Cyclic thermomechanical response of fine-grained soil-concrete interface for energy piles applications

2020 ◽  
Author(s):  
Elena Ravera ◽  
Melis Sutman ◽  
Lyesse Laloui
Keyword(s):  
Clayey Soil ◽  
Volumetric Strain ◽  
Thermal Cycles ◽  
Interface Failure ◽  
Thermal Tests ◽  
Analysis And Design ◽  
Direct Shear Tests ◽  
Energy Piles ◽  
Thermomechanical Testing ◽  
Vertical Effective Stress

Understanding the behaviour of soil-structure interfaces is critical for addressing the analysis and design of energy geostructures. In this study, the interface failure mechanism of energy piles (where a shear band is detached from the surrounding soil that behaves under oedometric conditions) is experimentally analysed in laboratory for saturated conditions. The choice of material (clayey soil and concrete), temperature range, and stress level is based on conditions that are likely to be encountered in practice. Specifically, cyclic thermal tests under constant vertical effective stress in oedometric conditions as well as constant normal stiffness (CNS) interface direct shear tests (in which samples have been subjected to thermal cycles between 10 and 40 °C) are presented. From a practical perspective, the results show very low volumetric strain variations and negligible effects on shear strength. The volumetric aspects do not appear to have significant impact on the shear resistance of the interfaces against cyclic thermal loads. Fundamental insight on the effects of thermal cycles on the concrete-soil interface behaviour which are relevant to energy piles are presented. In addition, the proposed interpretation procedure provides a basis for the standardisation of thermomechanical testing in geotechnical engineering.

scholarly journals Influence of thermal cycles on the deformation of soil-pile interface in energy piles

2019 ◽  
Vol 92 ◽  
pp. 13004
Author(s):  
Roxana Vasilescu ◽  
Kexin Yin ◽  
Anne-Laure Fauchille ◽  
Panagiotis Kotronis ◽  
Christophe Dano ◽  
...  
Keyword(s):  
Numerical Models ◽  
Seasonal Temperature ◽  
Direct Shear ◽  
Thermal Cycles ◽  
Shear Tests ◽  
Temperature Cycles ◽  
Direct Shear Tests ◽  
Energy Piles ◽  
The Impact ◽  
Submerged Conditions

Energy piles are double purpose foundation elements used both for transferring loads to the soil and temperature regulation in buildings. The response of the pile-soil interface is influenced by daily and seasonal temperature variations. In order to assess the impact of thermal cycles on the mobilization of shear strength in energy piles, a series of saturated soil-concrete interface direct shear tests were performed in the laboratory for different temperature gradients with a new interface direct shear device adapted for thermomechanical loading. As natural soils are very complex due to a high variability of mineralogy and anisotropy, silica and carbonate sands were chosen in this study. Those sands are considered as the main types of sandy soils commonly met in geotechnics. The experimental campaign is divided in two parts: (i) Concrete-soil direct shear tests at 13°C (constant temperature) to be used as a reference (ii) Concrete-soil direct shear tests after 10 temperature cycles with a gradient ΔT=10°C, under submerged conditions. For these two types of soils, realistic temperature cycles applied between 8 and 18°C cause the overall low contraction of the samples. However the interface friction angles are not significantly modified before and after the temperature cycles. Even if the vertical strains of soils are cumulative along temperature cycles, soil’s strains and friction angle changes are relatively negligible for the temperatures and water content tested, which support the low impact of temperature cycles on the deformation of soil concrete foundation under submerged conditions. These experimental results bring new features which will be implemented in numerical models to study the long-term use of energy piles.

scholarly journals Compression and shear strength characteristics of compacted loess at high suctions

2017 ◽  
Vol 54 (5) ◽  
pp. 690-699 ◽  
Author(s):  
Charles Wang Wai Ng ◽  
Hamed Sadeghi ◽  
Fardin Jafarzadeh
Keyword(s):  
Volumetric Strain ◽  
Degree Of Saturation ◽  
Continuous Increase ◽  
Direct Shear Tests ◽  
Vapor Transfer ◽  
Zero Degree ◽  
Reduced Rate ◽  
Shear Box ◽  
Compacted Loess ◽  
High Range

