Relationship between installation torque and uplift capacity of deep helical piles in sand

2010 ◽  
Vol 47 (6) ◽  
pp. 635-647 ◽  
Author(s):  
Cristina de Hollanda Cavalcanti Tsuha ◽  
Nelson Aoki
Keyword(s):  
Laboratory Tests ◽  
Friction Angle ◽  
Correlation Factor ◽  
Experimental Program ◽  
Uplift Capacity ◽  
Suggested Approach ◽  
Interface Friction ◽  
Helical Piles ◽  
Shear Interface ◽  
Good Agreement

The empirical torque correlation factor (KT), which relates the uplift capacity to the installation torque of helical piles, is routinely used as an on-site instrument for quality control with this type of foundation. This paper presents a theoretical relationship between uplift capacity and installation torque of deep helical piles in sand. An experimental program, including centrifuge and direct shear interface tests, was carried out to validate this expression. The experimental results were compared with the values predicted by the suggested approach and showed good agreement. As the developed model depends on the residual interface friction angle (δr) between the helix surface and the surrounding sand, results of δr, extracted from different sand samples, are presented for use in this suggested relationship on site. Also, the values of KT found in this work were compared with those of field and laboratory tests on helical piles in sand reported in the literature. From this analysis, it was found that the measured values of KT decrease with an increase in pile dimensions and, in most of cases, with an increase in sand friction angle. These results were explained by the presented model.

scholarly journals Review of torque models for offshore helical piles

2020 ◽  
Vol 205 ◽  
pp. 12007
Author(s):  
Giovanni Spagnoli ◽  
Cristina de Hollanda Cavalcanti Tsuha
Keyword(s):  
Strong Influence ◽  
Friction Angle ◽  
Soil Conditions ◽  
Uplift Capacity ◽  
Pile Installation ◽  
Pile Shaft ◽  
Geometrical Features ◽  
Helical Piles ◽  
Installation Depth ◽  
Torque Values

Helical (or screw) piles, sometimes defined as anchors, are a piled system consisting of one or multiple helices welded along the shaft. Piles are installed by applying a torque to the shaft. The pile is rotated into the soil and the rate of advancement should be an amount equal to the pitch for each rotation in order to minimize the disturbance of the original soil. Torque is maybe the most important parameter to be assessed during pile installation. In fact, torque and uplift capacity are directly proportional. Generally, torque depends on the soil conditions and on the geometrical features of the pile. Torque increases with sand density, installation depth, friction angle of sand, pile shaft and helix diameters. The geometry of the pile has a strong influence on the torque, the larger the helix-to-shaft ratio is, the larger the torque will be. In offshore applications helical piles are being considered as a valid alternative. However, one of the issues is still related to the assessment of the installation torque values. Several torque models have been considered and critical evaluated. Some simple comparisons among selected torque models have been also done and discussed.

Earth pressures on unyielding retaining walls of narrow backfill width

2001 ◽  
Vol 38 (6) ◽  
pp. 1220-1230 ◽  
Author(s):  
W A Take ◽  
A J Valsangkar
Keyword(s):  
Earth Pressure ◽  
Friction Angle ◽  
Retaining Walls ◽  
Centrifuge Modelling ◽  
Reasonable Estimate ◽  
Interface Friction ◽  
Centrifuge Tests ◽  
Earth Pressures ◽  
Nonlinear Calibration ◽  
Good Agreement

Arching theory predicts a significant reduction in earth pressures behind retaining walls of narrow backfill width. An extensive series of centrifuge tests has been performed to evaluate the use of flexible subminiature pressure cells in the centrifuge environment and their subsequent use to measure lateral earth pressures behind retaining walls of narrow backfill width. Although the flexible earth pressure cells exhibit hysteresis and nonlinear calibration behaviour, the extensive calibration studies indicate that stiff diaphragm type earth pressure cells may be used with replicate models to measure earth pressures. Measurements of lateral pressures acting on the unyielding model retaining walls show good agreement with Janssen's arching theory. Tests on backfills bounded by vertical planes of dissimilar frictional characteristics indicate arching theory with an average interface friction angle provides a reasonable estimate of lateral earth pressures.Key words: fascia retaining walls, silos, earth pressures, pressure cells, centrifuge modelling.

