 As the old saying goes, the chain is only as good as its weakest link. So it is with the dam and its foundation. The weakest link or element in a dam or the foundation will determine how long the reservoir and dam will function safely. To achieve a dam that will function safely for many decades, thorough field investigations and geologic evaluations are required. This allows the design engineers to assess the impact of weak elements in the foundation to design improvements that will make the foundation safe for dam construction. The dam is designed and constructed under tightly monitored and control condition, whereas the dam's foundation is a result of eons of geologic activity. Potentially weak elements can exist deep below the earth's surface. As a result, this can make it difficult for geologists and engineers to locate and identify them. A number of investigation methods can be used to detect these problem areas. Any single method may not be adequate if used alone, but when the methods are used together, they have proven successful in providing adequate information for the design of safe dams. When used together and interpreted correctly in the context of regional geology and geomorphology, this information guides engineers in deciding what needs to be done to the foundations to make them perform to accepted industry practice for supporting a dam and retaining water in a reservoir. This information helps guide the dam designers to excavate, shape, and treat the contact between the dam and foundation, a critical part of constructing a safe dam. It also aids the engineers in determining the best means to cut off water flows through the foundation under the dam. This is usually accomplished by grouting or constructing a barrier element in the foundation that will serve to control under-seapage and protect the base of the dam. In many instances, it is easier to carry out these explorations for the design of a new dam than for the investigation of conditions at an existing dam. When assessing whether an existing dam is safe or designing a modification, the dam and existing reservoir can be barriers to investigating the foundation. To thoroughly explore the foundation, drilling must be done through the dam and from barges on the reservoir. Also, a knowledge of how the dam was originally constructed is important when determining as-built conditions of the dam and foundation. Frequently, this knowledge is inadequate and investigations must be made to assess the condition of the dam foundation contact and to determine if the original cut-off is functioning as intended. The Federal Interagency Committee on Dam Safety recently invited the internationally renowned engineering geology and dams consultant, Dr. Dondir, to speak on these issues. His presentation has been divided on two tapes. This tape covers significant geologic features and exploration methods. The second tape covers remedial measures for both dam structures and foundations when geologic features are contributing to inadequate performance of a project. He is joined here today by several professional representatives from some of the federal agencies that are members of ICODES. Dr. Dondir has been an educator and consultant for almost his entire professional career. He is a member of both the National Academy of Sciences and the National Academy of Engineers. He spent a number of years on the civil engineering faculty at the University of Illinois. He has acted as a consultant for many federal agencies in the United States and several government and private organizations throughout the world. He has been a recipient of several prestigious awards including the Golden Beaver Award for Outstanding Achievement in Heavy Engineering Construction in 1990 and the Distinguished Practitioner Award from the Engineering Geology Division of the Geological Society of America in 1993. He was also appointed by the President of the United States to establish and head the U.S. Nuclear Waste Technical Review Board. Recently, he has been involved with the U.S. Bureau of Reclamation in the design and construction of New Waddell Dam in Arizona and has also worked on Pangidam in Chile. Together with Dr. Jim Coulson of the Tennessee Valley Authority, Mr. Constantine Umas of the Federal Energy Regulatory Commission and Mr. David Ackterberg and Dr. Dwayne Campbell of the Bureau of Reclamation, I will be joining Dr. Dier in this discussion today. It is my pleasure to present to you Dr. Don Dier. Thank you, Frank. In preparing for this session on dam foundations, I found four topics that I particularly wanted to discuss and to elicit responses from the panel. These are weak geologic features, common and uncommon exploratory methods, foundation remedial works, foundation assessment of existing dams. The first three topics apply directly to the design and construction of new dams. However, as you will see, they apply equally well to assessing the foundations of old dams. I believe that the topic for our discussion today, dam foundations, fits well into the general theme of this video series on dam safety topics. After all, no structure is better than its foundations. The statement is true not only for dams, but for buildings and bridges. While only a few dams have failed, a substantial percentage of those that have can be related to poor and inadequate foundation conditions. The poor foundation conditions are almost exclusively the result of one or more weak geologic features, be it in soil or rock. Where dam failure has taken place, the dam design team either missed the presence of the weak geologic feature or underestimated its engineering significance to the behavior of the dam. Engineering experience has shown that the safe design of a dam requires an ample knowledge of the weak geologic features present at the site, meaning the position, the orientation and the properties. An adequate analysis of their potential effects on dam performance using applied rock mechanics, soil mechanics and structural analysis. And an appropriate design with adequate foundation remedial measures properly constructed. Let us move on to our first topic, weak geologic features. In the late 1960s and 1970s, when I was teaching engineering geology and