SMEC's Quarterly Magazine - Geotech & Tunnelling

SME SMEC Geotech & Tunnels

This quarter, SMEC has featured Geotech and Tunneling group highlighting some of the key projects delivered by SMEC. It also features a Q&A with SMEC's Geotech Chief Technical Principal, Dr. Jeff Hsi.

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Brom's Method for Short Pile

Following the the Brinch Hansen's Method, I share similar spreadsheet using Brom's method. Major disadvantage of this method is, it can not handle c-phi soil.

This spreadsheet is set to calculate lateral pile capacity using Brom's method for short piles. The procedure for calculation is straight forward and is explained in detailed manner in "Pile foundations in engineering practice" book by Shamsher Prakash. Brom's method is also available for long pile and will share it in a later post.

This method is applicable to either purely cohesive soils or purely cohesionless soils and hence soil properties to be entered accordingly.

Download broms_shortpile
[Update: The link was broken, it has been updated]

Brinch Hansen - Lateral Resistance of Soils - Free Head

The Brinch Hansen spreadsheet is set up to calculate lateral resistance of short rigid piles, for free head condition. The method is based on earth pressure thory for c-phi soils. It consists of determining the centre of rotation by taking moment of all forces about the point of load application and equating it to zero.

The spreadsheet uses Brinch Hansen's coefficients Kq and Kc to calculate the capacity. For intermediate values of Phi and z/B values, the spreadsheet does a two dimensional interpolation to calculate Kq and Kc values.

"Notes" worksheet covers the assumptions and limitations of the spreadsheet. The spreadsheet also calculates the maximum deflection of pile under maximum lateral load. This sheet can be used as a quick check for lateral resistance and ofcourse, almost in all cases pile design is governed by pile deflection.

The spreadsheet uses MS Excel Add-In "Solver" to calculate the location of virtual point of rotation (instead of using trial and error method).s

Click here to Download

[Update: The link was broken, I updated it]

Bearing Capacity (Single Layer)

The SBC-Single Layered spreadsheet is set up to calculate Bearing pressure of single layered soil. Although this is an idealized case and is seldom a practical soil stratification, this sheet can be used to compare bearing capacity values computed by following methods:

• Mayerhof (1963)
• Terzaghi (1943)
  
• Hansen (1970)
• Vesic (1975)
• Mayerhof (1956, 1974) - Correlated from SPT
• Schmertmann (1978) - Correlated from CPT

Download here.

SBC from SPT

Here is a small User Defined Function (UDF) to quicly calculate safe bearing capacity from SPT Value. 

Download SPTSBC UDF

Formula used: Bowles Book (5th Edition) - Section 4-10

UDFs have no tooltips but there is a workaround to display tooltip-like hints while using the formula.

• First import the sbtsbc.bas (In VBA window, CTRL+M to import .bas file)
  
• Start typing the UDF: =sbtsbc(then press CTRL+SHIFT+A)  and your function parameter will be displayed

Parameters for input are:

Er - Energy efficiency of the SPT Hammer (55% or 70%)

B - Width of the footing (m)

N - Fild SPT N value (blows per 300mm)

D - Depth of footing (m)