1 TITLE PROCESS FOR EXPOSING UNDERGROUND UTILITIES FIELD OF THE INVENTION The present invention relates to the field of excavation. More particularly, 5 the invention relates to a process for excavating an area where there is a danger of damage to underground utilities and infrastructure. BACKGROUND TO THE INVENTION Modern cities require an extensive range of utilities to function. The utilities include at least water, electricity, gas, telephone, and fibre optics. These 10 utilities are typically provided through underground conduits. In theory the location of the utilities is carefully recorded and held centrally by city authorities. In practice this does not universally occur and the location of many utilities may be unrecorded or recorded incorrectly. This may happen for various reasons such as records of older utilities being lost or destroyed, errors being made at 15 the time of installing the utilities, or emergency repairs being made without proper recording of location. This latter occurrence can be particularly problematic if, for instance, an emergency bypass to a gas line is routed down an old communication conduit but not recorded (probably due to an expectation of imminent decommissioning). 20 From time to time it is necessary to excavate around or near the location of underground utilities. If the location of the underground utilities is known the excavation should present little or no risk since an excavation trench can be designed to avoid utilities or at least to approach utilities in a safe, non destructive manner. The presence of unknown utilities, or known utilities in an 25 unsuspected location, presents a significant risk. It will be appreciated that encountering a gas main when using a metal saw to dig a trench can have catastrophic outcomes. Experience has proven that the prudent approach to excavation, especially in towns and cities, is to assume there are unknown utilities in the 2 excavation zone. The problem with the prudent approach is that it significantly slows the excavation process, which adds to cost. For instance, the choice of excavation tools is determined by the ratio of the hardness of the excavator (eg. the metal teeth of a saw) and the hardness of the outer sheath of 5 the buried utility. If it is assumed there are unknown utilities of indeterminate nature the choice of excavation tool is limited to hand tools or "soft" non destructive excavation machines using pressurised air or water. Even pressurised water may not be suitable as test have shown that water pressures above 2000 psi can damage or destroy buried utilities. 10 Similar issues are encountered in relation to underground infrastructure inclusive of concrete and brick ducts, viaduct structures, manhole walls, underground tunnels and the like. This is particularly true in relation to historic cities which often conceal a plethora of buried infrastructure which, while not always in active use, have an important role in supporting the above ground 15 infrastructure including roads and pavements. After an extensive period of development the inventors have devised a process for excavating buried utilities and infrastructure that minimises the risk of damage to the utility but still permits the use of rapid excavation equipment. The process has been developed to mitigate the risk of damage, injury or 20 death that has been proven by experience to be present with existing processes for locating and exposing utilities and infrastructure encased in hard mediums that typically exist in city streets and pedestrian ways. Indeed, there are recent examples of deaths caused by gas explosions resulting from excavation of a city street. 25 SUMMARY OF THE INVENTION In one form, although it need not be the only or indeed the broadest form, the invention resides in a process for exposing underground utilities in an excavation zone which may contain known utilities and unknown utilities including the steps of: 30 identifying known utilities; planning an excavation trench taking into account known utilities; 3 excavating the trench by: (I) making a cut of the excavation trench at a selected depth; (ii) extracting material from the trench; (iii) observing the trench to identify signs of the presence of a utility; 5 (iv) adjusting the depth of cut based on the outcome of the observation such that the depth of cut is reduced at the first signs of the presence of a utility and further reduced as the cut approaches the utility; and repeating (i) to (iv) until the process is complete. 10 Suitably the step of identifying known utilities includes one or more of: checking records of utility locations; tracing likely utility routes from known nodes; tracing utilities using ground penetrating radar or other subterranean mapping techniques. The step of planning the excavation trench suitably includes selecting a 15 trench location to minimise disruption of known utilities. The step of planning the excavation trench may include marking the selected trench location on the ground together with known utility locations and depth. Suitably the markings of known utility locations and depths are colour coded to maximise visibility. 20 The step of a making a cut of the excavation trench is suitably performed by a mechanical saw that has controllable depth of cut. The first cut of a new trench is typically at a depth of 50mm but may be a lesser amount such as 40mm or 30mm or 20mm or 10mm or 5mm. It may be an intermediate distance, such as 25mm. A typical series of cuts may commence at 50mm, reduce to 25 25mm and finish at 5mm. The step of making a cut in the excavation trench may include using the mechanical saw to effectively plane the surface at known fixed increments. The width of the cut in each fixed increment may be greater than the depth of the cut. The location of the mechanical saw is suitably controllable in the X 30 direction (advancement along the trench), Y direction (lateral position of the cut) and Z direction (depth of cut).
