Site Investigation Essay Sample
- Word count: 2166
- Category: soil
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Site Investigation Essay Sample
In all civil engineering works, the most crucial is the reliability of the information about the ground on which the civil engineering project will be founded. We would call this SI, or Site Investigation Information or simply SI. There are various methods of obtaining SI information, in this paper we will concentrate on most widely used method, that involving Boring and Drilling.
IMPORTANCE OF SI INFORMATION
We, the Engineers, all will agree that SI is a specialist operation. Almost all SI is remotely carried out (we are testing grounds below from surface!) and because of this, it is necessarily the most procedure oriented operation. Therefore, for SI information to be meaningful, it requires strict adherence to procedures and good practice. Which simply translated means, adherence to Code of Practice and Specifications. All Engineers fully agree with these statements. On the basis of the data obtained via SI (costing less than 0.1 % of the project costs), millions or billions will be committed to the project. It therefore makes engineering sense that SI must only be carried out using suitable equipment and ancillaries and by trained persons under the supervision of equally if not better trained supervisors. All SI specifications for Site Investigation in use today in one way or another emphasize workmanship supervision and have similar requirements namely:
1. Method of boring must be such that observations are possible and soil volume to be tested remain undisturbed before being tested.
2. Boring to be carried out using Drill Rods with bits attached to be used for
3. advancing of bore holes
4. Judicial use of water
5. Testing requirements
6. References to SO, Supervisor or similar implying competent supervision
7. References to Code of Practice and Specification, in siting on adherence to procedures
SHORT COMINGS OF OUR SI PRACTICES
Surprising issue is, that all of us fully agree with nice statements like above, we even use reasonably good specification, yet if we were to visit any SI site anywhere in our country, we will find there is not a single SI site where any of these sentiments and requirements are met. Situation at each SI location is virtually the same, namely
1. No reference documents (CP or specifications) on site
2. Machines and ancillaries in non-compliance with specifications
3. Unacceptable procedures, sampling, testing, transporting
4. Untrained operators
5. Untrained, usually non existent supervisors
SI information produced from these worksites, in the form of SI REPORTS are equally compatible to situation on the worksites and have following in common
* All most all introduction portion of reports describe methods which are not same as on site
* All presentations and soil descriptions in bole logs vary from company to company and in some cases different locations and pay no relevance to say, laboratory tests, consistency etc
* From bore holes logs, based on presentation and lack of site observations, it also can be inferred that
* All strata changes in ground below occurs at 1.5 meter intervals in Malaysia
* There are never any occurrences of Water losses, change in water colors, water ingress, material changes.
HOW SUCH PRACTICES AFFECT PROJECTS
All above results in final product called SI REPORT or FACTUAL REPORT. Such “FACTUAL” SI Reports, based on information as obtained from methods adopted to day present information which are far from being reliable, costly in long run and even dangerous. This reinforces common, but a very basic premise, “GOOD DECISION CANNOT BE MADE ON BAD INFORMATION”.Project costs and safety are have direct bearing on information we use in our designs. With no information we have no choice but to over design and prepare for worst. At least we are prepared. With bad / unreliable information, we can make bad choice, and may not realize it is a bad choice, and we are worse off than in the case of no information, because in this case we are not even prepared to expect problems, but we do get caught in all sorts of problems.
Today there is a tacit awareness that something is wrong with our SI, but nothing is changing, bad equipment, bad ancillaries, bad operators and where possible experienced bad supervisors continue to provide us with doubtful information and we keep designing and constructing and wasting money. We then point to these structures and say, “If SI was bad how come these buildings are standing up?”in all these arguments we seem to forget the basics again, that every Civil structure is unique. Unlike motor vehicles which are tested to destruction at design stage, we cannot similarly test civil structures to destruction and rebuild it more economically.We have to be as correct as possible right from the beginning, and use Factors of Safety to mitigate some of these uncertainties. Due care and diligence is of prime importance in all Civil Engineering projects .This is a lot more so in SI, all work is remotely carried out, no same sample or test location can be tested twice, variables that can make results doubtful include equipment, ancillaries, how they are used , where and who they are used by. Results obtained from each location simply tell us how that location (the bore hole location) was like before testing (after testing it is no longer the same). We use number of these test results to develop a picture of the grounds below.
This picture will never be 100 % accurate. Again some uncertainties are taken care of by Factor of Safety. Even with this, in is necessary to ensure that the results we obtained are as accurate as possible and properly taken, ie reliable to allow us to develop as accurate picture of grounds below as possible. We do this by following set procedures in boring, testing and sampling and even in how each sample is described. (logging). This way we ensure uniformity of procedures, uniformity of description and uniformity of reporting and cut down as many variables as possible. Uniformity of procedural reporting is very important, because once SI is carried out we are left with nothing but the FACTUAL SI REPORT. This report has to be such that designer utilizing his past experience and knowledge can develop accurate picture. When reported as described, SI REPORT ALLOWS US TO assess variability in the ground reasonably accurately. Now please consider the present situation of the SI REPORT, where codes and specification are rarely followed, no adherence to procedures, no uniformity in reporting. Under these circumstances, no matter what Factor of Safety we use, we are still playing engineering version of Russian Rowlett.
