• Title/Summary/Keyword: Subgrade layer

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Estimation of the Mean CBR for the Subgrade Layer Including the Anti-Frost Layer (동상방지층을 포함한 노상층의 평균 CBR 산정에 관한 연구)

  • Min, Gyeong-Ho;Lee, Cheo-Keun;Heo, Yol
    • Journal of the Korean GEO-environmental Society
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    • v.3 no.1
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    • pp.57-66
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    • 2002
  • Generally, the California Bearing Ratio(CBR) for the material of subgrade is estimated without considering the anti-frost layer into the subgrade layer when pavements are designed. A pavement structure is determined according to the CBR. However, recently the design method taking the anti-frost layer into the subgrade layer is getting prevail. It makes the top of the subgrade layer strengthen and the thickness of the road pavement structure decreased. By the way, some confusion may be caused because theoretically the general equation for the mean CBR to combine the material of the subgrade layer and anti-frost layer have not been developed well. In this paper, laboratory and field CBR tests were performed to estimate of the mean CBR for the subgrade layer including the anti-frost layer. From the basis of the test results, modified equation which is calculating the mean CBR of the subgrade layer has been proposed. Finally, economical efficiency was considered by comparing the pavement thickness with the road pavement design using CBR of the subgrade layer alone and the road pavement design using the mean CBR including the anti-frost layer.

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A Study on Improvement of Road Compaction Method in Soft Ground (연약지반 상 노상다짐 방법 개선에 대한 연구)

  • Choi, Hyeonsuk;Jang, Hohun
    • The Journal of Engineering Geology
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    • v.29 no.4
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    • pp.427-437
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    • 2019
  • The purpose of this study is to improve construction cost, time, and field management when constructing a road on soft soil foundation by eliminating extra-banking of subgrade layer after completion of the consolidation process. The subgrade layer was pre-constructed before the soft ground improvement. And then it was confirmed by the field test that the compaction effect was maintained or not after consolidation settlement. As a result of the experiment, all subgrade layers were kept constant except for the top subgrade layer. So it would be advantageous to secure economical and practical in road construction if subgrade layers were constructed exclusive of the top subgrade layer.

Evaluation of extension in service life and layer thickness reduction of stabilized flexible pavement

  • Nagrale, Prashant P.;Patil, Atulya
    • Advances in Computational Design
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    • v.3 no.2
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    • pp.201-212
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    • 2018
  • Decrease in availability of suitable subbase and base course materials for highway construction leads to a search for economic method of converting locally available troublesome soil to suitable one for highway construction. Present study insights on evaluation of benefits of stabilization of subgrade soils in term of extension in service life (TBR) and layer thickness reduction (LTR). Laboratory investigation consisting of Atterberg limit, Compaction, California Bearing Ratio, unconfined compressive strength and triaxial shear strength tests were carried out on two types of soil for varying percentages of stabilizers. Vertical compressive strains at the top of unstabilized and stabilized subgrade soils were found out by elastoplastic finite element analysis using commercial software ANSYS. The values of vertical compressive strains at the top of unstabilized and stabilized subgrade, were further used to estimate layer thickness reduction or extension in service life of the pavement due to stabilization. Finite element modeling of the flexible pavement layered structure provides modern technology and sophisticated characterization of materials that can be accommodated in the analysis and enhances the reliability for the prediction of pavement response for improved design methodology. If the pavement section is kept same for unstabilized and stabilized subgrade soils, pavement resting on lime, fly ash and fiber stabilized subgrade soil B will have service life 2.84, 1.84 and 1.67 times than that of unstabilized pavement respectively. The flexible pavement resting on stabilized subgrade is beneficial in reducing the construction material. Actual savings would depend on the option exercised by the designer for reducing the thickness of an individual layer.

