Site investigations - Data presentation in offshore geotechnical site investigations Data presentation in offshore geotechnical site investigations Jens Galsgaard GEO, Denmark, jng@geo.dk ABSTRACT In recent years, offshore wind farm projects in several countries around the Baltic and North Sea have made heavy demands on GEO’s data presentation techniques and tools used in reporting offshore site investigations. Different requests from different clients with different backgrounds make it necessary to report data in many different ways, "tailored" to fit each type of investigation. So a borehole log is no longer a borehole log, several different log layouts are required. This calls for conditional tools that will allow logs to be multi-purpose. – In 2008 GEO began to use gINT software in data reporting. This paper shows examples of this reporting, with data from offshore subsurface investigations presented in multi-purpose borehole logs, cross sections and site maps. Keywords: data presentation, geology, geotechnics, renewable energy, site investigations from different methods are compared. And the best way to compare data is to arrange 1 INTRODUCTION them next to one another. In the field of geotechnics, like in any scien- 1.1 Presenting offshore data tific field, data plays a very important role. In recent years, GEO has carried out a num- Data provides the basis for the computations, ber of big offshore geotechnical investiga- modellings, classifications, evaluations, etc. tions, mainly for wind farms in sea territories that form the main part of a typical geo- technic ian’s work. Data is the input that later of both Denmark and her neighbouring countries. As the clients of these jobs were enables the design of a construction or other often foreign, they often requested sampling, engineering item to be put out. geological descriptions and laboratory tests to Data must, of course, be readily available be performed according to their own national for the geotechnician to work with, both as standards. For the first jobs, this posed some regards acquisition and presentation: e.g. first considerable challenges to data presentation, carry out boreholes in the field with insitu because GEO’s software used at the time for tests and sampling, then perform geological reporting borehole data did not have options classification and lab tests on retrieved sam- for these foreign approaches. It was therefore ples; and finally present all of this data. This decided to instead try and use the internation- paper addresses data presentation, with re- ally well-known gINT software for the re- spect to user-friendliness. porting of foreign offshore wind farm geo- For various reasons, e.g. lack of time, old technical investigations. habits or insufficient focus on user-friendli- This paper contains examples of various ness, data from different sources or acquisi- data presentations, i.e. borehole logs, cross tion methods are often being presented in sections and site maps that have been de- different places in a report, which makes it signed at GEO with gINT software. The difficult to get an overview. In fact, the au- thor believes it to be common knowledge – design of all the examples was chosen at even if not often expressed – that the best user-level, and none of the examples have been modified by other software after the way to arrange data is to enable the geotech- gINT processing. In the printed version the nician to view all of the relevant data on one examples are shown at reduced scale, due to piece of paper, or on one computer screen the layout, but in the electronic version they image, i.e. in one view. Because the best may be watched at full scale. technical overview is often gained, when data 1
Site investigations - Data presentation in offshore geotechnical site investigations Figure 1. Example of GEOs new offshore borehole log. Full scale log width (here height) 275 mm. 2
Site investigations - Data presentation in offshore geotechnical site investigations 2 LOG EXAMPLES Like its predecessor, GEO’s new multi -pur- pose offshore log is in A4 landscape format. The log is divided into 11 columns, some of which are further subdivided by thin lines, giving a total of 25 columns, see Figure 1. From left to right the columns display data from the sequence of processes pertaining to a borehole: 4 columns to the left show drill- ing and sampling methods and results, to- gether with a depth scale; the next quite wide column is subdivided into five columns that show both numerical, graphic and text results of geological classification; the next five col- umns, of which the first two are subdivided, all show numerical data, namely test results of samples and lab specimens, as well as from CPT insitu tests; the rightmost columns show the location of tests the results of which can not be displayed on the borehole log, like grain size distributions, consolidation and triaxial tests, and must be found elsewhere. The log is kept in black-and-white, except for the graphic log column in the geology section, where black grain size graphics are underlain by a coloured fill that corresponds to the geological formation, see Figure 1, or the standard Danish deposit-and-age codes, see Figure 3. Whereas these colours are, strictly speaking, redundant on the borehole log – although they do help to present the geological model – they are very useful on cross sections, or fences, where there is no text to explain the graphic log, see Figure 4. Especially with deep boreholes, some cli- ents prefer to view a longer section of the borehole in one page. The log therefore also has an A3 paper size option with 20 m per page, see Figure 2, instead of the normal 6 m, allowing more than three times as many data to be viewed in one view. One of the big challenges of designing the new borehole log was to fit all the columns with the necessary data into the 275 mm width of the log. Here the demand for over- view, i.e. fitting all the different data into one page, easily collides with the demand for legibility, i.e. to enable persons with a slight Figure 2. Part of A3 size borehole log with 20 m vision handicap – like most persons over the per page. Full scale height 337 mm. age of 50 – to also be able to read the log. 3
Site investigations - Data presentation in offshore geotechnical site investigations A B C Figure 3. Various log layouts, full scale width 275 mm. A: Core drilled borehole with competent limestone with fractures & hardness logging, overlain by glacial till. B: Flush drilled borehole with tube sampling through varied lithologies; notice N k and D r strength estimates from CPT data. C: Tube sampling in very soft seabed. Compare depth scales and shear strength and moisture content scales for A-C. 4
Site investigations - Data presentation in offshore geotechnical site investigations This matter was further complicated when new clients from other countries requested other tests on other soil or rock types to be included on the log. The solution was to allow different tests, not normally carried out together in that country or on those soil or rock types, to share the same column, or, in the case of the three gridded test result fields to the right, share the same column heading field, compare Figures 1 and 3A-C. In this way GEO’s new log developed into a multi - purpose borehole log, which can take many different appearances, depending on choises made by the user. One of the multi-purpose features of the log is it allows the user to change language, see Figure 5. 3 CROSS SECTION EXAMPLES Whereas the borehole log displays data from one borehole in great detail along one dimen- sion, borehole depth, the cross section dis- plays data from several boreholes in two geographical dimensions, along (the vertical) Figure 4. Fence with graphic log columns for two borehole depth and along a (horizontal) line boreholes, same project as Figure 1. Figure 5. Part of Danish language log of vibrocore drilled borehole. The client was mainly interested in grain size properties, and the five columns to the right normally used for core quality and density data were redesigned to instead show a summary of grain size data. 5
Site investigations - Data presentation in offshore geotechnical site investigations Figure 6. Series of boreholes through glacial till (beige) down into limestone (purple), separated by transitional zone of glacially disturbed limestone (white). Grey graphic to the right of each graphic log shows fracture degree of the limestone. Same project as Figure 3A. Figure 7. Series of boreholes through soils of varying strength (green and blue soils mainly soft/loose, red and beige soils mainly stiff/dense). Graphics to the right of each borehole show CPT tip resistance and CPT friction ratio (far right, scale reversed). Compare the grain size graphics of the coloured graphic log column with the grey-and- white “soil type” pattern produced by the two CPT curves . Same project as Figure 2. 6
Recommend
More recommend