Compression and shear behavior of a loosely compacted loess is investigated via two series of saturated and unsaturated direct shear tests. The vapor transfer mechanism is used to modify a shear box device for control of suction at high range. In spite of significant volumetric strain upon wetting (up to 14%), suction-induced volumetric shrinkage is less than 2% for all suction levels considered because of the as-compacted moisture content at the dry side of the optimum value. During shearing, all unsaturated tests dried to high suctions indicate a strain-softening mode of failure associated with noticeable dilation. There is a continuous increase in peak strength with suction but at a reduced rate, which cannot be captured by the improved Bishop’s effective stress model, as it underestimates the contribution of high suctions by approaching zero degree of saturation. Unsaturated tests at high suctions also show an increased rate of dilation with suction for both values of net stress, which cannot be predicted well by the classical stress–dilatancy models. It is shown that for suction values beyond 8 MPa, dilation angle increases by 2° and 6° per 100 MPa increase of suction under net stress of 50 and 200 kPa, respectively.

scholarly journals Generalized Interface Shear Strength Equation for Recycled Materials Reinforced with Geogrids

2021 ◽  
Vol 13 (16) ◽  
pp. 9446
Author(s):  
Artit Udomchai ◽  
Menglim Hoy ◽  
Apichat Suddeepong ◽  
Amornrit Phuangsombat ◽  
Suksun Horpibulsuk ◽  
...  
Keyword(s):  
Shear Strength ◽  
Interface Shear Strength ◽  
Interface Shear ◽  
Recycled Materials ◽  
Reclaimed Asphalt ◽  
Analysis And Design ◽  
Direct Shear Tests ◽  
Base Course Material ◽  
Base Course ◽  
Recycled Material

In this research, large direct shear tests were conducted to evaluate the interface shear strength between reclaimed asphalt pavement (RAP) and kenaf geogrid (RAP–geogrid) and to also assess their viability as an environmentally friendly base course material. The influence of factors such as the gradation of RAP particles and aperture sizes of geogrid (D) on interface shear strength of the RAP–geogrid interface was evaluated under different normal stresses. A critical analysis was conducted on the present and previous test data on geogrids reinforced recycled materials. The D/FD, in which FD is the recycled materials’ particle content finer than the aperture of geogrid, was proposed as a prime parameter governing the interface shear strength. A generalized equation was proposed for predicting the interface shear strength of the form: α = a(D/FD) + b, where α is the interface shear strength coefficient, which is the ratio of the interface shear strength to the shear strength of recycled material, and a and b are constants. The constant values of a and b were found to be dependent upon types of recycled material, irrespective of types of geogrids. A stepwise procedure to determine variable a, which is required for analysis and design of geogrids reinforced recycled materials in roads with various gradations was also suggested.

scholarly journals Laser-Milled Microslits Improve the Bonding Strength of Acrylic Resin to Zirconia Ceramics

Polymers ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 817
Author(s):  
Saiji Shimoe ◽  
Tzu-Yu Peng ◽  
Yuki Wakabayashi ◽  
Hiroto Takenaka ◽  
Shogo Iwaguro ◽  
...  
Keyword(s):  
Bond Strength ◽  
Bonding Strength ◽  
Failure Modes ◽  
Acrylic Resin ◽  
Thermal Cycles ◽  
Air Abrasion ◽  
Zirconia Ceramics ◽  
Interface Failure ◽  
Bonding Durability ◽  
Strength And Durability

