Patent Publication Number: US-2022235532-A1

Title: Methods and apparatus for foundation monitoring

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. provisional patent application Ser. No. 63/142,105, filed Jan. 27, 2021, and of U.S. provisional patent application Ser. No. 63/145,210, filed Feb. 3, 2021, which applications are herein incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     Field 
     The present disclosure generally relates to a method for monitoring the elevation and movement of a foundation upon which a structure is built, and an apparatus for autonomous capture of the data required for foundation monitoring of both new and existing foundations. 
     Description of the Related Art 
     The earth is constantly changing and moving, and this has an impact on the structures that are built upon it. Unfortunately, around 17% of the foundations in certain US regions will experience foundation damage over their lifetime and the cost to repair foundation damage can vary significantly. If the damage is caught early, repair costs are substantially less than if the damage is identified later; the repair costs may be minimal with the timely implementation of just a change to a foundation maintenance program. If left undetected, or if ignored, foundation damage can render a structure uninhabitable. 
     Effective early detection of foundation problems may be facilitated by the acquisition of competent measurements of the foundation itself. For example, a sensor may be moved within a conduit in a foundation, and may take readings of hydrostatic head of a surrounding fluid at various locations in the foundation, each reading indicative of the elevation of the conduit—and thus the foundation—at each location. However, such techniques are cumbersome, and are subject to error due to temperature effects and physical phenomena such as gas breakout/dissolution in the surrounding fluid. Furthermore, measurements taken at lengthy time intervals may not reveal the true extent of foundation movement over time. 
     Thus, there is a need for improved processes that facilitate efficient, effective, and accurate monitoring of foundations and other structures. 
     SUMMARY 
     The present disclosure generally relates to systems, apparatus, and methods for the evaluation of foundations. In one embodiment, a foundation monitoring system includes a sensor cartridge assembly. The sensor cartridge assembly includes a first sensor disposed in a sensor tube and a sensor head attached to an end of the sensor tube. The sensor head contains a second sensor. The foundation monitoring system further includes a raceway configured for attachment to a foundation. The sensor tube is configured to be inserted into the raceway. The foundation monitoring system further includes a data transmitter configured to receive data from the first and second sensors, and convey the data to a controller. 
     In another embodiment, a sensor cartridge assembly for a foundation monitoring system includes a first sensor disposed in a sensor tube. A payout line is disposed in the sensor tube. The payout line couples the first sensor to an anchor point at a first end of the sensor tube and to a guide shoe at a second end of the sensor tube. The sensor cartridge assembly further includes a sensor head attached to the first end of the sensor tube. 
     In another embodiment, a method of monitoring a foundation, includes acquiring temperature and pressure data from first and second sensors installed within a sensor tube attached to the foundation. The method further includes determining the temperature and pressure data from the first and second sensors to be stabilized. The method further includes deriving, from the temperature and pressure data, a first elevation of the first sensor and a second elevation of the second sensor with respect to a predetermined datum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, as the disclosure may admit to other equally effective embodiments. 
         FIG. 1  is a combined isometric and cross-sectional view of components of a foundation monitoring system. 
         FIG. 2  is a combined elevation and cross-sectional view of selected components of the foundation monitoring system of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a portion of the apparatus of  FIG. 2 . 
         FIG. 4  is a detailed view of a portion of  FIG. 1 . 
         FIG. 5  is a section view in a plan orientation of the components depicted in  FIG. 4 . 
         FIG. 6  is a combined isometric and cross-sectional view of components of a foundation monitoring system in an exemplary installation. 
         FIG. 7  is a detailed view of a portion of  FIG. 6 . 
         FIG. 8  is an isometric view of a sensor head assembly of a foundation monitoring system. 
         FIG. 9  is a combined isometric and cross-sectional view of the components depicted in  FIG. 8 . 
         FIG. 10  is a plan view of some of the components depicted in  FIG. 8 . 
         FIG. 11  is an elevation view of some of the components depicted in  FIG. 8 . 
         FIG. 12  is a section view of the components depicted in  FIG. 11 . 
         FIG. 13  is a detailed view of a portion of  FIG. 12 . 
         FIG. 14  is an elevation view of a portion of a foundation monitoring system installed on a structure. 
         FIGS. 15 to 18  are cross-sectional depictions of alternative deployments of an installation of a portion of a foundation monitoring system. 
         FIG. 19  depicts another embodiment of a foundation monitoring system. 
         FIG. 20  is a graph illustrating measurement accuracy obtainable by embodiments of the present disclosure in contrast to that obtained by other systems. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
     The present disclosure concerns systems, apparatus, and methods for the evaluation of foundations. Such evaluation may be undertaken for one or more purpose, such as, without limitation, an assessment of suitability for occupancy, identification of maintenance needs, success of completed repairs, independent confirmation of construction quality, prediction of future foundation issues, confirmation of engineering calculations, rapid testing of foundation performance evaluation during real estate transactions, or the creation of an actuarial database for the purpose of creating an insurance product. Other purposes for such evaluation are also contemplated. 
     Embodiments of the present disclosure include the use of sensors deployed at one or more discrete locations. Each sensor is fixed in place at a corresponding discrete location. Embodiments of the present disclosure include the use of sensors that are smaller than conventional, currently used sensors, and thus present greater utility regarding location access and power usage. Embodiments of the present disclosure include the use of sensors that are substantially insulated from the effects of changing atmospheric conditions. Examples of such changing atmospheric conditions include intra-day and inter-day heating and cooling, such as direct and indirect heating from sunshine and cooling during periods of rain or darkness. A further example of such changing atmospheric conditions includes instant localized variations in atmospheric pressure due to wind. 
       FIG. 1  is a combined isometric and cross-sectional view of components of a foundation monitoring system  1000 . The foundation monitoring system  1000  includes a sensor cartridge assembly  100 . Sensor cartridge assembly  100  includes a sensor head  110  coupled to a sensor tube  128 . The sensor head  110  is a container including a body  112  and a lid  114 . The sensor head  110  includes a datum  116  that is a reference point for measurements related to elevation of components, such as sensors, described below. The sensor head  110  includes a vent  118  that facilitates equalization of pressure between an interior and an exterior of the sensor head  110 . As illustrated, the vent  118  is located in the lid  114  of the sensor head  110 , however in some embodiments it is contemplated that the vent  118  may be positioned in the body  112  of the sensor head  110 . A tubing adapter  120  at the vent  118  facilitates the coupling to the sensor head  110  of tubing or equipment, such as a pressure balance tube  122 . The sensor head  110  contains a sensor  140  and associated wiring  130 . In some embodiments, it is contemplated that the sensor  140  measures and transmits data representative of a fluid pressure, such as a hydrostatic pressure. In some embodiments, it is contemplated that the sensor  140  measures and transmits data representative of a temperature. In some embodiments, it is contemplated that the sensor  140  measures and transmits data representative of a temperature and a fluid pressure (such as a hydrostatic pressure). 
     As illustrated, a single sensor tube  128  is coupled to the sensor head  110 . In some embodiments, it is contemplated that more than one sensor tube  128  may be coupled in parallel to the sensor head  110 . 
     The sensor tube  128  contains one or more additional sensors  140  similar to sensor  140  in the sensor head  110 , each additional sensor  140  coupled to associated wiring  130 . In some embodiments, it is contemplated that the sensors  140  within the sensor tube  128  are spaced at regular intervals along the sensor tube  128 . For example, each sensor  140  may be spaced ten feet (3 m) apart. Additionally, or alternatively, some sensors  140  may be spaced closer together along the sensor tube  128 , and other sensors  140  may be spaced further apart along the sensor tube  128 . For example, two sensors, A and B, may be spaced five feet (1.5 m) apart and a third sensor, C, may be spaced ten feet (3 m) from sensor B. Furthermore, in some embodiments, it is contemplated that each sensor  140  is positioned within the sensor tube  128  such that the location of each sensor  140  along the sensor tube  128  from a reference point (such as the datum  116 ) is known with reasonable accuracy, such as to within three inches (7.6 cm), to within two inches (5.1 cm), to within one inch (2.5 cm), to within half an inch (1.3 cm), or to within a quarter of an inch (0.6 cm). 