applied rock mechanics to my graduate students at the University of Illinois and later to students at the University of Florida, I used the term significant engineering geology features. The objective was to emphasize those weak geologic features that experience had shown could adversely influence dams and other engineering structures. These so-called significant engineering geology features exert their influence on dam behavior because they significantly affect one or more of the in-situ rock mass properties of modulus, sharing resistance or permeability. Four of the features are three-dimensional or zonal in aspect. Weathered rock, the weathered rock profile, fault zones, karstic limestone and interbedded volcanics with scoriaceous lava or weak clay-y tough. The other two significant features are narrow and have near planar aspect. Thin shear zones and master joints. The thin shear zones out of the most prevalent are the bedding plain shears that occur along weak shale interbeds in sedimentary rocks and the foliation shears that occur along weak mikesias, chloridic or graphitic interbeds in metamorphic rock. The master joints are the most prominent of the joints. They are continuous, they occur perhaps every 100 to 200 foot or 500 foot even of spacing and they may be weathered and permeable. Other features that could be considered for this list would be the pattern of stratification of soil deposits, rock lithology where strength and abrasiveness might be of concern or the groundwater occurrence. I will now come in in greater detail on the first three features of this list of significant engineering geology features starting with the weathered rock profile. The profile of weathered rock may range in thickness from 0 to many tens of feet, even reaching 100 to 200 feet or more in the tropics. It is convenient to consider the profile in three layers as shown here. An upper layer of residual soil, a second zone of weathered rock and a third zone of unweathered rock. The contacts between the zones are often transitional and may be highly irregular. The weathering agents, air, water and organic acids extend deeper along joints, faults and bedding planes. Also, different rock types will be affected differently. One may subdivide zone one, the residual soil zone, into the A horizon, which is a silty topsoil, a B horizon, a clay zone, and the C horizon, the saprolite zone. While the upper two horizons are only a few feet in thickness, the saprolite zone may be tens of feet thick or greater. The saprolite is predominantly silt with varying proportions of clay and sand, and it tends to be more compact with depth. The original rock structure and even the rock texture can be seen as relic structures. The weathered rock zone similarly may be divided into zones, zones 2A, a transitional zone of both rock material and soil material, and zone 2B, hard weathered rock but with much fresh rock, but still with soil-like materials along the joints. The transitional zone 2A is a very difficult zone for engineering projects. Containing both soil and rock, it is difficult to excavate and to support. The rock mass properties of shearing resistance, modulus, or permeability may vary greatly over short distances. Dam should never be constructed on zones 2A. Zone 2B, the hard weathered rock, may be acceptable if it is sufficiently uniform and the soil material along the joints is judged to be non-erodable and the hard weathered rock to be grottable. However, it is the zone of unweathered or fresh rock of zone 3, that is the most appropriate dam foundation. The natural groundwater level is often found to occur in this weathered rock zone, ranging and varying seasonally from 2A to 2B to 2A. These zones are also the most permeable parts of the profile. I hope that some of the panel will wish to comment on the weathered rock profile, but at the moment, let's go on to fault zones. The fault zones have been found at almost all dam sites, often only one, but too often, two, three, or even a half dozen, crossing the dam and its abutments. Fault widths are commonly of 1 to 10 feet, but may range to greater than 50 feet. In dam engineering, fault zones are important because they are continuous over long distances and they contain weak crust material that is compressible and low insuring resistance. The fault zone may be of low permeability in a direction across the zone because of the clay-silk sand gouge. However, the permeability may be high in parallel to the zone in the adjacent rock mass because of fracturing that has occurred related to the fault movement. The fault zone then may act as a permeable drain in one direction as an impermeable dam in the other. These characteristics influence the groundwater flow and pressure conditions and may affect the efficiency of the dam's grout curtain and drainage system. A fault zone may be considered a zonal feature where its width is large. However, it is also a near planar feature with a given orientation, that is, a given strike in depth and with a specific location at the dam site. The significance of a fault zone depends almost entirely on its location and orientation with respect to the dam and its line of thrust. Some relative positions are shown here to illustrate this point. You will note that sketches A and B represent problems of low shearing resistance while C and D represent problems of low modulus. Let us examine sketch A in greater detail. Certainly the question is, will the dam be stable under full reservoir? Three important factors will enter in to the shearing resistance along the fault zone. The particular dip angle of the fault and the hydraulic uplift not below the dam but below the fault zone. The magnitude of the uplift will depend on the efficiency of the grout curtain and on the efficiency of the drainage system. Sketch B has many of the same problems, but here the fault is dipping downstream. If the downstream powerhouse excavation had not been so deep or if it could have been farther downstream, the fault might not be so bad. In its present position, however, the entire stability of the dam would appear to reside in the capability of the piece of rock within the circle to take the complete reservoir thrust. This failure