Steel Reinforced Trench Fill for Ground Stabilization

The method of ground stabilization disclosed in this patent application uses the same steel reinforcing modification that was disclosed in U.S. Pat. No. 12,000,104 by the same inventor. For this application the use of steel reinforcing bars covered with cured concrete that has an undulating shape are referred to as modified rebar. This patent is entirely different from the previous patent and is not obvious in that discloser. The primary difference is U.S. Pat. No. 12,000,104 used modified rebars exclusively for the construction of gravity retaining walls. This application is for the construction of buried trenches in fill or natural soil for the purpose of improving the stability of the fill. This is done by installing into the soil internal stiffened linear trenches reinforced by modified rebars. Where U.S. Pat. No. 12,000,104 was for the construction of a new external gravity wall in front of existing soil.

This patent application also claims priority from Provisional Patent Applications 63/567,940 filed on Mar. 21, 2024, and 63/641,636 filed on May 2, 2024. These two provisional applications form the basis of this regular patent application. The first is for the construction of stable new fill with a permitter retaining wall built with precast concrete segments. The soil is stabilized by the excavation of new trenches into the new fill at an alignment perpendicular to the proposed wall face. The trenches are then filled and grouted to provide anchors for the precast wall segments. These same trenches will also provide stabilizing forces to the fill where it is in contact with the sides of the trenches, thus reducing the soil load on the wall segments.

The second provisional patent application uses similar steel reinforced trenches for general ground stabilization. These trenches could be used for a new or existing slope where additional stabilizing elements are desired. These trenches would be similar in construction, but they would be buried below the surface and discontinuous to prevent groundwater blockage. Also, they could be excavated in “T”, “L”, or “I” shape depending upon the soil conditions. The shapes shown on the enclosed figures are only intended to demonstrate the concept. Given the unlimited variations that trenches can take, this patent claims that any trench designed for ground stabilization and uses modified rebar as described herein is covered by this patent application. This patent is not limited to any or by any particular grouting method including the possibility of not grouting or only partially grouting the trench backfill.

Not Applicable

Not Applicable

Not Applicable

Not Applicable

This disclosure relates generally but not by way of limitation to the construction of in-situ ground improvement for either new compacted fill soil, existing fill soil, naturally occurring soil and rock formations and support of retaining walls by improving the stability of said formations and simultaneously acting as tie back anchors.

A number of ground stabilization systems exist for the purpose of either building new fill, or stabilization of existing ground. The methods for building new fill involve either building retaining walls or stable slopes at the perimeter of the new fill. The method presented herein will work to stabilize either new fill or existing ground using known engineering principals and construction elements.

New fill is commonly stabilized by placing stabilizing elements in the fill as the layers of fill are placed and compacted. This method is known as Mechanically Stabilized Earth or MSE. These are very effective methods of stabilizing new compacted granular fill. That method relies on developing friction between the stabilizing elements and the granular fill. It also requires some form of non-erosive wall face such as concrete interlocking segments. Therefore, it is limited to sand and sandy gravelly soils. Also, MSE cannot work with an exposed slope due to the erosive nature of granular soil. The method presented in this patent application will work with a wider range of soils because it relies on active and passive pressure as well as friction. Therefore, this system will work with a wider range of soils and it is possible to construct this system with a stable nonerosive perimeter slope face.

Existing soils, that are fill or natural, that require additional support to ensure stability, typically are very expensive to improve. One common method of support is to construct rows of steel reinforced concrete piles commonly known as soldier piles. To provide stability they need to be set deep enough that they are founded in stable material. Constructing these large diameter piles requires large equipment and significant time for the concrete to gain sufficient strength to improve the stability of the soil mass. The method of this patent does not require large equipment, and the stabilizing force of a grouted trench will be in effect as soon as the grout is injected. This would allow for the stabilization trenches to be constructed from the edges of the unstable area and be in full effect as soon as the function prior to or without grouting if it is so designed.