Improvement in engineering properties of subgrade soil due to stabilization and its effect on pavement response

  • Nagrale, Prashant P.;Patil, Atulya P.
    • Geomechanics and Engineering
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    • v.12 no.2
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    • pp.257-267
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    • 2017
  • This paper presents laboratory investigation of stabilization of subgrade soil. One type of soil and three types of stabilizers i.e., hydrated lime, class F fly ash and polypropylene fibres are selected in the study. Atterberg limit, compaction, california bearing ratio (CBR), unconfined compressive strength and triaxial shear strength tests are conducted on unstabilized and stabilized soil for varying percentage of stabilizers to analyze the effect of stabilizers on the properties of soil. Vertical compressive strains at the top of unstabilized and stabilized subgrade soil were found out by elasto-plastic finite element analysis using commercial software ANSYS. Strategy for design of optimum pavement section was based on extension in service life (TBR) and reduction in layer thickness (LTR). Extension in service life of stabilized subgrade soil is 6.49, 4.37 and 3.26 times more due to lime, fly ash and fibre stabilization respectively. For a given service life of the pavement, there is considerable reduction in layer thicknesses due to stabilization. It helps in reduction in construction cost of pavement and saving in natural resources as well.

The influence of fine particle migration on pore structure of overlying ballast under cyclic loading

  • Yu Ding;Yu Jia;Zhongling Zong;Xuan Wang;Jiasheng Zhang;Min Ni
    • Geomechanics and Engineering
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    • v.35 no.6
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    • pp.627-636
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    • 2023
  • The essence of subgrade mud pumping under train load is the migration of fine particles in subgrade soil. The migration of fine particles will change the pore structure of overlying ballast, thus affecting the mechanical properties and hydraulic properties of ballast layer. It is of great theoretical significance and engineering value to study the effect of fine particle migration on the pore structure of ballast layer under cyclic loading. In this paper, a tailor-made subgrade mud pumping test model and an X-ray computed tomography (CT) scanning equipment were used to study the influence of migration of fine particles in subgrade soil on the pore parameters (plane porosity, volume porosity, pore distribution and pore connectivity) of overlying ballast under cyclic loading. The results show that the compression of ballast pores and the blockage of migrated fine particles make the porosity of ballast layer decreases gradually. And the percentage of small pores in ballast layer increases, while the percentage of large pores decreases; the connectivity of pores also gradually decreases. Based on the test results, an empirical model of ballast porosity evolution under cyclic loading is established and verified.

Reinforcing Effect of Geocell on Soft Soil Subgrade for High-speed Railroad (연약지반상 고속철도 노반 축조시 지오셀 시스템의 효과)

  • 조삼덕;윤수호;김진만;정문경;김영윤
    • Journal of the Korean Geotechnical Society
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    • v.18 no.2
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    • pp.5-12
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    • 2002
  • This paper presents the results of plate load test and dynamic load test performed to evaluate the performance of geocell which is used to reinforce soft subgrade for high-speed railroad. Efficiency of geocell was observed in the increase in bearing capacity of subgrade and in the reduction of thickness of reinforced sub-ballast. One layer of geocell underlying a 10 cm thick cover soil led to an increase in bearing capacity three to four times larger than that of a crushed stone layer of the same thickness substituted for the geocell and cover soil layer Given the test conditions, the thickness of reinforced sub-ballast can be reduced by approximately 35 cm with the presence of geocell.

Reinforcement of Soft Soil Subgrade for High-Speed Railroad Using Geocell (연약지반상 고속철도 노반 축조시 지오셀 시스템의 효과)

  • 김진만;조삼덕;윤수호;정문경;김영윤
    • Proceedings of the Korean Geotechical Society Conference
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    • 1999.11c
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    • pp.129-141
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    • 1999
  • This paper presents the results of plate load test and dynamic load test performed to evaluate the performance of geocell where it is used to reinforce soft subgrade for high-speed railroad. Efficacy of geocell was observed in increase in bearing capacity of subgrade and reduction of thickness of reinforced sub-ballast. Plate load tests were carried out at four different places with varying foundation soil strength as a function of number of geocell layer, type of filler material, thickness of cover soil, and the presence of non-woven geotextile. Dynamic load tests were performed in a laboratory. The test soil chamber consists of, from the bottom, 50 cm thick clayey soil, one layer of geocell filled with crushed stone, 10 cm thick crushed stone cover, reinforced sub-ballast of varying thickness, 35 cm thick ballast. This configuration was determined based on the results of numerical analysis and plate load tests. For each set of the dynamic load tests, loads were applied more than 80,000 times. One layer of geocell underlying a 10 cm thick cover soil led to an increase in bearing capacity three to four times compared to a crushed stone layer of the same thickness substituted for the geocell and cover soil layer. Given the test conditions, the thickness of reinforced sub-ballast can be reduced by approximately 35 cm with the presence of geocell.

