Adfreeze Bond Strength Research Articles

Experimental investigation on the effect of fiberglass reinforced plastic cover on adfreeze bond strength

Structural damages due to frost jacking of a foundation depend on the adfreeze bond between the freezing soil and the structure. To reduce the adfreeze bond strength between the foundation surface and the frozen ground, a fiberglass reinforced plastic (FRP) cover was proposed for foundations along the Qinghai-Tibetan transmission line. Direct shear tests were carried out in the laboratory to assess the adfreeze strength between a frozen soil and FRP covers as well as concrete plates under varying conditions. The results show that the cohesive component of the adfreeze bond strength is controlled by the moisture content and temperature of the frozen soil. The frictional component has only a weak correlation with temperature, but is significantly affected by the moisture content. The FRP cover can significantly reduce the cohesive component of the bond strength but shows little effect on the frictional component. The tests further show that the FRP cover can also reduce both, the adfreeze bond strength and bond healing, especially for low-temperatures. The results indicate that a smooth FRP cover can be effective in reducing the adfreeze bond strength between a foundation and the frozen soil. Therefore, this new material is considered a powerful alternative for reducing damages caused by frost heave in cold regions.

투명 온도제어형 삼축셀을 이용한 흙의 동상 실내실험

최근 들어 우리나라에 이상한파가 자주 발생하고 있으며, 이로 인해 지반에서는 동상에 따른 도로, 철도, 사면과 같은 구조물을 대상으로 지반변형에 따른 문제가 야기되고 있다. 동상현상은 가장 대표적인 동토지반의 공학적 특성으로, 구조물 설계에 있어서 동착 및 크리프 현상과 함께 주요한 설계정수로서 고려된다. 그러므로 극한지 지반구조물 설계에 관한 연구를 위해서는 동상현상에 대한 기초적 연구가 선행되어야 한다. 이미 다양한 동상 관련 실험장비가 개발되어 연구에 활용되고 있지만, 기존의 동상 연구를 위한 실험장비들은 기초의 설계정수로서 동상현상을 분석하기에는 한계점이 나타난다고 판단된다. 국내에는 동상을 실험적 모사하기에는 필요한 장치와 냉동챔버의 고비용으로 시험방법 및 기준이 전무한 실정이다. 이에 본 논문에서는 다양한 방법으로 동결-융해를 모사할 수 있는 투명 온도제어형 삼축셀 을 소개하고자 한다. 새롭게 개발된 동결-융해 실험장치를 활용해 동상 실내실험을 수행하였으며, 본 장치를 활용한 실내실험법을 제안하고자 한다. Nowadays abnormal coldness happens frequently in Korea and frost heaving causes unexpected ground deformation which results in severe problems for structures such as roadway, railroad and cutoff slope. 'Frost heave' as one of the primary phenomenon is considered to be an important factor together with 'adfreeze bond-strength' and 'creep deformation' for structural design process in permafrost area. Therefore, the fundamental study for frost heave has to be preceded for design of geo-structures in cold region. While various experimental apparatuses have been developed, there still exist a certain level of limitation to evaluate the frost-heave characteristics as design parameters. There are no standard testing method and criteria for analyzing frost heaving in Korea because temperature controlled testing apparatuses including a freezing chamber are expensive. In this paper, a new standard freezing and thawing testing apparatus is introduced, which simulates various freezing and thawing conditions in a soil specimen by using a temperature controlled triaxial cell. Frost heaving tests were performed to assess the new testing apparatus and experimental procedure to evaluate frost heaving for soils is proposed.

Certain Results of Antiheave and Anticorrosion Tests of Protective Coatings for Metal Foundations on Permafrost

The results of shear tests on in the presence of adfreeze bonding between frozen soils having different compositions and metal billets coated with protective paints are presented. The investigations showed that the coatings reduce the adfreeze bond strength by 35%, which makes heaving of metal pile foundations less likely.