Tie back anchors for retaining walls typically use a dead man system as the earth anchor. The dead man anchor is typically a concrete block located beyond the active wedge or any calculated failure plane and attached to the wall by way of a small cable or tie rod. The cable or rod is then attached to the back of the wall.

New fill is commonly stabilized by placing stabilizing elements in the fill as the layers of fill are placed and compacted. This method is known as Mechanically Stabilized Earth or MSE. These are very effective methods of stabilizing new compacted granular fill. That method relies on developing friction between the stabilizing elements and the granular fill.

Ground improvement of existing soil and rock is typically by constructing rows of steel reinforced concrete piles commonly known as soldier piles. To provide stability they need to be set deep enough that they are founded in stable material. Constructing these large diameter piles requires large equipment and significant time for the concrete to gain sufficient strength to improve the stability of the soil mass.

This patent provides a method for building a safe stable soil fill by constructing grouted steel reinforced discontinuous trenches within soil. The purpose of these trenches is to provide a grouted rock stiffening system to improve the overall strength of existing soil or new compacted fill without creating an impermeable groundwater barrier. In addition, the method of trench construction is easy and quick and will not impede the construction process of building a new compacted soil fill.

This method of ground stabilization is similar to a known landslide stabilization system that uses drilled cast in place steel reinforced concrete piles that penetrate the failure plane of the landslide. That is a method of pinning the unstable landslide mass to the stable material below the failure plane where, these piles are known as soldier piles. The soldier piles are typically constructed in rows with a designed open space between the piles.

The process proposed herein is similar to the soldier pile method of inserting rows of strong piles within an unstable mass to improve its stability. The process proposed would accomplish the same improvement using smaller equipment such as a backhoe and in place of soldier piles the stabilization would be provided by steel reinforced grouted trenches. The trenches would be founded horizontally beyond any failure plane as opposed to the piles extending below the failure plane.

For the case of a new compacted fill the unstable mass is that portion of the fill near the edge of the fill. If there is not sufficient space for a long gentle slope, then the edge needs to be constructed with steep or vertical edges. Typically, steep edges of a new soil fill require very large strong retaining walls to support the loads created by gravity acting on the fill soil at the edge of the fill. What is proposed herein is that these large forces can be counteracted by installing hardened discontinuous trenches during construction. These trenches will only occupy a small percentage of the fill volume but increase the overall strength of the fill mass, thus making the new fill stable.

It should be noted that compacted soil typically has a saturated unconfined shear strength on the order of 2 to 4 Pounds Per Square Inch (PSI). A trench filled with rock and or inert debris such as broken pieces of concrete, and gravel and then grouted in place would have a minimum unconfined shear strength on the order of 200 to 400 PSI. This results in a hardened zone that when properly located will cross and provide support to a potential failure plane. To prevent the hardened trench fill from fracturing or pulling apart under a tensile load the trench fill includes steel rebars. These steel rebars will be precast in concrete cover where the concrete provides minimum corrosion cover and has an undulating shape. This method of modifying the rebar prior to construction allows the rebar to be structurally tied to the rock fill. The result of placing a designed number of hardened trenches within a new compacted fill is to increase the overall strength of the fill. Then the compacted fill will have sufficient strength to resist the gravitational force pushing the fill to failure at the edge. The gravitational force results in active pressure on a hardened trench. That active pressure is transmitted through the stronger trench to stable soil which provides support in the form of passive pressure or friction. The final result is a stable over steepened or vertical slope at the edge of the new compacted fill.

One advantage to this system is the grouting can be delayed until a large number of trenches are ready to be grouted. The grouting process is more efficient when a large number of trenches are grouted at one time. On the other hand, if the final strength of the trench is desired during construction, then once the trench fill is complete it can be grouted immediately. Typically, chemical grout has a set time is significantly shorter than cure time for Portland cement. Therefore, if quick setting grout is used then the structural benefit of having the steel and rock filled trench in the soil would be almost immediate.