could be sudden and of a brittle nature. Sketch C illustrates a wide fault zone. The potential for differential settlement is present. It is also a classic problem in structure-foundation interaction. Studies by finite element are helpful in analyzing the differential stresses and the potential for cracking. Sketch D shows a fault in a more downstream position where extreme stresses in the toe could result in cracking of the concrete. Keeping in mind your possible comments on fault problems, let us go on now to the condition of Karstig Limestone. Karstig Limestone refers to limestone or limestone where differential solutioning along faults, joints, bedding planes or in beds of pure limestone has occurred over geologic time, resulting in a network of various sized openings. Solution cavities are common along valley walls, back beneath the adjacent plateau and even beneath the river valley. Caves may form below massive beds that can bridge the solution opening. Youth collapse may allow the opening to migrate toward the surface sporadically, forming a sinkhole. The sinkhole usually contains clay, blocks and other debris from the collapse, from the weathering and from surface runoff. A sketch is shown here of limestone with solution openings. Note the structural control and the lithologic control of the groundwater solutioning. An area of potential sinkhole is located, as is a drill hole, which by chance will indicate good intact limestone of low permeability. The groundwater level has been found at many sites in limestone to be at river level and to rise very gently away from the river, usually less than one half percent. Potential for leakage from the reservoir in limestone terrains is always of concern because of the interconnected solution channels. The leakage problem is one involving the groundwater regime. Therefore, a groundwater hydrologist should always be part of the study team. Many reservoirs in limestone have performed satisfactory while others have suffered leakage of greater or lesser amounts. Close-in leakage is not the only question. Collapse of caverns below dams or auxiliary structures during operation must also be guarded against. Diligent exploration for openings and their backfilling with concrete when encountered are obvious requirements. I think also that we should include gypsum together with limestone as one of the soluble rocks that is able to have some rather cavernous openings. Gypsum, however, is much more soluble and even the reservoir filtration can cause new solution openings to occur. It is now time for the panel to comment on wheat geologic features, weathering rock, weathering rock profile, rather, fault zones in karstic limestone. I know that several of the agencies have had projects in areas of karstic limestone. It would be of interest to hear of your experiences, particularly of reservoir leakage in general and around the dam abutments as well as the inducement of sinkholes by the falling and rising of reservoir levels. Back when I was in school, TVA was building the Nickejack project to replace Hale's Bar Dam on the Main Tennessee River and it had more water going under the dam than it did over it and it got to the point where it was impossible to control and we had to build a new structure. We've always dealt with reservoir rim leakage problems. We have a project that we're dealing with currently that's about 25 years old. We had an extensive reservoir grouting program or rim grouting program prior to first filling and there were some minor seeps as the project was filled and those have increased over the years and one of them now is to the point where it's a real problem in the public's eye as well as just something that we need to be concerned about. We're in a very happy situation after having several projects where we've tried to grout unsuccessfully for one reason or another and this one we're going to be able to lower the reservoir low enough we feel to be below the intake and we'll be able to cut off the flow of water almost completely so we won't be grouting against the head I'm really looking forward to a much more successful project this time than what we've experienced in the past but rim leakage in the karstic topography is always a problem. I think it's always of concern and it becomes a problem of regional groundwater hydrology that's where you really need a groundwater geohydrologist to look at the regional geology as well as the piezometric levels throughout the zone and one of the zones that I studied was the zone 100 miles wide this was how far we were concerned about the travel of the new higher water level brought about by the new reservoir you mentioned Nickajack Dam one of the TVA projects that they purchased from a small company way back in the early 1900s I recall taking some of my graduate students from Illinois down to visit that project as well as others in the area and the thing that impressed me and certainly the students was standing on Hale's Bar looking upstream and seeing a gigantic whirlpool where the water was going down turning around looking downstream and seeing a big surge of water where the water was coming up it's about the most dramatic instance that I had ever seen of leakage through karstic openings I think we probably were going to have some other comments on this session I'd like to add to Jim's comments with respect to karstic limestone foundations and then with your comment just now about the dramatic leakage that one sees under the situation we have a situation where the leakage over many years has been around 700 CFS nothing as dramatic visually though thank goodness but coupled with that there have been sinkholes on occasion that have opened up downstream of the dam and unlike the TVA experience this particular dam that I'm referring to has to be worked at under a full reservoir head and what's happening now is we're attempting to look at a grouting program and that program is started in the initial stages as developing a target zone after a lot of geologic investigations to determine what zone to begin with and what they can learn from their experiences dealing with that zone they've gone through a lot of work in developing a scheme to be able to grout the foundation