     As illustrated, in some embodiments, it is contemplated that each sensor  140  within the sensor tube  128  is connected to wiring  130  that is routed within the sensor tube  128  from each sensor  140  to the sensor head  110 . In some embodiments, it is contemplated that the wiring  130  connected to each corresponding sensor  140  may be discrete from other wiring  130  connected to another sensor  140 . In some embodiments, it is contemplated that each sensor  140  may be connected to common wiring  130 . In some embodiments, it is contemplated that the wiring  130  for individual sensors  140  may be bundled together as an integrated unit. In an example, wiring  130  connected to a first sensor  140  may be attached to wiring  130  connected to a second sensor  140  by one or more clips, cable ties, encapsulations, or sheaths. 
     The wiring  130  conveys electrical power to each sensor  140  and/or facilitates telemetry of data from each sensor  140  to the sensor head  110 . In some embodiments, it is contemplated that one or more sensor  140  may be powered by a battery instead of, or in addition to, being powered via the wiring  130 . In some embodiments, it is contemplated that data from one or more sensor  140  may be telemetered wirelessly. In some embodiments, it is contemplated that the wiring  130  may include an optical fiber line for the telemetry of data from one or more sensor  140 . In some embodiments, it is contemplated that command signals may be sent to one or more sensor  140  via the wiring  130  and/or wirelessly. 
     A guide shoe  132  is located at an end of the sensor tube  128 . In some embodiments, it is contemplated that an exterior surface of the guide shoe  132  may be rounded or chamfered. In some embodiments, it is contemplated that the guide shoe  132  is vented to permit fluids to enter the sensor tube  128  but not exit the sensor tube  128 . In some embodiments, it is contemplated that the guide shoe  132  is vented to permit fluids to exit the sensor tube  128  but not enter the sensor tube  128 . In some embodiments, it is contemplated that the guide shoe  132  is vented to permit fluids to enter and exit the sensor tube  128 . In some embodiments, it is contemplated that the guide shoe  132  is not vented, thereby preventing entry of fluids into, and exit of fluids from, the sensor tube  128 . 
     A payout line  134  within the sensor tube  128  is coupled to the guide shoe. The payout line  134  is coupled to each sensor  140  within the sensor tube  128  and to an anchor point  136 . As illustrated, the anchor point  136  is situated at or near to the location where the sensor tube  128  is coupled to the sensor head  110 . In some embodiments, it is contemplated that the anchor point  136  may be situated at other locations, such as elsewhere within the sensor head  110 . 
     The payout line  134  facilitates the placement of each sensor  140  within the sensor tube  128  at predetermined locations and separation distances, as described above. When the foundation monitoring system  1000  is deployed at a foundation and/or structure to be monitored, an identification of the location of each sensor  140  within the sensor tube  128  with respect to the foundation/structure is facilitated by the use of the payout line  134  to place each sensor  140  within the sensor tube  128 . In some embodiments, it is contemplated that when deployed, the location of each sensor  140  within the sensor tube  128  with respect to the foundation/structure is correlated against a known reference point of the foundation/structure. For example, such a correlation may be achieved via photographs, a verification of a construction plan, or otherwise as known by one skilled in the art of geospatial location. 
     In some embodiments, it is contemplated that the payout line  134  may be a wire or rod that is sufficiently stiff to withstand an axial compression load associated with being pushed into the sensor tube  128 , yet sufficiently flexible to conform to curvatures encountered during deployment of the sensor tube  128  at the foundation/structure. In an example, the payout line  134  is a high tensile strength wire, such as a wire used for electric fences. In some embodiments, it is contemplated that the payout line  134  may be corrosion-resistant. In some embodiments, it is contemplated that the payout line  134  may be readily wetted to a fluid introduced into the sensor tube  128 . 
     In some embodiments, it is contemplated that the wiring  130  and the payout line  134  may be bundled together as an integrated unit. In an example, the wiring  130  may be attached to the payout line  134  by one or more clips, cable ties, encapsulations, or sheaths. 
     In some embodiments, it is contemplated that the wiring  130  or the payout line  134  may be adapted to perform the functions of both the wiring  130  and the payout line  134 . In an example, wiring  130  is electrically or optically coupled to one or more sensor  140 , and facilitates the placement of each sensor  140  within the sensor tube  128  at predetermined locations and separation distances, as described above. In another example, the payout line  134  is coupled to one or more sensor  140  within the sensor tube  128 , and conveys electrical power to each sensor  140  and/or facilitates telemetry of data from each sensor  140  to the sensor head  110 . 
     The payout line  134  mechanically couples each sensor  140  within the sensor tube  128  to restrict relative horizontal movement between each sensor  140  within the sensor tube  128  over time, such as due to thermal expansion or contraction of the payout line  134  and/or the wiring  130 . Thus, when the sensor tube  128  is deployed at a foundation/structure, the data obtained over time from each sensor  140  within the sensor tube  128  is readily correlated with a corresponding single specific location of the foundation/structure, thereby facilitating an accurate assessment of the foundation/structure over time. 
       FIG. 2  is a combined elevation and cross-sectional view of selected components of the foundation monitoring system  1000  of  FIG. 1 .  FIG. 3  is a cross-sectional view of a portion of the sensor cartridge assembly  100  of  FIG. 2 . 
     Referring to both  FIGS. 2 and 3 , sensor  140  disposed in sensor tube  128  is representative of any sensor  140  of the foundation monitoring system  1000 . In some embodiments, as illustrated, it is contemplated that sensor  140  includes a printed circuit board  142  with a surface  144  on which are attached a connector  146  for attaching to wiring  130 , one or more sensor chip  148 , and a communication chip  150 . As described above, the one or more sensor chip  148  is configured to measure a pressure and/or a temperature of the ambient environment at the sensor  140 . In some embodiments, it is contemplated that the sensor  140  may include additional circuitry (such as an additional chip, an accelerometer, or the like) for measuring additional parameters, such as motion, vibration, time, etc. In some embodiments, it is contemplated that the sensor  140  and/or the one or more sensor chip  148  itself may include a memory. 
     The communication chip  150  is configured to transmit data measured by the one or more sensor chip  148  and any additional circuitry. The communication chip  150  transmits such data via the connector  146  and associated wiring  130 . Additionally, or alternatively, in some embodiments it is contemplated that the communication chip  150  may transmit at least a portion of such data wirelessly. 
       FIG. 2  further depicts a payout distance  158  of the sensor  140  with respect to a known reference point, such as datum  116 . As illustrated, the payout distance  158  is representative of the distance along the sensor tube  128  of the sensor chip  148  of sensor  140  from the datum  116 . The payout distance  158  thus refers to the location of the sensor  140  along the sensor tube  128 . 
     As illustrated, in some embodiments it is contemplated that a portion  160  of the payout line  134  near to the sensor  140  may be contorted into a “u” shape, or the like. As shown in  FIG. 3 , the sensor  140  is attached to the payout line  134  by a centralizer  152  and a retainer  154  such that the contorted portion  160  of the payout line  134  is oriented along an axis  156  that is substantially perpendicular to the surface  144  of the printed circuit board  142  of the sensor  140 . In an example, the axis  156  is 85 to 90 degrees, such as 86 to 90 degrees, or 88 to 90 degrees from the surface  144  of the printed circuit board  142 . The contorted portion  160  of the payout line  134  enables the payout line  134  to transfer an axial force to the sensor  140  along the sensor tube  128 . 