동결된 화강풍화토와 알루미늄판 접촉면에서 발현되는 동착강도 측정 연구

Bearing capacity of pile is governed by only skin friction in frozen ground condition, while it is generally governed both by skin friction and end bearing capacity in typically unfrozen ground condition. Skin friction force, which arises from the interaction between pile and frozen soils, is defined as adfreeze bond strength, and adfreeze bond strength is one of the most important key parameters for design of pile in frozen soils. Many studies have been carried out in order to analyze adfreeze bond strength characteristics over the last fifty years. However, many studies for adfreeze bond strength have been conducted with limited circumstances, since adfreeze bond strength is sensitively affected by various influence factors such as intrinsic material properties, pile surface roughness, and externally imposed testing conditions. In this study, direct shear test is carried out inside of large-scaled freezing chamber in order to analyze the adfreeze bond strength characteristics with varying freezing temperature and normal stress. Also, the relationship between adfreeze bond strength and shear strength of the frozen soil obtained from previous study was analyzed. The coefficient of adfreeze bond strength was evaluated in order to predict adfreeze bond strength based on shear strength, and coefficients suggested from this and previous studies were compared.

인공신경망을 활용한 동착강도 예측

동착강도는 동토지반 말뚝기초 설계시 지지력을 결정하는 주요 설계정수이다. 동착강도는 동결온도, 구속응력, 말뚝표면 특성, 토사종류 등 다양한 인자들에 의해 동시다발적인 영향을 받는 것으로 보고되고 있다. 하지만 동착강도에 대한 연구는 소수의 인자들만 반영할 수 있는 실험연구를 중심으로 수행되어온 경향이 있으며, 설계정수로서 동착강도를 산정하기 위한 방법들은 동결온도, 말뚝재료 등의 주요 인자들만을 고려할 수 있는 한계가 있어 왔다. 본 연구는 인공신경망 이론을 동착강도 산정에 활용함으로서 다양한 영향인자 조건에서 동착강도를 예측할 수 있는 방안을 모색하기 위한 목적으로 수행되었다. 인공신경망 학습을 위하여 총 5종류의 연구사례로부터 137개의 자료를 수집하였으며, 그 중 100개를 학습자료로, 37개를 실증자료로 구분하였다. 연구결과 단계적 인공신경망 학습을 통하여 동착강도 산정 시 다양한 영향인지를 다차원적으로 고려하여 예측하는 방법이 병행되어야 할 필요성을 확인하였으며, 5개 영향인자를 동시에 고려하여 동착강도를 예측할 수 있는 신뢰성 높은 학습결과를 도출 및 검증하였다. 또한, 매개변수 연구결과 동착강도는 동결온도와 말뚝재료의 변화에 가장 민감하게 반응하는 것으로 나타났고 수직응력에 의한 영향은 일부 온도구간에서만 뚜렷하게 나타나며 토사종류와 재하속도의 변화에 따라 동착강도가 증가하는 경향이 변화하는 특성을 나타내었다. Adfreeze bond strength is a primary design parameter, which determines bearing capacity of pile foundation in frozen ground. It is reported that adfreeze bond strength is influenced by various affecting factors like freezing temperature, confining pressure, characteristics of pile surface, soil type, etc. However, several limited researches have been performed to obtain adfreeze bond strength, for past studies considered only few affecting factors such as freezing temperature and type of pile structures. Therefore, there exists a limitation of estimating the design parameter of pile foundation with various factors in frozen ground. In this study, artificial neural network algorithm was involved to predict adfreeze bond strength with various affecting factors. From past five studies, 137 data for various experimental conditions were collected. It was divided by 100 training data and 37 testing data in random manner. Based on the analysis result, it was found that it is necessary to consider various affecting factors for the prediction of adfreeze bond strength and the prediction with artificial neural network algorithm provides enough reliability. In addition, the result of parametric study showed that temperature and pile type are primary affecting factors for adfreeze bond strength. And it was also shown that vertical stress influences only certain temperature zone, and various soil types and loading speeds might cause the change of evolution trend for adfreeze bond strength.

