A method and structure for strengthening shoulders of reconstructed and expanded expressways with micro-piles

Abstract

The present invention discloses a method and structure for strengthening shoulder micro-piles based on reconstructed and expanded expressways, belonging to the micro-pile strengthening structure, and comprising the following steps: S1, designing pile positions; S2, punching and reaming holes at the designed pile positions; S3, inserting a perforated steel pipe into the micro-piles from the socket section; S4, external grouting; S5, successively performing sectional pressure grouting at the communication holes corresponding to the bottom end and the top end inside the perforated steel pipe; S6, waiting until the cement solidifies, removing the auxiliary pipe protruding from the road surface layer and then plugging and leveling; S7, repeating steps S2-S6, and strengthening the next pile position by means of grouting in alternate holes. By adopting the above method and structure for strengthening shoulder micro-piles based on reconstructed and expanded expressways, the contact zone between the water-stable layer and the road base layer and the relatively soft soil below are grouted and strengthened, while filling the voids, the physical and mechanical indexes of the soil in this section are improved, a complete strengthening belt is formed, and the overall stability and stiffness of the road surface are enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of shoulder micropile reinforcement, and particularly to a method and structure for reinforcing shoulders of a reconstructed and expanded expressway based on micropiles. Background Art

[0002] With the rapid progress of the reconstruction and expansion project of expressways, problems such as the expansion and widening of the original road surface and the re - division of lanes have emerged. The original shoulder of the expressway will be in the position of the heavy - vehicle lane of the new road surface. Since the sub - structure layer under the original expressway shoulder is relatively weak and the thickness of the water - stable layer is insufficient, the bearing capacity, deflection, modulus, service life and other indicators of the road surface cannot meet the long - term use requirements of the expressway. Therefore, it is necessary to improve and reinforce the subgrade structure under the original hard shoulder.

[0003] The existing shoulder road surfaces mainly have two forms. One is a thin shoulder mainly composed of asphalt pavement. Due to the good plasticity of asphalt, but the insufficient thickness of the stress - diffusion layer and the large difference in the modulus of subgrade soil, its failure forms are overall settlement and local uneven settlement. The other is a thin shoulder mainly composed of concrete. Due to the large stiffness of concrete, the punching shear stress caused by the insufficient thickness of concrete and the repeated tension between the road surface and the road base layer, its failure form is mainly fracture cracks.

[0004] To avoid settlement or cracking diseases of the subgrade after the expansion of the expressway, the existing scheme adopts the method of graded excavation and layered backfilling. The specific construction method is as follows: Generally, the excavation depth is 2m. After excavation, the subgrade filler is backfilled and compacted layer by layer, and then the water - stable layer and the road surface layer are filled layer by layer. However, this method has the following obvious disadvantages:

[0005] 1) During the subgrade excavation process, to ensure the normal operation of the original highway, the reconstructed and expanded highway generally adopts a state of semi - construction and semi - traffic. The position of the reconstructed and expanded shoulder is relatively close to the original lane, and the general side distance does not exceed 1m. If no protective measures are taken for the subgrade boundary during excavation, creep deformation or direct damage may occur under the action of dynamic loads, posing a serious threat to the safety of construction workers and passing vehicles. If protective measures such as steel sheet piles are taken, although the safety can be improved to a certain extent, the construction organization is more difficult in the expressway environment. The construction joints caused after the withdrawal of the steel sheet piles are difficult to handle, and at the same time, the cost is relatively high.

[0006] 2) There are a large number of waste materials formed during the subgrade excavation. These waste materials are mainly subgrade fillers, water - stable crushed stones, asphalt or concrete mixtures. The waste residue will seriously pollute the surrounding environment. At the same time, this behavior also causes a large amount of resource waste, which does not meet the requirements of low - carbon greening.

[0007] 3) During the process of layered compaction of the subgrade, since the width of the shoulder area is generally small, usually about 2.5 m, it is currently very difficult to find a suitable machine for compaction of such long-strip foundation pits, and the construction quality is difficult to guarantee. Summary of the Invention

[0008] To solve the above problems, the present invention provides a method and structure for strengthening shoulder micro-piles based on reconstructed and expanded expressways. By grouting and strengthening the contact zone between the water-stable layer and the subgrade layer and the relatively weak soil below, while filling the voids, the physical and mechanical indexes of the soil in this section are improved, a complete strengthening belt is formed, and the overall stability and stiffness of the road surface are enhanced.