     Additionally, the centralizer  152  facilitates the placement of the sensor chip  148  substantially at the radial center of the sensor tube  128 , such as within a half inch (1.3 cm), within a quarter inch (0.6 cm), or within an eighth of an inch (0.3 cm) of the radial center of the sensor tube  128 . In some embodiments, it is contemplated that the contorted portion  160  of the payout line  134  bears against one portion of a sidewall of the sensor tube  128  and the centralizer  152  and/or retainer  154  bear(s) against one or more other portions of the sidewall of the sensor tube  128  in order to facilitate placement of the sensor chip  148  at or near to the radial center of the sensor tube  128 . In some embodiments, the contorted portion  160  of the payout line  134 , the centralizer  152  and/or the retainer  154  maintain placement of the sensor chip  148  at or near to the radial center of the sensor tube  128  regardless of the rotational orientation of the printed circuit board  142  within the sensor tube  128 . 
     In some embodiments, it is contemplated that the contorted portion  160  of the payout line  134  may be omitted, such that the centralizer  152  and/or retainer  154  alone maintain placement of the sensor chip  148  at or near to the radial center of the sensor tube  128 . In some embodiments, it is contemplated that the centralizer  152  may be omitted. In such embodiments, the retainer  154  attaches the payout line  134  to the printed circuit board  142 . Additionally, the retainer  154 /printed circuit board  142  may be self-centralizing. 
     In some embodiments, it is contemplated that the sensor  140  may be configured such that the sensor chip  148  is not placed at or near the radial center of the sensor tube  128 . For example, the sensor  140  may include an attachment and/or retainer  154  configured to offset the sensor chip  148  from the radial center of the sensor tube  128 . Such an example may include the use of a weight attached to the sensor so that the rotational orientation of the sensor  140  is maintained relatively constant by the Earth&#39;s gravity. Alternatively, a biasing element, such as a bow spring, may be attached to the sensor  140  in order to force the sensor  140  against the sidewall of the sensor tube  128 , thereby holding the sensor  140  rotationally in place. 
     In another example, the sensor  140  may be configured such that the sensor chip  148  may be positioned in a zone that includes the radial center of the sensor tube  128  and includes a region surrounding the radial center of the sensor tube  128 . 
     In embodiments in which a sensor chip  148  of a sensor  140  is positioned at the radial center of a sensor tube  128 , it is contemplated that the elevation of the point of measurement of the sensor chip  148  remains at the radial center of the sensor tube  128 , and hence at the same elevation with respect to the sensor tube  128 , even if the sensor  140  is rotated within the sensor tube  128 . Therefore, even if the sensor  140  is rotated within the sensor tube  128 , such as during an interval between acquiring measurements from the sensor  140 , each measurement is indicative of the elevation of the sensor tube  128  itself with respect to the corresponding sensor head  110 . Thus, in comparing measurements taken at different times, a change in the magnitude of the data values obtained from the sensor  140  can indicate that there has occurred a change in the elevation of the sensor tube  128 , and hence a change in the elevation of the portion of the foundation to which the sensor tube  128  is attached. 
     In embodiments in which a sensor chip  148  of a sensor  140  is positioned near to the radial center of a sensor tube  128 , it is contemplated that should the sensor  140  become rotated within the sensor tube  128  between or during acquiring measurements, any error in later measurements due to a change in elevation of the point of measurement of the sensor chip  148  with respect to the sensor tube  128  may be minor compared to other sources of inaccuracy, such as density variations of the sensor fluid  162  (described below) within the sensor tube  128 . 
     Nevertheless, it is contemplated that the propensity is low for a sensor  140  to become rotated within a sensor tube  128  between or during acquiring measurements, after the sensor tube  128  has been installed at work location. Hence, the propensity is low for a change in elevation with respect to the sensor tube  128  of the point of measurement of the sensor chip  148 . Therefore, in embodiments in which a sensor chip  148  of a sensor  140  is positioned away from the radial center of a sensor tube  128 , it is contemplated that rotation of the sensor  140  between or during acquiring measurements would not be a root cause of error when comparing the measurements. 
     The sensor tube  128  contains a sensor fluid  162 , such as a single phase fluid. In some embodiments, the sensor fluid  162  is a dielectric fluid, such as distilled water. Alternatively, the sensor fluid  162  may be a dielectric fluid with natural low water absorption propensity, such as is commonly used in liquid filled transformers. In other embodiments, the sensor fluid  162  is a dielectric fluid such as is common in electric discharge machining. Such fluids are suitable for exposure to air in their natural use condition, and are approved for use around personnel. In other embodiments, the sensor fluid  162  is a synthetic dielectric fluid. In other embodiments, the sensor fluid  162  is a dielectric oil, such as a mineral oil. Selection of a sensor fluid  162  can depend upon such aspects as local temperature extremes, environmental considerations, local regulations, etc. The sensor fluid  162  fills the sensor tube  128  such that each sensor  140  within the sensor tube  128  is immersed in the sensor fluid  162 . 
       FIG. 3  further depicts an elevation  164  of the sensor  140  with respect to a known reference point, such as datum  116 . In some embodiments, it is contemplated that the elevation  164  is derived from a measurement of hydrostatic pressure of the sensor fluid  162  by the sensor chip  148 . The hydrostatic pressure of the sensor fluid  162  is a function of the density of the sensor fluid  162 . The density of the sensor fluid  162  is a function of the temperature of the sensor fluid  162 . Measurements of temperature and pressure by the sensor chip  148  of each sensor  140  thus provide data from which the elevation  164  of each sensor  140  is derived. The elevation  164  is recorded for each sensor  140  corresponding to measurements obtained from each sensor  140  over time. 
     During assembly of the sensor cartridge assembly  100 , the sensor tube  128  is filled with sensor fluid  162 . In some embodiments, it is contemplated that the sensor tube  128  is filled with sensor fluid  162  in a manner that removes air from the sensor tube  128 . For example, the sensor fluid  162  may be introduced into the sensor tube  128  via a capillary line. In another example, the sensor tube  128  is positioned at an incline to promote the escape of air during filling with sensor fluid  162 . Additionally, or alternatively, a vacuum may be applied to the sensor tube  128  to evacuate air while filling the sensor tube  128  with sensor fluid  162 . Furthermore, the sensor tube  128  may be vibrated during and/or after introduction of the sensor fluid  162  in order to dislodge air bubbles so that the air bubbles can escape from the sensor tube  128 . 
       FIG. 4  is a detailed view of a portion of  FIG. 1 , and  FIG. 5  is a section view in a plan orientation of the components depicted in  FIG. 4 . A seal  126  prevents ingress of foreign material and water between component parts of the sensor head  110 , such as the lid  114  and the body  112 . One or more mounting fastener  124  facilitates the attachment of the sensor head  110  to a suitable mounting platform, such as a sensor head base described below. The sensor head  110  is attached to sensor tube  128  before installation of the sensor cartridge assembly  100  at a desired location at a foundation or building. 
     A swivel  138  at the anchor point  136  allows the sensor head  110  to be rotated with respect to the sensor tube  128  and the payout line  134 . In some embodiments, it is contemplated that the swivel  138  may be omitted. A seal stem  166  inserted into a fluid port  168  of the swivel  138  (or into the sensor tube  128  itself) isolates the sensor fluid  162  in the sensor tube  128  from other fluid in the sensor head  110 . The seal stem  166  mitigates potential loss of sensor fluid  162  from the sensor cartridge assembly  100  from spillage during transport and installation of the sensor cartridge assembly  100 . Once the sensor tube  128  has been installed at a desired location at a foundation or building, the seal stem  166  is removed from the swivel  138 . In an alternative embodiment, a valve or a rupture disc is disposed at the swivel  138  in place of the seal stem  166 . Upon removal of the seal stem  166  from the swivel  138 , the fluid port  168  is open such that a pressure within the sensor head  110  is communicated to the sensor fluid  162  in the sensor tube  128 . 
