Stratigraphically Berea Red sand overlies the Basal Boulder Bed which overlies shales of the Pietermaritzburg Formation. Well, as the day went on I began to find boulders mixed in with weathered shales and the Berea sands, which was not tying up with the geology of the area. Then I began to find evidence of disturbance in the shales themselves and just after lunch came across a gun-metal grey clay horizon exposed in all four sidewalls of the pit. Some digging with the geological hammer and there lay exposed a highly polished, or what is known in the trade as a slickensided, surface. Hard evidence indeed for a land slip on the site at some stage in its geological past. To develop the site would have been foolhardy but unfortunately some of the stands had already been sold and the earthworks were in full swing, so of course my news wasn’t what the developer wanted to hear.

Well, we went back to that site twice more with a large excavator to prove to the client and the engineer what we already knew. There were of course some politics attached to the geotechnical report, and we were at one stage pressured to play down the significance of the findings, but could not for obvious reasons. There were several lessons to be learned from this experience. Firstly my blood ran cold at the thought that one of our young geologists might have done the fieldwork and may not have picked up on the significance of the disturbed geology, and that it was imperative that they be made aware of these kinds of situations and would be able to recognise them in the field should they arise.

Secondly, one needs an understanding of geology and the local stratigraphy to be able to subtle but vital changes in the local conditions. Thirdly, from a developers and civil engineering point of view it is imperative that a geotechnical investigation be carried out right at the outset to determine the underlying ground conditions. In our case the geotech had been done belatedly which caused a great deal of trouble for the developer but actually saved his bacon in the longer term, as a catastrophic slide of houses into the valley below would have had him tied up in litigation for years. I had an ex boss whose mantra was ‘you will get a geotechnical investigation whether you want one or not’ and he was right.

Settlement, subsidence, slope instability, collapse, influx of groundwater, or the failure of road pavements are just some examples of the type of damage that might occur to infrastructure founded on unforgiving soils or rock. Trouble may come knocking suddenly during a period of heavy rain, or may take place over a number of years as a house founded on an expansive clay is systematically demolished as the soils take up moisture or dry out over the seasonal wet and dry cycles. Only by carrying out a thorough assessment of the geology can one be sure that the long-term integrity of the structure is ensured. I think that I have made my point.

Geotechnical investigations are always carried out for large scale structures – tunnels, bridges, dams or large buildings. But too often it is neglected in the smaller projects, an approach, as we have seen, can be fraught with unforeseen hazards. Geotechnics has been part of my life for over twenty years, in a career that has included site investigation work in England, Germany, Southern Africa and Middle East. Some of these international jobs have been the large projects – both large dams on the Lesotho Highlands Project, a dam site in Oman, tunnels in the Italian Dolomites, the upgrade of Chapmans Peak drive, the massive bridge crossings for the proposed new N2 in the Transkei and finally the Gautrain Mass Rapid Transport project. Then of course there is a myriad of smaller jobs ranging from groundwater contamination assessments to 100 km long pipeline investigations for the local water utility. We are well positioned then to assist with any engineering project and it would be fantastic if we could be involved to prevent any unforeseen surprises from rearing their heads during the design life of a structure.

In 1956 the institute moved to a research park close to the University of Oslo and has had close associations with the Technical University of Norway since 1957. In 1972 the Norwegian Parliament made the NGI responsible for avalanche research in Norway, in 1983 the Institute for Rock Blasting Techniques was embodied into the NGI and in 1989 the institute was given an award by the ISSMGE (International Society for Soil Mechanics and Geotechnical Engineering) for ‘Outstanding contributions in the field of offshore geotechnical engineering. 2002 saw the NGI being appointed as a Centre of Excellence by The Research Council of Norway with responsibility for the International Centre for Geohazards and the establishment of a Houston office in the US.

Some of the geotechnical greats have been associated with the NGI, including Laurits Bjerrum and Nilmar Janbu, names familiar to anyone who has done a course in soil mechanics. Perhaps the highest accolade for the institute was when the acknowledged father of modern soil mechanics, Karl Terzaghi, donated all his books and papers to the institute, and which are now housed in the library bearing his name.