[0009] To achieve the above object, the present invention provides a method for strengthening shoulder micro-piles based on reconstructed and expanded expressways, including the following steps:

[0010] S1. Design pile positions: Design pile positions in a rectangular array in the area to be strengthened;

[0011] S2. Punch and ream holes at the designed pile positions: First, punch holes in the road surface layer and the water-stable layer in sequence, and then ream the subgrade layer to obtain an inserted hole section and a reamed hole section that are vertically connected and concentrically arranged. The inserted hole section and the reamed hole section form a micro-pile, and the upper and lower ends of the inserted hole section are respectively aligned with the road surface layer and the water-stable layer, and the reamed hole section is aligned with the subgrade layer;

[0012] S3. Insert a perforated steel pipe into the micro-pile from the inserted hole section until the bottom end of the perforated steel pipe contacts the inner wall of the bottom end of the reamed hole section. At this time, the top end of the perforated steel pipe is flush with the top end of the reamed hole section. The top end of the perforated steel pipe also extends out of the inserted hole section through an auxiliary pipe. The perforated steel pipe and the reamed hole section are concentrically arranged, and the auxiliary pipe and the inserted hole section are concentrically arranged. An external grouting cavity is left between the outer wall of the perforated steel pipe and the micro-pile;

[0013] At the same time, a plurality of communication holes are respectively opened on the side wall of the perforated steel pipe at positions corresponding to the bottom end and the top end of the subgrade layer, and plugs are clamped in the communication holes;

[0014] S4. External grouting: Grout into the external grouting cavity until it is filled, and wait until the external cement solidifies;

[0015] S5. Sequentially perform sectional pressure grouting into the perforated steel pipe at the communication holes corresponding to the bottom end and the top end respectively, and the cement injected in a pressure-layered manner will flush the plug down and enter the external grouting cavity through the communication hole. At the same time, the cement injected at the communication hole corresponding to the top end penetrates into the contact zone between the water-stable layer and the subgrade layer;

[0016] S6. Wait until the cement solidifies, remove the auxiliary pipe extending out of the road surface layer, then plug and level, and finally water for maintenance;

[0017] S7. Repeat steps S2 - S6, and strengthen the next pile position in a way of grouting every other hole.

[0018] Preferably, in step S2, the drilling head used for punching includes a first connecting rod fixedly connected to the punching machine at one end, a first drill bit skeleton fixedly connected to the other end of the first connecting rod at one side, and impact teeth connected to the other side of the first drill bit skeleton;

[0019] A first air inlet hole is formed in the center of the first connecting rod, and the first air inlet hole communicates with a first air outlet hole formed on the side of the first drill bit skeleton facing the impact teeth;

[0020] The reaming head used for reaming includes a second connecting rod connected to the drilling rig at one end, a second drill bit skeleton fixedly connected to the other end of the second connecting rod at one end, and a plurality of reaming wings radially slidably connected to the other end of the second drill bit skeleton. The plurality of reaming wings are arranged in an annular array on the circumferential side of the second drill bit skeleton;

[0021] A second air inlet hole is formed in the center of the second connecting rod, and the second air inlet hole communicates with a second air outlet hole formed at the end of the second drill bit skeleton close to the reaming wings;

[0022] When punching and reaming are realized, air is blown through the first air inlet hole and the second air inlet hole to the first air outlet hole and the second air outlet hole to blow out dust, and a dust removal device is used to remove the dust.

[0023] Preferably, a plurality of communication holes are formed at the bottom end of the steel flower tube described in step S3, and the plurality of communication holes formed at the bottom end of the steel flower tube are linearly arranged. The plurality of communication holes formed at the top end of the side wall of the steel flower tube and the plurality of communication holes at the bottom end are both arranged in an annular array; The manufacturing steps are as follows:

[0024] Take a pipe section equal to the height of the reaming section as the base pipe section, respectively form communication holes at the bottom end, the bottom end of the side wall and the top end of the side wall of the steel flower tube, and plug the communication holes, and tap internal threads on the inner wall of the top end of the steel flower tube for connecting the auxiliary pipe.

[0025] Preferably, the plug is made of water glass.

[0026] Preferably, step S4 specifically includes the following steps:

[0027] Insert the conduit into the bottom end of the external grouting cavity, and inject cement into the conduit. Inject cement into the external grouting cavity from bottom to top, and the cement used is PO42.5 cement with a water-cement ratio of 0.4 to 0.6. Wait for 7 to 10 hours to solidify.

[0028] Preferably, step S5 specifically includes the following steps:

[0029] S51. Wrap an elastic water injection cavity outside the grouting pipe, and a water injection pipe is communicated with the elastic water injection cavity;

[0030] S52. Place the grouting pipe with an elastic water injection cavity into the steel pipe pile, until the grouting port at the bottom end of the grouting pipe aligns with the communication hole at the bottom end.

[0031] S53. Inject water into the elastic water injection cavity through the water injection pipe. The elastic water injection cavity expands until it fits against the inner wall of the steel pipe pile.