동결토 전단강도를 활용한 동착강도 산정에 관한 연구

동토기반 말뚝기초의 지지력은 말뚝구조물 표면과 주변 토사의 접촉면에서 발현되는 동착강도에 의해 산정되며, 이는 동착-강도가 동토지반 기초설계를 위한 가장 주요한 설계정수임을 의미한다. 동착강도는 토사종류, 동결온도, 말뚝표면에 수직방향으로 작용하는 지중응력, 재하속도, 말뚝구조물의 표면 거칠기 등 다양한 인자들에 동시다발적인 영향을 받는 것으로 보고되고 있다. 1960년대부터 동토지반 기초설계를 위한 동착강도 산정방법들이 제안되어 왔으나, 대부분 동결온도와 말뚝구조물 표면특성에 대한 영향은 고려하고 있는 반면 동착강도의 주요 영향인자 중 하나인 지중응력에 의한 영향을 고려하지 않고 있어 소정깊이 이상의 말뚝기초 설계를 위한 동착강도 산정방법으로 활용되기에는 한계가 있는 것으로 판단된다. 본 연구에서는 동결온도뿐 아니라 지중응력이 동착강도에 미치는 영향을 파악하기 위하여 직접전단시험기를 활용한 동결토 전단강도 및 동착강도 측정실험을 각각 수행하였다. 실험결과 전단강도와 동착강도는 모두 동결온도 조건이 낮아질수록, 혹은 수직응력 조건이 커질수록 증가하는 경향을 보였다. 전단강도와 동착강도의 정량적 관계분석을 위해 정의된 전단강도와 동착강도의 비 <TEX>$r_s$</TEX>는 초기 동결온도에서는 급격하게 감소하는 경향을 나타냈으나, 동결온도가 낮아질수록 증가하며 수렴구간을 형성해가는 경향을 보였다. 본 연구에서는 최종적인 연구결과로서 동결온도 및 수직응력 조건을 바탕으로 결정된 <TEX>$r_s$</TEX>값을 이용하여 동결토의 전단강도로부터 동착강도를 예측할 수 있는 방법을 제안하고 있다. Bearing capacity of pile foundations in cold region is dominated by adfreeze bond strength between surrounding soil and pile perimeter. It denotes that adfreeze bond strength is the most important design parameter for foundations in cold region. Adfreeze bond strength is affected by various factors like 'soil type', 'frozen temperature', 'normal stress acting on soil/pile interface', 'loading rate', 'roughness of pile surface', etc. Several methods have already been proposed to estimate adfreeze bond strength during past 50 years. However, most methods have not considered the effect of normal stress for adfreeze bond strength. In this study, both freezing temperature and normal stress have been controlled as primary factors affecting adfreeze bond strength. A direct shear box was used to measure adfreeze bond strength between sand and aluminum under different temperature conditions. Based on the test results, the relation between shear strength of frozen sand and adfreeze bond strength have been investigated. The test results showed that both of shear strength and adfreeze bond strength tend to increase with decreasing frozen temperature or increasing confining pressure. The ratio of shear strength and adfreeze bond strength, expressed as <TEX>$r_s$</TEX>, decreased initially frozen section but increased at much lower frozen temperature and there were uniform intervals under the different normal stress conditions. A method for predicting adfreeze bond strength using <TEX>$r_s$</TEX> has finally been proposed in this study.

동결온도와 수직구속응력 변화에 따른 모래와 알루미늄 재료의 접촉면에서 작용하는 동착강도 실험 연구

Bearing capacity of pile foundations in cold region is dominated by adfreeze bond strength between surrounding soil and pile perimeter. Adfreeze bond strength is considered to be the most important design parameter for foundations in cold region. Many studies in last 50 years have been conducted to analyze characteristics of adfreeze bond strength. However, most studies have been performed under constant temperature and normal stress conditions in order to analyze affecting factors like soil type, pile material, loading speed, etc. In this study, both freezing temperature and normal stress acting on pile surface were considered to be primary factors affecting adfreeze bond strength, while other factors such as soil type, pile material and loading speed were predefined. Direct shear box was used to measure adfreeze bond strength between Joomoonjin sand and aluminium because it is easy to work for various roughness. Test was performed with temperatures of > , , , , and and vertical confining pressures of 1atm, 2atm, and 3atm. Based on the test results, the effects of temperature and vertical stress on adfreeze bond strength were analyzed. The test results showed that adfreeze bond strength increases with decreased temperature and increased vertical stress. It was also noted that two types of distinct sections exist, owing to the rate of increase of adfreeze bond strength along the change of freezing temperature: 1)rapidly increasing section and 2)gradually decreasing section. In addition, the results showed that a main factor affecting adfreeze bond strength switches from friction angle to adhesion as freezing temperature decreases.