Characterization of Shear Strength and Interface Friction of Organic Soil

2020 ◽  
Vol 857 ◽  
pp. 203-211
Author(s):  
Majid Hamed ◽  
Waleed S. Sidik ◽  
Hanifi Canakci ◽  
Fatih Celik ◽  
Romel N. Georgees
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Internal Friction ◽  
Moisture Content ◽  
Water Content ◽  
Friction Angle ◽  
Structural Materials ◽  
Organic Soil ◽  
Internal Friction Angle ◽  
Interface Friction

This study was undertaken to investigate some specific problems that limit a safe design and construction of structures on problematic soils. An experimental study was carried out to examine the influence of loading rate and moisture content on shear strength of organic soil. Influece of moisture content on interface friction between organic soil and structural materials was also attempted. A commonly used soil in Iraq was prepared at varying moisture contents of 39%, 57% and 75%. The experimental results showed that the increase in water content will decrease the shear stress and the internal friction angle. An increase of the shearing rate was found to decrease the shear stress and internal friction angle for all percetanges of water contents. Further, direct shear tests were carried out to detect the interface shear stress behavior between organic soil and structural materials. The results revealed that the increase in water content was shown to have significant negetavie effects on the interface internal friction and angle shear strength.

Seismic uplift capacity of inclined strip anchors

2005 ◽  
Vol 42 (1) ◽  
pp. 263-271 ◽  
Author(s):  
Deepankar Choudhury ◽  
K S Subba Rao
Keyword(s):  
Limit Equilibrium ◽  
Ground Surface ◽  
Failure Surface ◽  
Friction Angle ◽  
Uplift Capacity ◽  
Principle Of Superposition ◽  
Seismic Acceleration ◽  
Acceleration Coefficient ◽  
Angle Of Internal Friction ◽  
Seismic Forces

Uplift capacities of inclined strip anchors in soil with a horizontal ground surface are obtained under seismic conditions. Limit equilibrium approaches with a logarithm-spiral failure surface and pseudostatic seismic forces are adopted in the analysis. The results are presented in the form of seismic uplift capacity factors as functions of anchor inclination, embedment ratio, angle of internal friction of the soil, and horizontal and vertical seismic acceleration coefficients. The uplift capacity factors are worked out separately for cohesion, surcharge, and density components. Use of the principle of superposition for calculating anchor uplift capacity is validated. The vertical seismic acceleration coefficient always reduces the uplift capacity, whereas the horizontal seismic acceleration coefficient reduces the uplift capacity in most cases. The roles of anchor embedment ratio, soil friction angle, and anchor inclination in determination of the seismic uplift capacity are also discussed. Comparisons of the proposed method with available theories in the seismic case are also presented. The present study gives the minimum seismic uplift capacity factors compared with the existing theory.Key words: seismic uplift capacity factors, inclined strip anchors, limit equilibrium, pseudostatic, c–ϕ soil.

Flutter of Supercavitating Hydrofoils-Comparison of Theory and Experiment

1972 ◽  
Vol 16 (03) ◽  
pp. 153-166
Author(s):  
Charles C. S. Song
Keyword(s):  
Leading Edge ◽  
Experimental Program ◽  
Finite Width ◽  
Free Surfaces ◽  
First Order ◽  
Free Jet ◽  
Analytical Work ◽  
Proper Interpretation ◽  
First Order Perturbation ◽  
Good Agreement

Unsteady flow due to harmonic oscillations of a two-dimensional supercavitating flat-plate hydrofoil in a free jet of finite width has been analyzed using first-order perturbation theory. The hydrodynamic loading coefficients thus obtained were used to study the hydroelastic instabilities: flutter and divergence. In conjunction with the analytical work, an experimental program was carried out using a free-jet water tunnel. Special attention was given to the influence of the free surfaces and the point of separation on the critical flutter speed. With proper interpretation of the location of the separation point near the leading edge, the theory and the experimental data were shown to be in fairly good agreement.

Study of Correlation on Unconfined Compressive Strength between Different Soil

2013 ◽  
Vol 838-841 ◽  
pp. 926-929
Author(s):  
Xia Zhao
Keyword(s):  
Compressive Strength ◽  
Soil Moisture ◽  
Moisture Content ◽  
Unconfined Compressive Strength ◽  
Laboratory Tests ◽  
Soil Moisture Content ◽  
Correlation Coefficients ◽  
Friction Angle ◽  
Silty Clay ◽  
Soil Cohesion

Take the silty clay and clay as the research object, the correlation between bulk density, moisture content, cohesion, friction angle and unconfined compressive strength was analyzed using laboratory tests, and the results showed that soil cohesion, friction angle and unconfined compressive strength with good correlation, the correlation coefficients were all above 0.9, while severe and soil moisture content and unconfined compressive strength of correlation is weak, followed by the correlation formulas of the index and unconfined compressive strength were established, these formulas can used to predict the unconfined compressive strength of soil.

scholarly journals Observations and numerical simulations of the braking effect of forests on large-scale avalanches

