Mechanical and Microscopic Properties of Cement Stabilized Silt

Shaoyun Pu,Zhiduo Zhu,Weilong Song,Yu Wan,Hairong Wang,Shigong Song,Jun Zhang 대한토목학회 2020 KSCE Journal of Civil Engineering Vol.24 No.8

In order to explore the strength, water stability, compressibility, shear properties of cement stabilized silt, the one-dimensional consolidation tests, direct shear and unconfined compressiontests were conducted on cement solidified silt. In addition, the microscopic characteristics of cement stabilized silt were investigated by using scanning electron microscope (SEM) and X-ray diffraction (XRD) tests. The unconfined compression tests showed that the unconfined compressive strength (UCS) raised with cement dosage increasing, and first increased rapidly and then raised slowly with the prolongation of curing time. As curing time prolonged, the water stability coefficient (Kr) of 2% cement stabilized silt raised significantly, while the Kr of 4% and 6% cement stabilized silt almost hardly changed. As cement dosage increased, at 7 days of curing age, the compressive modulus of cement stabilized silt raised. However, at 28 and 90 days of curing, the compressive modulus first raised and then reduced. As curing time increased, the compressive modulus increased at first and then deceased slightly. The direct shear tests demonstrated that the internal friction angle of cement solidified silt was almost unchanged with increasing cement dosage, but the internal friction angle increased slightly with the prolongation of curing time. For 2% and 4% cement stabilized silt, the cohesion raised with the prolongation of curing time. Meanwhile, the cohesion of 6% cement solidified silt at 7 days was slightly larger that of 28 days. Besides, the SEM and XRD analysis indicated that the loose structure of silt was improved due to cement addition.

Experimental Study on the Physical-Mechanical Properties of Frozen Silt

Martin Christ,김영진 대한토목학회 2009 KSCE JOURNAL OF CIVIL ENGINEERING Vol.13 No.5

The objective of this study was to investigate the physical-mechanical characteristics of frozen Siberian silt. Unfrozen water content, uniaxial compressive strength and direct-tensile strength of frozen silt samples at different moisture contents were determined in the laboratory. Experimental results revealed that the amount of unfrozen water in the silt decreased with descending temperature and stabilized at temperatures below -10˚C. Even at very low temperatures a considerable amount of unfrozen water remained. Mechanical strength test results showed a strong dependence of the stress-strain behavior of the frozen silt on the moisture content and temperature. The strength for compression and tension increased with decreasing temperature and increasing moisture content. At any given temperature and moisture content compressive strength was significantly greater than tensile strength. Based on the compressive and tensile stress-strain relationship at a given temperature and moisture content, approximate values of strength ratio, failure strain ratio and deformation modulus ratio were established. The objective of this study was to investigate the physical-mechanical characteristics of frozen Siberian silt. Unfrozen water content, uniaxial compressive strength and direct-tensile strength of frozen silt samples at different moisture contents were determined in the laboratory. Experimental results revealed that the amount of unfrozen water in the silt decreased with descending temperature and stabilized at temperatures below -10˚C. Even at very low temperatures a considerable amount of unfrozen water remained. Mechanical strength test results showed a strong dependence of the stress-strain behavior of the frozen silt on the moisture content and temperature. The strength for compression and tension increased with decreasing temperature and increasing moisture content. At any given temperature and moisture content compressive strength was significantly greater than tensile strength. Based on the compressive and tensile stress-strain relationship at a given temperature and moisture content, approximate values of strength ratio, failure strain ratio and deformation modulus ratio were established.

Engineering Properties and Microstructural Characteristics of Foundation Silt Stabilized By Lignin-based Industrial By-product

Tao Zhang,Guojun Cai,Songyu Liu,Anand J. Puppala 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.7

This paper presents details of a study that deals with determination of engineering properties and microstructural characteristics of a foundation soil (silt) sedimented in Jiangsu Province of China when it is stabilized by lignin-based industrial by-product. A series of laboratory tests were carried out with respect to evaluate the effect of lignin content and curing time on the overall soil properties including Atterberg limits, pH, unconfined compressive strength, stress-strain characteristics, secant modulus, and California bearing ratio. In addition, scanning electron microscopy, X-ray diffraction, and mercury intrusion porosimetry studies were conducted to understand the microstructural characteristics and stabilization mechanism of the stabilized silt. The results reveal that lignin has a great potential to improve engineering properties of silt and shows a promising prospect as a new environmentally friendly soil stabilizer. Curing time and lignin content have significant influence on the basic engineering properties and microstructural characteristics of the lignin stabilized silt. The optimum content of lignin for foundation silt in Jiangsu Province of China is approximately 12%. The precipitated cementing material is formed after stabilization of lignin with a period of curing. The stabilized silt switches over its response from a brittle to ductile material in the presence of lignin. Peak analysis results of the pore-size distribution curves demonstrates that the lignin stabilized silt exhibits bimodal behavior when the lignin content less than 8%, whereas it displays unimodal type when the lignin content is more than or equal to 8%. These observations provide enhanced understanding of lignin-based industrial by-product as a soil stabilizer at the foundation construction.