3a Material is preferably extracted from the trench using a vacuum excavation machine, preferably a hydro excavator. The step of extracting material from the trench uses a vacuum excavation machine and the vacuum 4 excavation machine follows closely behind the mechanical saw to continuously remove material from the trench. The vacuum excavation machine is preferably a hydro excavator that can operate in a low pressure mode of about 200 psi and a high pressure mode of about 2000 psi. 5 The bottom and/or sides of the trench are suitably observed to identify any sign of the presence of a utility. The signs may include one or more of: change in colour; change in material; cracking, pitting or lifting. Suitably the depth of cut is adjusted based on the observation of the trench. For instance, if a minor change in material is observed the depth of cut 10 may be reduced to 5mm. In one embodiment, the adjustment to the depth of cut may be Omm. The process is repeated until utilities are uncovered or the trench is complete. The inventors have found through testing that the invention can quickly 15 and safely excavate a trench with minimal risk of damaging unidentified utilities. Further features and advantages of the present invention will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS To assist in understanding the invention and to enable a person skilled in 20 the art to put the invention into practical effect, preferred embodiments of the invention will be described by way of example only with reference to the accompanying drawings, in which: FIG 1 is a flowchart of a process for exposing underground utilities; FIG 2 is a sketch of a saw with depth control; 25 FIG 3 displays a change in material at the bottom of a trench, and FIG 4 depicts an application of the process. DETAILED DESCRIPTION OF THE INVENTION 5 Embodiments of the present invention reside primarily in a process for exposing underground utilities. Accordingly, the method steps have been illustrated in concise schematic form in the drawings, showing only those specific details that are necessary for understanding the embodiments of the present 5 invention, but so as not to obscure the disclosure with excessive detail that will be readily apparent to those of ordinary skill in the art having the benefit of the present description. In this specification, adjectives such as first and second, left and right, and the like may be used solely to distinguish one element or action from another 10 element or action without necessarily requiring or implying any actual such relationship or order. Words such as "comprises" or "includes" are intended to define a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed, including elements that are 15 inherent to such a process, method, article, or apparatus. The term "underground utilities", as used herein, is used in a broad sense to include typical relatively modern utility service infrastructure such as water, electricity, gas, telephone and fibre optic structures as well as older or even historic buried infrastructure including sewers, ducts, archways, tunnels, burial 20 chambers and the like. Referring to FIG 1 there is a shown a flowchart that outlines a process for exposing underground utilities. Briefly the steps are: identify known utilities; plan the excavation trench; make a saw cut; extract material from the cut; observe the trench for signs of utilities; if utilities are visible stop excavating; if not adjust 25 depth (which may mean leaving the depth the same) and make another cut. Each step will now be described in greater detail. The first step in the process is to use all available information to identify utilities in the potential trench zone. This may include original survey data from when utilities were installed or later survey data from previous activity in the 30 potential trench zone. From experience the inventors have found information from these sources to be dangerously unreliable. There are many reasons why 6 survey data may be unreliable. Old records may have been amended by hand making changes difficult to read. Printing on old records may have faded and paper may have become stained. The information originally placed on paper records may be incorrect due to human error. It is often the case that utilities are 5 moved after initial installation but the survey records are not updated. Many of these problems also apply to electronic records with the additional problem of human error during conversion of old paper records to electronic form. To supplement survey data direct investigation of the potential trench area may be made using non-invasive techniques such as ground penetrating radar 10 and metal detection. These techniques can give an indication of the presence of suspicious material in a trench location but cannot unambiguously identify the nature of the material. It is also useful to identify local nodes and to trace likely utility paths. For instance, it is a reasonable assumption that there is a water pipe joining two fire 15 hydrants. A signal from a ground penetrating radar scan together with an assumption about a likely utility path will increase the confidence of the presence of a utility, even if there is no corresponding survey data. Once all available information is collected a "desktop" study is conducted