This patent provides a ground stabilization method that uses common building materials to construct stabilization trenches in the ground where improved stability is desired. This system will overcome some of the common limitations of existing ground improvement systems such as only working with granular soil or needing large equipment and long-time delay for the stabilization to take effect. This system would require excavating into new compacted fill or existing soil to create a series of discontinuous trenches at designed elevations and locations. The trenches would be filled with granular fill, and/or rock, modified rebar, and a grouting system as they are being constructed. The grouting system shown on the Figures uses a manifold system to improve the grout distribution. It should be noted that the same grouting could be accomplished using multiple vertical injection pipes if that would provide the desired improvement. The primary goal is to fill the naturally occurring voids when making granular deposits in the trench. If needed, each trench could be grouted as soon as the backfilling process is complete, and before the next trench is excavated. This would allow the improvement process to develop as the work is being done.

Once grouted the trench fill may be impermeable to ground water. This can become a problem for long or deep trenches filled with material less permeable than the surrounding soil. This is known as a groundwater barrier. Therefore, this trench design is intended to be discontinuous to ensure that the natural flow of groundwater is not impeded. Continuous trenches over long distances could be grouted provided the design includes provisions to allow for ground water to flow through the barrier or account for the change in ground water hydrology.

It should be noted that compacted soil typically has a saturated unconfined shear strength on the order of 2 to 4 Pounds Per Square Inch (PSI). A trench filled with rock and/or inert debris such as broken pieces of concrete, and gravel and then grouted in place would have a minimum unconfined shear strength on the order of 200 to 400 PSI. This results in a hardened zone that when properly located will cross and provide support to a potential failure plane. To prevent the hardened trench fill from fracturing or pulling apart under a tensile load the trench fill needs to include steel rebars. To prevent the corrosion of the steel rebars they will be precast in concrete, where the concrete provides minimum corrosion cover and has an undulating shape. This method of modifying the rebar prior to construction allows the rebar to be structurally tied to the rock fill. The result of placing a designed number of hardened trenches within a new compacted fill is to increase the overall strength of the fill, and thus improve the global and surficial stability. Then the compacted fill will have sufficient strength to resist the gravitational force pushing the fill to failure at the edge. The gravitational force results in active pressure on one end of the hardened trench. That active pressure is transmitted through the stronger steel reinforced trench to stable soil which provides support in the form of passive pressure or friction. The final result is a stable over steepened or vertical slope at the edge of the new compacted fill.

A short description of the trench construction is:

The above nine steps may look long or involved but if a backhoe or similar equipment is used along with a well-organized small crew, it could be completed in a relatively short period of time. It should be noted that the various parts do not need to be placed in a very precise manner for the trench to have a shear strength at least 100 times the strength of the compacted fill. As long as the modified rebars are placed near the middle of the trench and surrounded by rock or broken pieces of concrete then the transfer load from the rebar to the rock fill and visa versa will occur. This load transfer occurs directly between the rock and the concrete cover on the rebar. The purpose of the grout is not to add strength to the matrix but to lock the various parts in place such that the rocks and the modified rebar will not shift or move. In addition to locking the trench fill in place it is possible that the grout will expand into the fill helping to tie the trench to the compacted fill.

First the trench size and locations need to be determined during the design phase of a project. This will vary from project to project and must be designed site specific. What will be the same for any project is the basic ground improvement system of installing steel reinforced trenches within a soil mass to improve the overall strength of the mass,

Second, the plans need to identify specific locations, elevation, shapes of the trenches, and the material to be used in the trench backfill. The findings of the design analyses and engineering requirements need to be incorporated into the plans.

Third, because this is not a typical compacted fill the inspection and verification of the process will need to be very through. In addition, the engineer of record will need to be kept abreast of the project continuously. Because this system uses discontinuous trenches it will be easy to modify the design during construction by adding additional trenches on short notice when necessary.