Heightened aesthetic considerations in modern dentistry have generated increased interest in metal-free “zirconia-supported dentures.” The lifespan of the denture is largely determined by the strength of adhesion between zirconia and the acrylic resin. Thus, the effect on shear bond strength (SBS) was investigated by using an acrylic resin on two types of zirconia ceramics with differently sized microslits. Micromechanical reticular retention was created on the zirconia surface as the novel treatment (microslits (MS)), and air-abrasion was used as the control (CON). All samples were primed prior to acrylic resin polymerization. After the resin was cured, the SBS was tested. The obtained data were analyzed by using multivariate analysis of variance(α = 0.05). After the SBS test, the interface failure modes were observed by scanning electron microscopy. The MS exhibited significantly higher bond strength after thermal cycles (p < 0.05) than the CON. Nevertheless, statistically comparisons resulted in no significant effect of the differently sized microslits on SBS (p > 0.05). Additionally, MS (before thermal cycles: 34.8 ± 3.6 to 35.7 ± 4.0 MPa; after thermal cycles: 26.9 ± 3.1 to 32.6 ± 3.3 MPa) demonstrated greater SBS and bonding durability than that of CON (before thermal cycles: 17.3 ± 4.7 to 17.9 ± 5.8 MPa; after thermal cycles: 1.0 ± 0.3 to 1.7 ± 1.1 MPa), confirming that the micromechanical retention with laser-milled microslits was effective at enhancing the bonding strength and durability of the acrylic resin and zirconia. Polycrystalline zirconia-based ceramics are a newly accessible material for improving removable prosthodontic treatment, as the bond strength with acrylic resin can be greatly enhanced by laser milling.

Experimental Study on Structural Properties Influencing on Shear Strength of Soft Clay

2011 ◽  
Vol 243-249 ◽  
pp. 2487-2490
Author(s):  
Jiang Feng Wang ◽  
Yong Le Li ◽  
Yan Bin Gao ◽  
Yong Xiang Yang
Keyword(s):  
Shear Strength ◽  
Internal Friction ◽  
Shear Failure ◽  
Clayey Soil ◽  
Soft Clay ◽  
Friction Angle ◽  
Internal Friction Angle ◽  
Undisturbed Soil ◽  
Direct Shear Tests ◽  
Reconstituted Soil

The direct shear tests were conducted with undisturbed and reconstituted soft clay, then the structural influence on shear strength was studied, and the laws were got. No matter shear strength of slow shear or consolidated quick shear on undisturbed and reconstituted soil have not peak values, strength line of reconstituted soil is a slash, but the shear strength line of undisturbed soil is obviously a broken line. The internal friction angle of undisturbed and reconstituted soil is basically the same. There are good linear relationship between internal friction angle and plastic index of clayey soil. The amplitude of internal friction angle of reconstituted soil decreasing with plastic index increasing is less than that of undisturbed soil. From wf-lgp curve can be seen, with the increasing of vertical stress, water content of shear failure decrease gradually, and linear correlation of each curve is very good.

scholarly journals Effect of one cycle of heating-cooling on the clay-concrete pile interface behavior

2020 ◽  
Vol 205 ◽  
pp. 05012
Author(s):  
Abedalqader Idries ◽  
Ismaail Ghaaowd ◽  
Murad Abu-Farsakh
Keyword(s):  
Room Temperature ◽  
Clayey Soil ◽  
Volumetric Strain ◽  
Experimental Tests ◽  
Concrete Block ◽  
Friction Angle ◽  
Heating Process ◽  
Strength Parameters ◽  
Interface Shear ◽  
Cooling Cycle

