• Title/Summary/Keyword: unconfined compression strength of DCM specimens

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A Case Study on the High-quality DCM applied to the Foundation of Breakwater (방파제 기초에 적용된 고품질 DCM공법의 설계 및 시공 사례)

  • Kang, Yeoun-Ike;Shim, Min-Bo;Shim, Sung-Hyun;Kim, Ha-Young;Shim, Jae-Bum;Chun, Youn-Chul;Yoon, Jung-Ik
    • Proceedings of the Korean Geotechical Society Conference
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    • 2009.09a
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    • pp.815-826
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    • 2009
  • The paper presents a case study addressing the design and construction aspects for DCM(Deep Cement Mixing) method employed as the foundation of a caisson type breakwater with heavy weight(10,700 ton/EA) and a high design wave height($H_{1/3}$=8.7m). The DCM was designed for the project(Ulsan New Port North Breakwater Phase 1) by optimizing the pattern of DCM columns with a combination of short and long columns (i.e., block type(upper 3m)+wall type(lower)) and considering overlapped section between columns as a critical section against shear force where the coefficient of effective width of treated column($\alpha$) was estimated with caution. It was shown that the value can be 0.9 under the condition with the overlapped width of 30cm. In addition to that, a field trial test was performed after improving conventional DCM equipment (e.g., mixing blades, cement paste supplying pipes, multi auger motor, etc.) to establish a standardized DCM construction cycle (withdrawal rate of mixing blades) which can provide the prescribed strength. The result of the field strength test for cored DCM specimens shows that the averaged strength is larger than the target strength and the distribution of the strength(with a defect rate of 7%) also satisfies with the quality control normal distribution curve which allows defect rate of 15.9%.

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Geotechnical Characteristics of DCM-Improved Specimen Under Artesian Pressure (피압 작용에 따른 DCM 개량체의 지반공학적 특성)

  • Yun, Dae-Ho;Kim, Yun-Tae
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.42 no.2
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    • pp.187-195
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    • 2022
  • This study investigated the effect of artesian pressure on mechanical properties of deep cement mixing (DCM)-improved specimens. Various laboratory tests such as unconfined compression test and scanning electron microscope (SEM) were conducted on DCM specimens which curied in a water tank with different artesian pressures. The artesian pressure was determined in consideration of the laboratory scale and the hydraulic gradient in field conditions. Results of experimental tests indicated that unconfined compressive strength, secant modulus, and unit weight of specimen decreased and water content tended to increase as an artesian pressure increased. The stress-strain behavior changed brittle to ductile behaviors as an artesian pressure increased. The outflow water from the water tank reacted with the phenolphthalein solution due to the leaching phenomenon of the improved specimen. SEM analysis also confirmed that a small amount of ettringite was formed between soil particles in the specimens with artesian pressure.

Strain-dependent dynamic properties of cemented Busan clay (부산 고결점토의 변형률 의존적 동적거동특성에 관한 연구)

  • Kim, Ah-Ram;Chang, Il-Han;Cho, Gye-Chun;Shim, Sung-Hyun;Kang, Yeoun-Ike
    • Proceedings of the Korean Geotechical Society Conference
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    • 2010.09b
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    • pp.61-67
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    • 2010
  • Thick soft clay deposits which are generally located at the west and south coast of the Korean peninsula have complicated characteristics according to their orientation and formation history. Thus, several geotechnical problems could possibly occur when those soft clay deposits are used as foundations for marine structures. Deep cement mixing (DCM) method is one of the most widely used soft soil improvement method for various marine structures, nowadays. DCM method injects binders such as cement into the soft ground directly and mixes with the in-situ soil to improve the strength and other geotechnical properties sufficiently. However, the natural impacts induced by dynamic motions such as ocean waves, wind, typhoon, and tusnami give significant influences on the stability of marine structures and their underlaying foundations. Thus, the dynamic properties become important design criteria to insure the seismic stability of marine structures. In this study, the dynamic behavior of cemented Busan clay is evaluated. Laboratory unconfined compression test and resonant column test are performed on natural in-situ soil and cement mixed specimens to confirm the strength and strain-dependent dynamic behavior variation induced by cement mixing treatment. Results show that the unconfined compressive strength and shear modulus increase with curing time and cement content increment. Finally, the optimized cement mixing ratio for sufficient dynamic stability is obtained through this study. The results of this study are expected to be widely used to improve the reliability of seismic design for marine structures.

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