only recently and a few months back they ended up grabbing a zone that they had a hole down in that they've been grouting and they continued to grout tons and tons of gravel and grout have been injected into that hole and it's still taking so now everybody's sitting back a little bit trying to decide what's the best way to tackle this problem there's a lot of uncertainties involved in trying to deal with this especially with an existing dam with a full reservoir behind it so a lot of people are trying to put their heads together now to better understand what can be done and what would be a solution to assist them in plugging this off I appreciate those comments it's a very difficult problem and it's faced in quite a number of projects around the world are there other comments on other rock types or more on limestone even yes Don, I'd like to move to a different geology a sandstone horizontally bedded with a less competent zone of material at some depth below the surface a site for a concrete gravity dam that also had a near vertical joint system running parallel to the dam axis and then a fault daylighting downstream of the dam and during the investigation designed why we figured that there would be some movement across that weaker zone so instrumentation was installed in order to look at the extensions that occurred the displacements and on first filling the load on the dam gave us between an inch and two inches of non-recoverable movement in the foundation due to the joint system downstream closing before the passive pressures came fully into play that's rather impressive case history and I'm glad that you had the owners had the foresight to instrument the dam so they could measure any displacement the preceding discussion gave emphasis to the specific geologic features that may occur at any dam site and that may impact adversely the dam's behavior the next discussion will address exploration methods used to locate these weak features knowledge about the geologic origin of the features and something about the physical characteristics of the various weak features will help in planning a site exploration program either for a new dam or for an existing one I have divided the exploratory methods into common and uncommon methods I will review first the common methods starting with geologic mapping the first stage in site exploration involves a collection of background material to get an appreciation of the regional and the local geology such information may be obtained from available geologic maps and published reports of the region from aerial photographs and satellite images and from field reconnaissance of soil and rock exposures in nearby quarries and road cuts a geologic map of the project geologic sites should be made showing the overburdened soil rock outcrops and rock structure new aerial photographs may be desirable at different scales to cover the dam and reservoir areas the photos may be used for preparing a new base map and for geologic interpretation the goal of the geologic mapping is to allow preliminary geologic profiles to be constructed along the dam axes together with geologic cross sections perpendicular perpendicular to the axes at each abutment and at the valley bottom such an exercise is enlightening in identifying areas where we don't really know the geology in areas where potential faults or deep soil cover makes it very difficult to get the information the second common method is exploratory borings numerous diamond drill holes will be required along the dam axes and along a dam upstream along a line upstream and another downstream of the dam in order to obtain a three dimensional understanding of the site wire line drill rigs and in-queue size cores or larger are common requirements for better recovery of wheat materials either four inch or larger cores are preferred using a triple tube core barrel the information to be obtained from the borings includes the following thickness and kind of overburden soils kind and quality of bedrock with depth the presence, orientation and physical characteristics of joints, faults and the profile of weathering the permeability by LeFranc and Lejeune infiltration test and the depth to the water table careful core logging is necessary to determine the soil and rock types, the rock structure and the general rock quality for example by the RQD method with the new drill hole information at hand the previous prepared geologic profiles and sections can be corrected and updated whatever geologic weaknesses that occur at the site should now be known additional borings may be programmed to define boundaries and to fill in data between the first borings where of course we may discover additional weak zones the dam design team can now study the feasibility of different dam types the layout of the dam and of pertinent structures and the possible extent of foundation excavation and treatment the dam engineer together with the engineering geologist can identify the areas being additional study by borings or other procedures our third common method of excavation or is the excavation of exploratory trenches and test pits trenches and pits excavated by bulldozers, back hose or occasionally by hand are commonly used for investigating the kind of overburden soils their thicknesses and their pattern of stratification they are useful in determining the depth to the water table and the details of a weathered rock profile their obvious advantage over borings is the three-dimensional picture that they provide and the opportunity for detail sampling and for in situ testing if desired the depths of these excavations are limited by the equipment capabilities and are usually less than 50 or 60 feet geophysical surveys comprise the fourth method of exploration geophysical surveys by refraction or reflection sizing methods and by various types of electrical resistivity procedures have been used at a high percentage of dam sites they are occasionally done before the borings to estimate the bedrock depth formation contacts or groundwater depth in order to aid in developing the boring program however I believe they be used more efficiently after the boring program is well along to fill in data between borings the big advantage is