Abstract:
A method for trenching below the water table in environmentally sensitive areas such as the Florida Keys is shown. A first pass made by a trencher digs a first trench from the surface to the water table. During the first pass, relatively dry spoil is removed from the first trench. Next, a much deeper second trench is dug below the first trench; however, wet spoil remains in the now combined first and second trench, the combined first and second trench being large enough to accumulate the wet spoil with expansion. Thereafter, the combined first and second trench may be filled with the relatively dry spoil, packed and driven upon. Later, the packed spoil may be removed and water pipes, electric cables, sewer lines or the like buried in the trench. According to the requirements of the work area, the spoil may be used to partially fill the combined first and second trench or be hauled away.

Description:
1. FIELD OF THE INVENTION 
     This invention relates generally to a method of trenching and, more particularly, a method of trenching below the water table in a porous formation. 
     2. BRIEF DESCRIPTION OF THE PRIOR ART 
     The making of trenches is as old as civilization itself. Canals and aqueducts have been built to move water from one location to another. However, at the beginning of recorded time, such channels or aquaducts were built by hand. Later, domesticated animals were used in some of the digging or trenching. 
     As the industrial revolution progressed, machines were used to dig or excavate trenches. The machines varied in size from a hand held walk behind machines to large earth moving devices. When encountering rock, in addition to the machines, dynamite and other blasting devices were used to break up the rock. In approximately the 1970s, milling machines with cutting teeth having carbide hardened tips were used to mill away or cut the rock. By this century, the most common way of excavation or cutting new road beds through rocky portions of the earth&#39;s crust was the use of rock milling type machines. 
     Similar types of milling processes were used in the excavation or digging of trenches in rock formation, except the cutting teeth would be on trenching chains rotating around a boom that could be raised and lower. One of the largest manufacturers of trenching equipment is Astec Industries, Inc. which manufactures and sells a line of trenchers under that mark Trencor®. The Trencor® products range from walk behind trenchers, ride on trenchers, track mounted trenchers to road milling equipment. 
     Another large manufacturer of similar type of trenching equipment is sold under the mark Vermeer®. Again, the various types of trenching equipment sold under the Vermeer® brand range from walk behind trenchers, ride on trenchers, rock wheels, and track trenchers. 
     More and more trenches are now being excavated or dug in which to bury electrical cables, water pipes, sewer lines and the like. Many times the trenches being dug for public utilities are dug along existing streets or right of ways. If a trench is being dug along an existing street, it is very important there be a minimum amount of interruption with the normal traffic flow, plus a minimum clean up effort afterwards. In some areas, due to environmental constraints, the excavation or digging of the trench cannot interfere with natural habitat in the area. This means waste from the trenching may not wash off, or be disposed of, in the environmentally sensitive area. 
     A particularly unique environmentally sensitive area in which applicant has worked is the Florida Keys. Typically the surface of the earth is only a few feet above the water table. Because the rock in the Florida Keys is coral that has formed on the ocean floor, it is still porous. Therefore, when trenching below the water table in the porous rock, the material removed (sometimes called “spoil”) is very pliable like wet cement due to inflowing water. The wet spoil will spread over everything and is almost impossible to remove. However, in the same area when trenching above the water table, the spoil removed is relatively dry. 
     The problem with trenching below the water table in the Florida Keys is the wet spoil will inevitably get on everything, and despite the best efforts to clean up, some will remain. The part that remains will wash into the natural habitat surrounding the Florida Keys causing damage to the environment. 
     Areas other than the Florida Keys that have shallow water tables encounter the same problem of wet spoil when trenching below the water table. The wet spoil flows everywhere and is almost impossible to remove. 
     3. SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for trenching below the water table in the earth&#39;s surface. 
     It is yet another object of the present invention to provide for trenching below the water table in the earth&#39;s surface, yet maintaining wet spoil in the trench. 
     It is still another object of the present invention to excavate or dig relatively dry spoil from the earth&#39;s surface down to the water table in a first pass and excavate or dig from the water table to the completed depth in a second pass, while maintaining the wet spoil inside the trench during the second pass. 
     It is yet another object of the present invention to prevent spoil removed from a trench from polluting the environment, especially in areas where trenching occurs below the water table. 
     In an environmentally sensitive area such as the Florida Keys, a first pass is made with a trencher having a boom with a digging chain thereon. During the first pass, the boom is lowered so that the digging chain excavates or digs the trench to an intermediate depth from the earth&#39;s surface to the water table. The relatively dry spoil removed during the first pass can be moved to one side of the intermediate depth trench. 
     Thereafter, a second pass occurs where the intermediate depth trench is excavated or dug from the water table to a full depth trench in a second pass. During the second pass, wet spoil is dug up, but drops back into the full depth trench and is retained therein. Also, during the second pass, the belts or conveyors are tuned OFF causing the wet spoil to drop back in to the full depth trench. 