[0032] S54. Grout into the bottom end of the steel pipe pile through the grouting pipe. The cement at the bottom is washed down and sealed, and then seeps into the external grouting cavity through the communication hole at the bottom end. Wait for a set time until the bottom grouting solidifies.

[0033] S55. Draw out the water in the elastic water injection cavity, lift the grouting pipe upward until the grouting pipe aligns with the communication hole at the top end. Grout into the steel pipe pile again through the grouting pipe. The cement at the top is washed down and sealed, and then seeps into the external grouting cavity through the communication hole at the top end, and seeps into the contact zone between the water-stable layer and the road base layer until the cement is flush with the top end of the road surface layer. Pull out the grouting pipe and seal the auxiliary pipe.

[0034] Preferably, in step S53, the water injection pressure is 3.5 MPa to 4.5 MPa.

[0035] In step S54 and step S55, the water-cement ratio of the grouting cement used is 0.8 to 1.1, the grouting splitting pressure is 3.8 MPa to 5.0 MPa, and the grouting pressure after washing down and sealing is 0.8 MPa to 1.3 MPa.

[0036] Preferably, in step S6, wait for 8 to 12 hours, and seal and level with cement slurry with a water-cement ratio of 0.4 to 0.6.

[0037] A structure of a shoulder micropile reinforcement method based on reconstructed and expanded expressways includes micropiles and steel pipe piles concentrically inserted into the micropiles. The micropiles include an insertion hole section and an expanded hole section that are vertically connected and concentrically arranged. Among them, the insertion hole section sequentially penetrates through the road surface layer and the water-stable layer, and the expanded hole section is opened on the side of the road base layer facing the water-stable layer, and there is a contact zone between the water-stable layer and the road base layer.

[0038] The bottom end of the steel pipe pile contacts the inner wall of the bottom end of the expanded hole section. The top end of the steel pipe pile is flush with the top end of the expanded hole section, and the top end of the steel pipe pile extends out of the insertion hole section through the auxiliary pipe. Communication holes are respectively opened at positions on the steel pipe pile corresponding to the bottom end and the top end of the expanded hole section, and plugs are clamped in the communication holes.

[0039] Cement is filled in layers inside the steel pipe pile corresponding to the communication holes at the bottom end and the communication holes at the top end. The cement corresponding to the communication holes at the top end seeps out of the communication holes and into the contact zone.

[0040] The space between the outside of the steel pipe pile and the micropile is filled with external grouting.

[0041] Preferably, a plug is clamped in the communication hole, and the plug is made of sodium silicate.

[0042] The present invention has the following beneficial effects:

[0043] 1. By grouting and strengthening the contact zone between the water-stable layer and the road base layer and the relatively soft soil mass below, while filling the voids, the physical and mechanical indexes of the soil mass in this section are improved, forming a complete reinforcement zone, which enhances the overall stability and stiffness of the road surface;

[0044] 2. By means of bottom grouting of the micro-piles, the overall bearing capacity of the micro-piles is improved, and at the same time, the settlement deformation is reduced. In terms of the force mechanism, it combines classical soil mechanics and pile foundation engineering. Compared with the existing technology, it has the characteristics of small construction disturbance, low carbon and environmental protection, convenient and fast, safe and reliable, controllable progress and low construction cost.

[0045] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a construction schematic diagram of a method for strengthening the shoulder micro-piles of a reconstructed and expanded expressway according to the present invention;

[0047] Figure 2 is a structural schematic diagram of a steel flower pipe of a method for strengthening the shoulder micro-piles of a reconstructed and expanded expressway according to the present invention;

[0048] Figure 3 is a structural schematic diagram of a grouting pipe of a method for strengthening the shoulder micro-piles of a reconstructed and expanded expressway according to the present invention;

[0049] Figure 4 is a structural schematic diagram of a drilling head of a method for strengthening the shoulder micro-piles of a reconstructed and expanded expressway according to the present invention;

[0050] Figure 5 is a structural schematic diagram of an under-reamer of a method for strengthening the shoulder micro-piles of a reconstructed and expanded expressway according to the present invention;

[0051] Figure 6 is a pile position layout diagram of an embodiment of the present invention;

[0052] Figure 7 is a pile position layout diagram of a comparative example of the present invention.

[0053] Wherein: 1, road surface layer; 2, cement stabilized layer; 3, road base layer; 4, micro-piles; 41, socket section; 42, reaming section; 5, elastic water injection cavity; 6, perforated steel pipe; 61, communication holes; 7, grouting pipe; 8, water injection pipe; 9, auxiliary pipe; 10, drill bit; 101, impact teeth; 102, first drill bit skeleton; 103, first connecting rod; 104, first air inlet hole; 11, reaming head; 111, second air inlet hole; 112, second connecting rod; 113, second drill bit skeleton; 114, reaming wings; 115, second air outlet hole. Detailed implementation manners

[0054] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the following further describes the embodiments of the present invention in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention, and are not used to limit the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the scope of protection of this application. Examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals indicate the same or similar elements or elements with the same or similar functions throughout.

