Anchor Piles Research Articles

Physical Modelling of Helical Pile Anchors

Physical Modelling of Helical Pile Anchors

Use of a new type of anchor piles for stability of offshore structures

Use of a new type of anchor piles for stability of offshore structures

Pullout Behavior of Granular Pile-Anchors in Expansive Clay Beds In Situ

Granular pile anchors (GPA) are one of the recent innovative foundation techniques devised for mitigating the problems posed by swelling clay beds. In a granular pile anchor, the footing is anchored to an anchor plate at the bottom of the granular pile. This makes the granular pile tension resistant and enables it to absorb the tensile force caused on the foundation by the swelling clay. An understanding of the amount of uplift resistance offered by the GPA is important in the design of granular pile-anchor foundations in field situations causing tensile forces on foundations, such as in expansive clay beds. This paper presents the results of a field-scale test program conducted to study the pullout response of GPAs embedded in expansive clay beds. Pullout load tests were conducted on GPAs of varying lengths and diameters. It was found from the field pullout load tests that granular pile anchors of larger surface area resulted in higher pullout capacity. Of the various single granular pile anchors with l∕...

Uplift capacity of pile group anchors

Experimental investigations on model single pile anchor and pile group anchors of configuration 2 × 2 subjected to uplift loads were conducted on dry Ennore sand, obtained from Madras, India. The embedment length to shaft width ratios, L/d = 20 and L/d = 30, and enlarged base width to shaft width ratios, B/d = 1,2,3, center to center spacing of pile anchors in the groups, 3d, 4d, 6d and 8d were used. The load displacement response, ultimate resistance and variation of group efficiency with L/d, B/d and spacing have been studied quantitatively and qualitatively. For short pile group anchors (L/d = 20), the isolation spacing appears to be at a spacing of about 4d to 6d and 8d for B/d = 1 and B/d = 2 and 3, respectively. For long pile group anchors (L/d = 30), the isolation spacing appears to be at a spacing of about 4d, 6d and 8d for B/d = 1, 2 and 3, respectively. The analytical model of limit equilibrium method has been proposed to predict the net uplift capacity of pile group anchors. The predicted results compare reasonably well with the experimental results.

Repairs to River Trent navigation locks 1981–2002

A series of repairs to three large concrete locks on the River Trent navigation was carried out between 1981 and 2002, involving works to counter the effects of degrading Mercia Mudstone foundation material and unsatisfactory stability of the structures. The current paper describes the history of the locks and the problems which developed, the assessments and investigation undertaken to determine the failure modes and the development of appropriate repair strategies. Significant factors included closure of the navigation, dewatering arrangements and temporary load cases, the preservation of existing stability and the effects of difficult site access. Construction activities are also briefly described. The projects originated from emergency works following a near failure at Stoke Lock (1981–1983), reactive works following monitoring at Newark Nether Lock (1993/1994) and preventative works identified through an asset inspection process at Cromwell Lock (2001/2002). The 1981–1983 works involved external sheet pile anchors and ties and a reinforced concrete trough section built in the lock chamber together with major temporary works. At Newark Nether, mini-piling was installed through the lock walls to improve stability prior to replacement of the lock floor, avoiding many of the temporary works needed at Stoke Lock. The Cromwell Lock works were similar to Nether Lock but utilised vertical mini-piling and an underfloor drainage system in a refinement of earlier designs. Use was made of British Waterways' own temporary works equipment where available.

Studies on pullout capacity of anchors in marine clays for mooring systems

In marine applications, single point or spread mooring systems are used for providing temporary berthing of vessels. In this investigation, it is suggested that pile anchors and suction anchors can be used depending on the water depth. By testing a model, the influence of parameters like mooring chain inclination, consistency of the clayey soil in the seabed and anchor embedment ratios on pullout capacity has been brought out. Tests were carried out on single pile, 2-pile, 4-pile anchors made out of pipe piles of 25.4 mm dia with length to diameter ratios, L / D of 10, 14 and 18 and model suction anchors (closed-top caisson) of 113 mm dia with L / D = 2 , 3 and 4. These were installed in a model test bed made out of soft marine clay. The results indicate that in respect of pile anchors as of the chain inclination changes from horizontal to vertical direction, the pullout resistance shifts from passive earth pressure to skin friction. The results in respect of suction anchors can be interpreted in terms of various components proposed.