     The anchor point  136  for the payout line  134  is at the swivel  138 , and the wiring  130  from the sensor tube  128  is routed through the swivel  138 . In some embodiments, it is contemplated that the wiring  130  from the sensor tube  128  is routed through a sealed penetration through the swivel. In some embodiments, it is contemplated that the wiring  130  may terminate at an electrical connector within or outside the sensor head  110  to facilitate connection to additional wiring  130  routed to other components of the foundation monitoring system  1000 , such as another sensor head  110 , a power supply, and/or a controller. In such embodiments, it is contemplated that the electrical connector is suitable for use in a wet environment. 
     The swivel  138  permits relative rotation between the sensor head  110  and the sensor tube  128 . In some embodiments, it is contemplated that the swivel  138  includes a design incorporating a slip ring. 
       FIG. 6  is a combined isometric and cross-sectional view of components of the foundation monitoring system  1000  in an exemplary installation. Depicted are the typical soil layers found near a building foundation. For example, where a site initially is developed for construction, there exists a layer of native soil  302  with particular geotechnical properties. Often, a site is prepared first by a developer that brings in imported soil  304  to place on top of the native soil  302 . Imported soil  304  is placed for a variety of reasons, including the compensation of native soil  302  geotechnical properties, an adjustment to the site elevation, a modification to the drainage plan, etc. Topsoil  306  is usually placed on top of the soils surrounding the construction site. 
     A sensor head assembly  200  that includes one or more sensor heads  110  is located in a container  212 , such as a utility box, that is located below ground level  310 . Each sensor head  110  is part of a discrete sensor cartridge assembly  100 . In some embodiments, it is contemplated that the container  212  is fitted with a cover  214 , which, in the illustrated example, is at ground level  310 . In some of such embodiments, it is contemplated that the cover  214  may be thermally insulated. In some embodiments, the cover  214  may be omitted. In some embodiments, it is contemplated that at least a portion of the container  212  may be above ground level  310 . 
     The sensor head assembly  200  is affixed to an anchor base  218  via connectors  216 . In some embodiments, it is contemplated that the anchor base  218  is set in concrete. In some embodiments, it is contemplated that the anchor base  218  is set in a soil, such as native soil  302 , imported soil  304 , or backfill soil  308 . 
     A tubular conduit, such as raceway  220 , extends below each corresponding sensor head  110  below ground level  310 , such as through concrete, through the native soil  302 , through the imported soil  304 , and/or through backfill soil  308 . The sensor tube  128  of each sensor cartridge assembly  100  extends within a corresponding raceway  220 . As illustrated, a plurality of raceways  220  are routed through a raceway protector  222 . The raceway protector  222  is shown as being deployed in backfill soil  308 . In some embodiments, it is contemplated that the raceway protector  222  may be deployed in concrete. Sensors  140  within an individual sensor tube  128  are afforded at least some protection from external elements by being situated within the sensor tube  128 , which is within a raceway  220 , which is within the raceway protector  222 , which is within backfill soil  308  and/or concrete. Moreover, placing the sensor head assembly  100  below ground level  310  allows the sensor fluid  162  inside each sensor cartridge assembly  100 , raceway  220 , and sensor tube  128  to benefit from the thermal insulating properties of the topsoil  306 , imported soil  304 , backfill soil  308 , and (depending on the depth) the native soil  302  at the construction site. 
     In some embodiments, it is contemplated that a drain is included to route water out of the container  212 . In an example, the drain includes a hole or excavation backfilled with sand or gravel. 
       FIG. 7  is a detailed view of a portion of  FIG. 6 . The raceway protector  222  is illustrated as containing a plurality of raceways  220  and an electrical raceway  236 . Each raceway  220  contains a sensor tube  128  of a corresponding sensor cartridge assembly  100 . The wiring  130  in the electrical raceway  236  (at the 12 o&#39;clock position) is routed between the sensor head assembly  200  and a power supply, and/or a controller. In each of the raceways  220 , a sensor tube  128 , payout line  134 , and sensor fluid  162  are depicted; wiring  130  has been omitted for clarity. An annulus  228  exists between each raceway  220  and the corresponding sensor tube  128 . In some embodiments, it is contemplated that the annulus  228  contains a fluid, such as sensor fluid  162 . 
       FIG. 8  is an isometric view of components of sensor head assembly  200  of foundation monitoring system  1000 . The sensor head assembly  200  is illustrated as including a plurality of sensor heads  110 . In some embodiments, it is contemplated that the sensor head assembly  200  may include a single sensor head  110 . In an example, a plurality of sensor cartridge assemblies  100 , and hence a plurality of sensor heads  110 , could be required if the foundation being measured has a relatively large surface area (such as about 2,500 square feet (about 232 square meters) or greater), or if readings are required from within the foundation in addition to perimeter readings. 
     Each sensor head  110  is mounted on a sensor head base  202 . The pressure balance tube  122  from each sensor head  110  is coupled to a pressure balance chamber  204  that is also mounted on the sensor head base  202 . As shown, each pressure balance tube  122  is coupled to the pressure balance chamber  204  in parallel. In some embodiments, it is contemplated that the pressure balance tubes  122  of at least two sensor heads  110  may be coupled in series with the pressure balance chamber  204 . 
     Each pressure balance tube  122  is looped from the top of a corresponding sensor head  110  to the top of the pressure balance chamber  204 . Each loop is oriented upwards from the top of the corresponding sensor head  110  then downwards to the top of the pressure balance chamber  204 . Such an arrangement is beneficial in the event of flooding, such that rising water is inhibited from entering the sensor head  110 . The ability of the sensor cartridge assembly  100  to remain submersed and still acquire sensor data has particular utility in establishing early indications of foundation damage during events like floods and hurricanes. 
     In some embodiments, not shown, it is contemplated that each sensor head  110  may be coupled to a corresponding individual pressure balance chamber instead of a common pressure balance chamber  204 . In such embodiments, it is contemplated that each individual pressure balance chamber is connected to the corresponding sensor head  110  at the tubing adapter  120  of the sensor head  110 . It is further contemplated that each individual pressure balance chamber may include a bladder filled with air or with nitrogen, such as pure nitrogen at 95% or greater purity. It is further contemplated that the bladder may be pressurized, such that the contents are released into the sensor head  110  upon opening a valve between the sensor head  110  and the individual pressure balance chamber. 
     Returning to  FIG. 8 , wiring  130  external to the sensor head  110  can be routed as needed. As illustrated, in an exemplary installation, wiring  130  is routed from a sensor head  110  through a cord grip  232  and a conduit adapter  234  into an electrical raceway  236 . Such an installation is waterproof. It is contemplated that the electrical raceway  236  routes the wiring  130  to a power source and/or control unit, such as a data transmitter as described below. 
     The sensor head assembly  200  includes an assembly base  203  below the sensor head base  202 . The assembly base  203  is coupled to a threaded portion of each connector  216  from the anchor base  218  by one or more fasteners  238 , such as nuts. The sensor head base  202  is also coupled to the threaded portion of each connector  216  from the anchor base  218  by one or more fasteners  240 , such as nuts. As illustrated, in some embodiments it is contemplated that the sensor head assembly  200  includes a levelling indicator  242 . The levelling indicator  242  provides a reference showing whether or not the sensor head base  202  is oriented horizontally. Modification of the orientation of the sensor head base  202  with respect to horizontal is achieved by adjusting the fasteners  240  with respect to one or more connector  216 . 