[0055] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or server that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0056] Similar reference numerals and letters indicate similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0057] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the present invention is usually placed during use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0058] In the description of the present invention, it should also be noted that, unless otherwise clearly specified and defined, the terms "set", "installed", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0059] As Figures 1-5 shown, a method for strengthening the shoulder micro-piles of a reconstructed and expanded expressway includes the following steps:

[0060] S1. Design the pile positions: Design the pile positions in a rectangular array in the area to be strengthened;

[0061] S2. First, punch holes in the pavement layer 1 and the cement stabilized layer 2 in sequence, and then ream the road base layer 3 to obtain an inserted hole section 41 and a reamed hole section 42 that are vertically connected and concentrically arranged. The inserted hole section 41 and the reamed hole section 42 form the micro-pile 4, and the upper and lower ends of the inserted hole section 41 are respectively aligned with the pavement layer 1 and the cement stabilized layer 2, and the reamed hole section 42 is aligned with the road base layer 3. In this embodiment, the pavement layer 1 is an asphalt layer or a concrete layer.

[0062] In step S2, the drilling head 10 used for punching holes includes a first connecting rod 103 with one end fixedly connected to a drilling machine, a first drill bit skeleton 102 with one side fixedly connected to the other end of the first connecting rod 103, and impact teeth 101 connected to the other side of the first drill bit skeleton 102; a first air inlet hole 104 is opened in the center of the first connecting rod 103, and the first air inlet hole 104 is communicated with a first air outlet hole opened on the side of the first drill bit skeleton 102 facing the impact teeth 101;

[0063] The reaming head 11 used for reaming includes a second connecting rod 112 with one end connected to a drilling rig, a second drill bit skeleton 113 with one end fixedly connected to the other end of the second connecting rod 112, and a plurality of reaming wings 114 that are radially slidably connected to the other end of the second drill bit skeleton 113. The plurality of reaming wings 114 are arranged in a circular array on the circumferential side of the second drill bit skeleton 113; a second air inlet hole 111 is opened in the center of the second connecting rod 112, and the second air inlet hole 111 is communicated with a second air outlet hole 115 opened at one end of the second drill bit skeleton 113 close to the reaming wings 114. Under the squeezing and rotational driving action of the drilling rig, the reaming wings 114 open to carry out reaming;

[0064] It realizes that when punching holes and reaming, air is blown through the first air inlet hole 104 and the second air inlet hole 111 to the first air outlet hole and the second air outlet hole 115 to blow out dust, and a dust removal device is used to remove the dust.

[0065] S3. Insert the perforated steel pipe 6 into the micro-pile 4 from the socket section 41 (the perforated steel pipe 6 can be replaced by a high-strength PVC pipe in a formation with relatively low pressure). Insert it until the bottom end of the perforated steel pipe 6 touches the inner wall of the bottom end of the reamed section 42. At this time, the top end of the perforated steel pipe 6 is flush with the top end of the reamed section 42. The top end of the perforated steel pipe 6 also extends out of the socket section 41 through the auxiliary pipe 9. And the perforated steel pipe 6 and the reamed section 42 are concentrically arranged, the auxiliary pipe 9 and the socket section 41 are concentrically arranged. An external grouting cavity is left between the outer wall of the perforated steel pipe 6 and the micro-pile 4;

[0066] At the same time, a plurality of communication holes are respectively opened on the side wall of the perforated steel pipe 6 at positions corresponding to the bottom end and the top end of the road base course 3. Plugs are clamped in the communication holes;

[0067] A plurality of communication holes are opened at the bottom end of the perforated steel pipe 6 described in step S3. And the plurality of communication holes 61 opened at the bottom end of the perforated steel pipe 6 are linearly arranged. The plurality of communication holes opened at the top end of the side wall of the perforated steel pipe 6 and the plurality of communication holes 61 at the bottom end are both arranged in a circular array. The manufacturing steps are as follows:

[0068] Take a pipe section with the same height as the reamed section 42 as the base pipe section. Respectively open communication holes at the bottom end, the bottom end of the side wall and the top end of the side wall of the perforated steel pipe 6, and insert plugs into the communication holes. Tap internal threads on the inner wall of the top end of the perforated steel pipe 6 for connecting the auxiliary pipe 9.

[0069] The plug is made of water glass.