Since 1953 the institute has built a formidable reputation and is internationally recognised for its technical excellence, having carried out research on soft clays, tunnels, embankment dams, slurry walls, marine clays, foundation solutions for offshore structures for the oil industry, rock engineering, avalanche protection, environmental geotechnics, georadar, geomechanics mapping oil reservoirs, earthquake hazards, and tsunami risk evaluation. Some of its projects have been world firsts, attesting to the unerring pursuit of excellence which embodies the organisation.

The NGI is a global player, with approximately 30 per cent of its work on projects outside Norway. For those interested, have a look at www.ngi.no/en/. Impressive to say the least and one wonders if they are subject to the pernicious 3 quote system or whether their services are treated as a disbursement.

Ralph B Peck, 1988

For those not in the know, Ralph Peck is known as “the godfather of soil mechanics”, and in his day was directly responsible for a succession of celebrated tunnelling and earth dam projects that pushed the boundaries of what was believed to be possible.  In a way, Peck has summed things up totally and it could be argued that there is nothing more to be added on why geotechnical engineering in general, and instrumentation in particular, is so important.  But then again, some elaboration may be called for and here is why we should instrument our civil engineering and mining projects.

Firstly, there are enormous benefits to be had during the design of a project.  Instrumentation may be used to assist in assessing the in situ geotechnical conditions during the design phase.   A simple example is the installation of piezometers to monitor groundwater levels and hydraulic head.  More complex examples include the assessment of in situ stress and deformability conditions in the design of tunnel linings or large, underground excavations.  By understanding the geotechnical conditions, a more focussed and optimal design can be arrived at.

Furthermore as Peck indicated earlier, designs have inherent uncertainties and to a large extent these are circumvented by using conservative design parameters and that fantastic fudge factor called the Factor of Safety.  However if we were to reduce the degree of uncertainty in a design by carrying out a proof test, then the advantages thereof need not be spelled out.  A proof test will include observations on behaviour, and may well include instrumentation.  A proof test allows the designer to choose an economical design over an ultra conservative one when ground conditions are not fully understood or construction methods are uncertain.

Then there is the issue of crisis management.  Should a crisis arise, the nature of the problem needs to be defined so that remedial measures can be implemented, and instrumentation, if correctly installed, can play a crucial role in this.

Secondly there are benefits to be had during construction, including improvements in safety for the construction workers and the public, a reduction in construction costs, greater control over construction procedures, and an enhancement of public relations, particular with regard to the very large projects which will affect the public if any crisis were to occur.  The installation and monitoring of instruments also provides legal protection in an increasingly litigious environment, indicating firstly a ‘duty of care’ to the project, including personnel, public and the client, as well as providing hard evidence should a failure occur.  And perhaps almost as importantly, by installing instruments we get to sleep easy.

We are already comfortable with the idea of instruments to remotely monitor behaviour.  A broken fuel gauge is going to eventually lead to a long hike to the filling station; a broken speedometer will lead to friendly discussions with a traffic officer and we wouldn’t dream of operating without these feedback systems.  We should apply the same philosophy to our civil engineering and mining projects.

SISGeo Geotechnical Instrumentation is officially represented by GeoZone GeoServices here in Southern Africa and as such are well placed to supply a wide range of instruments for any civil engineering or mining project.  The Italian based company designs, builds, calibrates, sells, installs and monitors instrumentation systems for use in the areas of rock and soil measurement throughout the world.

We are able to supply, install and monitor the following range of instruments:
•    Pressure Transducers
•    Inclinometers Settlement Gauges
•    Pressure and Load Cells Extensometers & Joint meters
•    Pendulums & Readouts
•    Strain Gauges & Thermometers Readouts,
•    Dataloggers & Accessories
•    Dual Height Tell Tales

We have a duty of care, perhaps a sacred trust, to ensure that our projects are designed and managed with integrity, and instrumentation can go a long way in assisting in this regard.

