Introduction Permafrost underlying the foundation was initially suspected due to cracks found in the wallboard and in the concrete slab floors in the garages. A test hole was drilled by The Drilling Company and samples were taken at 5, 9, 10.5, 15 and 20 foot depths. The exploration revealed loose silt to a depth of 17 feet and loose sand to 24 feet with loose sandy gravel from 24 feet to the bottom of the hole at 39 feet. Seasonally frozen ground was found in the upper 4 feet, but no permafrost was found in the hole. An engineering report by Stutzmann Engineering Assoc. Inc. proposed that the loose soils be stabilized by injecting a gelling grout. They estimated the cost of this procedure at $65,000. When PTF received the house, two additional borehole explorations were drilled, hole number 1 on the southwest corner 51.5 feet deep and hole number 2 on the northeast corner of the house 45 feet deep. Neither hole encountered any frozen ground, but both showed "heaving sands" at various depths. The driving resistance varied widely from very low at the 20 ft depth in hole 1 to high near the bottom of hole 2 (45 ft depth). Layers of loose sand as indicated by these drilling reports are subject to settlement, especially during dynamic events such as earthquakes, compaction during street repair etc. Based on this information, and the recommendations by Stutzmann Engineering, a search for a professional grouting service was initiated. While the search for a grouting firm that was both affordable and reliable was ongoing, measurements of foundation stability using floor level surveys, crack width monitoring, and temperature-depth measurements were established and collected on a regular schedule. During this time, Dr. Kinney attended an international conference on grouting and grout jacking in New Orleans, Louisiana. The conclusions were interesting and appropriate to this study. In general, grouting is an inexact science. There are places where it works well and places where it doesn't. Even under good conditions, success of a project is heavily dependent upon the skill of the operators. The concept is that grout, usually a sand, cement and water slurry, is forced through holes in the floor. The pressure raises the floor and footings and the grout solidifies keeping the floor and footings in their new position. It is fairly easy to get good grout coverage and to get enough pressure to lift a residential structure. The problem comes in getting the right pressure to lift the light floor slabs and the heavy spread footings at the same time and by the same amount. Cement grouts have several disadvantages particularly in permafrost environments. First, cement grout has a high coefficient of thermal conductivity and will accentuate the melting problem. Second, grouting does nothing to mitigate the root problem of thawing permafrost and may make any mitigation technique more difficult. Third, if there is future settlement, which should always be considered a possibility when dealing with permafrost, subsequent releveling will be much more difficult. In view of the above considerations, and since the Permafrost Technology Foundation's purpose is to develop permafrost foundation solutions, it was decided not to try grouting at this site at this time. The technique was too expensive considering our research budget restrictions and alternative options for releveling houses on permafrost terrain. Cement grouts are not appropriate on permafrost terrain, and it is possible that after spending a lot of money on an inappropriate technology, the short-term result may not even be acceptable. Structure Description Level Measurements It should be noted however that when level measurement are this precise, that perturbations can and do occur. These small changes are due to the placement of the rod from one measurement set to the next. Often the rod had to be placed behind furniture, and it was impossible to determine if it was sitting on the same spot as the previous measurement or if an electrical cord or a magazine etc. happened to be under the rod (even the thickness of several sheets of paper will show up at this precision). There was also the possibility for a gross error in reading the rod, since the level had the standard three cross hairs (center, upper and lower) used for measuring distances in surveying. If the operator was inexperienced (student labor was used for these measurements) a reading could be made using either the upper or lower cross hair instead of the center one. This error would yield an elevation that was in error by several tens of millimeters to as much as a few inches. These errors however are readily discernible when the data is plotted as a function of time. Level data on the concrete slab floor in both the garage and the lower level apartments were collected several times a year and accumulated for a period of six years. The level- data charts plotted as a function of time are shown in the appendix of this report. On the charts, each measurement location is designated on the floor plan by a letter (Figure 2). In each chart a group of letters representing various locations were plotted together to show relevant comparisons such as the south wall or the diagonal across the structure. In each chart, all levels are referenced to a single reference point "A". This allows the elevation of each point to be compared as a relative elevation on the floor plan with respect to point A. From this data, differential elevations between different parts of the floor can easily be seen and tracked with time. This system, however does not give information as to the absolute elevation of the house with respect to the ground outside, and therefore any elevation variation of point A is also reflected in all other points. Determining absolute elevations requires a stable surveyor's benchmark or other stable reference outside of the structure. No such reliable benchmark or reference was available at this location, so a nail was driven into a large tree to attempt to provide a stable reference, however this did not prove to be reliably stable. Nevertheless, the relative elevations allow differential settlement to be tracked, and that is the most important information for these studies. For perspective, a differential floor elevation of one to two inches (25 mm to 50 mm) is not noticeable to the unaided eye, and up to four inches (100 mm) over the distance across a normal room, although