Estimation of the axial capacity of piles driven into sand involves considerable uncertainty, and design rules are generally not consistent with the physical processes involved. This Paper reviews current understanding of the factors that determine the axial capacity of piles driven into sand, and outlines a new framework for design which takes account of the physical processes, is consistent with the existing database of load test results, and is sufficiently flexible to permit refinement as new data become available. It allows for the effects of confining stress on the frictional and compressibility characteristics of sand, and hence on end-bearing capacity. In keeping with field observations, shaft friction is assumed to degrade with driving of the pile past a particular location, from an initial maximum value linked to the local end-bearing capacity. The resulting design approach is compared with field data, and effects of factors such as the direction of loading are discussed. L'estimation de la resi...

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Design of driven piles in sand

This paper summarizes the parameters that influence the axial capacity of pipe piles driven into sands. The parameters that affect pile behavior are for convenience divided into four categories: (1) Soil characteristics; (2) pile characteristics; (3) method of pile installation; and (4) type of loading. When possible, the influence that these parameters have on the capacity is quantified. In addition, the paper describes supporting evidence from pile load test data, small‐scale laboratory tests, and in situ cone probings that has been used to justify limiting values for unit shaft and toe resistances. The use of limiting values has significant economic impact on long piles, especially those used for offshore applications. This information is, therefore, evaluated and critiqued to place the use of limiting values in proper perspective. The results of this paper are based on a synthesis of literature on (1) pile load test data on piles in sand, (2) data from cone penetrometer tests in sands, and (3) informa...

Performance of axially loaded pipe piles in sand

Pile foundations play an essential role in many structures, therefore it is vital that they be designed with the utmost reliability. The cost of failure is potentially huge. Covering a whole range of design issues relating to pile design, Theory and Practice of Pile Foundations presents economical and efficient design solutions and demonstrates them using real-world examples. The author presents his systematic approach to modelling pile responses in the context of load transfer models—an approach that leads to methods that require fewer parameters but can potentially solve more problems.

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Theory and Practice of Pile Foundations

With increased urbanization, deep foundation (bridges, signage, walls, etc) selection is moving toward the minimization of disturbance and installation time, as well as addressing quality control and assurance issues Unfortunately, many types of deep foundations involve noise and vibration during installation (eg, driven piles) or integrity and reduced resistance issues (eg, drilled shafts, both conventional and post grouted tip, continuous flight auger piles) This paper presents a new foundation type, a jetted and grouted precast pile, which uses the advantages of several proven deep foundation installation techniques The installation of the new pile is comprised of three distinct phases: (1) pressurized water-jetting of a precast pile into the ground; (2) side grouting of the pile; and (3) tip grouting The pile has two separate side grouting zones, each with its own grout delivery system Each grout zone is covered with a semirigid membrane, which results in radial expansion of the soil

Measured and Predicted Response of a New Jetted and Grouted Precast Pile with Membranes in Cohesionless Soils

Design and Construction of Continuous Flight Auger Piles

Auger‐cast piles are formed by drilling a continuous flight auger into the ground and, on reaching the required depth, pumping grout or concrete down the hollow stem as the auger is steadily withdrawn. The sides of the hole are supported by the soil‐filled auger, eliminating the need for temporary casing or bentonite slurry. This paper outlines important features of auger‐cast pile installation that influence the structural integrity and geotechnical capacity of completed piles. These include soil decompression, correlation between the rotational and vertical speeds of the auger, and precise coordination of auger extraction and grout supply. The results of 66 loading tests on auger‐cast piles in sand are presented. Shaft resistance is found to be independent of the relative density of the sand, while point resistance can be directly correlated with results of standard penetration and cone penetrometer tests. Empirical design methods for bored piles were found to underestimate the failure loads of auger‐ca...

Bearing capacity of auger-cast piles in sand

Working Stress Design Method for Reinforced Soil Walls

The results of loading tests are used to develop empirical correlations between the point‐bearing resistance of expanded‐base piles and the results of standard penetration tests. The resistance is shown to be proportional to depth for piles having shaft lengths not exceeding 10 base diameters. The results also show that there is no significant difference between the point resistance of piles in relatively homogeneous soils and piles founded in a bearing stratum overlain by soft, compressible soil at the same overall depth/base diameter ratio measured from ground surface. Values of the bearing capacity factor Nq were calculated by dividing the point resistance at failure by the effective overburden pressure at the level of the maximum cross section of the base. Nq was found to decrease dramatically with increasing effective overburden pressure, indicating that ambient stress level must be considered in bearing capacity analysis. The results show no evidence of a critical depth below which point resistance ...

Bearing capacity of expanded-base piles in sand

A data base of 70 loading tests on expanded-base piles with compacted concrete shafts has been collected to develop empirical design correlations based on standard penetration \IN\N-values. Both shaft and point resistances, \If\ds\N and \Iq\dp,\N were found to increase with depth and with increasing \IN\N-value. It appears that limiting values of \If\ds\N and \Iq\dp\N might be approached for initially loose sands at \ID\N/\IB\N (and \ID\db\N/\IB\db\N) ratios greater than 12; however, at greater relative densities, both \If\ds\N and \Iq\dp\N continue to increase with depth, but at a decreasing rate, indicating an important scale effect. A modification to traditional bearing capacity theory is used to show that the so-called scale effect arises because the bearing capacity factor \IN\dq,\N which is a function of the friction angle of the soil, decreases with depth or increasing effective overburden pressure; consequently, point resistance increases with depth at a decreasing rate. About 40% of the data base was used as an independent means of evaluating the accuracy of the empirical correlations developed.

Bearing capacity of expanded-base piles with compacted concrete shafts

A data base of 70 loading tests on expanded-base piles with compacted concrete shafts has been collected to develop empirical design correlations based on standard penetration \\IN\\N-values. Both shaft and point resistances, \\If\\ds\\N and \\Iq\\dp,\\N were found to increase with depth and with increasing \\IN\\N-value. It appears that limiting values of \\If\\ds\\N and \\Iq\\dp\\N might be approached for initially loose sands at \\ID\\N/\\IB\\N (and \\ID\\db\\N/\\IB\\db\\N) ratios greater than 12; however, at greater relative densities, both \\If\\ds\\N and \\Iq\\dp\\N continue to increase with depth, but at a decreasing rate, indicating an important scale effect. A modification to traditional bearing capacity theory is used to show that the so-called scale effect arises because the bearing capacity factor \\IN\\dq,\\N which is a function of the friction angle of the soil, decreases with depth or increasing effective overburden pressure; consequently, point resistance increases with depth at a decreasing rate. About 40% of the data base was used as an independent means of evaluating the accuracy of the empirical correlations developed.

William J. Neely

Papers

Bearing capacity of auger-cast piles in sand

Working Stress Design Method for Reinforced Soil Walls

Bearing capacity of expanded-base piles in sand

Bearing capacity of expanded-base piles with compacted concrete shafts

Closure of "Bearing Capacity of Expanded-Base Piles with Compacted Concrete Shafts"