Ralph Peck

Influential American civil engineer whose innovations earned him the sobriquet ‘the godfather of soil mechanics’

This is a sobering statistic and it certainly doesn’t get the dramatic coverage that say Hurricane Katrina received. Admittedly there wasn’t the same loss of life and human suffering, but having said that the costs and problems associated with damage to structures brings its fair share of heartache. South Africa is no less susceptible to heaving soils and it was de Bruyn, Collins and Williams in 1956, consolidated by van der Merwe in 1964, who did much of our pioneering work on heaving clays in the Highveld. Heaves in excess of 23 cm over a 5 year period have been recorded and it takes no imagination to realise that any structure founded on this material will be irreparably damaged if no precautions are taken during construction.

However many people are totally unaware of the effects of heaving soils and this is probably due to the slow rate at which the damage occurs. The effect is insidious and cannot be attributed to a single event – the damage then being ascribed to poor construction methods. Clays have an inherent ability to expand as they take up water into their crystal lattice. Similarly they are able to contract as they become desiccated. Most of you will have seen desiccation cracks in dry river beds, where layers of mud have dried out to form a crazy-paved surface with the underlying sand clearly visible through the cracks. These contractions are due to loss of water from the clay. Perhaps one of the most radical clays around, Sodium Montmorillonite – commercially known as Bentonite –can expand up to twelve times its volume when wetted up. Imagine a cubic centimetre of this material, not much larger than a sugar cube, swelling to 12 times that size. The addition of water causes the sodium ions to hydrate, generating a negative charge on the Bentonite plate. Since like electric charges repel each other the platelets are moved apart causing heave. This is an extreme example, but montmorillonite clays in general have a propensity to heave with associated damage to any structure founded thereon.

The National Home Builders Registration Council has acknowledged the dangers of expansive soils and set out regulations on how best to mitigate these effects. The amount of heave which may take place is a function of both the activity of the clay and the thickness of the clay deposit. The cumulative heave of say three metres of low expansive clay will be greater than that of say one metre of highly expansive material.

In this light then it is important that the geology of any site is understood, that an assessment of the underlying soil moisture condition is made, that the soil structure is examined for fissuring and slickensiding and that the buildings in the vicinity are inspected to determine if they have been subject to heave damage. Foundation indicator tests will determine the clay content and Atterberg Limits of the material, from which an indirect assessment of the mineralogy and the heave potential can be made. Only then can a realistic assessment be made of the founding conditions of the site, and based on this the correct foundation recommendations be given. It always astounds me however that more money will be spent on the Italian tiles for a house than on a decent foundation assessment. Any unforeseen heave will put paid to any fancy tiles, finishes and perhaps the entire structure.

Collapsible soils are known to comprise a mixture of coarser sand grains in a matrix of finer material, with intermolecular, electrostatic, capillary and chemical bonds assisting in holding the soil mass together.  They generally have a low density, are highly voided and the soil fabric may well collapse if they are loaded and allowed to take up moisture.  Which is exactly what often happens on a site when construction starts.  Earthworks upsets the natural ground conditions, there is increased run off due to the vegetation being stripped, water ponds on badly drained platforms, and then sewer and water lines are installed, both of which have the potential of leaking water into the soils.  Or perhaps a septic tank and French drain system is installed which, by its very nature, is designed to put water into the ground.  Once the soil is wetted up, collapse may well be imminent with, of course, associated damage to the structure.

In short then, great care must be taken in identifying problem soils on site, and once identified, preventing the collapse described above.  Various methods are available for determining if soils are potentially collapsible, beginning with identifying the geology, in situ observation of voids in the soil,  cone penetrometer tests, density tests, and more comprehensively but perhaps not more conclusively, collapse potential and one dimensional triaxial tests.  If problem soils are identified on a site, then the necessary precautions need to be taken to prevent damage occurring, which include drainage precautions, removing and recompacting the offending soil horizons below the structure, attending to drainage or perhaps piling through the collapsible soils if the building is particularly sensitive.

