Abstract:
A method for taking soil samples from horizontal boreholes. A first step involves making a substantially horizontal borehole from an entry pit to an exit pit. A second step involves towing a soil sampling apparatus through the borehole. It is preferred that the apparatus be pulled by the drill string as the drill string is withdrawn from the borehole. By using a soil sampling apparatus that is capable of taking multiple soil samples, all necessary soil sampling along the horizontal borehole may be completed in a single pass.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for taking a soil sample from a horizontal borehole. 
     BACKGROUND OF THE INVENTION 
     The need to develop improved soil sampling techniques for horizontally drilled boreholes has become apparent by the increasing use of horizontal drilling to characterize soil at contaminated sites and on linear projects such as tunnels. Horizontal boreholes are presently used for installing utility lines, such as gas lines, electrical or communications conduit and the like. When using horizontal boreholes to characterize sites they provide some obvious advantages over vertical drilling. With vertical drilling, the drilling rig must be positioned directly above the location from which samples are to be taken. With horizontal drilling samples can be taken by extending a borehole horizontally underneath rivers, structures, highways, or environmentally sensitive areas. In addition, vertical drilling is associated with the risk of penetrating impermeable layers, potentially causing crosscontamination between aquifers. This risk can be avoided by horizontal drilling technology. 
     There are two soil samplers presently in use in conjunction with horizontal directional drilling. One soil sampler is being produced under the Trademark PunchMaster 2000 Core Barrel, by Eastman Christensen Environmental Systems corporation. This soil sampler c onsists of an inner barrel which is encased in an outer tube. The sampler works on a principal similar to a split-spoon or a Shelby Tube core sampler. First a horizontal borehole is drilled up to the target area. The drill string is than withdrawn from the borehole and the boring head is replaced with the sampling tool. The PunchMaster 2000™ is advanced into the borehole to the target area while the load on the outer tube is kept constant with an applied hydraulic pressure. At a predetermined location an inner tube is accelerated into the formation by hydraulic pressure. The sample is then drawn back into the outer tube while pressure on the outer tube is maintained to prevent drilling media from contaminating the sample, and the PunchMaster is brought to the surface. This process is repeated for each sample. Another soil sampler is being produced under the by DitchWitch Environmental Systems corporation, located in Perry Okla. This soil sampler consists of a long metal tube with a spring loaded cone-shape cap. A pilot bore is drilled to a distance of approximately 0.3-0.6 of a meter (1 to 2 ft) from the target area. The drill string is then retracted, the cutting head removed, and a soil sampler is connected to the end of the drill string. The sampler is pushed through the bore, then continued to be pushed through the undisturbed soil until the target area is reached. The drill string is retracted approximately 0.46 of a meter (18 inches), and the sampler tube is automatically locked in open position. The sampler is pushed forward 0.3 to 0.6 of a meter (1 to 2 ft), filling the tube with soil. The sampler and drill string are then removed from the bore. The sampling tube is removed and replaced with the drilling head, and the process is repeated. 
     One disadvantage of both the PUNCHMASTER 2000™ and the DITCHWITCH™ soil samplers is that the sample must be collected ahead of the drilling bit. To facilitate this the drill string is withdrawn from the borehole and the drill bit is removed in order to attach the soil sampler. A sample is then taken, the drill string is withdrawn from the borehole and the soil sampler is recovered, then the drill bit is reattached in order to drill to the next target location. This requires the entire length of the drill string to be removed from the borehole twice for every sample that is taken. In addition, for contaminated site assessment the soil sampler must be de-contaminated between successive samples to avoid cross-contamination. 
     SUMMARY OF THE INVENTION 
     What is required is a less time consuming method for taking a soil sample from a horizontal borehole. 
     According to the present invention there is provided a method for taking soil samples from horizontal boreholes. A first step involves making a substantially horizontal borehole from an entry pit to an exit pit. A second step involves towing a soil sampling apparatus through the borehole. 