Fourth, along with a higher level of inspection this system will need more testing and verification systems during and shortly after construction. Typical settlement monuments should be included in the fill to track the movement of the fill as more fill soil is placed and compacted. It should be noted that movement of fill soil during the placement of additional fill is normal. What needs to be tracked is making sure the movement is within the anticipated range of movement. Another test should be made to track the air pressure inside the trench when the trench is grouted. This along with the volume of grout injected would provide confidence that the grouting operation was complete and successful.

The following is a list of the numbers for the Figures and what each number represents.

Presents a perspective view of the initial stage of the construction of a fill that will be supported by a retaining wall. This view is prior to any of the prefabricated wall segments being installed. Fillis initially constructed beyond the location of the proposed wall segments to form the temporary slope. The temporary fill section beyond the wall is typically sloped and is known as a false slopebecause it will be removed as the work progresses. The figure shows two slot cuts with a distance between the slots. The distancebetween the two slotsis shown as distance Z. This distance varies from one project to the next. This distance Z is determined based upon the parameters of a given project, analyses and recommendation of the Engineer of Record. In addition to the excavated slotsin the false slope each slot is shown with a narrow trenchbehind the proposed location of the wall. These slots are for the construction of stabilization trenches that will include modified rebars that will be attached to each of the wall segments.shows the location of two typical section views labeledand.

This figure shows a typical cross section of the new fillplaced upon the existing soil. This section shows the fill placed against an existing soil slope. This is only an example and not a limit to the use of this design. With two or more walls this same design could be used to rase the grade a significant distance one row of wall segments at a time. Fillhas a slope that extends beyond the alignmentof the proposed retaining wall to ensure temporary stability.

This figure is drawn through one of the slot cutsthe trenchthat will extend beyond and behind the proposed wall face alignment. Because the slot has been cut into fillthe slot has removed the false slopewhich is now shown as a dashed line. The existing groundbelow and beyond the fill is shown.

Presents a perspective view of a completed retaining wall showing several wall segmentswith each connected and to a completed trench. Each trenchhas a grout injection tubethat extends down into the trenchfill. One of the segments is presented in a cut away view which is enlarged in. The cut away exposes the internal section of the wall segmentand the support system located inside the trenchalong with the grout system. Also shown are the weep holesin the base of the wall segments. These are located just above the concrete channel footing. Just in front of footingand behind the fill is the existing or native soil.

is a perspective enlargement of the wall segmentfromand the cut away section where the supporting trenchsystem intersects the wall segment. The wall segmentsare shown with the weep holesand the concrete footing. Within the cut away the original compacted fillis exposed behind the wall and next to the trench. Within the trench the modified rebaris shown with the undulating concrete coverinside the trench. The same rebaris shown without concrete coveras it enters the formed pocketin the back of the wall segment. The pocket will be filled with concrete grout which will also cover the exposed portion of rebar. It should be noted that the rebarwith its modified concrete covered sectionis the top rebar. Under the top rebar is the grout distribution pipewhich is surrounded by coarse sandall within the protective geotextile wrap. This prevents pipefrom being damaged by the rock or inert concrete debristhat is placed on top and on the sides of the grout pipe. Along with rock fillthe larger voids are filled with gravel. The grout delivery pipevertically rises out of the filter clothto an elevation above the trenchwhere it can be attached to a grout generating system which is not shown.

shows the alignment of section drawings for,,, and. Theare longitudinal sections of the trenches.being made when the trenchis only partially filled andshows the trenchfilled but not grouted.shows a cross section of the trenchpartially filled andpresents a cross section of the trenchcompleted and grouted.

This shows a partially filled trench where a bed of rockand gravelhas been placed in the bottom of the trenchup to the elevation of the lower modified rebar. A zone of sandhas been compacted in the front of the trenchbetween the rockand where the back side of the wall segmentwill be placed on top of concrete footing. Above the footingis the rebarwhich is the same rebar shown as a dashed rebar within the concrete cover. The modified concrete covered rebarhas been placed on top of rockand gravelfill that has been placed at that time. At the back of the trenchis the vertical cut that was made into the initial compacted fill.