EXPERIMENTAL STUDY ON ADFREEZE BOND STRENGTH BETWEEN SEA ICE AND VARIOUS MATERIALS

In cold regions, vertical ice load acts on pile structures due to water level changes, such as tides and swells, as the ice sheet adheres to them. Therefore the vertical ice loads must be fully considered in the design of maritime structures constructed in icy sea areas. When we calculate the ice load, many parameters are needed. One of them, the adfeeze bond strength is an important parameter to calculate the ice load at abfreeze bond failure. And Terashima et al. reported when ice sheet is thick, adferrze bond failure is easy to occur.In this study, we show the characteristic of five testing method for adferrze bond strength between sea ice and various materials, and make the experiment about three testing method for comparison of the influence by changing the testing method. Finally the authors proposed the adfreeze bond strength which is directry used in design.

Effects of Various Cross-sections and Adfreeze Bond Strength on Vertical Ice Load

In cold regions, ice sheets adfreeze to pile structures constructed in the sea. Due to changes in the water level, vertical ice loads act on the structures. These ice loads need to be considered to design pile structures affected by ice sheets.Ice loads acting on pile structures with circular cross-sections have been explained analytically. However, ice loads acting on pile structures with other cross-sections have never been researched. In this report, we study ice loads acting on pile structures with elliptical or rectangular cross-sections theoretically and experimentally. Furthermore we consider effects of various cross-sections and adfreeze bond strength.

Comparative Experiments On Various AdfreezeBond Strength Tests Between Ice And Materials

This paper summarizes systematic experiments on the adfreeze bond strength between sea ice and construction materials used for offshore structures, such as steel and concrete, as well as various coating materials. As a result of comparing test methods to determine the adfreeze bond strength between ice and the materials of structures, very little difference was observed among these methods. We also confirmed that the adfreeze bond strength depends more on the coarseness of the surface of construction materials than on the free surface energy on the surface.

ICE LOADS ACTING ON STRUCTURES TO WHICH ICE SHEETS ARE ADFROZEN DURING FLOODING AND MEASURES TO INCREASE ICE LOADS

In frozen sea waters, when the water level rises with the ice sheet adfrozen to a structure, sea water gathers on the ice sheet near the structures. This phenomenon is called flooding and arises when sea water rises to the ice surface through brine channels and cracks of the ice sheet. Under these conditions, where flooding occurs, the ice sheet functions as a bearing and is affected by elasticity. However, under the conditions where flooding has no influence, the sheet is affected only by buoyancy. In this paper, the authors logically clarified the upward vertical ice loads acting on the structure due to the rise of the water level when flooding occurs. Also, a comparison was made of ice loads when flooding occurs and when it does not. They have also systematically proven the method to gradually decrease ice loads caused by the change in the water level because ice loads are smaller when flooding occurs. In addition, it has been made clear by experiments, the adfreeze bond strength between various materials and the ice sheet, which is required for the calculation of ice loads caused by the change in the water level.

The Comparative Experiments on Various Adfreeze bond strength Test between ice and materials

This paper summarizes systematic experiments on the adfreeze bond strength between sea ice and building materiarus used for offshore structures as steel, concrete, as well as a variety of coating materials.As a result of comparative experiments on various test methods for determining the adfreeze bond strength between ice and different materials, very little difference was observed among the result of those methods . It was also confirmed that a factor affecting the asfreeze bonnd strength depends more on the coarseness of the surface of building materials than the interfacial free energy on that surface.

