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I frequently have to scan through pdf's and make sure certain entries are in them. Is there a way I can do this easily with excel? What I do is export the pdf as text (I will post an example below) and then will have a list of terms I need to make sure are in the text, for example:
List to check
ground
probing
300mm
british standard
in situ
Text to Check it in
Chapter 5
Subsurface exploration: boring, drilling, probing and trial pitting
INTRODUCTION
Chapter 4 considered the various indirect methods by which the ground can be investigated, using geophysical techniques. Whilst these methods can be extremely valuable for ground investigation purposes, they are not in everyday use. The bulk of ground investigation is carried out using the direct methods of investigation described in this chapter, coupled with in situ or laboratory tests.
The primary functions of any ground investigation process will be one of the following:
1. locating specific ‘targets’, such as dissolution features or abandoned mineworkings
2. determining the lateral variability of the ground;
3. profiling, including the determination of groundwater conditions;
4. index testing;
5. classification;
6. parameter determination.
Geophysical methods can be very good at giving information on the location of specific targets, and investigating the lateral variability of the ground, but their results are often more qualitative than is preferred by design engineers. Parameters for engineering design most commonly are derived from in situ tests carried out in boreholes or from self-penetrating probes although, as was noted at the end of Chapter 4, seismic geophysics methods can give valuable information on the stiffness of the ground. Most profiling is done on the basis of soil and rock descriptions, carried out either on samples obtained from boreholes, or on the faces of trial pits or shafts. And the majority of classification and index testing is carried out on samples taken from boreholes and trial pits.
Therefore the direct methods of testing described in this chapter are at the centre of routine ground investigation. They provide the opportunity to obtain samples for visual description and index testing, which are the primary ways in which the strata at a site are recognized, and for sampling and much of the in situ testing needed for parameter determination, as well as allowing the installation of instrumentation such as piezometers.
Boring is carried out in the relatively soft and uncemented ground (engineering ‘soil’) which is normally found close to ground surface. The techniques used vary widely across the world. The most common methods are augering, washboring and (in the UK) light percussion drilling. This latter technique is well adapted to stoney soils, and has its origin in water well drilling techniques.
Drilling has traditionally been used in the more competent and cemented, deeper deposits (engineering ‘rock’). It is now also widely used to obtain high-quality samples of heavily overconsolidated clays, for specialist laboratory testing. Both of the above methods can produce holes to great depths, which can be used for in situ tests as well as for sampling, and can allow the installation of instrumentation (for example, to measure groundwater pressures).
Probing is increasingly being used as a cheap alternative to boring and drilling. It is used as a qualitative guide to the variation of ground conditions, and is particularly valuable for profiling. The
Boring, Drilling, Probing and Trial Pitting
techniques used are often fast, and are generally cheaper than boring and drilling, but they cannot be used to obtain samples or to install instruments.
Finally, examination in situ, by trial pits and shafts, provides by far the best method of recording both the vertical and lateral ground conditions. Borehole methods generally only take restricted samples, perhaps at every metre or so of depth, for engineering description. Rotary coring normally attempts to recover continuous core, but cannot give a guide to lateral variability, and gives only restricted information on discontinuity patterns in the rock. But trial pitting allows continuous description of soil conditions over the entire face of the pit or shaft, allows measurements of discontinuities in rock, and in addition permits very high quality samples to be obtained.
An understanding of these techniques is important not only because they represent the major element of cost in a ground investigation, and must therefore be used with care, but also because the way in which they are selected and used can have a great effect on the quality of site investigation.
BORING
A large number of methods are available for advancing boreholes to obtain samples or details of soil strata. The particular methods used any country will tend to be restricted, based on their suitability for local ground conditions. The principal methods used worldwide are:
• light percussion drilling;
• power augering; and
• washboring.
Light percussion drilling
Often called ‘shell and auger’ drilling, this method is more properly termed light percussion drilling since the barrel auger is now rarely used with this type of equipment. The drilling rig (Fig. 5.1) consists of:
1. a collapsible ‘A’ frame, with a pulley at its top;
2. a diesel engine; connected via a hand-operated friction clutch (based on a brake drum system) to
3. a winch drum which provides pulling power to the rig rope and can be held still with a friction brake which is foot-operated.