that the boring data are available for calibrating the geophysical results thus giving more credence to the interpretation of later results the exploration methods that I will discuss now are less commonly used but there are methods that can provide significant additional information the use of shafts and addits as exploratory methods is simply an extension of the more common method of trenches and pits they are deeper, longer and often require rock blasting consequently they are more time consuming more expensive and are therefore used less often however exploratory addits are excavated for nearly all concrete arch dams and for many concrete gravity dams usually two or three on each abutment to depths of 50 or 250 feet they are valuable for investigating the depth of weathering and destressing in the abutment assisting in determining the foundation depth for the dam under study on a number of important embankment dams exploratory addits have also been excavated for the same purpose the addits for both embankment and concrete dams can be located so as to be incorporated in the abutment drainage system the characteristics of fault and shear zones can best be determined by exploratory addits crossing them or following them along their strike direction critical observations being made as well as in situ rock mechanics test or seismic velocity measurements along the addit or between addits if desired at several projects fairly deep exploratory shafts have been excavated for investigating a fault or shear zone or a deep profile of weathering occasionally an addit has been driven under the river from the base of the shaft where rock mechanics test may possibly be desired the shaft or addit allow access and also the opportunity of choosing the most appropriate part of the feature for testing for example I like to do in situ modulus test or direct shear test at three locations along a particular weak geologic feature representing the worst condition an intermediate condition and the best condition a number of specialized geophysical methods have been developed over the last few decades that have been applied to dam site investigations to a limited extent these include microgravity ground penetrating radar and electromagnetic methods all three methods have had some success in discovering solution cavities in limestone and fault zones in any rock type I believe that we may find these types of surveys use more in the future probably in combination with each other or with other geophysical methods and with the boring program special ground water studies in certain conditions may be required there are certain geological conditions involving particular stratigraphy or complex geologic structure that may merit large scale pumping test these have been done on several projects in recent years for instance to investigate possible reservoir leakage across a divide multi-port piezometers which allow piezometric levels permeabilities and even water sampling to be obtained at a number of depths in the same drill hole have been used as control piezometers they also have been used to monitor ground water changes in abutments and reservoir slopes with the filling of the reservoir I believe that we will see increasing use made of these in the future considering the early excavation of the dam foundation as an exploration method may seem to be stretching the point nevertheless in areas of complex geology where the results of each boring or each geophysical line leads to new interpretation and further uncertainty as to the appropriate foundation grade pre-excavation by an early and separate contract may be the preferred method of exploration in employing this procedure sufficient exploratory work must be done to allow an approximate excavation depth to be selected a contract is unprepared on the basis of this assumed excavation depth a contract is unprepared on the basis of the excavation limits with the excavation width some 20 to 30 feet wider than actually required so that the final position of the axis of the dam can be moved somewhat if desired the excavation is conducted in two stages the first stage includes overburdened soils and the weathered rock that can be removed by dozer, ripper and backhoe the exposed harder rock is cleaned up to allow geologic and possibly a few shallow drill holes or geophysical lines to be carried out the design team then prepares geologic cross sections at each dam block with the new design depth for the foundation for that dam block frequently it is a stepped foundation level the excavation contractor then proceeds with his second stage of rock excavation using controlled blasting minor changes may be made during this stage in accordance with local variations in the rock frequently dental excavation along a fault zone will be the final excavation task recent experience has demonstrated that the advantages of the foundation pre-excavation procedure are many-fold the drawing specifications in contract for the access roads and the foundation excavation can be made ahead of the final design of the dam and the other upburdened structures although these must be fairly well advanced the excavation contract may be let six to twelve months ahead of the main dam for the dam construction the bidding for the excavation contract can be quite competitive as local contractors can be pre-qualified many times international contractors may also bid because they want to get their foot inside the door on this particular project the bidding for the main dam contract can be lower and very competitive because the potential delays and costs associated with foundation excavation are no longer factors last but not least a better foundation for the dam will probably have been achieved because of the spatial and focused attention devoted to this task panel do you have comments on common and uncommon excavation methods? Don I'd like to talk a little bit about excavation, a separate contract and just note before I talk about a case history that we've used that in a couple of instances to show what does not exist at the site as well as to find out what does exist and in terms of what doesn't exist at the site would be for example the trace of an active fault daylighting under the