     In some embodiments, it is contemplated that data from a sensor  140  within each of three (or more) sensor heads  110  mounted on the sensor head base  202  may be used to indicate whether or not the sensor head base  202  is horizontal. 
     In some embodiments, it is contemplated that the sensor head base  202  may be substantially horizontal, such as within ten degrees, within five degrees, within three degrees, or within one degree of horizontal. In some embodiments, it is contemplated that the sensor head base  202  may not be substantially horizontal, for example, where only a single sensor head  110  is installed on the sensor head base  202 . Nevertheless, maintaining the sensor head base  202  substantially horizontal facilitates appropriate positioning of the pressure balance chamber  204  to provide for pressure balancing between each sensor head  110 , and to mitigate a risk of flood water ingress into a sensor head  110 . 
       FIG. 9  is a combined isometric and cross-sectional view of the components depicted in  FIG. 8 . Each raceway  220  is connected to the assembly base  203  via a corresponding raceway adapter  224 . The sensor tube  128  of each sensor cartridge assembly  100  extends from each corresponding sensor head  110  and through a corresponding raceway adapter  224  into the corresponding raceway  220 . Each sensor tube  128  extends between the sensor head base  202  and the assembly base  203 , and is surrounded by a corresponding boot  226  that is coupled to the sensor head base  202  and to the assembly base  203 . Each boot  226  inhibits the entry of debris or other foreign matter into each raceway  220 . 
     In some embodiments, it is contemplated that each boot  226  is sufficiently flexible to allow for adjustment of the sensor head base  202  when positioning the sensor head base  202  substantially horizontal, while maintaining contact with the sensor head base  202  and with the assembly base  203 . In an example, the boot  226  is made of an elastomer. In some embodiments, it is contemplated that each boot  226  may seal against the sensor head base  202 . In some embodiments, it is contemplated that each boot  226  may seal against the assembly base  203 . 
     In some embodiments, it is contemplated that a single boot  226  may surround a single sensor tube  128 . In some embodiments, it is contemplated that a single boot  226  may surround a plurality of sensor tubes  128 . 
     In some embodiments, it is contemplated that the assembly base  203  and the boot  226  may be omitted. In such embodiments, the sensor head  110  may be coupled to the sensor tube  128  and to the corresponding raceway  220  by a bushing. In an example, the bushing includes a top connection to the sensor head  110 , an outer bottom connection to the raceway  220 , and an inner bottom connection to the sensor tube  128 . 
       FIG. 10  is a plan view of some of the components depicted in  FIG. 8 , and  FIG. 11  is an elevation view of some of the components depicted in  FIG. 8 . In some embodiments, it is contemplated that by affixing all sensor heads  110  onto the sensor head base  202 , the sensor head base  202  provides a reference point—such as the top surface of the sensor head base  202 —for determining the elevation of each sensor  140 . Such a reference point can be the same as, or equivalent to, datum  116  for an individual sensor cartridge assembly  100 . Additionally, such a reference point is useful if a first (originally installed) sensor cartridge assembly  100  is removed and replaced by a second (replacement) sensor cartridge assembly  100 . Such a reference point can provide a consistent comparison basis for data derived from each sensor  140  of both the first and second sensor cartridge assemblies  100 . Thus, data derived from sensor(s)  140  of the first sensor cartridge assembly  100  may be readily compared with data derived from sensor(s)  140  of the second cartridge assembly  100 . 
     As illustrated, a first levelling indicator  242  is aligned between two connectors  216 , and a second levelling indicator  242  is aligned between the first levelling indicator  242  and a third connector  216 . Adjustment of the fasteners  240  while monitoring the levelling indicators  242  enables an operator to configure the sensor head base  202  to be substantially horizontal. Once so leveled, an operator can determine whether the sensor head base  202  continues to remain level, such as by periodic inspection of the levelling indicators  242 , or via sensor readings from three or more non-collinear sensor heads  110  mounted on the sensor head base  202 . In some embodiments, it is contemplated that an operator may not perform a levelling operation, such as if only a single sensor cartridge assembly  100  is to be installed at the sensor head base  202 . 
       FIG. 12  is a section view of the components depicted in  FIG. 11 . Sensor fluid  162  fills each sensor tube  128  and up to a sensor fluid level  244  within each sensor head  110 . In some embodiments, it is contemplated that the sensor fluid level  244  within each sensor head  110  is substantially the same, such as within 0.2 inches (5 mm). In some embodiments, it is contemplated that the sensor fluid level  244  within each sensor head  110  is not substantially the same. In some embodiments, it is contemplated that the sensor fluid level  244  within each sensor head  110  is managed such that a known offset exists between the sensor fluid level  244  in one sensor head  110  and the sensor fluid level  244  in another sensor head  110 . 
     In some embodiments, it is contemplated that the sensor fluid level  244  within each sensor head  110  is above each corresponding sensor  140  within each sensor head  110 . The monitoring and adjustment of sensor fluid level  244  may be performed during maintenance. In some embodiments, it is contemplated that anomalous readings from a sensor  140  in a sensor head  110  may indicate that a drop of sensor fluid level  244  below the sensor  140  has occurred. In an example, the anomalous readings may relate to changes in the data obtained from a single sensor  140  over time. In another example, the anomalous readings may relate to changes in the data obtained from a single sensor  140  compared to data obtained from other sensors  140  in other sensor heads  110 . 
       FIG. 13  is a detailed view of a portion of  FIG. 12 . A seal  210  prevents ingress of foreign material and water between component parts of the pressure balance chamber  204 . Air pressure acting on the sensor fluid  162  at the sensor fluid level  244  in a sensor head  110  is communicated via pressure balance tube  122  linking the sensor head  110  with the pressure balance chamber  204 . A pressure balance passage  208  out of the bottom of the pressure balance chamber  204  and through the sensor head base  202  enables air pressure within the pressure balance chamber  204  to be equalized against atmospheric pressure. A filter  206  inhibits ingress of foreign material, such as dust, debris, organic material (such as plant roots or insects), or other material transported by other contaminating sources such as ants, into the pressure balance chamber  204 . 
     In some embodiments, it is contemplated that the pressure balance passage  208  may include a valve that regulates movement of air through the pressure balance passage  208 . In an example, the valve may operate like a float valve in a cistern such that rising water causes the valve to close, thereby inhibiting flood water from entering the pressure balance chamber  204 . Similarly, when the water level drops below a predetermined point, the valve may open to reestablish pressure communication between the pressure balance chamber  204  and the atmosphere. In another example, the valve may be actuated to close and open by a controller. 
     In another embodiment, a diaphragm within the pressure balance chamber  204  separates the air that is communicated through the pressure balance tube(s)  122  from the atmosphere within the container  212 . For example, an elastomeric diaphragm may be sufficiently flexible to deform when subject to a pressure difference, but also effect a seal to prevent contamination of the air communicated through the pressure balance tube(s)  122  by foreign material and water. 
     The above measures assist in preserving the quality of the sensor fluid  162 . In an example, the filter  206 , seal  210 , valve, and/or diaphragm inhibit impurities from being introduced into the sensor fluid  162  that may alter the density or other properties of the sensor fluid  162 . In some embodiments, the pressure balance chamber  204  may contain a desiccant. 
     In some embodiments, it is contemplated that installation of the foundation monitoring system  1000  at a work site includes pre-installing one or more raceway  220  at a foundation. The sensor head base  202 , assembly base  203 , and anchor base  218  are put in place. In some embodiments, it is contemplated that the sensor head base  202  is then adjusted to be horizontal, such as by manipulation of the fasteners coupling the sensor head base  202  to the connectors  216  (see  FIG. 8 ). 