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Measurements and Analysis of Deformation States in Roadbed in Gyeongbu High Speed Railway (경부고속철도 토공부에 대한 변형상태 계측 및 분석)

  • Jin, Nam-Hee;Kim, Nam-Hyuk;Shim, Hyun-Woo
    • Proceedings of the KSR Conference
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    • 2009.05a
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    • pp.1542-1549
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    • 2009
  • The function of subgrade in the railway is to support track load on the subgrade as well as train load. Unlike the traditional railway, the uppermost subgrade layer in the Gyeongbu high speed railway was constructed as the reinforced road bed. The reinforced road bed comprises sub-ballast in the upper part and grade ballast in the lower part. The filling material such as soil and rocks in the subgrade can be settled by consolidation of original ground, compression due to self weight, plastic displacement due to train operation, and unequal settlement due to embankment material or improper compaction, therefore many efforts have been given for sufficient compaction and use of proper filling materials in the construction stage. The purpose of this study is to investigate the deformation state of subgrade in the Gyeongbu high speed railway. The investigation on the subgrade settlement was performed by choosing representative sections suspected to be settled based on the previous GPR test results and track maintenance history, measuring the settlement for some time period after installing settlement measuring instruments on and under the reinforced road bed. and analyzing the long-term subgrade settlement data from monitoring system which was installed at the construction stage of the high speed railway.

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A Case Study on the Adaptation of Soil-cement for the Subgrade Treatmentin the Seohean-Expressway (서해안 고속도로의 노상처리를 위한 Soil-cement 적용 사례연구)

  • Chang, Yong-Chai;Kim, Hong-Jong;Jeon, Han-Yong
    • Journal of Navigation and Port Research
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    • v.27 no.4
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    • pp.485-489
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    • 2003
  • The region of Kochang(Chollabuk-Do) located in the west-southern area of the Korea and passed by the West Coast Expressway has the yellow collar soil(Hwang-To) primarily containing clay. Hwang-To serves as a soil appropriate for growing the watermelon and yam, but as a subgrade material not strong for constructing the roads. Particularly, the subgrade material of this study site was not qualified for the standard of the subgrade material quality. The properties of the subgrade layer showed that the strength of the subgrade material was not strong enough to sustain the subgrade strength in constructing the roads since the passing ratio of the No. 200 sieve was about 25% to 82% and the ground water level was early equal to subgrade one. Thus, the objective of this study was to present the methods obtaining the proper subgrade strength of cutting area to construct the secure and solid expressways in the fragile area.

Evaluation of Lightweight Soil as a Subgrade Material (경량혼합토의 도로 노상층 재료 사용 가능성 평가)

  • Park, Dae-Wook;Vo, Viet Hai
    • International Journal of Highway Engineering
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    • v.15 no.5
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    • pp.57-64
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    • 2013
  • PURPOSES : It is to evaluate lightweight soil as a subgrade material based on mechanical tests and calculation of pavement performance. METHODS : In this research, various contents of cement and air foam are used to make lightweight soil using wasted dredged soil. Uniaxial compressive strength test is conducted to evaluate strength of 7 and 28 day cured specimens. Secant modulus was calculated based on the stress and strain relationship of uniaxial compressive strength test. Resilient modulus test was measured using by repeated triaxial compression test. The measured resilient modulus was used in layered elastic program to predict fatigue and rutting life at a given pavement structure. RESULTS : Uniaxial compressive strength increases as cement content increases but decrease as air foam content increases. Resilient modulus also increases as cement content increases and decrease as air foam content decrease. CONCLUSIONS : It is concluded that dredge clay soil can be used as subgrade layer material using by lightweight treated soil method.