Treating urban dredged silt with ethanol improves settling and solidification properties

Guo-Lu Yang,Zhao-Hui Chai,Meng Chen 한국화학공학회 2013 Korean Journal of Chemical Engineering Vol.30 No.1

The organic matter content in urban dredged silt is high for the indraft of municipal sewage, and it seriously influences the utilization of urban dredged silt. It is necessary to find a method to solve this problem. This paper presents a method of treating the silt with ethanol (STE), considering that ethanol is a good organic solvent which can dissolve many kinds of organic matter, and optimizes the treatment conditions through Box-Benhnken design (BBD) experiment with organic matter removal efficiency as the response. The ideal conditions were as follows: action time, 47 min; ethanol concentration, 41%; ratio of ethanol to silt, 54 : 1 ml/g with organic matter removal efficiency of 51.12%. Then, settling and solidification properties of raw silt and STE were explored through laboratory experiments. The results show treating urban dredged silt improved the settling and solidification properties of silt.

Characteristics of Shear Behavior of Remolded Nak-dong River Sandy Silt

김영수,틴킨스웨,김대만 한국지반공학회 2007 한국지반공학회논문집 Vol.23 No.3

The results from normally consolidated isotropic drained and undrained triaxial compression tests (NCIU and NCID) on sand with high silt content were presented in this paper. The experiments were performed on specimens of Nak-dong River sand with 63% silt content under effective confined pressures, 100 kPa to 400 kPa. From test results, Sandy silt became initially compressive but eventually appeared to provide dilatancy response throughout the entire stress-strain curve. The behavior of sandy silt was more difficult to characterize than that of clay and sand due to lower plastic characteristic. Especially, the samples exhibited dilatancy development during shear after failure. The shear behavior and shear strength parameters of sandy silt can be determined as stress-strain behaviors are described by the Mohr-Coulomb failure criterion. The shear behaviors were observed increasing dilatancy volume change tendency with strain-softening tendency after failure. In this paper, the behavior of dilatancy depends on not only sand content but also fine content with low-cohesion during shear in the samples of sandy silt.

실트질 함유량에 따른 낙동강 모래의 비배수 반복전단거동 특성

김영수,김대만,Kim, Young-Su,Kim, Dae-Man 한국지반공학회 2008 한국지반공학회논문집 Vol.24 No.11

In this study, a series of undrained cyclic triaxial tests were performed with three different consolidation stress ratios ($K_c$=1.0, 1.5, 2.0) to investigate the undrained shear strength characteristics of sands with respect to the amount of contained silt located around the basin of Nak-dong River. The test results show that the more the sand has silt, the lower is cyclic shear stress ratio (CSR) in all $K_c$ and that the higher $K_c$ goes, the larger CSR decreases due to the increase of contained silt. The excessive pore pressure caused during shearing has an influence on the decrease of CSR by the high initial pore pressure in proportion to the amount of contained silt regardless of the $K_c$ value. After consolidation, the analysis of the skeleton void ratio of the sample reveals that the main cause of the decrease of CSR as well as the increase of the initial excessive pore pressure is the increase of the skeleton void ratio in proportion to the amount of contained silt.

비소성실트지반의 액상화 및 측방유동량 예측

양태선(Yang, Taeseon),송병웅(Song, Byungwoong) 한국지반환경공학회 2011 한국지반환경공학회논문집 Vol.12 No.11

모래지반의 액상화 발생 가능성 및 측방유동 평가 방법에 대한 연구는 많이 알려져 있다. 최근에는 비소성 실트의 액상화 발생 가능성에 대해서도 연구하고 있다. 그러나 비소성실트의 동적하중이 작용하는 동안과 그 이후의 거동에 대해서는 세계적으로도 다소 알려져 있을 뿐이다. 특히 비소성실트의 측방유동에 대한 평가방법에 대해서는 거의 알려져 있지 않다. 이에 본 연구에서는 비소성실트지반에서의 액상화 발생 가능성 및 측방유동량의 평가 방법을 제안하는 것을 목적으로 하였다. 연구방법은 정적 및 동적 시험을 수행할 수 있는 직접단순전단시험기를 이용하여 동적하중을 받은 비소성실트의 액상화 가능성을 평가하였으며, 그 후 정적 시험을 수행하여 잔류강도를 측정하였다. 이 시험결과 비소성실트는 유효응력이 완전이 소멸되는 것은 곤란하지만 액상화에 거의 가깝게 발생하는 것을 확인하였다. 특히, 전단응력의 증가에 따른 강도저하는 매우 현저한 것을 확인하였다. 이 시험결과를 이용하여 액상화 발생 가능성 및 측방유동량을 추정할 수 있는 방법을 제안하였다. It is well known all much information for evaluation on possibility of liquefaction and lateral flow for sand over the world. Recently, it is started to be known that liquefaction happens on non-plastic silt, too. But cyclic and post-cyclic characteristics for non-plastic silt is a few familiar to the world. Specially, it is not aware of the estimating method for lateral flow on non-plastic silt. The main purpose in this paper is to propose the evaluation for liquefaction and lateral flow on non-plastic silt. The method used in this research is that possibility for liquefaction on non-plastic silt was evaluated with cyclic direct simple shear test, and then residental strength was estimated with static shear test. Through the test results liquefaction on non-plastic silt is well not happened but strength decreases rapidly with increasing shear stress. With the proposed method it can be evaluated possibility of liquefaction and propose lateral flow.