[0070] S4. External grouting: Grout into the external grouting cavity until it is full, and wait until the external cement solidifies;

[0071] Step S4 specifically includes the following steps:

[0072] Insert the conduit into the bottom end of the external grouting cavity, and inject cement into the conduit. Inject cement into the external grouting cavity from bottom to top. And the cement used is PO42.5 cement with a water-cement ratio of 0.4 - 0.6. Wait for 7 - 10 hours to solidify.

[0073] S5. Carry out staged pressure grouting into the perforated steel pipe 6 respectively corresponding to the communication holes 61 at the bottom end and the communication holes 61 at the top end. And the cement injected in a pressure stratified manner will wash down the plug and enter the external grouting cavity through the communication holes 61. At the same time, the cement injected corresponding to the communication holes 61 at the top end penetrates into the contact zone between the water-stable layer 2 and the road base course 3;

[0074] Step S5 specifically includes the following steps:

[0075] S51. Wrap the elastic water injection cavity 5 outside the grouting pipe 7, and a water injection pipe 8 is communicated with the elastic water injection cavity 5;

[0076] S52. Place the grouting pipe 7 with the elastic water injection cavity 5 into the steel flower pipe 6 until the grouting port at the bottom end of the grouting pipe 7 aligns with the communication hole 61 at the bottom end.

[0077] S53. Inject water into the elastic water injection cavity 5 through the water injection pipe 8. The elastic water injection cavity 5 expands until it fits against the inner wall of the steel flower pipe.

[0078] In step S53, the water injection pressure is 3.5 MPa to 4.5 MPa.

[0079] S54. Grout into the bottom end of the steel flower pipe through the grouting pipe 7. The cement at the bottom is washed down and sealed, and then seeps into the external grouting cavity through the communication hole 61 at the bottom end. Wait for a set time until the bottom grouting solidifies.

[0080] S55. Drain the water in the elastic water injection cavity 5, lift the grouting pipe 7 upward until the grouting pipe 7 aligns with the communication hole 61 at the top end. Grout into the steel flower pipe again through the grouting pipe 7. The cement at the top is washed down and sealed, and then seeps into the external grouting cavity through the communication hole 61 at the top end, and seeps into the contact zone between the water stable layer 2 and the road base layer 3 until the cement is flush with the top end of the road surface layer 1. Pull out the grouting pipe 7 and seal the auxiliary pipe 9.

[0081] In steps S54 and S55, the water-cement ratio of the grouting cement used is 0.8 to 1.1, the grouting splitting pressure is 3.8 MPa to 5.0 MPa, and the grouting pressure after washing down and sealing is 0.8 MPa to 1.3 MPa.

[0082] S6. Wait until the cement solidifies, remove the auxiliary pipe 9 protruding from the road surface layer 1 and then seal and level it, and finally water for maintenance.

[0083] In step S6, wait for 8 to 12 hours and use cement slurry with a water-cement ratio of 0.4 to 0.6 for sealing and leveling.

[0084] S7. Repeat steps S2 - S6 and use the method of grouting every other hole to reinforce the next pile position.

[0085] A structure of a reinforcement method for a shoulder micropile 4 based on a reconstructed and expanded expressway includes a micropile 4 and a perforated steel pipe 6 concentrically inserted into the micropile 4. The micropile 4 includes an insertion hole section 41 and an expanded hole section 42 that are vertically connected and concentrically arranged. Among them, the insertion hole section 41 sequentially penetrates through the road surface layer 1 and the cement stabilized layer 2, and the expanded hole section 42 is opened on one side of the road base layer 3 facing the cement stabilized layer 2, and there is a contact zone left between the cement stabilized layer 2 and the road base layer 3; the bottom end of the perforated steel pipe 6 contacts the inner wall of the bottom end of the expanded hole section 42, the top end of the perforated steel pipe 6 is flush with the top end of the expanded hole section 42, and the top end of the perforated steel pipe 6 extends out of the insertion hole section 41 through the auxiliary pipe 9; communication holes 61 are opened at positions corresponding to the bottom end and the top end of the expanded hole section 42 on the perforated steel pipe 6, and plugs are clamped in the communication holes 61; cement is filled in layers at positions corresponding to the communication hole 61 at the bottom end and the communication hole 61 at the top end inside the perforated steel pipe 6, and the cement that flushes out of the communication hole 61 corresponding to the top end seeps into the contact zone; the outside of the perforated steel pipe 6 and the micropile 4 are filled with external grouting. A plug is clamped in the communication hole 61, and the plug is made of sodium silicate. In this embodiment, a plurality of connecting pipes are also opened at the bottom end of the perforated steel pipe 6.