to identify areas of high risk and low risk from which a suitable trench is 20 designed. A trench that avoids all known utilities would be ideal, but is seldom practical. Thus it is likely that the selected trench location will have known utilities to be avoided as well as unknown utilities to be detected. The experience of the inventors is that in many cases only 60% of sub-surface utilities are "known". The selected trench location is laid on the ground using suitable markings, such 25 as paint. A colour-code scheme is used to minimise the risk of error. For instance, the location of a dangerous utility, such as a gas pipe, may be marked using industry standard colour coding, which may vary from country to country. Once the trench is marked out an initial cut is made using a depth controlled rock saw. A suitable rock saw is capable of making cuts up to 1 metre 30 wide at a depth up to 2 metres but a more typical saw will be limited to cuts up to 250 millimetre wide at a depth up to 800 millimetre in as small as 5 millimetre 7 steps. The rock saw is used to effectively plane the surface at known fixed increments. In many cases the initial plane depth will be around 50 mm and a number of plane cuts may be made before the depth of cut needs to be reduced. The depth of cut is controlled by hydraulic stops explained in greater detail 5 below. The cut depth in one embodiment can be controlled to steps of 5 millimetres, and this has been found by the inventors to be suitable for the process. Turning to FIG 2, there is depicted a schematic of a saw 1 that would be suitable for the process. The saw 1 may be fitted to a variety of machines 10 including but not limited to skid steer loaders, track loaders, wheel loaders, excavators. The saw 1 has a blade or saw wheel 2 driven by a motor 3, which may be hydraulic, diesel or petrol. Preferably, the motor 3 is a high torque hydraulic drive motor. The blade 2 and motor 3 are mounted on a body 4 that is locatable by skids 5, shown in FIG 2 in the form of body skid plates 5. The body 15 4 is preferably a hydraulic actuated adjustable body which can be raised or lowered to provide positive depth control. The depth of cut of the blade 2 is adjusted by hydraulic or mechanical rams 6 that adjust the position of the blade 2 relative to the body 4. Typically one ram 6 will be located on either side of the body 4. The rams are controllable to within an accuracy of about 5 millimetre 20 from a control panel 7. The control panel 7 may be mounted within or may be part of the driving machine itself. In another embodiment of the saw it may be self-propelled and operate on tracks rather than have a separate propulsion unit as shown in FIG 2. Tracks provide a stable platform that result in greater cutting accuracy. Being self 25 propelled allows the apparatus to be more compact and more maneuverable, thus allowing for adjustment in the X, Y and Z directions. To provide further stability the body 4 may be staked to the ground. A stable body and depth control of the saw also helps to prevent run away of the saw. After the initial cut the area is then made clean. The cleaning step may be 30 accomplished by any mechanical means such as brushing, blowing, vacuuming etc. The cleaning step is important to the process as it can be difficult to identify typical signs of the presence of a utility, such as the change in colour when brick 8 is encountered or a change in consistency of cut material, when the trench still contains rubble and, particularly, fines. The fines effectively mask the identifiers which could otherwise be observed. It is only upon cleaning that observation by a trained individual becomes practical. It is preferred that the cleaning step 5 includes a washing step as the water helps remove the fines and brings out the colour in any unearthed brick and the like. Preferably, the cleaning is accomplished using a hydro excavator. A suitable hydro excavator is our Vac-U Digga Vacuum Excavator described on our website at http://www.vacgroup.com.au/services/vacuum-excavation. The hydro excavator 10 uses water to wash the area clean and suck the resultant water/dust slurry into a tank for removal and disposal. The hydro excavator can be positioned immediately behind the rock saw so that evacuation of cut material can happen as the cut is made, thus significantly shortening the time required for the excavation process. 15 It is particularly useful if the hydro excavator can operate in two pressure modes. A low pressure mode of about 200 psi is useful for cleaning the trench and a high pressure mode of about 2000 psi is useful for breaking out loose material in the bottom or sides of the trench. After each cut a visual inspection of the cut is made for any signs that a 20 utility may be close. For example, a buried utility will normally have a different colour than the surrounding concrete. The first appearance of a different colour or different consistency will be an indicator that a utility is close by. Another indicator is if hard material cracks out rather than being cleanly planed. A change in consistency of material may also result in a change in the pitch of operation of 25 the motor 3 of the saw 1. The change in pitch will give an indication that an inspection of the trench should be made to identify the nature of the change. An example of how a utility may be exposed is explained by reference to FIG 3. A utility 11 is buried in a pit of concrete 12 beneath a surrounding deposit of compacted aggregate 13. Beyond the aggregate 13 may be clay or other soil. 30 In some cases there may not be any surrounding aggregate and the concrete may be deposited