The trenchhas now been filled to become trenchas it now matches the top of the existing grade of the initial compacted fill. This design shows two modified rebar, however what is claimed is that each project will require an individual design which may require more or fewer modified rebar, or wall segmentssupported by more than one supporting trench. The upper modified rebaris shown angling down to be anchored deeper into the rockfill, and closer to the grout distribution pipe. Between the two modified rebarsis the grout distribution pipesurrounded by the sandand the geotechnical clothwrapped around to protect the pipefrom damage during construction. The grout injection piperises out of the trench fill starting from a “T” connection with the distribution pipe. The rockfill is capped with the same compacted fill soilused for the initial compacted soilfill. At the front of the rockfill is a zone of sandbehind the wall segment. The wall segmentwhich is supported by the concrete footingand held in place by the two rebarsinserted into the back of the wall segment. With the weight of the rockon and around the two modified rebarit is possible that the wall segmentis temporarily stable and although it is ready for groutto be injected into the trench the injection of the groutcould wait until all, or a large number of segmentsare ready for grouting. This flexibility in timing of injecting groutcould improve the economy of the overall project.

is a cross section of the trenchpartially filled with rock, modified rebarand the grouting system. The grouting system consists of the central grout distribution pipesurrounded by sandwrapped in geotechnical filter cloth. Also shown is the grout injection pipeconnected to grout distribution pipe. The void spacebetween the rockis where the grout will flow into the fill to solidify the entire mass once the trench fill is complete.

shows a cross section of a completed support trenchthat has been grouted. The section drawing shows two modified rebarand one grout distribution system where the grouthas flowed out between the grains of sandand through the geotechnical filter clothand out into the void space. Depending on the groutand the compacted fill soilthe groutmay flow beyond the trench wall into the compacted fill soil. This would tie the trench rockfill to the compacted soil fillbeyond the limit of the initial trenchexcavation. At the top of the trench is a layer of the fill soilthat has been recompacted over the rockfill prior to grouting to help keep the groutflowing between the rockthrough the interconnected void space. With groutsurrounding the rocks, the rocksare now locked in place such that modified rebarsare also locked in place. This results in the wall segmentbecoming stable because it is attached to the modified rebar.

shows the back side of a possible design for wall segments. The drawing shows a wall segmentwith a rectangular indentationwith horizontal rebarthat cross the opening such that the unmodified rebarsection can be inserted into the space between the concrete of the segmentand the horizontal rebar. Once the rebarsection of the modified rebaris in place then a cover can be placed over the opening and the opening can be filled with concrete to make the modified rebara permanent part of the wall segment.

shows an alternate method of modifying rebarto increase the rebarability to transfer load to or from the surrounding material. A section of sheet metalhas been bent and has holes in each folded such that the rebarcan be inserted through the hole to join the two items together. For this design there is no concrete corrosion protection. For some conditions this may be acceptable. Another method would be to place groutor cementaround the rebarafter the two parts are assembled. It is possible to use this design for the trench stabilization system described herein.

presents another alternate design for creating modifying rebarsuch that the rebarhas a minimum concretecover to protect the steel from corrosion. Then spaced at designed intervals are washer shaped enlarged sections. The purpose of the enlarged sections is to improve the load transfer from surrounding material to the rebarthat runs through the center portion of the concrete to form a modified rebarsystem. Depending upon the anticipated loading and the size of the enlarged washer shaped section the enlarged section may need additional rebarformed into a circular shape to reinforce that portion of the modification of the center rebaras shown for one of the washers presented on this figure. It is possible to use this design for the trench stabilization system described herein.

