the pore pressure remains constant. Since the hydraulic conductivity of soft ground is very small, it takes very long time to finish the PPD test. This research is performed to develop a method overcoming this problem of the PPD test and reducing the test time. The analyses are carried out in the following ways : an equilibrium pore pressure can be determined by using pore pressure measured in the middle of the test, which is predicted by hyperbolic, Asaoka and Hoshino methods. And this equilibrium pore pressure is compared with the one measured in a test of long duration. As a result of the study, it is found that Hoshino method is the best way to predict the equilibrium pore pressure in a teat of short duration. And it is proposed as a methodology to fond a minimal time in which we can get an equilibrium pore pressure.

• Journal of the Korean Geosynthetics Society
• /
• v.7 no.4
• /
• pp.37-45
• /
• 2008

A pilot test using environmentally friendly drains, was carried out to evaluate their applicability potential in the field. The pilot test site was divided into 5 different areas, with several combinations of vertical and horizontal drains installed for evaluation. Conventional natural fiber drains (FDB), new developed straw drain board (SDB) and plastic drain board (PDB) were used as vertical drains, while sand and fiber mats were used as horizontal drains. Surface settlement rates and excess pore pressure generation/dissipation tendency of PDB and FDB are almost identical except those of SDB. Cone tip resistance obtained from cone penetration test measured at the end of 1st consolidation stage for upper soft layer definitely increased irrespective of types of vertical drains. The monitoring and site investigation test data obtained at the pilot test site prove the vertical natural fiber drains can be used as substitutes of conventional plastic and sand material.

• Journal of the Korean GEO-environmental Society
• /
• v.15 no.12
• /
• pp.43-51
• /
• 2014

Organic matter in dredged soil has a lot of engineering problem in ground including a large settlement, crack propagation, low bearing capacity and low friction angle. From an agricultural point of view, however, organic matter contributes greatly soil quality and plant health. This paper investigated the relationship between engineering and germination characteristics of stabilized mixture consisting of different ratios of organic content (0 %, 10 %, 20 %, 30 %) for recycling dredged soil including organic matter. Several series of laboratory tests such as flow test, unconfined compressive test and consolidation test were performed to find out engineering characteristics. pH, percent of germination and growth of plants were also measured to investigate the germination characteristics. The experimental results indicated that, as organic content increased, unconfined compressive stress decreased and compression and swelling indices increased. However, percent of germination and plant growth increases as organic content increases.

• Journal of the Korean Geosynthetics Society
• /
• v.13 no.1
• /
• pp.85-92
• /
• 2014

Structures that have constructed in soft clay might suffer from many issues related to consolidation settlement or lateral movement of soft-clay during long-term period. Therefore, it is important to establish proper design and construction processes related to site investigation, soil improvement, construction management, and so on. This case study focused on the construction of the rahmen structure supported by pile foundations. Especially, the structure in this case had been constructed without improving underlying soft clay and before constructing backfill embankment due to the limited construction time and the traffic connection of the old road crossing new highway. Therefore, in order to satisfy the structural stability, the construction processes and countermeasure methods were carefully planned based on the results of preliminary numerical analyses and monitoring of ground behaviors. Through the trial and error precess during the construction, the structures had been successfully constructed.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.28 no.3
• /
• pp.89-98
• /
• 1986

This study was carried out for the settlement and camber of earth dam by the changes of the density. The testing material was taken five kinds of Soil used as banking material and it was compacted by 100, 95, 90, 85 and 80% compaction degree. The results of the settlement of earth dam whose height ranges from 10m to 50m are as follows. 1.The more the fine particle (n) increases, the higher the liquid limit (WL) and the lower the dry density (rd) becomes as follows; rd=2. 22-0. 0052n (gr/cm$_3$) rd=2. 394-0. 0164WL rd=2. 185-(5. 8n-2. 5WL)X10-$_3$ 2. The higher the optimum moisture content (Wo) becomes, the lower the density becomes as follows; rt,=2. 68-0. 028Wo rd=2. 578-0. 04Wo 3. 3.Most of the consolidation occurs immediately by loading and the more the fine particle increases, the lower the coefficient of consolidation becomes. 4.The more the fine particle increases and lower the compaction degree (D) becomes,the lower the pre-consolidation load (Pc) becomes but on the contrary the compression index (Cc) becomes higher. Those equation is as follows. Pc=3. 32-(4. 3n-3. 0D) X10-2 (kg/cm$^2$) Cc=0. 41+(1. 33n-4. 44D) X10-$^3$ 5.The more the consolidation load (P) increases, the lower the coefficient of volume change (mv) becomes with mv=ap-b, the higher the consolidation ratio (u) becomes with U= (0. 6~1. 35)PO.4 6.The more the fine particle (n) increases, the more the settlement of dam occurs with U=anb and 60-80% of the settlement occurs under construction. 7.The camber of dam has higher value in condition that has more fine particle, poorer compaction and higher height of dam. In the dam construction about twice value of table 7 is required for dam safety.