杭式アンカーの海中落下挙動と海底地盤への貫入に関する実験及び解析

In order to moor a floating offshore wind farm with a generator as large as 5000 kW, the cost of construction will be higher by using conventional anchors because of its small holding capacity. Therefore, a free fall tubular pile anchor has been developed which can be easily penetrated into clayey sea bed by dropping from a height above seabed. We conducted model test to evaluate the dynamic characteristics in water and soil by using the anchors with or without four sheets of fin to stabilize and increase the pullout capacity. This paper describes the comparison of analysis and measurement for the dynamic characteristics, along with the obtained friction and resistance factors in water and soil.

Granular Pile Anchor Foundation (GPAF) System for Improving the Engineering Behavior of Expansive Clay Beds

Abstract Several innovative foundation techniques have been suggested for reducing the detrimental heave of foundations in expansive clays. This paper presents another innovative technique in the form of a granular pile anchor-foundation (GPAF) system for arresting heave and for improving the overall engineering behavior of expansive clay beds. In the GPAF system, the foundation is anchored at the bottom of the granular pile to an anchor plate through an anchor rod. As a result, heave of the foundation is reduced. The laboratory model tests using this new concept of the GPAF system revealed that the heave of the expansive clay beds was reduced by about 96 %. The development of final heave was faster in the case of the expansive clay beds reinforced with the GPAF system. The undrained strength of the clay surrounding the granular pile anchor improved by about 20 %. The tests on two-group granular pile anchors indicated that heave was reduced to a minimum value when the spacing between the granular pile anchors was kept at twice the pile diameter. The compressive load response of the expansive clay bed reinforced with granular pile anchors also improved. The pull-out load of the granular pile anchors increased with increasing diameter and the relative density of the pile.

Procedure for Analyzing Foundations with Anchor Piles Subjected to Moments in Two Directions

A procedure is proposed for analysis of a combined foundation consisting of a rigid slab and short anchor piles situated around its perimeter; for large eccentricities of vertical loads, this reduces, or eliminates separation of the lower surface, and diminishes tilting of a foundation with smaller planform dimensions as compared with a conventional foundation.

Underground engineering pile anchor wall protection system

Underground engineering pile anchor wall protection system

Research on equivalent processes of rock mass parameters with anchor piles

Using normal and shear rigid coefficients of intact rock and fracture plane, rigidly normal, shear equivalent rigid coefficients of fissure rock mass are conducted. On the basis of hypotheses of small displacement of rock mass, principle of superposition, irrelevance of strength parameters C and ϕ and Coulomb theory, formulas to calculate equivalent strength parameters C and ϕ of equivalent continuous mass from fissured rock mass with anchor piles are given. The achievement is extremely valuable in integral stability analysis of the rock mass slope and important in promoting the research of the rock mass's constitutive relation.

Stress-Strain State of Pile Beds Tested under a Static Loading

The stress-strain state of the beds of prismatic piles subjected to static testing is analyzed, and the influence exerted by the distance between test and anchor piles and the depth of their embedment on the stress-strain state of the soil is examined.

Increasing pull-out capacity of granular pile anchors in expansive soils using base geosynthetics

Granular pile anchors are innovative and effective in resisting the uplift pressure exerted on the foundation by a swelling expansive soil. In a granular pile anchor, the foundation is anchored at the bottom of the granular pile to an anchor plate with the help of a mild steel rod. This renders the granular pile tension-resistant and enables it to offer resistance to the uplift force exerted on the foundation by the swelling soil. This resistance to uplift or pull-out load depends mainly upon the shear parameters of the pile-soil interface and the lateral swelling pressure of the soil, which confines the pile radially and prevents it from being uplifted. The resistance to uplift can be increased by placing a base geosynthetic above the anchor plate so that it forms an integral part of the granular pile anchor. The increase in resistance is due to the friction mobilized between the geosynthetic and the confining media when the uplift load acts on the pile and the geosynthetic moves along with the pile. Hence it depends on the friction between the geosynthetic and the confining media and the area and stiffness of the geosynthetic. This paper discusses the effects of these parameters on pull-out load, rate of heave, and relative ground movement near the pile surface.Key words: expansive soil, granular pile anchor, base geosynthetic, ground movement, rate of heave, pull-out load.