Armed with all this knowledge I came home to apply it, only to find that it was in many ways irrelevant, due to a number of reasons.  I found that I was digging test pits at 200 to 300 m spacings, that no one was doing any kind of real laboratory testing, shear strengths were being guessed at, SPT N values, so much at the heart of bearing-capacity calculations, were unavailable. The bearing capacity equation became a trifling, discarded on the rubbish heap labelled ‘no budget’. What were the characteristics of a soil or rock for which we were providing recommendations? No one was entirely sure.

Perhaps there was another factor playing itself out – a lack of understanding by management of the subtleties of soil mechanics and an unspoken acceptance that this work was beyond the scope of the engineering geological community.  Maybe this was due to many ‘engineering’ geologists having received no formal training in the subject, with associated lack of numerical skills and a lack of a profound understanding of the testing and interpretation thereof.  For whatever reason, the outcomes have not been entirely satisfactory.  There are too many cases of broad brush, fudged, reports – written to cover a lack of knowledge due to inadequate site investigations, lack of laboratory testing and to some extent a lack of understanding of the geotechnical complexities which often prevail on a site.  There is also a willingness by the engineering geological community to defer to the engineers, which is understandable seeing that the engineers are ultimately responsible for their designs.  However if the engineering geologists are to ensure the integrity of their profession, they need to be more forthright in their view of what needs to be done in terms of characterising a site.

It all boils down to getting good information.  I need to dig enough test pits, take enough samples and conduct enough laboratory tests to build my geotechnical model.  In my opinion one test pit per 10 hectares is not enough, which is part of the recommendations given in the Guidelines for Urban Engineering Geological Investigations in South Africa.  I know some of you will say that the guidelines cover various scenarios – namely, investigations for planning, investigations for urban development and specialized geotechnical investigations.  But all too often a site only gets one geotechnical investigation, and that is the low budget, planning one – and as a result there is not enough information to thoroughly assess the prevailing geotechnical conditions.  And bear in mind that the guidelines themselves state that they are “the minimum requirements.”  Why do we have to go with ‘minimum?’  What happened to ‘best?’ And then the title says it all – ‘guidelines’.

Don’t get me wrong – I am grateful that there are such guidelines, and it in some ways they make our lives easier.  But it means that everyone in the engineering geological community, particularly when the insidious 3 quote system is being applied, will price a job based on the minimum requirements to win the work.  I don’t think I need to spell it out, but as we all know, we get what we pay for.  So to all the engineers out there, it is probably not be in your best interests to insist on the 3 quote system as you may well be getting a substandard product.

And in this light I am going to tell you my geotechnical fantasy and in doing so I beg your indulgence.   Wouldn’t it be absolutely fantastic to have a well written geotechnical report based on a decent number of test pits, dynamic probing and laboratory tests?  If a multi-storey structure is to be built, well, I would like to drill boreholes and carry out Standard Penetration Tests.  If I am looking at the stability of a slope I need to know the shear strength parameters of the soils which make up that slope and so undrained and drained triaxial tests are necessary.  It might of course be a cutting in rock – again I need to characterise the shear strength of the discontinuities.  And on another note, there has been so little triaxial testing carried out in South Africa in recent years that it can be argued that those skills have been lost to the engineering fraternity, which is a tragedy in its own right.

In summary then, all of us, whether engineering geologists, civil engineers or planners, need to beware of adopting a laid back attitude to the substrate on which all our civils projects are founded.  Dedicated geotechnical professionals with an eye both for the geological and civil implications of any project are to be valued.  Geotechnics is in many ways a dark art, and only by throwing the cold light of enquiry into those dark recesses can we hope to be of benefit not only to our clients, but to ourselves.  We here in South Africa are so good at many different things, often working under difficult circumstances, and in spite of this we are at times world beaters.  Perhaps we could beat the world on the geotechnical front too, or at least aspire to a far higher standard to which we currently hold ourselves.