     Deployment of a sensor cartridge assembly  100  at a location where there exists a pre-installed raceway  220  involves inserting the sensor tube  128 —containing one or more sensor  140  and sensor fluid  162 —of the sensor cartridge assembly  110  into the corresponding raceway  220 . During insertion of the sensor tube  128  into the corresponding raceway  220 , friction between the sensor tube  128  and the raceway  220  can hinder travel of the sensor tube  128  through the raceway  220 . In some embodiments, such friction is mitigated by a selection of materials of the raceway  220  and/or of the sensor tube  128 . For example, one or both of the sensor tube  128  and/or the raceway  220  may be manufactured from a low friction material, such as a plastic, such as polyvinylchloride or polytetrafluoroethylene. In another example, one or both of the sensor tube  128  and/or the raceway  220  may include a coating of a low friction material, such as polytetrafluoroethylene. 
     In some embodiments, it is contemplated that the raceway  220  is cleaned prior to inserting the sensor tube  128 . In some embodiments, it is contemplated that fluid in the annulus  228  between the raceway  220  and the sensor tube  128  is configured to lubricate the passage of the sensor tube  128  through the raceway  220 . In an example, the fluid in the annulus  228  may include a lubricant. In a further example, the fluid in the annulus  228  may be selected to provide a low friction interface between the sensor tube  128  and the raceway  220 . For instance, the fluid in the annulus  228  may be a mineral oil. In another example, a lubricant may be added to the exterior of the sensor tube  128  and/or to the interior of the raceway  220 . In such embodiments, it is contemplated that the lubricant may be added before and/or during insertion of the sensor tube  128  into the raceway  220 . In some embodiments, it is contemplated that the fluid in the annulus  228  may mitigate friction between the sensor tube  128  and the raceway  220  due to buoyancy of the sensor tube  128  in the fluid in the annulus  228 . 
     Deployment of the sensor cartridge assembly  100  continues until the sensor head  110  is positioned close to the sensor head base  202  of the sensor head assembly  200 . In embodiments in which the sensor tube  128  is connected to the sensor head  110  via a swivel  138 , the swivel  138  allows the sensor head  110  to be rotated relative to the sensor tube  128  as needed to align the mounting fasteners  124  with corresponding mounting points on the sensor head base  202 . In embodiments in which the swivel  138  is omitted, the sensor head  110  and the sensor tube  128  are rotated as needed to align the mounting fasteners  124  with corresponding mounting points on the sensor head base  202 . 
     When the sensor head  110  is then lowered and positioned on the sensor head base  202 , the mounting fasteners  124  are operated to secure the sensor head  110  to the sensor head base  202 . The wiring  130  is interconnected and routed as needed. The seal stem  166  is removed from the sensor head, and the sensor fluid  162  may be topped up as needed such that the sensor  140  within the sensor head  110  becomes submerged in sensor fluid  162 . The pressure balance tube  122  is connected to the sensor head  110 . 
     Removal of a sensor cartridge assembly  100  from an installation involves disconnecting the pressure balance tube  122 , disconnecting the wiring  130 , and disconnecting the mounting fasteners  124 . In some embodiments, it is contemplated that the seal stem  166  is reinstalled in the sensor head  110 , for example, to prevent loss of sensor fluid  162  via drainage during subsequent removal and transport of the sensor cartridge assembly  100 . Removal of the sensor cartridge assembly  100  continues by pulling on the sensor head  110  to cause the sensor tube  128  and all components therein to be withdrawn. Thus, individual sensor cartridge assemblies  100  can be removed and replaced as needed. 
     In some embodiments, it is contemplated that a raceway  220  may be routed around and/or within a foundation such that there exist multiple bends of the raceway  220 . Deployment (and/or retrieval) of the sensor tube  128  within such a raceway  220  may be accomplished by employing one or more friction mitigation measures discussed above. In an example, a single sensor tube  128  may be deployed in a raceway  220  to a total payout distance  158  of more than 350 feet (107 m) and including a number of bends that total 1,440°. Thus, in some embodiments, it is contemplated that the monitoring of some foundations may be accomplished with the installation of a single sensor cartridge assembly  100 . Nevertheless, in some embodiments it is contemplated that the monitoring of some foundations may be accomplished with the installation of a plurality of sensor cartridge assemblies  100 . 
     With the ability to push sensor tube  128  around bends in a raceway  220  and achieve long runs, a foundation may be monitored by sensors  140  in a sensor tube  128  that is placed within a raceway  220  mounted to the perimeter of a foundation. The foundation may be newly constructed or pre-existing. As discussed above, the accuracy of the data obtained from the sensors  140  is enhanced by thermally insulating the raceway  220  and sensor tube  128  therein from daily thermal and atmospheric pressure changes, and by placing the raceway  220  below ground level  310 . A raceway  220  may be fitted to a perimeter of an existing foundation and/or a perimeter of an existing structure, and sensor tube  128  with sensors  140  may be installed in the raceway  220  in order to provide monitoring of the perimeter of the foundation and/or the perimeter of the structure, respectively. Such an installation may be planned prior to the creation of the foundation and/or the structure. Alternatively, or additionally, such installation may be planned and executed as a retrofit to an existing foundation and/or an existing structure. 
       FIG. 14  is an elevation view of a portion of foundation monitoring system  1000  installed on a structure. The structure includes a building  320  atop a foundation  322 . Wiring  130  from one or more sensor head assembly  200  is routed via electrical raceway  236  to a data transmitter  250 . In some embodiments, it is contemplated that the wiring  130  conveys power and/or control signals to the sensors  140  deployed in the foundation monitoring system  1000 . In some embodiments, it is contemplated that the wiring  130  conveys sensor data to the data transmitter  250 . In some embodiments, it is contemplated that sensor data is conveyed to the data transmitter  250  wirelessly. 
     In some embodiments, it is contemplated that the data transmitter  250  is an Internet of Things gateway. It is further contemplated that the data transmitter  250  may transmit data via any one or more of a cellular network, an Ethernet cable, Wi-Fi, Bluetooth, or another communication protocol. As illustrated, the data transmitter  250  is powered via a power connection  252 , such as to an electrical outlet. In some embodiments, it is contemplated that the data transmitter  250  may be powered by any one or more of an electrical supply to the building, a battery, or a solar panel. The data transmitter  250  receives data from each sensor  140 , and conveys the data to a controller, such as a computer. 
       FIGS. 15 to 18  are cross-sectional depictions of alternative deployments of a portion of an installation of foundation monitoring system  1000 . In  FIG. 15 , a spacer  314  is provided between a foundation  322  and another structure, such as flatwork  312 . It is contemplated that the spacer  314  may be any convenient material, such as wood or loose brick, that is removable without disturbing the foundation  322  or the flatwork  312 . Beneath the spacer  314 , and against the foundation  322 , is a provision  316  for a raceway. In some embodiments, it is contemplated that the provision  316  for the raceway is an excavated portion of the ground that has been backfilled with soil, sand, and/or gravel. As illustrated, a raceway anchor  260  is attached to the foundation  322  at the time of constructing the provision  316  for the raceway. In some embodiments, it is contemplated that the raceway anchor may be attached to the foundation at the time when the raceway itself is installed. In the event that a raceway is to be installed against the foundation  322  as a retrofit, the spacer  314  and provision  316  for the raceway are removed. Then a raceway is anchored to the foundation  322  by raceway anchor  260 , and the soil, sand, and/or gravel is returned and packed around the raceway. Then the spacer  314  is replaced. 
     In  FIG. 16 , a raceway anchor  260  is attached to the foundation  322  at the time of constructing the provision  316  for the raceway. In some embodiments, it is contemplated that the raceway anchor  260  may be attached to the foundation at the time when the raceway itself is installed. In the event that a raceway is to be installed against the foundation  322  as a retrofit, the flatwork  312  (or topsoil, if present) abutting the foundation  322  is removed, and then a raceway is anchored to the foundation  322  by raceway anchor  260 . Thereafter, the flatwork  312  is replaced, such as by pouring concrete over the raceway. Alternatively, the topsoil is replaced as desired. 