noticeable, is not an overly unpleasant condition with which to live. Loose soils also raise the concern of settlement during a dynamic event such as an earthquake. During the period over which the level measurements were made on this house there were 15 earthquakes over Richter 4.0 in the general Fairbanks area. Of those, one was 5.0 on Nov 1, 1992 and one was 6.2 on October 6, 1995. This last one was the most significant event, since it was not only the largest but it was also the shallowest at only 9 km below the surface. It was felt very strongly by residents of Fairbanks. However, reviewing the data on level measurements shows that no significant measurable settlement can be identified in our data during any of these events. This suggests that either settlement into the loose soils beneath the structure was not triggered by a dynamic event of this magnitude or that settlement into the loose soils was already complete before the Permafrost Technology Foundation started monitoring the structure. These circumstances and observations do not preclude the possibility of settlement during a more severe earthquake or other type of dynamic event. Temperature Measurement Thermistors are capable of measuring temperature to the nearest one thousandth of a °C. However, the nearest one tenth of a degree is probably satisfactory for all relevant purposes except, perhaps, the precise location of the actual freezing front (although this location is not really very important to our studies here). Thermistors are more accurate than thermocouples; however, they have the disadvantage of being more fragile, and they can drift a few thousands of a degree over time. To obtain the maximum accuracy, the strings must be calibrated in a standard reference bath both before and after their use. These thermistor strings were calibrated before placing them in the hole, but since once installed they are buried, it is impractical to remove them without destroying them, therefore the secondary calibration cannot be made. The accuracy of the temperatures could, therefore, drift due to thermistor error by several one-thousands of a degree celsius and therefore, we cannot rely upon their accuracy to more than about a tenth of a degree. Nevertheless one tenth of a degree is adequate for the purposes of these studies and is better accuracy than would have been obtained using thermocouples. Thermistors located at various depths allow us to track the temperatures at those depths to determine if the permafrost is getting deeper, remaining stable, or actually rising. The data also alerts us to any anomalies in temperature that may occur due to outside influences such as new construction nearby, landscaping modifications, or damage or deterioration of protective insulation. Since there was no permafrost at this location, the temperature data is not as important as sites underlain by permafrost. However, the temperature trends over the years of measurement are valuable data to be used for control and reference to other sites that do have permafrost. Geotechnical Exploration The water table was encountered at 12.8 and 12.7 feet respectively in the two holes. The earlier hole drilled by The Drilling Co. in March 1989 found the water table at 17 feet. The difference shows the variation in water table that occurs in the area from its traditional low in March to its high level in spring during breakup or late midsummer when rain and glacial melt sometimes create high water levels. A small amount of seasonal frost was found at 5.9 ft in the hole on the northeast corner. This is consistent with conditions in this area in early July when this hole was drilled. The Drilling Co. hole which was drilled in March encountered frozen ground from the surface to a depth of 4 feet. Results and Conclusions The data on the levels and the crack width monitoring, however, did provide a good deal of information on the stability of the structure as it now stands. Figure 3 shows the increase of differential settlement in millimeters at each measuring point on the lower level of the structure for the period over which measurements were made. In the six years of record, the differential settlement of the concrete floor in the lower level (i.e. the daylight basement apartments and the garages) increased at nearly every point of measurement. The increase was not great. The maximum increase was 27 mm (1-1/8 in.), which indicates that the building is still moving since all but two points (J and AM) showed a change in the differential. The elevation vs. time plots indicate that this is a uniform gradual increase rather than an abrupt increase as might be brought on by a one-time dynamic event such as an earthquake. Since the differential increase is generally positive, with respect to point A, it suggests that either point A is settling more rapidly that all other points, or that the other points are actually rising (heaving) with respect to point A. Since the structure has been heated for the entire period, it seems unlikely that frost heaving has taken place beneath the house to progressively raise the structure. Individual points in the structure such as the corners of the garage may have frost develop beneath them, but points well inside the structure are very unlikely to be experiencing frost heaving. It is obvious in Figure 3 that the maximum rise with respect to A occurs along a ridge through the center of the structure from the front entrance to the back wall of the basement apartments. This is not indicative of frost heaving. This leaves us with the implication that point A has subsided more than the other measurement points. If this is the case, then the settlement has been predominantly along the northwest and north wall of the west garage. With similar settlement along the north and east sides of the east garage. The settlement is small and gradual, amounting to approximately an average of 18 mm (3/4 in.) over a six year period. If this rate continues, some compensation in the foundation will probably have to be made sometime in the next 10 to 12 years. This could be as minor as jacking and filling under the footings along the north one half of the structure to as major as a complete releveling of the entire structure and repairing of the cracked floor slab, footings, and foundation wall. The question that is left unresolved is whether the present rate will continue. 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