SISGEO Geotechnical Instruments, based in Milan, Italy has an operation comprising more than 1200 square metres of laboratories, production facilities and warehousing with an associated technical staff to design, build, calibrate, sell and install their systems. Sisgeo manufactures all of their instruments, only importing GPRS technology for on-site monitoring of their equipment.  The company is a leading designer and manufacturer of a wide selection of instruments for use in the area of rock and soil measurement and has an ISO 9001 Certification which forms the basis of their continuous improvements and quality control programmes.

So why instrument?

Well, to spell things out, here are the reasons why we should instrument our civil engineering and mining projects:

1)      Benefits During Design

1.1    Definition of Initial Site Conditions

Instrumentation may be used to assist in assessing the in situ geotechnical conditions during the design phase.  A simple example is the installation of piezometers to monitor groundwater levels and hydraulic head.  More complex examples include assessments of in situ stress and deformability conditions for design of tunnel linings or large underground excavations.  By understanding the geotechnical conditions, a more focussed and optimal design can be arrived at.

1.2    Proof Testing

All designs have inherent uncertainties and to a large extent these are circumvented by using conservative design parameters and that fantastic fudge factor called the Factor of Safety.  However if we were to reduce the degree of uncertainty in a design by carrying out a proof test, then the advantages thereof need not be spelled out.  A proof test will include observations on behaviour, and may well include instrumentation.  A proof test allows the designer to choose an economical design over an ultra conservative one when ground conditions are not fully understood or construction methods are uncertain.

1.3    Fact Finding in a Crisis Situation

Should a crisis arise, the nature of the problem needs to be defined so that remedial measures can be implemented, and instrumentation, if correctly installed, can play a crucial role in this.

2)      Benefits during Construction

These include:

•        Improvements in safety for the construction workers and the public

•        Reduce construction costs

•        Control construction procedures

•        Provide legal protection

•        Provide data for measurement of quantities

•        Enhance public relations

•        Advance the state of the art, and finally

•        We get to sleep well at night.

Safety of course is paramount and instrumentation can provide the needed safeguards.  In addition there is a need to monitor the effects of construction on neighbouring structures.  Use of instrumentation for safety monitoring is routine during excavations for builds, tunnels and highways.

SISGEO manufactures and installs the following range of instruments:

•        Pressure Transducers

•        Inclinometers

•        Settlement Gauges

•        Pressure and Load Cells

•        Extensometers & Joint meters

•        Pendulums & Readouts

•        Strain Gauges & Thermometers

•        Readouts, Dataloggers & Accessories

For more information please see our Instrumentation page.
We also have experience of installing Golders RMT dual height tell tales in mines to monitor movement in the roof of excavations.  These instruments are relatively cheap and easy to install and are extremely useful for monitoring stability in temporary excavations.  The beauty of this system lies in their easily understood, readily readable tell-tales.  Any movement within the roof is immediately registered on the mm scale on the tell tale, and larger movements move the tell tales from green to orange and finally into the red zone.

I shall digress somewhat now and talk about a book I keep beside my bed – “The Little Big Things” by Tom Peters.  Now Tom is an American, and Americans can be prone to lapses into Pollyanna niceties and the ‘feel good’ syndrome, but Tom is another creature altogether.  He tells it as it is.  He is also an engineer which says a great deal.  The book is about the pursuit of excellence, a subject to which he brings his own particular brand of passion.  Mostly the book is about paying attention to the small things, which are actually the big things.  He talks of integrity and sacred trust, which may be old fashioned concepts in this day and age, but he is perhaps of an earlier generation.  And talking of telling things as they are, on his blog he got on his high horse about the oil spill in the Gulf of Mexico last year, and had this to say:

I also find myself beset with newfound anger-outrage at numerous engineers employed by BP, et al. (Many an “al.” it would appear.) Outrage not at “BP engineers,” but outrage at Arthur N. Smith [fictitious name], certified and licensed engineer. And doubtless dozens and dozens, probably hundreds, of his cohorts.
BP seems to have gotten it wrong on a dozen dozen dozen engineering dimensions. In the name of cost control or whatever. I don’t give a shit about the cost control issues, real as I know they are. I give a hundred shits about the fact that Arthur Engineer and Ralph Engineer and Mary Engineer, cross-pressures notwithstanding (that’s life), abrogated their professional responsibilities as … individuals. Arthur and Ralph and Mary are probably good parents—but professionally they screwed their fellow citizens to a fare-thee-well.
And I’m pissed off.
Very pissed off.

Arthur and Ralph and Mary have bills to pay. And the economy is tough. And their bosses, responding to their bosses, doubtless did put merciless pressure on them.
Hence my empathy is high.

But in the end I am appalled. They have cost us lives and economic and environmental damage of epic proportion. Because they lacked the will and integrity to blow their professional whistles and stand up for the discipline to which they have sworn allegiance.

They are (individually) a disgrace to the great tradition of engineering of which I am the smallest part. So I’m taking this personally.

www.tompeters.com/dispatches/011687.php

Strong words perhaps, but I admire his passion.  Which now brings me back to geotechnics.  I seem to spend much of my time writing proposals and filling in BoQ’s.  Some of these BoQ’s are for large dam contracts which I get to see only because we are pricing the instrumentation side of things.  What I find appalling is that in so many of these projects, ranging from the smallest house investigation to a large dam, the geotechnical aspects are not given the attention they deserve.  In fact on the last dam job we priced there was no provision for any geotechnical staff in the BoQ.  Perhaps worse, the geotechnical scope of works has been written by someone who doesn’t understand the subject, and we, the geotechnical consultants, have to price a job which we believe does not adequately address the geotechnical issues.  Putting in money for some extra testing for example makes my bid uncompetitive, but then there are salaries to pay, mouths to feed and the landlord wants his money by the 1st of the month, so let us just do the minimum to get the job.  Excellence indeed!

Which brings me back to those shear strength parameters we were discussing earlier. I want to know what the behaviour of a soil is.  I don’t want to suck my thumb, or whatever else we are meant to do to arrive at those numbers.  I have a duty of care, a sacred trust, a professional responsibility to make sure it is done right.  We do not want to find ourselves in the same position of our erstwhile BP engineers discussed above.  And so I must take a leaf out of Tom’s book and bring some passion to this issue.  And so we need to run that race of excellence, all of us, from the foundations to the top structure. Please.

“I believe that the Mother of … all Innovation is fury. Abiding anger at the way things are….. coupled with “irrational” determination to beat back the innumerable protectors of the status quo and find and implement a better way.”

Tom Peters 2010

Desk study

Someone may pay you to do this, and if so then you will have a bit of time to scratch out what is available and go through the historical documents pertaining to the site. A desk top study can mean a number of things to different people. Working in the UK we had a duty of care to lay our hands on every map, every drawing and every document that we could to ascertain the history of the site. This was time consuming and expensive but would often reveal a wealth of information on the development and geological history of the site. However the circumstances are slightly different as there can be a 300 year development history attached to some of those sites, and one needs to get an understanding of what has gone on over the centuries to be able to assess contamination levels, the location of fills, water courses and so on. That said here in South Africa we are often dealing with green field sites (i.e., no developmental history) or sites where there has been limited human impact and in this light the desk top study might not be as critical.

Whether you are getting paid or not for a desk top study, it is always worthwhile trying to get an insight into what underlies the site before actually carrying out any fieldwork. The first stop is the geological map – these are one of the greatest repositories of geological information available and we must take our hats off to the geologists of the Geological Survey who have braved heat, dust, rough camps, political instability, buffalo bean, mosquitoes, flooded rivers, wild drillers and probably every affliction that you can list to produce those wonderfully coloured and amazingly informative sheets of paper. But I digress. Get the geological map out, find your site, find out what the geology is and you are part of the way to building a good geological model of the area. Google Earth is a wonderful tool, so have a look at the satellite imagery if you can. Then of course there are orthophotos and topographical maps available from the Surveyor General should the need arise or you need contour data. Garmaps also will sell your contoured mapping data if you need integration with your GPS handset.