[0086] Verification example

[0087] Embodiment

[0088] As Figure 6 shown, the following experiments were carried out in the third experimental area of a certain expressway from October to December 2023:

[0089] First step: Design the pile positions: Borehole layout plan: Select a micropile with a diameter of 170 mm and an expansion of 300 mm, the total pile length is 1.0 m, the length of the expanded hole section is 63 mm, the thickness of the road surface layer is 37 mm, the longitudinal borehole spacing is 1100 mm, and the transverse borehole spacing is 800 mm and 650 mm;

[0090] Second step: Punch and expand the holes at the designed pile positions:

[0091] First, use a 170 mm punching drill bit to punch a hole of 370 mm, and punch until the position of 370 mm; then use a 170 mm drill bit with an expansion of 300 mm to expand the hole, and the length of the lower expanded hole section is 630 mm;

[0092] Third step: First, prepare a perforated steel pipe with a diameter of 40 - 60 mm. The length of the perforated steel pipe is equal to the length of the expanded hole section, taking 630 mm, and the length error is controlled within the range of 50 mm. There are no less than 2 grouting holes at the bottom end of the perforated steel pipe, and there are no less than 8 communication holes at the bottom end and the top end of the side wall of the perforated steel pipe. All the grouting holes are plugged with sodium silicate. The length of the auxiliary pipe is 60 cm - 100 cm to ensure convenient construction and disassembly;

[0093] Then, place the prepared perforated steel pipe into the micropile, and ensure that the center line of the perforated steel pipe is collinear with the center line of the micropile hole. The verticality is controlled within the range of plus or minus 5 degrees, and the overall deviation is controlled within 2 cm. Ensure that the grouting area at the top of the perforated steel pipe is within the contact zone between the cement stabilized base and the road base, so as to ensure that the grouting liquid can penetrate into the contact zone.

[0094] Step 4, External Grouting: Use PO42.5 cement grout with a water-cement ratio of 0.4 - 0.6, and use a conduit to grout from the bottom upwards. During the grouting process, ensure that there is no grout inside the perforated steel pipe.

[0095] Step 5, After 7 - 10 hours (adjust appropriately according to weather and temperature conditions), at this time, the grout outside the perforated steel pipe has a certain strength. Place a grouting pipe with a diameter of 30 - 40 mm inside the perforated steel pipe, and the grouting port is 1 cm - 2 cm away from the inner wall at the bottom end of the perforated steel pipe. Inject water into the elastic water injection cavity through the water injection pipe, and control the water injection pressure within 3.5 - 4.5 MPa, so that the elastic water injection cavity expands and fits against the inner wall of the perforated steel pipe to seal the perforated steel pipe.

[0096] Step 6, Grout the lower end and bottom of the perforated steel pipe through the grouting pipe. The water-cement ratio is 0.8 - 1.1, and the grouting fracture pressure is controlled within 3.8 MPa - 5.0 MPa. The grout uses pressure to break through the sodium silicate seal of the perforated steel pipe. After breaking through, the grouting pressure is maintained between 0.8 MPa - 1.3 MPa. After injecting 0.13 - 0.15 cubic meters of cement grout, lift the grouting pipe to the position of the auxiliary pipe, ensure that the grouting port is at the communication hole at the top of the perforated steel pipe, and then grout (the grouting volume is controlled within 0.12 - 0.14 cubic meters, and the total grouting volume of single-pile grouting and fracture grouting is controlled within 0.25 - 0.28 cubic meters). After the grouting is completed, pull out the grouting pipe, and use a plug to seal the hole opening.

[0097] Step 7, After the grouting of one pile is completed, construct the next pile in the order of alternate hole injection. Finally, complete all the micropiles in the same batch. After 8 - 12 hours, disassemble the auxiliary pipe by twisting the section of the auxiliary pipe exposed on the road surface. The small holes after disassembly are sealed and leveled with cement grout with a water-cement ratio of 0.4 - 0.6. After all are completed, conduct natural watering and curing.

[0098] Test Results:

[0099] Since the expansion from 170 mm to 300 mm is within the range of 650 - 1100 mm spacing, the theoretically calculated bearing capacity is much greater than the designed required bearing capacity. Therefore, the detection mainly focuses on the deformation index.

[0100] 1) Plate Load Test

[0101] According to the modulus test results, the average deformation modulus of the ungrouted area is 522.3 MPa. The average deformation modulus at the position of the soil between piles in the test area is 838.6 MPa, and the average deformation modulus at the pile top position is 986.3 MPa. The modulus at the position of the soil between piles has increased by 1.60 times, and the modulus at the pile top position has increased by 1.89 times. Through the comprehensive stress diffusion angle of about 39.1 degrees for the previously tested road surface and the water-stabilized layer, it can be known that in this embodiment, the overall index of the soil body has been strengthened, the stress has been reasonably diffused, and has been appropriately concentrated at the pile body position.

[0102] 2) Benkelman beam test

[0103] The completion of the ungrouted area is between 18 and 35, with an average value of 25.5. The Benkelman beam deflection values after grouting are shown in Table 1.