       FIG. 17  depicts a raceway  220  placed within the foundation  322 . In some embodiments, it is contemplated that at least a portion of the raceway  220  may be installed within the foundation  322 , and at least a portion of the raceway  220  may be attached to an external portion of the foundation  322 . Thus, sensors  140  installed in such a raceway  220  may be placed within the foundation  322  and along a perimeter of the foundation  322 . Additionally, or alternatively, a first raceway  220  may be installed within the foundation, and a second raceway  220  may be attached to an external portion of the foundation  322 . Hence, sensors  140  of a first sensor cartridge assembly  100  may be placed within the foundation  322 , and sensors  140  of a second sensor cartridge assembly  100  may be placed along a perimeter of the foundation  322 . 
     The placement of sensors  140  within a foundation  322 , and optionally at the perimeter of a foundation  322 , enables the curing of the concrete of the foundation  322  to be monitored. In some embodiments, it is contemplated that the monitoring may be achieved by sensors  140  at spaced intervals, such as at 10 feet (3 m) intervals, across the foundation  322 —centrally and peripherally. Since the curing of concrete is exothermic, the monitoring may include measuring temperatures at each sensor location continuously or at regular time intervals. Thus, a temperature map of the foundation  322  may be created that is akin to a map of the progress of curing over time. Hence, when temperature stabilization is observed, the timing of further work, such as the building of a structure on the foundation  322 , may be optimized. It is contemplated that the monitoring of curing at specific locations and then monitoring subsequent vertical movement has particular utility in facilitating improving engineering design guidelines. 
       FIG. 18  depicts an embodiment in which a sensor tube  128  is deployed against a foundation  322  without a raceway. Such an embodiment is of utility for short term readings, such as during a real estate transaction to determine the relative movement of a foundation  322  in a matter of weeks or days. The sensor tubing  128  is clipped to a tubing anchor  262  that is attached to the foundation  322 . The tubing anchor  262  is attached to the foundation  322  by a fastener, such as a screw that penetrates into the foundation. In some embodiments, it is contemplated that the location of fastening the tubing anchor  262  to the foundation  322  may serve as a reference point for data measured by a sensor  140  in the attached sensor tube  128 . Such an installation of a sensor tube  128  enables removal and replacement of the sensor tube  128  despite the lack of a raceway. 
     A tubing protector  264  is attached to the foundation  322  and covers the sensor tube  128 . The tubing protector  264  prevents materials, such as soil, from impacting and distorting or damaging the sensor tube  128 . In some embodiments, it is contemplated that thermal insulation  266  may be placed in the tubing protector  264  and around the sensor tube  128 . In some embodiments, it is contemplated that the thermal insulation  266  may be omitted. In some embodiments, it is contemplated that the tubing protector  264  may be omitted. 
       FIG. 19  depicts another embodiment in which a sensor tube  128  is deployed against a foundation  322  without a raceway. Sensor tube  128  containing sensors  140  is attached to the foundation  322  by one or more tubing anchor  262 , and is coupled to a sensor head  110  that is disposed below ground level  310  in a container  212 , such as utility box. In some embodiments, it is contemplated that the container  212  is fitted with a cover  214 , which in the illustrated example is at ground level  310 . In some of such embodiments, it is contemplated that the cover  214  may be thermally insulated. In some embodiments, the cover  214  may be omitted. In some embodiments, it is contemplated that at least a portion of the container  212  may be above ground level  310 . 
     As in other embodiments described above, the sensor head  110  contains a sensor  140 , and the sensors  140  in the sensor tube  128  and sensor head  110  are immersed in sensor fluid  162 . A pressure balance tube  122  from the sensor head  110  includes a valve  270  and a vent  272 . In some embodiments, measurements from the sensors  140  are taken when the valve  270  is open in order to prevent buildup of pressure inside the sensor head  110  and sensor tube  128 . In some embodiments, the valve  270  is closed while obtaining measurements from the sensors  140 . The closed valve  270  isolates the sensor fluid  162  from intrusion of foreign matter (such as air, moisture, and debris), and in the absence of a physical pressure compensation, sensor measurements are corrected as a function of pressure variations inside the closed system of sensor head  110  plus sensor tube  128  as temperatures change. In some embodiments, measurements from the sensors  140  are taken when the valve  270  is open and when the valve  270  is closed. In another embodiment, a fluid cap may be used in place of the valve  270 . 
     In all of the above embodiments, measurements from each sensor  140  are utilized for any one of a variety of assessments of a foundation and/or a structure built upon a foundation. Example structures include, without limitation, buildings, dams, walls, tunnels, bridges, storage tanks, wind turbine, or any other construction upon the Earth&#39;s surface. Example assessments include, without limitation, maintenance interval prediction, repair evaluation, performance evaluation of contractors, actuarial data and insurance, intentional stress testing of foundation designs, and comparative performance analysis of foundation designs. 
     In all of the above embodiments, measurements from each sensor  140  are obtained without moving the sensor  140  from one measurement location to another measurement location in between taking measurements. The sensor  140  is used to acquire measurements over the course of a time period that may be seconds, minutes, hours, days, weeks, months, or years in duration. Measurements from each sensor  140  may be taken whenever necessary. For example, measurements from each sensor  140  may be taken at regular time intervals, such as hourly, daily, weekly, bi-weekly, monthly, bi-monthly, quarterly, semi-annually, annually, etc. In another example, measurements from each sensor  140  are taken continuously or continually over a time period, such as every few seconds or every few minutes. 
     Each measurement may involve taking a set of readings from a sensor for several seconds, minutes, or hours. Each set of readings may involve taking a reading every second, or every multiple of seconds (such as every two seconds), or every fraction of a second (such as every tenth of a second). An interval between successive measurements may last a number of minutes, a number of hours, a number of days, a number of weeks, a number of months, or a number of years. In an example, readings from each sensor  140  are taken continually over a short time period, such as two minutes, and repeat batches of readings are taken at regular time intervals, such as hourly, daily, weekly, bi-weekly, monthly, bi-monthly, quarterly, semi-annually, annually, etc. 
     In another example, measurements from each sensor  140  are obtained based on the existence of a predetermined environmental condition, such as an ambient temperature condition, such as a daily low temperature. For instance, readings from each sensor  140  may be obtained continually over a predetermined time period, and correlated against local ambient temperature data. In another example, readings from each sensor  140  are taken continually over a time period such that a stabilization of the readings from individual sensors  140  can be established. Stabilized readings from each sensor  140  can then be selected for analysis. 
     In some embodiments, it is contemplated that readings from each sensor  140  are deemed to be stabilized when a magnitude of a difference between successive readings, or a standard deviation of a set of readings, is less than or equal to a threshold value, such as 1 psi (0.07 bar) or 1° F. (0.56° C.). Threshold values of other magnitudes are also contemplated, according to a selection by an operator or by an algorithm executed by a controller of the foundation monitoring system  1000 . In some embodiments, it is contemplated that the threshold value may be determined as a fraction of the value of a selected reading, such as 10%, 5%, 2%, 1%, or 0.5%. 
     In some embodiments, it is contemplated that readings from each sensor  140  are deemed to be stabilized when a magnitude of a difference between calculated elevations derived from successive readings, or a standard deviation of calculated elevations derived from each reading of a set of readings, is less than or equal to a threshold value. In an example, readings from each sensor  140  are deemed to be stabilized when a standard deviation of calculated elevations derived from each reading of a set of readings is less than or equal to 0.5 inches (1.27 cm). Threshold values of other magnitudes are also contemplated, according to a selection by an operator or by an algorithm executed by a controller of the foundation monitoring system  1000 . 