• Journal of the Korean Geotechnical Society
• /
• v.16 no.4
• /
• pp.117-128
• /
• 2000

Sand compaction pile(SCP) is one of the ground improvement techniques which is being used for not only accelerating consolidation but also increasing bearing capacity of loose sands or soft clay grounds. In this study, laboratory model test and large-scale direct shear test were performed to investigate the effects of area replacement ratio of composite ground in order to find out the optimum value of area replacement ratio for the ground improvement purpose. Area replacement ratios of 20%, 30%, 40%, 50%, 60% were chosen respectively in the model tests to study the effects of area replacement ratio on variations of stress concentration ratio, settlement and shear strength characteristics of composite ground. In large-scale direct she4ar tests, area replacement ratios of 20%, 30%, 46% were applied to study their effects on shear strength characteristics of composite ground.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.1
• /
• pp.21-29
• /
• 2003

In this study, practical guidelines to check the possibility of some lateral movement of piled abutment were investigated. In these tests, both the depth of soft clay and the rate of embankment construction are chosen to examine the effect on lateral soil movements. The depth of soft clay layer varies from 5.2 m to 11.6 m, and the rate of embankment construction has two types : staged construction(1m/30days, 1m/15days) and instant construction. Various measuring instruments such as LVDTs, strain gauges, pressure cells, and pore pressure transducers are installed in designed positions in ordo. to clarify the soil - pile interaction and the short and long term behavior f3. piled bridge abutments adjacent to surcharge loads. The validity of the proposed guidelines by centrifuge test was compared with the observed performance by lateral movement index, F(Japan Highway Public Corporation) and modified I index(Korea Highway Corporation). Based on the results obtained, the critical values off and modified I, as a practical guidelines, are proposed as 0.03 and 2.0, respectively.

• Journal of the Korean GEO-environmental Society
• /
• v.6 no.1
• /
• pp.33-44
• /
• 2005

The 'Silt Pond' is 180 hectares in size and contained ultra soft slurry-like soil varying between 3 to 20 meters in thickness. Soil improvement work in the Silt Pond commenced by installing vertical drains in the mid of 1996, following completion of sand spreading up to +4.0m CD. Prior to soil improvement work in the main area of Silt Pond, experimental tests including laboratory tests with a large diameter consolidation cell and pilot tests were carried out to investigate the deformation behavior of an extremely soft soil. Due to its high compressibility, large strain usually occurred in the initial stage of deformation does not comply with Terzaghi's one dimensional consolidation theory. Taking into consideration experimental test results, the soil improvement works were carried out in main area of Silt Pond containing ultra soft soil. This paper presents the case study on improvement of ultra-soft soil.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.13 no.4
• /
• pp.227-237
• /
• 1993

This paper dealt with numerical analysis of sand drain considering the smear effect around drain wells and discontinuous deformation behavior due to difference in rigidity between drain materials and adjacent clayey soils. Biot's equation was selected as governing equation coupled with MODCAM (Modified Cam-clay) model or EVP(Elasto-Viscoplastic) model as constitutive equation. The validity as well as the accuracy of the method developed by author was checked by comparing the proposed method with those by Siriwardane and Ghaboussi using joint element. The FEM analysis developed in this study was applied to both 2-dimensional model foundation and actual foundation. the result of which proved to be satisfactory.