This study investigated the effect of applying one heating-cooling cycle on the interface strength parameters of saturated clay soil-concrete, and the potential use of the heating process to improve the side capacity of piles driven in clayey soil. A large direct shear test device with inner dimensions of 300 mm, 300 mm, and 200 mm for width, length, and height, respectively was modified to perform the interface soil-concrete tests. A concrete block (300 mm × 300 mm × 100 mm) was built and placed at the bottom section of the shear device. Watlaw heating fire rods system was used to heat the circulating water that heat the specimens. The experimental tests were conducted on Low Plasticity Index soil with PI=12. The specimens were first consolidated to a target normal stress prior to shearing. Two specimens at different testing temperature (room temperature = 20 °C, 70 °C) were tested for each of the four different normal stresses (30, 69, 110, and 150 kPa). The temperature for the heated specimens was increased gradually during the heating process from the room temperature (20 °C ± 2 °C) to 70 °C ± 2 °C in 3 hours. The specimens were then cooled back to room temperature. The test results showed significant increase in both peak and residual interface shear strength parameters by 13.6% and 15.6% increase in friction angle, respectively. Also, volumetric strain under shearing decreased after the heating and cooling cycle by 30.0%, 24.4%, 11.3%, and 24.2% under 30 kPa, 69 kPa, 110 kPa, and 150 kPa, respectively.

scholarly journals Experimental and Numerical Study on the Behavior of Energy Piles Subjected to Thermal Cycles

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Kang Fei ◽  
Di Dai
Keyword(s):  
Mechanical Behavior ◽  
Mechanical Response ◽  
Numerical Study ◽  
Heat Transfer Analysis ◽  
Sensitivity Analyses ◽  
Scale Model ◽  
Measured Temperature ◽  
Pile Head ◽  
Thermal Cycles ◽  
Energy Piles

A laboratory-scale model test is conducted to improve the understanding of the effects of thermal cycles on the mechanical behavior of energy piles. The model pile is composed of cement mortar and dry sand with a relative density of 30% is used for the model ground. After applying the working load to the pile head, the pile is subjected to three thermal cycles with a magnitude of 15°C. The measured temperature response and mechanical behavior are analyzed and used to validate the proposed numerical approach. In the numerical analysis, the temperature variation due to thermal cycles is calculated using uncoupled heat transfer analysis. Then, the computed temperature field is used as the boundary condition in the sequence stress analysis. A series of numerical sensitivity analyses are carried out using the sequentially coupled method to investigate the long-term performance of energy piles under different soil and pile head restraint conditions. The numerical results suggest that the restraint condition at the pile head plays an important role in the mechanical response of energy piles. The ultimate pile resistance after thermal cycles does not decrease significantly. The accumulation of settlement of the free head pile and the reduction in the axial force of the restrained head pile should be considered in the design.

scholarly journals Energy geostructures: Theory and application

2020 ◽  
Vol 205 ◽  
pp. 01004
Author(s):  
Alessandro F. Rotta Loria
Keyword(s):  
Contact Structures ◽  
Future Research ◽  
Built Environments ◽  
Geothermal Heat ◽  
Analysis And Design ◽  
Structural Support ◽  
Energy Piles ◽  
And Performance ◽  
Successful Analysis

The subsurface represents space and resource of ever-growing importance to meet human activity needs associated with the availability of built environments and energy. So-called energy geostructures represent a breakthrough technology in this context. By integrating the structural support role of earth-contact structures with the heating-cooling role of shallow geothermal heat exchangers, energy geostructures can sustain or enclose built environments while providing them with renewable thermal energy. Despite such promising features, the integrated roles of energy geostructures pose various challenges to understand their behavior and performance, and to address the related analysis and design. Appropriate formulation and application of scientific theory are crucial for the successful analysis and design of energy geostructures. This Bright Spark Lecture Paper presents selected theory for addressing the behavior and performance of energy geostructures, and discusses the application of this theory to analysis and design. In this context, the work focuses on energy piles and barrettes, energy tunnels, as well as energy walls and slabs. The ultimate goal of this paper is to provide competence for facilitating future research and development of energy geostructures across science and engineering.

Effects of thermal cycles on microstructural and functional properties of nano treated clayey soil

2021 ◽  
Vol 280 ◽  
pp. 105929
Author(s):  
Shervin Ahmadi ◽  
Hasan Ghasemzadeh ◽  
Foad Changizi
Keyword(s):  
Functional Properties ◽  
Clayey Soil ◽  
Thermal Cycles
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