presents a longitudinal section through a concrete covered modified rebar. The purpose of this drawing is to show the different variables that would need to be addressed for every project to have the optimum shape. These variables would apply regardless of the cross-sectional shape. As shown variable “D” is the minimum distance to provide safe cover for the rebarto ensure that the rebarshave proper corrosion protection. Variable “A” is the angle of the slope between the minimum cover cylinderalignment and the slope up to the outer portion of the undulating concrete cover. Variable “A” could range from 10 to 90 degrees. Variable “F” is the angle of the slope between the minimum cover cylinderalignment and the slope down from the outer portion of the undulating concrete cover. Variable “F” could range from 10 to 90 degrees. Distance “C” is the space between the base points along the minimum cover cylinderbetween two ridges. Variable “B” is the width of the extreme limit of the ridge. Variable “E” is the height of the ridge beyond the minimum cover cylinder. Theis cross-section through a typical ridge.is also a cross-section through another design of a ridge.

This view shows an alternative cross section of the washer shaped enlarged section described and shown on. Fora hexagonal shape is presented, however this is only to demonstrate that a geometric shape could be used in place of a round shaped washer. This view shows the primary rebarin the center and a secondary rebarin a circular shape to reinforce the hexagon.

is a cross section of the washer shape presented in perspective in. This view shows the primary rebarin the center and a secondary rebarin a circular shape to reinforce the circle.

This view provides a cutaway view showing the stabilizing trenchbehind a retaining walland under the sloping compacted fillbehind the wall. The trench directly behind the wall has modified rebarsthat are attached to the wall at slot. Inside slotis the rebar. This trench acts as a tie back for stabilizing the wall. Above and behind the wall are two “T” shaped stabilizing trenchesthat have sufficient space between them to allow for drainage. It should be noted that the trenchesin this view only show the outline of the trench and the modified rebar. The completed trenches would include the rock and gravel fill that has been grouted in place and surrounding the modified steel rebar. The scale of this Figure does not allow for these details to be shown but they would be the same as presented on. The grouted fill will obscure view of the modified steel rebar. The “T” shape is intended to provide stabilization for the fill located behind the trench that runs up the slope. The modified rebarstie the trench fill together and tie the front trenchto the back section of the trenchfor stability.

Presents a section through a partially completed wallwith soilfill compacted up to the elevation of the lower wallsegment. The lower section of wallis supported horizontally by a trench that was excavated into the partially completed fill soil. The section is drawn through the middle of the trench exposing the modified rebarand the grout system. The grouting system consists of the grout injection pipegoing into the geotechnical filter clothto the grout distribution pipesurrounded by sandwrapped in geotechnical filter cloth. Along with the stabilizing system the section cuts through the subdrain system including the sandpocket and the drainpipe. Also shown is the pocketin the back of the wall along with rebar. The wall segmentis supported by footingfounded in the existing soil. The top of wall segmenthas a slotfor the next segment to fit into.

This shows the same view asexcept the next wallsegment has been added along with new compacted soilfill and an additional trench of the same design and construction. The trenches are staggered both horizontally and vertically to ensure that drainage is not blocked. Both trenches have the same grouting system. The grouting system consists of the grout injection pipegoing into the geotechnical filter clothto the grout distribution pipesurrounded by sandwrapped in geotechnical filter cloth. The lower trench is shown to be grouted with groutfilling the void space around the rockand the modified rebar. The upper trench has not been grouted as demonstrated by the void spacebetween the rockand only filled with gravel. The rebaris only shown as a dashed line inside the concrete modified rebar. This is because this modified rebardoes not connect to anything beyond the trench, The proposed top of the fill lineis shown behind wall. The top wall has a plugon the bottom that has been fitted into the slotof the lower segment.

This perspective view is looking down on a completed walland several rows of discontinuous “T” shaped trenches. At this scale it is not possible to show all of the detail parts of each trench so only the modified rebarsare shown. The intent of the figure is to show how a retaining wallcan be stabilized using the modified rebarand the trenchsystem as described in this patent application. There is no distinction on the ground type as this system will work with either new fill soil or existing ground.