     The method, as described above, represents a radical departure from the teachings in the prior art. Instead of disrupting the drilling process by requiring the drill string to be withdrawn from the borehole, the soil sampling apparatus is pulled through the borehole after the drilling has been completed. The soil sampler can be pulled through the horizontal borehole from the exit pit to the entry pit, or vice versa, by a variety of mechanical means. 
     Although beneficial results may be obtained through the use of the method, as described above, it is preferred that the soil sampling apparatus be pulled back through the borehole from the exit pit to the entry pit by the drill string as the drill string is withdrawn from the borehole. The drilling drill string must always be withdrawn from the borehole upon completion of the drilling process. Collecting samples during the pull-back operation rather than during the forward drilling operation not only eliminates disruption of the drilling process, it conveniently incorporates the sampling procedure into existing drilling procedures. The sampling procedure, therefore, does not involve any additional steps that would increase the cost of drilling the borehole. This represents a significant cost saving over the prior art. 
     Although beneficial results may be obtained through the use of the method, as described above, even more beneficial results may be obtained when the soil sampling apparatus used includes means for taking more than one soil sample. The pulling of the soil sampling apparatus through the borehole can be temporarily halted at spaced intervals along the borehole in order to take soil samples at such spaced intervals. This allows all necessary soil sampling along the horizontal borehole to be completed in a single pass. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings, wherein: 
     FIG. 1 is a side elevation view, in section, of a soil sampler constructed in accordance with the teachings of the present invention, with the actuator pushing a selected sample container to the extended sample collecting position. 
     FIG. 2 is a side elevation view, in section, of a soil sampler constructed in accordance with the teachings of the present invention, with the actuator holding a selected sample container in the retracted rest position. 
     FIG. 3 is a transverse section view of the sample container support cylinder of the soil sampler illustrated in FIGS. 1 and 2. 
     FIG. 4 is a side elevation view of the soil sampler illustrated in FIGS. 1 and 2, showing the connection between the remote end of the actuator and the sampling tube. 
     FIG. 5 is a detailed side elevation view of the soil sampler illustrated in FIG. 4 showing the connection between the remote end of the actuator and the sampling tube. 
     FIG. 6 is a side elevation view, in section, showing a first of a two-stage sampling process. 
     FIG. 7 is a side elevation view, in section, showing a second of a two-stage sampling process with the preferred manner in which the soil sampler is to be advanced from one sampling location to the next. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment, a soil sampler generally identified by reference numeral  10 , will now be described with reference to FIGS. 1 through 7. 
     Referring to FIGS. 1 and 2, soil sampler  10  has a hollow cylindrical housing  12  with a longitudinal axis, generally indicated by reference numeral  14 . Housing  12  has a peripheral sidewall  16 , a rear end wall  18  and a front end wall  20  that define an interior cavity  22 . A sampling port  24  extends through peripheral sidewall  16 . A cylindrical container support  26  is rotatably mounted on a base  28  within interior cavity  22 . Base  28  is offset at an angle to longitudinal axis  14 . The preferred angle is in a range of between 30 degrees and 45 degrees. Referring to FIG. 3, container support  26  has a plurality of sample container retaining chambers  30 . There is provided a plurality of tubular sample containers  32 . One of sample containers  32  is positioned in each of sample container retaining chambers  30  of container support  26 . Referring to FIGS. 1 and 2, a stepper motor  34  is provided for rotating container support  26  until one of sample container retaining chambers  30  for a selected sample container  32  is aligned with sampling port  24 . Associated with the operation of stepper motor  34  are drive gears  35 . A worm-gear driven actuator  36  is positioned within interior cavity  22  of housing  12  for moving the selected sample container  32  between an extended sample collecting position illustrated in FIG.  1  and a retracted rest position illustrated in FIG.  2 . In the illustrated embodiment, the worm-gear actuator  36  is electric and has an associated electric motor  38 . Referring to FIG. 1, in the extended sample collecting position a remote end  40  of the selected sample container  32  extends through sampling port  24  at an angle to longitudinal axis  14 . The angle is determined by the angular positioning of base  28 . Referring to FIG. 2, in the retracted rest position the selected sample container  32  is wholly within interior cavity  22  of housing  12 . A control processing unit (CPU) or microprocessor  42  is also positioned within interior cavity  22  of housing  12 . Microprocessor  42  is connected by wires  44  to stepper motor  34  and by wires  46  to electric motor  38 . Microprocessor accepts signals relayed by wireline  48 . Batteries  50  provide a source of power to stepper motor  34 , electric motor  38  and microprocessor  42 . Electrical batteries  50  are connected to Microprocessor  42  by wires  52 , to electric motor  38  by wires  54  and to stepper motor  34  by wires  56 . 