[0104] Table 1 Benkelman beam deflection statistics for Test Area 3

[0105]

[0106] It can be seen that the overall Benkelman beam deflection has been greatly reduced and can meet the requirements of the current code design.

[0107] Comparative example

[0108] As Figure 7 shown, the following experiment was carried out in the first high-speed test area from October to December 2023:

[0109] 1. Borehole layout plan: Select micro-piles with a diameter of 75 mm, a total pile length of 1.0 m, an enlarged hole section length of 63 mm, a road surface and structural layer thickness of 37 mm, a longitudinal borehole spacing of 800 mm, and transverse borehole spacings of 800 mm and 650 mm. The grouting volume is quantitatively grouted in two sections according to the calculation.

[0110] 2. Detection plan: Plate load test and Benkelman beam test are respectively used for detection.

[0111] 3. The specific plan is as follows:

[0112] 1) Use a 75 mm impact drill bit to punch holes to a depth of 1000 mm;

[0113] 2) Prepare a perforated steel pipe. The diameter of the perforated steel pipe is selected as a 40 - 60 mm ordinary steel pipe. The length of the steel pipe is equivalent to the length of the lower enlarged hole section, taking 630 mm, and the length error is controlled within a range of 50 mm. There are no less than 2 grouting small holes at the end of the perforated steel pipe, and the small holes in the opening areas at the top and bottom of the side wall of the grouting device should not be less than 8. All grouting small holes are temporarily blocked with water glass. The length of the auxiliary pipe of the perforated steel pipe is controlled within the range of 60 cm - 100 cm to ensure convenient construction and disassembly;

[0114] 3) Place the prepared steel flower pipe into the empty hole of the micro-pile after reaming, ensuring that the center line of the steel flower pipe is collinear with the center line of the micro-pile hole, with the verticality controlled within the range of plus or minus 5 degrees and the overall deviation controlled within 1 cm; ensure that the upper grouting area of the steel flower pipe is within the contact zone between the water-stable layer and the road base layer to ensure that the grouting liquid can penetrate into the contact zone;

[0115] 4) Grout the area outside the steel flower pipe of the micro-pile. Use PO42.5 cement for grouting (other types of cement can be used in special strata), with the water-cement ratio of 0.4 - 0.6. Grout from the bottom upwards using a conduit, and ensure that there is no grout inside the steel flower pipe during the grouting process;

[0116] 5) After 7 - 10 hours (adjust appropriately according to weather and temperature conditions), when the grout outside the steel flower pipe has a certain strength, place a grouting pipe with a diameter of 30 - 40 mm inside the steel flower pipe. Place the grouting port 1 - 2 cm from the bottom of the steel flower pipe, and inject water into the elastic water injection cavity through the water injection pipe. Control the water injection pressure at 3.5 - 4.5 MPa to ensure that the elastic water injection cavity expands and adheres to the steel flower pipe, and seal the steel flower pipe;

[0117] 6) Grout the lower end and bottom of the steel flower pipe through the grouting pipe. Use a water-cement ratio of 0.8 - 1.1, and control the grouting splitting pressure at 3.8 - 5.0 MPa. The grout uses pressure to break through the temporary sodium silicate seal of the grouting small holes on the steel flower pipe. After breaking through, keep the grouting pressure between 0.8 - 1.3 MPa. After injecting 0.15 - 0.18 cubic meters of cement slurry, lift the grouting pipe to the position of the auxiliary pipe, ensure that the grouting port of the grouting pipe is in the area of the upper grouting small holes of the steel flower pipe, and then grout the upper section with the same grouting steps as the lower end (control the grouting volume at 0.14 - 0.16 cubic meters, and control the total grouting volume of single-pile grouting and splitting grouting at 0.30 - 0.34 cubic meters). After grouting is completed, pull out the grouting pipe, and immediately use a plug to seal the hole opening;

[0118] 7) After grouting one pile is completed, construct the next pile in the sequence of grouting every other hole, and finally complete all the micro-piles of the same batch.

[0119] 9) After 8 - 12 hours, disassemble the auxiliary pipe by twisting the section of the auxiliary pipe exposed on the road surface;

[0120] 10) Seal and level the removed small holes with cement slurry with a water-cement ratio of 0.4 - 0.6, and conduct natural watering maintenance after all are completed.

[0121] 6. Test Results

[0122] Since the 75-mm micro-pile is mainly controlled by the bearing capacity and deformation indexes, the tests are mainly carried out on these two aspects of indexes.

