INSITU is a program for analysing the pressure versus displacement curves obtained from tests carried out with Cambridge Insitu pressuremeters. The program runs under MSDOS. It was first used in 1989 and has been updated many times to keep pace with new developments.
The program will run successfully on the simplest IBM compatible computer using versions of MSDOS 3.2 or later. Higher specification computers offer some speed advantages but do not improve the quality of the analysis. The program can also be run as a DOS application under Windows 3.1. The screen display can be colour or monochrome, but the printed output is black on white. The printed output is independent of the resolution of the screen.
The analysis that INSITU offers reduces the pressuremeter test curve to the soil properties of strength and of stiffness. The program incorporates all the standard solutions and these are implemented in a graphical manner. Typically, any single analysis routine offers a view of part of the pressure:strain curve plotted on appropriate scales. Changes of gradient or breakpoints in the plotted data denote significant soil parameters. The user is provided with on screen tools to mark these breakpoints or to obtain the slope. The tools can be visualised as rulers, and the final position of a ruler is remembered and stored by the program. It is usual to support any decision taken by providing a print-out of the screen display showing the placing of the ruler and quoting the parameters obtained.
Input for INSITU is either new data or a previously analysed test on disk. New data is a text file of pressuremeter test readings in engineering units. The logging software supplied with Cambridge Insitu pressuremeters makes a suitable file automatically. INSITU reads the text file once, and makes a single file special to the program which carries the ending FIL. Thereafter all operations are carried out on the data in the FIL file.
The FIL file includes all the pressuremeter test data including details of the calibrations. In addition the file includes a record of all the decisions made concerning the analysis of the test. This allows a particular analysis to be reproduced exactly at a later time. There is no requirement to print out the results of the analysis at the time of making the decisions. The FIL file is compact and despite incorporating much additional information is usually no more than 20% larger than the text file source.
Printout is on A4 sheets or similar, the plots are landscape and arranged to fill the page as fully as possible. Sub sets of the data can be written to disk as text files for manipulating with other software such as spreadsheet programs.
Setting up the program
There are four tasks that the user must carry out before any analysis can be undertaken.
As the figure shows, categories of data are labelled by shape as well as by colour. This makes it possible to identify the type of point on a monochrome display. Once the points are labelled the user can enter additional information about the test including any comments.
Fig.1 The editing screen
The analyses
For insitu horizontal stress:
For undrained shear strength and limit pressure:
For drawing the complete undrained shear stress:cavity strain curve:
For drained angles of friction and dilation:
For shear modulus:
Other graphs: The program allows any part of the curve to be separately plotted using axes of pressure or strain against strain or time. Log scales can be applied to assist in the derivation of time constants for the analysis of a holding test.
Future developments
The analysis of the pressuremeter test is subject to constant innovation.
At the present time there are two main areas of activity, not yet fully supported
by the Insitu program:
The analysis of the non-linear elastic response of soils is being incorporated into the program at the present time.
Iterative forward modelling is essentially the opposite of analysis. The purpose is to generate pressure:strain curves from strength and stiffness parameters chosen by the user. A good match between a generated curve and the measured data implies appropriate and self consistent parameters have been entered. There are no firm plans at the moment to implement this procedure although close attention is being paid to developments in this area.
Support
A comprehensive manual is provided that gives step by step guidance to the
use of the program as well as details of how each analysis is implemented
so that the results can be checked.
Free updates of the program are supplied on a regular basis. Improvements to the program are backward compatible. Files made on early versions of the program can still be read and used by later versions.
Only a few common types of printer are supported directly by INSITU. However a separate program for writing custom printer drivers is supplied, and this is straightforward to use.
Customising
The program as issued is anonymous. There is no reference to Cambridge Insitu
on any of the screens or print-outs. The option to enter two lines of footer
text is provided, allowing the user to quote any additional background
information that may be pertinent. This footer text is added automatically
to every printed page.
AGS format
There is a separate program which reads the FIL file and makes additional
files of the data and parameters to AGS (Association of Geotechnical Specialists)
format. There are plans to merge this separate program into the main program
as well as enable INSITU to accept such files as input.