     Because during the first pass, the relatively dry spoil was removed from the intermediate depth trench, during the second pass, even with the expansion of the wet spoil, the full depth trench can accommodate the wet spoil even with its expansion. 
     In digging the trench, a predetermined line is normally followed as to where the trench will go. The trencher, which is normally a track mounted trencher, follows the predetermined line with the boom and digging chain excavating or digging along the predetermined line in a first direction to excavate from the surface to the water table. However, during the second pass, it can be by either of the following two methods. 
     In the first method, a second digging machine moves in the same direction with the digging chain reversed and the belts or conveyors turned OFF so that the wet spoil removed when digging from the water table to the full depth will fall back into the full depth trench. The full depth trench has enough space to accommodate the wet spoil even with expansion. 
     The second method is for the first digging machine after making the first pass along the predetermined line to dig from the earth&#39;s surface to the water table, simply operates in reverse, but with the belt and/or conveyors turned OFF and raised, plus the boom lowered, to dig from the water table to the full depth trench. The wet spoil drops back into the full depth trench. Again, the full depth trench can accommodate the wet spoil plus the expansion. The only problem is that in this second method, the digging is on the end of the boom which causes more vibrations back in the trencher than would be caused using the first method. 
     Also, during the second pass of either method, the speed of the trencher and the digging chain should be slowed down during the second pass (1) to prevent spillage of the wet spoil outside of the completed trench and (2) to provide the best trenching performance. 
     A third method may be used wherein the first digging machine makes a first pass along the predetermined line, but has the digging chain rotating in a counter clockwise direction so that the upwardly rotating side of digging chain digs on the downward rotation. Some of the loosened spoil will travel up the digging chain onto the belt and be removed to the side of the trench being dug. During the first pass the trench is dug from the surface to the water table. 
     Thereafter, the same digging machine makes a second pass in the same direction, but (1) with the boom lowered so that the trench is dug from the water table to the full depth and (2) the belt is turned OFF. By turning the belt OFF, the wet spoil will accumulate, ride up the digging chain, but will fall back into the trench. Due to a removal of a portion of the dry spoil when digging from the surface to the water table, the trench now has enough space to accommodate the wet spoil and have room for expansion. 
    
    
     
       4. BRIEF DESCRIPTION OF THE PRIOR ART 
       Brief Description of the Drawings 
         FIG. 1  is a side elevational view of the present method with the earth&#39;s crust being cut away to show a trench being dug. 
         FIG. 2A  is a cross-sectional view of  FIG. 1  taken along section lines  2 A- 2 A of  FIG. 1  illustrating the first pass. 
         FIG. 2B  is a cross-sectional view of  FIG. 1  taken along section lines  2 B- 2 B of  FIG. 1  illustrating the second pass. 
         FIGS. 3A and 3B  are sequential side elevated views of a trench being dug in the earth&#39;s surface to illustrate an alternative embodiment of the second pass. 
         FIGS. 4A ,  4 B,  4 C,  4 D and  4 E are sequential views showing a method of completion of a trench dug according to the present invention. 
         FIG. 5A  is an elevated pictorial view illustrating trenching at a first depth. 
         FIG. 5B  is an elevated pictorial view illustrating trenching at a second depth. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     When trenching in an area of South Florida or the Florida Keys, the surface  10  may be only a few feet above the water table  12  as shown in  FIG. 1 . In the Florida Keys, most of the rock is porous coral rock that allows the water to flow therethrough. Therefore, as the tide of the ocean rises and falls, the water table  12  will rise and fall accordingly. If a hole is dug below the water table  12 , it will quickly fill up with water due to the porous nature of the rock. 
     In the present invention as shown in  FIG. 1 , a first trencher  14  makes a first pass in the direction indicated along a predetermined line along which a trench is to be dug or excavated. The boom  16  is lowered so that the cutting teeth  18  dig into the earth&#39;s crust  20  digging and excavating an intermediate trench  22  from the surface  10  down to approximately the water table  12 . The belt  24  is lowered and rotating to remove relatively dry spoil  26  from the intermediate trench  22  to the opposite side of first trencher  14 . The belt  24  is rotating so the digging chain  28  rotates in the direction indicated by the arrows, cutting teeth  18  dig into the earth&#39;s crust to excavate relatively dry spoil  26  therefrom, which relatively dry spoil  26  will be moved to one side to a wind row  30  (see  FIG. 2A ). However some of the relatively dry spoil  26  will fall down into mounds  32  on either side of the intermediate trench  22  (see  FIG. 2A ). 