2018 ◽  
Vol 59 (77) ◽  
pp. 50-58 ◽  
Author(s):  
Yukari Takeuchi ◽  
Koichi Nishimura ◽  
Abani Patra
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Friction Angle ◽  
Subalpine Forest ◽  
Trial And Error ◽  
Disaster Reduction ◽  
Forested Area ◽  
Avalanche Dynamics ◽  
Bed Friction ◽  
Good Agreement

ABSTRACTAlthough the disaster reduction effects of forest braking have long been known empirically, they have not been known in detail down to recent. In this study, we ascertained forest braking effect by numerical simulations using the avalanche dynamics program, TITAN2D, to model large-scale avalanches. One of these avalanches occurred in the Makunosawa valley, Myoko, and damaged a cedar forest; the others occurred on Mt. Iwate and damaged a subalpine forest. All avalanches damaged many trees and terminated within the forests. In our simulations, the resistance of the forests to avalanches is simulated using a larger bed friction angle. Fitting the observations from the Makunosawa avalanche by trial and error, a bed friction angle of 13–14° in the non-forested area and of 25° in the forested area is obtained. We conducted simulations of the Mt. Iwate avalanches using the same method as for the Makunosawa valley avalanche, and obtained good agreement between observations and simulations. Simulations reveal that without the forest, the avalanche would have traveled at least 200 m farther than the forest's actual end in the Makunosawa valley, and at least 200 m and possibly up to 600 m farther on Mt. Iwate. This study therefore clearly shows that forests provide a braking effect for avalanches.

Performance of cement-stabilized retaining walls

2005 ◽  
Vol 42 (3) ◽  
pp. 876-891 ◽  
Author(s):  
M A Ismail
Keyword(s):  
Finite Element ◽  
Retaining Wall ◽  
Friction Angle ◽  
Experimental Program ◽  
Centrifuge Model Test ◽  
Element Analysis ◽  
Centrifuge Testing ◽  
Load Carrying ◽  
The Stability ◽  
Surrounding Soil

This paper investigates the performance of a cement-stabilized retaining wall as a potentially economic solution for supporting vertical cuts in roads and embankments. This investigation was carried out through a comprehensive numerical and experimental program in which the stabilized wall was treated as a c′–ϕ soil. To optimize the design of the stabilized wall, a plane-strain finite element analysis was carried out, using the PLAXIS code, in a parametric study that varied the wall geometry and the shear strength parameters for both the wall and its surrounding soil. The performance of the stabilized retaining wall was verified by a centrifuge model test carried out at an equivalent acceleration of 67g for a sand treated with 3% Portland cement. The results have shown that the load-carrying capacity of the wall is affected primarily by both the cementation of the wall and the friction angle of the surrounding soil. There exists a threshold of cementation beyond which the stability does not increase when the failure mechanism is located completely inside the in situ soil. This critical cementation appears to be a crucial factor in maintaining an economic design for this type of wall. Centrifuge test results confirmed the satisfactory behaviour of cement-stabilized retaining walls.Key words: cement stabilization, retaining wall, cohesion, finite element, centrifuge testing.

RECENT ADVANCES IN DISPERSANT EFFECTIVENESS EVALUATION: EXPERIMENTAL AND FIELD ASPECTS

1985 ◽  
Vol 1985 (1) ◽  
pp. 445-452 ◽  
Author(s):  
J. P. Desmarquest ◽  
J. Croquette ◽  
F. Merlin ◽  
C. Bocard ◽  
G. Castaing ◽  
...  
Keyword(s):  
Laboratory Tests ◽  
Oil Spills ◽  
Practical Interest ◽  
Field Tests ◽  
Field Trials ◽  
Large Field ◽  
Experimental Program ◽  
Experimental Conditions ◽  
Good Accord ◽  
Dispersant Effectiveness

ABSTRACT Although dispersants are used in different countries, it appeared from recent international meetings that more knowledge concerning dispersant effectiveness is still needed for a better response to oil spills. Large field trials which were conducted during the past two years raised some questions as to how dispersants work at sea. Even though the results obtained in different laboratory tests are generally in good accord, significant discrepancies of practical interest may be observed because of variations in the experimental conditions. With EEC support, an experimental program has been conducted by CEDRE and Institut Français du Pétrole (IFP), both with the already-described French middle scale field test and with different laboratory tests (U.K. and French standard tests and the recently developed dilution test). With the objective of correlating the results obtained in field tests and in laboratory tests, several parameters were investigated at sea with different dispersants: the type and viscosity of the oil, slick thickness, and oil to dispersant ratio. Based mainly on the results obtained in the laboratory with dilution tests, new aspects of dispersant behavior have been identified, relating to the nature of the oil and the energy input.

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