FIELDWORK

There are different levels of fieldwork, ranging from a cheap and nasty walkover survey to a full blown test pitting and borehole drilling exercise that can last for months in some instances.

Walk Over Survey

Geologists will be familiar with the walkover survey – it is in essence a mapping exercise in which the following issues need to addressed:

· Geological boundaries

· Thicknesses of soil and soil types

· Location of hard rock outcrop and boulder fields

· Presence of surface water

· Presence of wetland areas

· Areas showing signs of previous instability, mass wastage or potential rock falls

· A very South African concern – the location of graves

· Location of houses, buildings or other infrastructure

· The nature of neighbouring properties and the state of the infrastructure

· Slope gradients

· Vegetation

· Access

· Presence of services, servitudes and overhead powerlines

Test Pit Investigations

The next step up, and perhaps one in which you will be consistently involved, is the test pitting investigation. You may not have the luxury of walking over the site beforehand so you will need to address all the issues listed under the Walk-over survey above, as well as dig, log and sample the test pits. Please have a look at the advice on test pitting, as much has been written on this already. However a few points need to be discussed here. Once on site with the TLB, get the operator digging as soon as possible. The location of the first pit is not that critical, so once he is set up you can catch your breath and get organised. The number of test pits that you need to dig will depend on the proposed budget. If there is a day’s fieldwork set aside for the job, then aim to dig 12 to 15 pits at least. Judicious use of a scale rule will quickly allow you to pencil in provisional pit positions across the site based on the site dimensions divided by the number of pits required. It is perhaps better not to number them at this early stage as some of the provisional positions might have to be bombed due to access issues, lack of time or other unforeseen circumstances.

Plan on at least 2 pits per hour, and if you put your mind to it 3 is very attainable. If you really get into your stride, and if the geology is simple, access is easy, and the level of pit logging is not critical, then it may be possible to increase this number even more. But it is not a case of quantity over quality – far better a properly logged pit with good and thoughtful sampling than a slap-dash approach with all its attendant errors. For example when test pitting for a development it is important to spend time logging the pits. However if the investigation is for a pipeline where the bearing capacity is not so critical but depth to bedrock, pit stability and the water table are important, then a little less time can be devoted to the logging and the pits can also be logged from the surface.

It is perhaps best to postpone the sampling until say the third test pit of the morning, for it is only at this stage that a feel for the geology is beginning to develop. Bear in mind that for roads the action is all going to take place in the upper 0.5 m or so, so this is where you need to sample. However cognisance also needs to be taken of the fact that there will be cuts to accommodate the road and at times you will need to sample the deeper subgrade material. Take a minimum of two large sample bags of material, with say 10 to 12 shovels full in each bag. In terms of housing developments, heave is going to be one of your issues so take an indicator sample between 1.0 and 1.5 m as it is in this zone that heave will take place. Send the sample to the laboratory for a full indicator test including hydrometer. Pay attention to slickensiding, high clay content and pinholing. A fissured and slickensided soil is a good indicator of the presence of highly expansive clays. Bring this feature out in the logs – I sketch a skull and crossed bones to remind of my discovery when I have a pile of undifferentiated soil logs on my desk back in the office.

Try not to renumber log sheets back in the office. The field sheet may correspond to a label in a sample bag in a laboratory or a list of photographs of the test holes or a GPS position. If you really have to renumber, then make a list of all the old pit numbers and in a separate column list the corresponding new number. It may be worthwhile adding samples and/or photo numbers etc to this data base. Put this in the file with all the original data. When trouble then comes calling you always have the original data base to fall back on. It all sounds simple now, but it is exceptionally easy for things to go wrong when the house keeping isn’t in order.