footprint of the dam you can show conclusively that it's not there the example I want to talk about is one in the desert southwest of the dam on a site of volcanic origin that had several pre-construction contracts for the main dam it had a contract for a concrete cutoff wall in the valley in order to accommodate some rock overhangs that were buried in the valley alluviums the contract for pre-excavation included grouting the footprint of the dam and even though fairly extensive boring and trenching explorations had gone on covered some eroded joints that were vertical that went from upstream to downstream and allowed us to put a secant cutoff through the area of the joints it also allowed us to do some other special fill treatments that we needed and exposed some unusual topography that would have been under the footprint of the dam that would not have been recognized through the common exploration methods that were used I think that is a very good example and on the particular one that you gave I think that also uncovered by this pre-excavation was a zone of scoracious weathered very blocky lava and the designers upon studying it in detail decided that grouting would not be a permanent solution to cutting off the reservoir leakage past the dam and they therefore preferred to go with some kind of cutoff wall a positive cutoff wall which they did by these overlapping secant piles that's right Don we've had quite a bit of experience in using the excavation for exploration as well and really it's the primary way that we do projects on limestone the early preliminary exploration using the techniques most of the ones that you've mentioned will define the top of rock the depth of the general depth of the foundation locate other anomalies that are important and help to design and locate the coffer cells and then the exploration is culminated in the final excavation and really that's the only way that you can discover everything that needs to be treated in karstic limestone there's really no other way to do it we have two new locks currently in the planning stages at existing projects both on limestone and both of these will be handled this way both the schedules and the construction contracts will be set up so that the exploratory work will be culminated in the excavations themselves utilizing the same techniques that you've described Jim I'm glad to hear that I didn't realize that this was coming up, sounds very interesting Gus I think you had a comment that you wanted to make on this particular subject echo again some of the words that Jim has said with respect to the advantages of the pre-excavation I know we had one project that we were looking at that was in the design stage and during the explorations several warrings were put down and a lot of information was developed but then it was determined that additional warrings were needed so that was done as a result of that the board on the project seeing the results of the warrings determined that it would be best to have an open excavation and evaluate the geologic features and a contract was let to do this and it was done and it was amazing that there was a lot of information that was already known but the open excavation certainly added many many times more information to what was already known and it made a big difference in the final design of the dam before the contract was let. One of the other fringe benefits of this I refer to as fringe benefits the one abutment that had some potential problems in opening up and they went up into the abutment and with respect to the design elevation of the crest of the dam it was pretty close as to whether they'd have a tie-out but this was determined well in advance of the construction and the design incorporated all the features necessary to make it a project that would hold water essentially so it turned out to be a good experience I think that was another good example of the benefits to be achieved from this early and pre-excavation contract and I think gentlemen there's a trend going. Don, what I'd like to offer from the comments that we've heard is the need to have the dam designer substantially involved during the construction and very definitely the contract management particularly during the foundation exploration it's very important to be able to verify the design intent to this point there's special emphasis within the federal guidelines for dam safety on the role and responsibility the designer should play during the dam construction and this role of the designer really needs to extend through the excavation through the construction and actually monitoring the performance of the dam during first filling to be able to verify once again that the design intent has been carried out and that the dam is really performing as designed and as intended. I think that in the past this was definitely the case it used to be that most of the designers or the design firm or the design agency were also the ones who were in charge of the field inspection and the contract management so there was this continuity at least in organizations and usually with the designer having a chance to observe all of the final foundation treatment and all the changes that might be involved and be present all the way during the construction and the first filling stages for the reservoir however probably couple decades ago changes were made and the number of owners and owner agencies decided that to have more competition once they finished the design they would go out for bids again for the supervision and the construction control and construction management so there became a time when those people who were hired were so jealous of their new role that the designers were really not welcome and many times changes were made in the design without consulting the original designer this didn't happen too many times but enough that it was of concern so I think that the designer the dam must be kept aboard even though he may only be in the field with a small office and a staff of three or four people he is able to follow all the way through any changing conditions or any design changes that might be necessary and he can do something under the context of a background of experience on that particular design