The strength and deformation behaviour of model adfreeze and grouted piles in saline frozen soils

The results of a laboratory study to determine the influence of soil salinity, pile surface treatment, pile backfill material, and temperature on the adfreeze bond strength and deformation of model piles are presented. The influence of salinity and temperature on the adfreeze strength is shown to be related through the unfrozen water, and similar strength results were obtained at similar unfrozen water contents. Salinity in the backfill material of 10 and 30 ppt caused reductions in the adfreeze bond strength of 80–99%. Similar salinities within the native soil reduced its shear strength causing the location of the failure to change from the pile–backfill interface to the backfill – native soil interface when nonsaline backfill was used. Sandblasting of the pile surface to remove any surface coating resulted in adfreeze bond strengths two to three times greater than those measured on nonsandblasted piles. The use of cementitious grout to replace the sand slurry backfill resulted in greater pile load carrying capacity as the failure surface was transferred to the grout (backfill) – native soil interface instead of the pile–backfill interface. Use of backfill made from saline native soil cutting should be discouraged because of the detrimental effects of pore-fluid salinity on the adfreeze bond strength. Key words : frozen soil, saline, model pile, adfreeze, strength, deformation, grout, temperature.

Ice Forces due to Changes in Water Level and Adfreeze Bond Strength Between Sea Ice and Various Materials

In cold regions, changes in water level can induce vertical forces on offshore structures (such as caisson and tower types) when sea ice cover to structure adfreeze bonding is present. This paper summarized the theoretical analyses of vertical ice forces as well as the results of experiments which identified the parameters required when estimating sea ice adfreeze bond strength. 1) Vertical Ice Forces. The authors have proposed a method of calculation that estimates the vertical ice forces taking the following into account: bending failure of the ice cover and adfreeze bond failure (shear induced). Calculation of vertical ice forces by this method requires the following information: bending strength of ice. Young’s modulus of ice, Poisson’s ratio of ice, and adfreeze bond strength to various materials. 2) Adfreeze Bond Strength of Sea Ice. The authors have been conducting, for 6 yr, adfreeze bond strength experiments between sea ice and various common construction materials for offshore structures such as concrete and steel. The following conclusions have been drawn from this study: (i) under certain conditions, the adfreeze bond strength of sea ice greatly depends on the surface roughness of construction materials; (ii) adfreeze bond strength increases with decreasing sea ice temperature; (iii) adfreeze bond strength decreases, approaching a constant, with increasing structure diameter; (iv) adfreeze bond strength increases, approaching a constant, with increasing ice thickness; (v) adfreeze bond strength is not greatly affected by push out velocity and stress rate.

Considerations on the use of cast-in-place piles in permafrost

Conventional cements have proven to be unsuitable for subsurface concreting in permafrost and as a result cast-in-place piles have seldom been used in arctic regions. The petroleum industry has developed a gypsum-based cement that has been satisfactorily used to grout well casings through permafrost.Laboratory studies have been undertaken to evaluate the suitability of this cement for subsurface concreting in permafrost. It is concluded that this cement does have an adverse effect on the adfreeze bond strength and hence should not be used for cylindrical friction piles. However, it appears from this preliminary study that the cement does have potential for use as a construction material for cast-in-place belled and tapered piles.

Adfreeze strength of frozen sand to model piles

Laboratory measurements of adfreeze strength of Ottawa fine sand to three different types of model piles under constant rates of loading are reported in this paper. Adfreeze strength, [Formula: see text]f, at peak load increased with increasing loading rate (i.e., rate of displacement of cross-head of the testing machine), İ, and followed a power law[Formula: see text]The maximum adfreeze bond strength developed with uncoated wood piles (B.C. fir and spruce). Concrete piles developed adfreeze bond strengths lower than wood but higher than steel and coated piles. Coatings (creosote, paint, etc.) reduced adfreeze bond strength considerably. In decreasing order of adfreeze bond strength, the piles rated as follows: uncoated B.C. fir, uncoated spruce, concrete, unpainted steel cylindrical and H-sections, creosoted B.C. fir, and, finally, painted steel pipe.