     In a further example, readings from each sensor  140  are used to calculate a set of raw elevation values of each sensor  140  with respect to the datum  116 . A standard deviation of the set of raw elevation values of each sensor  140  is then determined and compared to a threshold value. In one example, the threshold value 0.5 inches (1.27 cm). Threshold values of other magnitudes are also contemplated, according to a selection by an operator or by an algorithm executed by a controller of the foundation monitoring system  1000 . The readings from a particular sensor  140  are determined to be stabilized if the standard deviation of the set of raw elevation values is less than or equal to the threshold value. Additionally, or alternatively, the readings from a plurality of sensors  140  are determined to be stabilized if the standard deviations of the sets of raw elevation values from each sensor  140  is less than or equal to the threshold value. 
     It is contemplated that derivation of an elevation of a sensor  140  relative to the datum  116  may include a statistical analysis of the raw elevation values calculated for the sensor  140 . In an example, the statistical analysis includes calculating a mean of the raw elevation values, such as an arithmetic mean, a weighted mean, a geometric mean, or a harmonic mean. 
     It is contemplated that any of the above examples of sensor measurement regimes may be combined. It is further contemplated that the data from any of the above examples of sensor measurement regimes may be filtered according to one or more data reliability indicator, such as the values obtained, the stability of the measurements over time, and the like. 
     Moreover, in some embodiments, it is contemplated that measurements are acquired from any two or more sensors  140  simultaneously. In an example, a set of first readings is obtained from a first sensor  140  over the course of a first time period, such as ten minutes. A set of second readings is acquired from a second sensor  140  over the course of a second time period that at least partially overlaps with the first time period. It is contemplated that the second time period may be coincident with the first time period. It is also contemplated that the second time period may be longer in duration than the first time period. It is also contemplated that the second time period may be shorter in duration than the first time period. The first and second sensors  140  may be included in the same sensor cartridge  100 , or may be included in different sensor cartridges  100 . In some embodiments, the first and second sensors  140  may be located in the same sensor tube  128 . In some embodiments, the first sensor  140  is located in a sensor tube  128 , and the second sensor is located in a sensor head  110 . 
     In conventional systems in which a single sensor is moved to a plurality of locations within a tube in order to acquire readings at those locations, environmental changes may occur between the taking of readings from the sensor at the first location and the taking of readings at one or more subsequent locations. Such environmental changes may include changes in ambient temperature or pressure, and can adversely affect the accuracy of any correlation between the data acquired at each location. 
     In contrast, embodiments described herein facilitate the synchronization of reading acquisition from each sensor  140 . Thus, readings from each sensor  140 —and hence at each measurement location within each sensor tube  128 —may be acquired simultaneously. Additionally, or alternatively, readings from a first sensor  140  may be acquired at a short time interval, such as a few seconds, 30 seconds, one minute, etc., before readings from a second sensor  140  are acquired. By obtaining readings from two or more sensors  140  simultaneously (such as described above), a user is able to acquire data pertaining to a foundation in which any adverse effect of environmental changes during the acquisition of the data is mitigated. 
       FIG. 20  is a graph illustrating an exemplary measurement accuracy obtainable by embodiments of the present disclosure in contrast to that obtained by other systems. The x axis represents the payout distance  158  of each sensor  140  from the reference point datum  116  (referenced in  FIG. 2 ); the y axis represents a standard deviation of measured/derived elevation data produced by the represented systems. The dashed line  280  represents the standard deviation of elevation data produced by a comparative system that involves moving a single sensor within a raceway  220  to a number of measuring stations. The solid line  282  represents the standard deviation of measured/derived elevation data produced by a foundation monitoring system  1000  of the present disclosure. 
     In the comparative system, a single sensor is placed at a distal end of a tube that is analogous to the sensor tube  128  of the present disclosure. The tube contains a fluid. The tube with the sensor therein is translated inside of a raceway to a first measuring station (at a payout distance 110 ft (33.5 m) in this example). Then, a waiting period (such as 20 minutes) is undertaken to allow for thermal stabilization of the fluid within the tube. At least a portion of the fluid is above ground level  310  in this apparatus, while the raceway and sensor are below ground level  310 . Next, once the fluid within the tube has thermally stabilized, a first set of measurements is taken by the sensor. Then the sensor is moved to a second measuring station, such as at a location ten feet (3 m) from the first measuring station. Movement of the sensor to the second measuring station causes hydraulic pressure waves in the fluid within the tube, and may also cause further thermal instability of the fluid within the tube. Because temperature and pressure fluctuations of the fluid within the tube affect the measurements taken by the sensor, another waiting period is undertaken before capturing measurements from the sensor at the second measuring station. The sensor is then moved to successive measuring stations at which the above operations are repeated. 
     The dashed line  280  represents the standard deviation of elevation data produced by the comparative system. In the example presented, the data was acquired daily over a period of a few months. Although the standard deviations at payout distances from about 40 feet (12 m) to 110 feet (33.5 m) appear acceptable, the standard deviations at payout distances less than about 40 feet (12 m) are unacceptable. It has been determined that the source of the unacceptable standard deviations is thermal in nature, such as resulting from at least a portion of the fluid within the tube being above ground level while another portion of the fluid within the tube is below ground level at the time the measurements are obtained from the sensor. For example, a temperature gradient exists between the different portions of the fluid within the tube, resulting in the fluid within the tube having a density gradient that influences pressure measurements taken by the sensor. 
     In contrast, embodiments of the foundation monitoring system  1000  of the present disclosure do not suffer from the stability issues of the comparative system.  FIG. 20  shows that repeated measurements by an exemplary foundation monitoring system  1000  provide consistently accurate data along an entire length of payout distance  158 . 
       FIG. 20  illustrates that with a system that involves moving a single sensor within a raceway to a number of measuring stations, the standard deviation of elevation data deteriorates markedly with the shorter the length of payout distance. However, with a foundation monitoring system  1000  of the present disclosure, the standard deviation of elevation data is not only as good as that of the comparative system at longer payout distances, but also is maintained even at the shorter payout distances at which the standard deviation of elevation data of the comparative system deteriorates. Thus, embodiments of the present disclosure provide consistently good data accuracy along an entire length of payout distance. 
     Embodiments of the present disclosure present improvements over current techniques because the need to convey a sensor from one measuring station to another is eliminated. Such improvements include, for example, the elimination of temperature corrections, the elimination of the need for a device to apply a positive pressure to the sensor fluid, the avoidance of gas dissociation in the sensor fluid resulting from movement, and the elimination of error due to the inability to replicate the exact locations of previous readings. Furthermore, embodiments of the present disclosure enable measurements to be obtained even when physical access to individual locations is prevented, such as by flooding. 
     Embodiments of the present disclosure have utility in the evaluation of foundation movement before, during, and/or after the building of a structure thereon, and for continuing measurement over time. Additionally, embodiments of the present disclosure include an ability to assess the temperature within the foundation to establish such aspects as an acceptable time to begin construction upon a foundation, an unacceptable time at which to avoid beginning construction upon the foundation, and to monitor deflection of the foundation during construction and maintenance. 
     Embodiments of the present disclosure are useful in evaluating the performance of foundations that do not have a conduit network disposed within the foundations during construction. Further, embodiments of the present disclosure provide methods for evaluating and predicting the utility of foundations that are easier than conventional methods to execute in order to achieve a requisite accuracy. 
     The systems, apparatus, and methods of the present disclosure may be adapted in many different forms and should not be construed as being limited to the illustrated embodiments set forth herein. It is to be understood further that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. It is further contemplated that each described embodiment may be combined with one or more other described embodiments. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, which is determined by the claims that follow.