The rope from the winch drum passes over the pulley at the top of the ‘A’ frame and is used to raise and lower a series of weighted tools on to the soil being drilled. The rig is very light, and can be readily towed with a four-wheel drive vehicle. It is also very easy to erect, and on a level site can be ready to drill in about 15 mm. Where access is very limited, it can be dismantled, and rebuilt on the other side of an obstruction such as a doorway.
In clays, progress is made by dropping a steel tube known as a ‘claycutter’ into the soil (see Fig. 5.2). This is slowly pulled out of the borehole and is then generally found to have soil wedged inside it. The claycutter normally has a solid or slotted weight, called a sinker bar, attached to its upper end, the top of which is connected to the winch rope. When the claycutter is withdrawn from the top of the hole, the soil is removed with a metal bar which is driven into it through the open slot in the claycutter side.
In granular materials, such as sands or gravels, a shell is used. At least 2 m of water is put in the bottom of the borehole, and the shell is then surged, moving about 300mm up and down every second or so. Surging the shell upwards causes water to be drawn into the bottom of the hole, and this water loosens the soil at the base of the hole and forces it to go into suspension. As the shell is dropped on the bottom of the hole the mixture of soil and water passes up the tube of the shell, past the simple
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Site Investigation
non- return valve (sometimes called a ‘clack’). As the shell is raised, the clack closes and retains the soil, which precipitates above it.
Fig. 5.1 Light percussion drilling rig (Pilcon Engineering Ltd).
By repeatedly surging the shell up and down at the base of the hole, soil can be collected and removed from the hole. The casing should either be allowed to follow the hole down (if it is loose) or should be driven so that it is just above the base of the hole, otherwise progress will be slow, and either large cavities will be formed on the outside of the casing or the soil will be loosened for a considerable distance around the hole. Of course, casing is nearly always used with the shell, because most granular soils will not stand vertically if unsupported in the presence of water.
Casing is not only used when drilling in granular soils, but is also necessary when drilling in very soft soils or when drilling in clays, to seal off groundwater after it is encountered. The presence of water in the base of the hole will allow samples to swell, but the reason that most drillers seal off water is more basic: stiff plastic clays become difficult to recover with the claycutter if large quantities of water are present and if this water cannot be controlled the driller will usually be forced to drill more slowly using the shell.
In the UK, where large parts of the South-east have stiff clays which provide ideal drilling conditions, the light percussion rig normally has 1000—1500kg capacity and most commonly uses 150—200mm dia. casing and tools. It will have little difficulty in boring to 45 m depth in a very stiff clay such as the London clay, but in sandy soils more casing sizes will often be needed to reduce friction.
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Boring, Drilling, Probing and Trial Pitting
Fig. 5.2 Light percussion drilling tools.
The friction transmitted by sand or chalk to the outside of casing will often be too great to allow the rig to pull more than 10—20m of casing out of the ground without the use of short-stroke hydraulic jacks. Under these conditions strings of casing of different diameters are used to allow a greater depth of drilling. As an example, if a borehole were to be advanced to 50m in sand, the driller might start the boring using 300 mm dia. casing and tools and drill until the rig began to have problems pulling the casing, which might occur at 15 m depth. At this stage the driller would insert a string of 250 mm dia. casing and pull back the larger casing 1 m or so to make sure that it would still be loose at the end of boring the hole. The inner 250 mm dia. casing, of course, would receive no friction on the upper 14m of its length, and the hole could now be advanced until its second string became tight, when a 200mm string of casing would be inserted at, say 30 m below ground level (GL). At the end of boring the hole might be cased with four different sizes, as in Table 5.1.
The minimum casing size possible in Britain is 150mm dia., because this is the smallest size allowing the use of the British Standard General Purpose 100mm dia. sampler (BS 5930). The casing used in the UK is square threaded and flush coupled, in contrast to the drive pipe’ in use in the USA which is
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