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Data, databases, and Machine Learning for Geotechnical Engineers

Data, databases, and machine learning for civil engineers

Starts Sep 23rd

The future of civil engineering is approaching

Online Deep Excavation and Soil nail wall design Workshop

16 PDH

Nov 18-19, 2020

Deep excavation in Las Vegas

Early registration ends soon!

DeepEX 2020

Solving Deep Excavation Design

DeepEX 2017 talk to it and design your deep excavation!

Online Slope Stability, Soil Nailing, and Inclinometer Monitoring Workshop

4 hours each day, 8 PDH

Slope stability, soil nailing, and inclinometer worksho

July 15, 16, 2020

Deep Foundation Software, Pile Rafts, Pile Groups

From soil estimation to axial and lateral pile capacity

DeepFND - Deep Foundation Software, caissons, CFA, drilled piles, driven piles, concrete, timber

From soil estimation to helical pile settlement estimation.

New helical pile software HelixPile
Signup for a free trial and get our free pdf on the five most common errors in deep excavation design
What do you want to design?
DeepFND 2020: Deep Foundation software (NEW: Pile-Group/Pile Raft Analysis!)
DeepEX 2020: Deep Excavation software
Soldier pile walls
Sheet pile walls
Secant pile Walls
Tangent piles
Diaphragm Walls
Soldier and Tremied Concrete
Soil Mix walls
Combined king pile sheet piles
Slope stability
Cost estimation for braced excavations
Waler-Strut Cofferdams
Snail-Plus 2019: Soil nailing - soil nailing walls
SiteMaster: Inclinometer software (adopted by Geokon)
HelixPile: Helical Pile Software
RC-Solver: Concrete Design ACI-318, EC2, EC8
Steel-Beam: Steel beam column design, full equations, AISC, EC3

Helical anchor design for excavations.

Helical anchor design is governed by simple geotechnical engineering principles. In excavations, helical anchor design is controlled primarily by the bearing resistance on each helical plate. In some cases, the shaft resistance can also be included. Since the helix shaft is in tension the helical anchor does not have to be examined in buckling. In principle the ultimate capacity of a helical anchor is determined as the most critical of the two basic modes of failure:

a) Individual bearing method: This is the sum of the bearing capacity at each helical plate. In this mode the total ultimate pullout resistance of a helical anchor is determined as:

Qtotal = sum {Ahelix (9 c + gamma' x Depth x Nq)}

The geotechnical helical anchor capacity should be smaller than the individual structural capacity of each plate.

b) Cylinder strength method: In this mode the capacity is calculated as the shear resistance of a cylinder of soil contained by the helical plates, plus the bearing resistance of the helical plate closer to the excavation. The cylinder method can be applied only in cases where the helical anchor has atleast two plates.

Qcylinder = AhelixPlate1 (9 c + gamma' x D x Nq) + side resistance

In practice the individual bearing method and the cylinder strength method have generally produced smaller geotechnical capacities than actually experienced by pullout tests. For this reason, a number of researchers have proposed the torque installation method that relates the pullout resistance to the installation torque which can be measured during each helical anchor installation.

c) Torque correlation method: The Torque Correlation Method is an empirical method that distinguishes the relationship between helical pile capacity and installation torque and has been widely used since the 1960's. The process of a helical plate shearing through the soil or weathered bedrock in a circular motion is equivalent to a plate penetrometer test. The method gained notoriety based on the study performed by Hoyt and Clemence (1989). Their study analyzed 91 helical pile load tests at 24 different sites within various soil types ranging from sand, silt and clay soils. They demonstrated the direct correlation of the installation torque of a helical pile to its ultimate capacity in compression or tension. The common denominator discovered from the study was a parameter referred to as the torque correlation factor, Kt.

The equation is:
Pu = Kt T
Pu is the ultimate capacity of the helical pile or anchor [lb (kN)].
Kt is the empirical torque factor of the central shaft of the pile [ft-1 (m-1)].
T is the final installation torque [ft-lb (m-kN)].

It's important to point out that the tests analyzed by Hoyt and Clemence (1989) were in tension. It was shown in sub-sequential studies that the tension capacity of helical piles was 16 to 33 percent less than the measured compression capacity. The difference is attributed to the fact that the lead helical plate is bearing on relatively undisturbed soil in compression applications. In tension applications, the leading and trailing helical plates are bearing on soil affected by the installation of the helical plates. It has become common practice to use the same torque correlation factor for a helical pile of the same size for tension and compression and ignore the slight increase in compression capacity. This creates a more conservative compression capacity for helical piles when compared to the Individual Bearing Method. Also unlike the Individual Bearing Method, the number of helical plates on a pile is completely independent of the piles capacity based on the Torque Correlation Method.

Helical pile failure modes

You might want to also consider our Helical pile analysis software HelixPile 2012

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