     Referring to FIGS. 4 and 5, an end piece  62  is attached to the remote end of the actuator  36  to facilitate the extension and retraction of the tubular sample container  32 . The end piece  62  consists of two components, a conical rod  64  and a hook  66 , and is attached to the remote end of the actuator by the mean of a pin  68 . The end of hook  66  sits in a groove  70  in sampling tube  32 . When actuator  36  is extended, conical rod  64  engage the back of sample container  32  pushing it forwards and upwards along sample container retaining chamber  30  which acts as a guiding conduit. Referring to FIG. 1, sample container  32  is aligned with sampling port  24  and upon extension of actuator  36  is pushed to the extended position. When the actuator  36  has been extended to its maximum length it stops. When actuator  36  retracts sample container  32  to drawn to the retracted position by the mean of hook  66  which engages groove  70  of sampling container  32 . Referring to FIGS. 1 and 2, housing  12  has a pulling head  58  secured to front end wall  20 . A pulling eye  60  is located within pulling head  58  and is used as a means to connect the soil sampler  10  to the drill string or a cable, as will hereinafter be further described in relation to the use and operation of soil sampler  10 . 
     The use and operation of soil sampling apparatus  10  will now be described with reference to FIGS. 1 through 7. Referring to FIG. 6 a drilling bit  80  connected to a drill string  76  is used to create a borehole  82  that extends from an entry pit  84  to an exit pit  86 . Upon borehole  82  being completed, drilling bit  80  is removed and soil sampler  10  is connected to drilling string  76 . Soil sampler  10  is then pulled-back along borehole  82  from exit pit  86  towards entry pit  84  by a drilling rig  88  (or another mechanical means) across a soil sampling target area, generally indicated by reference numeral  90 . Soil sampler  10  is connected to drill string  76  by the means of a backreamer  78 , which enlarges borehole  82  to a diameter slightly larger than the diameter of the soil sampler  10 . Periodically during the pullback process, the pullback operation is temporarily discontinued in order to permit a soil sample to be taken. Referring to FIG. 1, a signal is sent to microprocessor  42  via wireline  48 . Upon receiving the signal from wireline  48 , microprocessor  42  activates stepper motor  34  to rotate container support  26  to select an unused sample container  32 . Actuator  36  is then activated to move the selected sample container  32  to the extended sample collecting position. Referring to FIG. 2, once the sample has been taken a signal is sent to microprocessor  42  via wireline  48  causing microprocessor  42  to activate actuator  36  to move the selected sample container  32  back into the retracted rest position so that the pullback operation may resume. When a further sample is desired the pull back operation is again temporarily discontinued to allow the further sample to be taken. Referring to FIG. 1, a signal is again sent to microprocessor  42  via wireline  48 . Upon receiving the signal from wireline  48 , microprocessor activates stepper motor  34  to rotate container support  26  to select the next unused sample container  32 . Actuator  36  is then activated to move the selected sample container  32  to the extended sample collecting position. Referring to FIG. 2, once the sample has been taken a signal is sent to microprocessor  42  via wireline  48  causing microprocessor  42  to activate actuator  36  to move the selected sample container  32  back into the retracted rest position so that the withdrawal of the drilling string may again resume. 
     It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the spirit and scope of the invention as hereinafter defined in the Claims.