directly into the surrounding ground. Over the old pit may be a layer of different concrete or tarmac 14 of a road. The trench to be cut is 9 depicted by vertical lines 15. An initial cut of 50 mm is made into the tarmac 14. Further cuts are made until a change in concrete is seen as the trench approaches the utility 11. Cuts of 50 mm may continue to be made if the risk of encountering a utility is considered low. When the appearance of the concrete 5 changes or the pitch of the saw motor changes the cut depth may be reduced to 25 mm. After a number of cuts the concrete 12 may be seen to chip or crack. At this time cutting with the rock saw may be ceased and further material may be removed with the hydro excavator or by hand until the utility 11 is exposed. Indicators of unexpected utilities may also be visible in the side of a 10 trench. A utility that enters a trench at an angle may first show signs such as a change in colour or consistency of material in the trench wall. This may particularly be the case if the depth of the trench is not the same along the length. The process is assisted by good lighting so it is an advantage to have 15 strong lights illuminating the trench, even during daylight. Although the process has been described in terms of digging a trench to find underground utilities, the process has other related applications as previously discussed. When excavating for buried infrastructure, for example, small layers of concrete will be removed incrementally and the inventors have 20 found this is a very safe method for defining the extremities of, for example, buried chambers without causing significant damage. Typically many underground vaults, tunnels and sewers are often located within or just under the soffit of the concrete roadway. When trenches are made in the roadway using conventional concrete saw and breaker methods these facilities are often 25 damaged; especially if their location and extent is unknown. By using the process as described herein the various concrete components, brickwork or stone pitching are progressively uncovered and become highly visible during that process. Steps can thus be taken to locate the extremities and joints etc. of the buried infrastructure without smashing into the void and thereby severely 30 damaging the structure. This is equally applicable when accessing these structures from above or from the side. Brick and stone work which are generally more fragile than concrete structures have been found by the inventors to show 10 up very clearly against the concrete encasement. Further, the process may be used to dig a new trench for laying a new utility. Digging a new trench will run the same risk of encountering an unexpected utility as discussed above. The process may also be used for 5 exploration and mapping. In some cases there are no records of buried utilities yet it is evident by the operating services that utilities must be buried somewhere. The process can be used to dig a number of exploratory trenches to map unknown utilities. The process may also be quite useful for lifting sections of unwanted 10 roadway. For instance, many cities have elected to cease operating trams but the tram tracks remain. The process can be used to cut tramways into manageable blocks. Referring to FIG 4, there is depicted a patch of roadway 41 with a pair of parallel tram tracks 42. To lift the tram tracks is a major job but the task can be made easier by using the process to cut the roadway 41 into blocks, 15 such as 43, which can be more easily managed by standard available equipment. Each block can be cut using the trenching process described herein and then the block can be undercut using an excavation process. Lifting bolts can be fixed into each block so it may be lifted using modest lifting equipment. It may be convenient to backfill the trenches with sand until such time as all blocks 20 can be lifted together. If an unexpected utility, such as 44, is discovered during trenching the block size can be changed to avoid the utility. In the example of FIG 4 two smaller blocks 45 are cut to avoid the utility 44. The process described above is quick yet safe as it minimizes the 25 likelihood of damaging a utility. The process is particularly advantageous because many underground vaults, tunnels and sewers are often located within or just under the soffit of the concrete roadway. Using conventional processes often leads to damage, even when the location of utilities is apparently known. The innovative process described above significantly minimizes risk of damage 30 to hidden utilities because concrete, brickwork or stonework is progressively uncovered, which allows the extremities to be located without causing damage.
11 The process is equally effective when approaching utilities from above or the side. The above description of various embodiments of the present invention is provided for purposes of description to one of ordinary skill in the related art. It is 5 not intended to be exhaustive or to limit the invention to a single disclosed embodiment. As mentioned above, numerous alternatives and variations to the present invention will be apparent to those skilled in the art of the above teaching. Accordingly, while some alternative embodiments have been discussed specifically, other embodiments will be apparent or relatively easily 10 developed by those of ordinary skill in the art. Accordingly, this invention is intended to embrace all alternatives, modifications and variations of the present invention that have been discussed herein, and other embodiments that fall within the spirit and scope of the above described invention.