Increasing pull-out capacity of granular pile anchors in expansive soils using base geosynthetics

Increasing pull-out capacity of granular pile anchors in expansive soils using base geosynthetics

Design and Installation of Suction Anchor Piles at Soft Clay Site

Innovative suction anchor piles have been used for permanent mooring of a process and accommodation barge at an oil and gas field developed by ELF Congo in the Gulf of Guinea. Twelve mooring lines, equipped with steel suction anchor piles, were successfully preinstalled at the site in July–August 1995, and the process barge was connected in early 1996 for the start of production. With a water depth ranging between 150 and 300 m, the Nkossa field is among the deepest ones offshore Western Africa to date, and the soils at the site consist of soft normally consolidated clays, representative of deep water sites. The anchoring system design is presented together with a description of the suction pile installation operations. The monitored performance of the suction piles during installation is evaluated, including the orientation and tilt at touchdown and the penetration rate during suction penetration. The installation behavior appeared to be easy and smooth, and the measured penetration resistances were in p...

Evaluation of Cyclic Model Tests on Anchor Piles in Clay

The response of anchor piles in clay subjected to cyclic loading was investigated in a series of tests on small size model piles, 40 cm long and 1.9 cm in diameter, jacked into a reconstituted and normally consolidated clay. Evaluation of the test results focusses upon the degradation of cyclic pile stiffness, the accumulation of permanent displacements, the degradation of cyclic pullout capacity, as well as the short time effects of cyclic loading on the post-cyclic static pile response. The cyclic response of the model piles was correlated to that of the surrounding soil elements, observed in a series of undrained cyclic triaxial tests. In addition, the influence of the small scale of the model piles on the experimental results was assessed through comparison to similar data from large scale model and field tests reported in the literature. Cyclic load and displacement magnitudes, number of cycles and cyclic preshearing were identified as the main factors which control the pile response. The small size of the pile influences the experimental results at low cyclic loading intensities when radial drainage leads to partially drained conditions during cyclic loading.

Vertical pullout capacity of model batter anchor piles in marine clays

Many offshore structures are subjected to overturning moments due to wind load, wave pressure, and ship impacts. For foundations in such structures, usually a combination of vertical and batter piles is used. Little information is available in the literature about estimating the capacity of piles under uplift. In cases where these supporting piles are not vertical, the behavior under vertical pullout is not well established. In this article the vertical pullout behavior of batter piles is examined through an experimental investigation carried out on model batter anchor piles. The tests are conducted on model aluminum pipe piles of 19 mm diameter with different embedment ratios in a soft marine clayey bed at different consistencies and with various batter angles of 0°, 10°, 20°, and 30°. Results indicate that the pullout capacity of a batter pile is less than that of a vertical pile. This reduction is explained in terms of reduced area available for skin friction. Based on this, pullout behavior of batter ...

Pullout behaviour of model pile and helical pile anchors subjected to lateral cyclic loading : Y. V. S. N. Prasad & S. N. Rao, Canadian Geotechnical Journal, 31(1), 1994, pp 110–119

Pullout behaviour of model pile and helical pile anchors subjected to lateral cyclic loading : Y. V. S. N. Prasad & S. N. Rao, Canadian Geotechnical Journal, 31(1), 1994, pp 110–119

Pullout behaviour of model pile and helical pile anchors Subjected to lateral cyclic loading

This paper presents the effect of lateral cyclic loading on the pullout capacity of model and helical piles in clayey soil. The tests were conducted on short rigid model piles in the laboratory in three phases, namely lateral static load tests, lateral cyclic load tests, and vertical pullout tests. From the test results it was found that the lateral cyclic loading affects the pullout capacity of piles substantially. Reduction in pullout capacity mainly depends upon the lateral deflection of the pile during cyclic loading and the embedment ratio of the pile. This reduction in the pullout capacity of model piles is presented in terms of nondimensional parameters, viz., degradation factor, lateral deflection ratio, and embedment ratio of pile. However, in the case of helical piles under similar conditions, it was found that the lateral cyclic loading has very little influence on the pullout capacity. The reasons for the better performance of helical piles over ordinary piles are explained. Key words : clay, degradation factor, helical pile, lateral cyclic loading, lateral deflection, Joading level, pile, pullout capacity.

Uplift behaviour of pile anchors subjected to lateral cyclic loading. Technical note : Rao, S N; Prasa, Y V S N J Geotech Engng div ASCE V119, N4, Aprila 1993, P786–790

Uplift behaviour of pile anchors subjected to lateral cyclic loading. Technical note : Rao, S N; Prasa, Y V S N J Geotech Engng div ASCE V119, N4, Aprila 1993, P786–790