     Forward movement of the first trencher  14  is controlled by tracks  34  on either side thereof. The tracks  34  have the proper amount of rotation to maintain the cutting teeth  18  in excavating contact with the earth&#39;s crust  20  and to maintain close to optimum cutting conditions for digging the intermediate trench  22 . A better view of the cutting chain  28  with the cutting teeth  18  thereon is shown in  FIG. 2A . Also, a better illustration of the removal of the relatively dry spoil  26  into wind row  30  and mounds  32  is illustrated. 
     If the trenching as shown in  FIG. 1  is occurring in the Florida Keys, the boom  16  will have to be raised or lowered as the tide comes in or goes out, which tide causes the water table  12  to fluctuate accordingly. In other words, according to the time of day the intermediate trench  22  is dug or excavated, the depth will vary. 
     After the first pass by the first trencher  14 , a second trencher  36  makes a pass along the same predetermined line so that the intermediate trench  22  is dug in to increase the depth from approximately the water table  12  to the completed depth  38  to form a full depth trench  40 . However, in making the second pass and digging from the water table  12  to the completed depth  38 , wet spoil  42  is created. While the amount of water content and consistency of the wet spoil  42  varies depending upon a number of factors, it is normally very pliable and flowable. The wet spoil  42  is similar in texture to wet concrete with gravel therein. 
     In making the second pass with the second trencher  36 , the digging chain  44  is reversed so that the cutting teeth cut on the way down because the direction of rotation of the digging chain  44  for second trencher  36  is the opposite of the direction of rotation of the digging chain  28  of first trencher  14 , both directions being shown with the direction of the arrows. Also, the belt  48  is turned OFF and raised. The wet spoil  42  will tend to be carried upward on the boom  50  where the digging chain  44  is moving upward as is shown in  FIG. 1 . In this manner, the digging action is as close to the second trencher  36  as is possible. Also, the wet spoil  42  simply falls back into the full depth trench  40 . The part of the full depth trench  40  that was the intermediate trench  22  will take care of any expansion of the wet spoil  42  after being dug from below the water table  12  to the completed depth  38  to form the full depth trench  40 . 
     Tracks  52  will control the forward motion of the second trencher  36 . It has been found the operation of the second trencher  36  and the rotational speed of the digging chain  44  may have to be adjusted downward to prevent wet spoil  42  from spilling outside of the full depth trench  40 . Also, by slowing the speed of the digging chain  40  and forward motion of second trencher  36 , the cutting teeth  46  will cut larger size chunks for including in the wet spoil  42 . Both the rotational speed of the tracks  52  and the rotational speed of the digging chain  44  control the spillage of wet spoil  42  from the full depth trench  40 , plus the size of the rock in the wet spoil  42 . 
       FIG. 2B  shows an end view of the second trencher  36  along section lines  2 B- 2 B of  FIG. 1 . The wet spoil  42  is retained inside of the full depth trench  40  with portions of the relatively dry spoil  26  being shown in mounds  32  and wind row  30 . The full depth trench  40  is dug from the surface  10  through the water table  12  to completed depth  38 . The digging chain  44  with the cutting teeth  46  will tend to drag the wet spoil  42  upwards, which wet spoil  42  will fall back into the full depth trench  40  due to gravity. 
     Referring now to  FIGS. 3A and 3B , an alternative method of digging a trench below the water table  12  is shown. The trencher  54  is identical to the first trencher  14  with a boom  16 , digging chain  28 , cutting teeth  18  and belt  24 . The trencher  54  operates on tracks  34 , the same as first trencher  14 . Trencher  54  digs and excavates from the surface  10  to approximately the water table  12  in a first pass to form a first trench  56  therein. The relatively dry spoil  26  is excavated out of the first trench  56  into either a wind row  30  or mounds  32  as shown in conjunction with  FIG. 2A . The trencher  54  is moving in the direction indicated by the arrow along a predetermined line where a trench is to be dug. The digging chain  28  is rotating in the direction indicated by the arrows in  FIG. 3A . 
     After completing the first pass as shown in  FIG. 3A , the same trencher  54  has the belt  24  raised, the boom  16  lowered and is operated in the opposite direction as indicated by the direction of the arrow. The digging chain  28  is rotating in the same clockwise manner in  FIG. 3B  as in  FIG. 3A . The trencher  54  digs a second trench  58  below the first trench  56 , which second trench  58  is dug from approximately the water table  12  to the completed depth  38 . Because the belt  24  is turned OFF and raised, the wet spoil  42  falls back into the combined first trench  56  and second trench  58 . Due to the combination of the first trench  56  and second trench  58 , expansion of the wet spoil  42  is accommodated without spillage outside of the combined trenches. 