GPS technology is fantastic and we often wonder how we managed without it. But it can also be a curse for it makes us lazy. From bitter experience, put the test position onto the site plan – whether it is a borehole, test pit, DCP position or percolation test. It is all too easy to forget to mark the waypoint, only to find a log for a test pit in the file, but with no waypoint position. Now if it is marked on the site plan then your problems are pretty much solved.

Perhaps some more needs to be said with regard to sampling. I never believe that there is enough budget for this. However you will no doubt be working with a budget produced by others so you will need to try and get representative samples of the various geological materials. Rather sample too much than too little – it is far cheaper to throw samples out than to have to go back to site and resample. Try and get a representative bulk sample of all the various soil and rock types which occur on the site. Colluvium, residual soils and highly weathered bedrock are all worth bagging. Make sure the samples are labelled and it is good practice to write on the outside of the bag too, as this assists the laboratory in finding your samples. Otherwise they have to scratch around in the soil itself for an often soggy, barely legible label. Cable ties are a good idea – it stops sample falling about in the back of the vehicle and maintains the moisture content until such time as the testing can be done. In this regard then the bulk sample can double up as an indicator sample. Indicator samples comprise generally around 1 kg or so of soil sealed up on a plastic bag. Self sealing plastic bags have made our lives a lot easier in this regard. Indicator samples are great if you are uncertain of the geology, feel a need to bring something home for the boss to see, if the material is highly slickensided or very clayey and you suspect that it is expansive and a test is required. They are cheap, quick and easy to take and give everyone peace of mind. Take those indicator samples – rather too many than too few.

Be careful with your log sheets. Some write their logs into a field notebook which they photocopy and put into the file and pass on for typing. I am not a fan of this method as it increases the chance for errors. It is infinitely preferable to make a pro forma sheet which you take to the field. The MCCSSO system can be listed, along with boxes in which the test pit number, descriptions, samples, founding levels and the occurrence of water are written. This forces you to tick the boxes so to speak. If there is no water, then say so, if there are no samples, then say so. It is removes uncertainty and inspires confidence in the logger’s abilities and thoroughness. For a copy of a pro forma logging sheet click here.

GPS technology aside, it is in most instances important that you keep a rough track of where you are on site. Setting out test pits at 200 m intervals can be a bind if you are alone, you don’t have a tape measure and the GPS is not helping. Get some idea of the length of your pace, and then pace things out. It can be remarkably accurate provided that you try to make it consistent. By knowing that you have walked approximately 300 m from a known position along the contour for example can be of great assistance in keeping track of where you are on site. So get used to pacing, and get used to counting.

Services

The bane of all our lives. If you dig test pits, get used to the idea that you are going to rip up power lines, sewer lines and water lines. It is always great entertainment when it happens, and generally speaking it is always late in the day when everyone is winding down and thinking of going home. So reduce the risks. Firstly try to get a drawing of where the services are. This is generally not possible, so take care of where you dig to reduce the chances of hitting services. Here are some tips.

• Don’t dig underneath power lines, as they often run pipes along the same servitude but below ground.

• Don’t dig on a line between manhole covers or other obvious markers

• Look out for pipeline markers – often white concrete beacons set in the ground at 100 to 200 m spacings. Don’t dig on these lines

• Water line off-takes run at 90 degrees from the main bulk water line to a water meter or tap in the front of a property. Needless to say, stay away.

• Sewer lines are often laid along the valley inverts as they are gravity driven, so avoid digging near the valley floor in built up areas

• Pipes are generally bedded in a sand pipe bedding, so pay attention to any subtle shift in colour within the soils or the appearance of sand in the excavator bucket.

• Hard digging when not expected may indicate a concrete water pipe, so get the operator to stop, get in the hole with a spade and find out what is going on down there.

• And finally, try to go to site armed with the local authority’s phone numbers. This is very useful when water starts to spray everywhere and you need to let someone know that you have just deprived the local community of their water supply for the night.

Good luck!