OUR BORING METHODS
Method of advancing of boreholes as we ask for in our specifications provides us with reliability of sampling and testing. This means, each method has to be such that it must not allow that volume of subsoil, (which we will test or sample,) to be changed or altered before it is tested. Basic in all this, is how the “hole” is made to reach the sampling/testing depth. This is referred to as boring. In case of boring in soils, most accepted method are Percussion Boring, Rotary Boring, Auger Boring. Properly used all these methods allow for reliable sampling and testing. Properly used methods we would define as that using adequate and suitable equipment and ancillaries under the care of trained operators and supervised by trained supervisors. Most commonly used methods is Rotary Boring (or Rotary Wash Boring) which involves a boring hole using drilling fluid (water or mud) pumped down a rod fitted at the bottom some sort of cutting bit. Advancing of hole is achieved by dislodging of soil below the rod by the cutting bit and the transport of these cuttings to surface by drilling fluid. (water or mud). Drilling fluid, under some pressure, is discharged from the drill bit at the bottom, mostly sideways and returns to surface bringing with it cuttings of soil dislodged by cutting bit.
If casings are used to stabilize the hole, these always follow behind the rods. Most important issue to note is that drilling fluid is not discharged downwards into soils below but sideways and thus very little volume of soil below the rod is disturbed or contaminated and almost all of the fluid used is returned to the surface to gather with soil cuttings. This is the method we ask for in all our specifications. Method we actually use very different. It is more of water jetting than rotary boring. All good elements of Rotary Boring are missing. It involves advancing of borehole using only the Casing (no rod with cutting bit attached) under very heavy water pressures. All dislodging of soils below is achieved by brute force of water and surging/rotating action of the casing (water jetting). In short it only uses casing and water. This is a very crude method. This method requires very little skill, and it is fast and most important, it is cheap. However, as all water under high pressures is discharged from downwards. Considerable amount of water is lost in soils below thus considerable volume of soil to be tested is contaminated or disturbed. This makes all testing and sampling unacceptable because we are now testing soils which are no longer representative of soil mass around it. Add to this situation lack of trained operators and untrained supervisors, no procedure, no uniformity and we have Malaysian SI.
OTHER SI METHODS OF OBTAINING SI INFORMATION
There are numerous other SI methods, which method used will depend upon site and expected soil types. There is no universal method for every condition. The other methods include CPT, Pressure Meter, Dilatometer, Seismic and so on. Because of our lack of awareness, which allows us to expect cheapest at fastest speeds, just about every method of SI practiced is subject to suspicion and likely to be unacceptable since comments on basics like training and adherence to procedures apply here as well. Every method used today has element of MAKE-DO about it. (CPT cone with friction sleeve smaller than cone to speed penetration, Electric Cones on Mechanical CPT Machines, Pressure meter tests without pressure regulators, shear vane tests with homemade vanes and so on) .This element of MAKE-DO will remain until we accept need for training, adherence to procedures and rejection of make-do equipment and ancillaries. Until this happens, no matter what method is used, it is not likely to inspire confidence in SI information.
PRACTICE OF SI TODAY
We must stop brushing off our present state of SI industry by assuming it has always been bad any way and therefore whatever will be, will be. This is not true. Practitioners of SI around seventies used boring methods using Hydraulic fed, top driven machine, using compatible rods and casings, usually B, N, H sized casings and B and N sized rods. Every job required careful consideration of compatible and suitable equipment which included rods, casings, core barrels, various cutting bits and drilling bits. Each borehole took almost four times longer and nearly three times costlier than today.
SI information, we like to believe, was at least reliable. These equipment still exist and are available even today, but because of high operation costs, its practitioners cannot compete with today’s wash boring or “WATER JETTING”. By late eighties, numerous operators with access to cheap machines entered the SI market. The machines they used were not right machines for boring and testing, but they were fast, and again very important, they were very cheap. They produced fast reports, in some cases even instantaneous reports. Quality and reliability of information became secondary to speed and price. Those with proper equipment and ancillaries could not compete and either left the field or simply joined in. Cost of SI kept coming down even though the cost of labor, fuel, ancillaries and equipment has almost doubled or tripled. There are no drastic innovations in basic SI technology. Nevertheless SI costs today are about ONE THIRD that used to be in seventies or early eighties. Today SI operations are come to be regarded as lowest form of contracting and it seem as we just do not care.
WHAT IS REQUIRED
Most important thing required is CONSCIOUS AWARENESS amongst engineers that quality of SI needs improving and why. We must stop making excuses to justify bad SI instead we must at highest levels, start paying attention to awareness and training. This must also follow awareness amongst Project Owners to the importance of SI information to their projects. Next most important issue to be addressed must be training of personnel involved in SI, both from contractors and supervisors and entrusting all SI operations are entrusted only to them. Thirdly standardization of specifications, bill of quantities and reporting formats etc. Last and most important awareness must be that good quality SI will not be cheap, but these costs are nothing compared to gains in cost reductions and reduction in construction and post construction problems. This has to be acceptable to both clients and engineers.