Cavitation–silt erosion in sand suspensions

Yu Wang,Jianhua Wu,Fei Ma 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.12

Cavitation–silt erosion in sand suspensions has elicited research attention. However, erosion characteristics in various conditions of liquids remain unknown due to their complex mechanisms. Thus, the effects of sand size, concentration, and temperature of sand suspensions on cavitation–silt erosion and viscosity were experimentally investigated in the present work. The findings proved the existence of critical sand size. The silt–cavitation erosion decreased with the increase of sand concentration when the sand was smaller than the critical size, and it increased with the increment of the sand size and temperature. A good relationship between the viscosity and the sand size, concentration, and temperature was determined. Moreover, the cavitation–silt erosion mechanisms were obtained on the basis of the viscosity and impingement erosion analysis standpoint.

Performance characteristics of dredged silt and high-performance lightweight aggregate concrete

H.Y. Wang,Y.N. Sheen,M.F. Hung 사단법인 한국계산역학회 2010 Computers and Concrete, An International Journal Vol.7 No.1

Dredged silt from reservoirs in southern Taiwan was sintered to make lightweight aggregates (LWA), which were then used to produce high-performance lightweight aggregate concrete (HPLWC). The HPLWC was manufactured using different amounts of mixing water (140, 150, and 160 kg/m³) and LWA of different particle densities (700, 1100, and 1500 kg/m³) at different W/b ratios (0.28, 0.32, and 0.4). Results show that the lightweight aggregates of dredged silt taken in southern Taiwan perform better than the general lightweight aggregates. In addition, the HPLWC possessed high workability with a slump of 230-270 mm, and a slump flow of 450-610 mm, high compressive strength of over 40 MPa after 28 days of curing, good strength efficiency of cement exceeding 0.1MPa/kg/㎥, low thermal conductivity of 0.4-0.8 kcal/mh℃, shrinkage of less than 4.8 × 10⁻⁴, and high electrical resistivity of above 40 kΩ-cm. The above findings prove that HPLWC made from dredged silt can help enhance durability of concrete and provide and an ecological alternative use of dredged silt.

Shear Behavior of Overconsolidated Nakdong River Sandy Silt

Khin Swe Tint,Young Su Kim,In-Shik Seo,Dae-Man Kim KOREAN SOCIETY OF CIVIL ENGINEERS 2007 KSCE JOURNAL OF CIVIL ENGINEERING Vol.11 No.5

<P>In this research, overconsolidated drained, undrained and unconsolidated undrained of Nakdong river sandy silt in triaxial compression tests were performed on specimens of silt with 26% sand content. In CIU and CID tests, the specimens were consolidated isotropically from 100 to 400 ㎪ and unloaded to 200 ㎪ for OCR = 2, unloaded to 100 ㎪ for OCR = 4 and unloaded to 50 ㎪ for OCR = 8 before shear condition. In UU tests, the samples were carried out under effective confining pressure 100 to 400 ㎪ during shear. In CIU-OC tests, the flowing characteristics were observed: the deviator stress decreased with higher OCRs and showed strain-softening behavior after failure. Pore water pressure decreased to negative; that the samples were higher dilative volume change tendency under unloading due to increasing OCRs. CID-OC tests indicated that the deviator stresses increased and presented strain-softening tendency after failure. Became negative due to dilatancy with higher OCRs under small strains. In VU tests, peak deviator stresses were different and displayed strain-softening tendency under higher effective confining pressure after peak value. The pore water pressures increased with small strains before failure and depended on saturation condition at failure. The undrained shear strength and the internal friction angle in UU test cannot be determined accurately due to dilative effect and low-cohesion of sandy silt. By using the concepts of critical state, the stress paths showed similar and all failure points followed to a unique slope line which forms a critical state line (CSL) in stress path diagram.</P>