     One of the problems with the second pass as shown in  FIG. 3B , is that the cutting by the cutting teeth  18  on the digging chain  28  is on the far end of the boom  16 . This can cause vibrations along the boom back to the trencher  54 . Also, the speed of the tracks  34  and the cutting chain  28  will have to be adjusted to accommodate the backward digging of the trencher  54  as shown in  FIG. 3B . Normally the rotational speed of the tracks  34  and the digging chain  28  will have to be reduced for the second pass as shown in  FIG. 3B . 
     If the methods as shown either in  FIG. 1  or  FIGS. 3A and 3B  are followed, a trench can be dug below the water table in an environmentally sensitive area such as the Florida Keys without spillage of wet spoil  42  outside of the full depth trench  40 . However, normally there is a requirement to use a road surface if the full depth trench  40  is being dug in a road, before the item going in to the trench (such as electrical cables, water pipe or sewer lines) are ready to install. It may be weeks or even months later before installation occurs inside the full depth trench  40 . Therefore, referring to  FIGS. 4A-4E  respectively, a sequence of steps is shown so that the surface  10  can be used before completing installation in the full depth trench  40 . The relatively dry spoil  26  may be pushed by a scoop  60  attached to a suitable tractor (not shown) into full depth trench  40 . The scoop  60  moves the relatively dry spoil  26  on top of the wet spoil  42  in the full depth trench  40  (see  FIG. 4A ). Thereafter, the relatively dry spoil  26  and the wet spoil  42  are compacted into the full depth trench  40  by a roller/compactor  62  (see  FIG. 4B ). After the relatively dry spoil  26  and the wet spoil  42  have been compacted into the full depth trench  40 , the surface  10  may again be used by traffic or other types of designated use. 
     Months later when the decision is made to lay, for example, a sewer line in the full depth trench  40 , a backhoe  64  may be used to excavate the relatively dry spoil  26  and the wet spoil  42  from the full depth trench  40  (see  FIG. 4C ). The combined relatively dry spoil  26  and the wet spoil  42  may be loaded into a truck and hauled away. Assuming a sewer line  66  is installed as shown in  FIG. 4D , first a bed of gravel  68  or other suitable material is placed in the bottom of the full depth trench  40  (see  FIG. 4D ). Thereafter, the sewer line  66  is laid thereon. Next, the sewer line  66  is covered with more gravel  68  and other suitable surface material  70  is applied above the gravel  68 . The suitable surface material  70  may be pavement, concrete or even part of the removed spoil, depending upon the circumstances. Thereafter, the surface  10  as shown in  FIG. 4E  is complete and can be utilized for its normal purpose. 
     By use of the methods just described, a trench can be dug or excavated below the water table in an environmentally sensitive area such as the Florida Keys. The relatively dry spoil  26  can be easily controlled and scooped up. However, wet spoil  42  flows everywhere and is almost impossible to remove under normal trenching conditions. By use of the current method, the wet spoil  42  is retained inside of the trench until it is excavated with a backhole  64  and carried away. This prevents the spoil from contaminating the environment therearound, especially in environmentally sensitive areas like the Florida Keys. 
     A third method of digging or excavation of a trench in an environmentally sensitive area is illustrated in  FIGS. 5A and 5B . Referring to  FIG. 5A , the trencher  14  is identical to the first trencher  14  shown in  FIG. 1 ; however, the digging chain  28  has been reversed and the direction of rotation thereof as indicated by the arrows has been reversed. The digging chain  28  now has the cutting teeth  18  digging the intermediate trench  22  during the first pass. Some of the relatively dry spoil  26  rides up the outside of the digging chain  28  and is deposited on the belt  24 . The relatively dry spoil  26  on the belt  24  is moved to the side into wind rows  30  (see  FIG. 2A ); however, some of the relatively dry spoil  26  will remain in intermediate trench  22  or on the banks thereof. 
     The same trencher  14  can be used for a second pass as illustrated in  FIG. 5B ; however, the belt  24  will need to be turned OFF. During the second pass, the trencher  14  will dig from the water table  12  to the completed depth  38 . Because the belt  24  is turned OFF, all of the wet spoil  42  being dug, along with any remainder of dry spoil  26  that is in the intermediate trench  22 , will fall into the full depth trench  40  as shown. The digging by teeth  18  is on the downward part of the counter clockwise rotation as shown in the arrows of  FIG. 5B . In both  FIGS. 5A and 5B , the digging chain  28  is rotating in a counter clockwise direction and the digging is on the downward rotation by the digging teeth  18 . 
     The rotational speed of the tracks  34  and digging chain  28  may have to be adjusted in  FIG. 5B  to retain the combination of wet and dry spoil in the full depth trench  40 . 
     After digging of the full depth trench  40  as explained in conjunction with  FIGS. 5A and 5B , the sequential steps as explained in conjunction with  FIGS. 4A-4E  may be utilized.