[0123] 1) Single-pile static load test

[0124] According to the results of the static load test, when the pile body was not grouted by secondary splitting, the ultimate bearing capacity was 60 kN. When the pile body was grouted quantitatively, the bearing capacity was 80 kN. When the pile body was grouted sufficiently, the bearing capacity was 120 kN. Since it was calculated by the model that the bearing capacity of a single pile needed to reach more than 100 kN, the entire comparison plan was carried out around the sufficient grouting plan. According to the results of the single-pile static load test, the indexes of the small-diameter non-expanded pile itself were relatively low, and a large amount of grouting was required to make up for the short board of the pile body itself.

[0125] 2) Load plate test

[0126] (1) Modulus test results

[0127] According to the modulus test results, the average deformation modulus in the non-grouted area was 522.3 MPa, the average deformation modulus at the position of the soil between piles in the test area was 701.5 MPa, and the average deformation modulus at the pile top position was 682.3 MPa. The modulus at the position of the soil between piles increased by 1.34 times, and the modulus at the pile top position increased by 1.31 times. Although the overall indexes of the small-diameter micro piles have been greatly improved, the improvement amplitude is not large, and the grouting volume is large, which cannot meet the design requirements. Moreover, through model analysis and on-site testing, it can be seen that the micro piles themselves play a small role, mainly in the effect of strengthening the soil body, resulting in defects in the model (the reason why the modulus of the soil between piles is greater than that of the pile body position is that more piles are covered by the stress diffused in the upper part of the soil between piles, resulting in a small difference).

[0128] (2) Deflection test

[0129] The values in the non-grouted area were between 18 and 35, with an average value of 25.5. The deflection values after grouting are shown in Table 2.

[0130] Table 2 Deflection statistics table of Test Area 1

[0131]

[0132] It can be seen that although the overall deflection has been reduced, the reduction amplitude is limited.

[0133] Conclusion: Through model calculation and analysis of test results, the scheme described in the comparative example has an overall strengthening effect on the weak road shoulder, but the grouting volume is large, the construction cost is high, and the strengthening effect is limited, so it is not suitable to be adopted.

[0134] Therefore, the present invention adopts the above-mentioned method and structure for strengthening the road shoulder micro piles based on the reconstruction and expansion of expressways. By grouting and strengthening the contact zone between the water-stable layer and the road base layer and the relatively weak soil body below, while filling the voids, the physical and mechanical indexes of the soil body in this section are improved, a complete strengthening belt is formed, and the overall stability and stiffness of the road surface are enhanced.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements do not enable the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for reinforcing the shoulder of a highway based on micro-pile construction and expansion, characterized in that: The following steps are involved: S1. Design pile positions: Design pile positions in a rectangular array in the area to be reinforced; S2, punching and expanding holes at the designed pile positions: first, punch holes in the pavement layer and the water-stable layer in sequence, and then expand holes in the roadbed, to obtain an inserting hole section and an expanding hole section that are connected up and down and concentrically arranged, the inserting hole section and the expanding hole section form a micropile, and the upper and lower ends of the inserting hole section are aligned with the pavement layer and the water-stable layer respectively, and the expanding hole section is aligned with the roadbed; S3, inserting the steel flower tube from the jack section into the micropile until the bottom end of the steel flower tube contacts the bottom inner wall of the reaming section, at which time the top of the steel flower tube is flush with the top of the reaming section, and the top of the steel flower tube also extends out of the jack section through the auxiliary tube, and the steel flower tube is arranged concentrically with the reaming section, the auxiliary tube is arranged concentrically with the jack section, and an external grouting cavity is left between the outer wall of the steel flower tube and the micropile; At the same time, a plurality of connecting holes are opened on the side wall of the steel flower tube at positions corresponding to the bottom end and the top end of the roadbed, and plugs are stuck in the connecting holes; S4, external grouting: grouting into the external grouting cavity until the external grouting cavity is filled, and waiting for the external cement to solidify; S5, grouting is performed in sections in sequence at the connecting holes at the bottom and the top of the steel tube, and the cement injected by pressure in layers flushes the plugging down and enters the external grouting cavity through the connecting holes, and at the same time, the cement injected at the corresponding connecting holes at the top penetrates into the contact zone between the water-stable layer and the roadbed; S6. Wait until the cement solidifies, remove the auxiliary pipes extending out of the pavement layer, seal and level them, and finally water them for maintenance; S7, repeat steps S2-S6, and reinforce the next pile position by skipping injection in alternate holes.

2. A method for reinforcing a road shoulder with micro piles based on the reconstruction and expansion of a highway according to claim 1, characterized in that: In step S2, the drilling head used for punching includes a first connecting rod having one end fixedly connected to the punching machine, a first drill bit frame having one side fixedly connected to the other end of the first connecting rod, and an impact tooth connected to the other side of the first drill bit frame; A first air inlet hole is provided at the center of the first connecting rod, and the first air inlet hole is connected to a first air outlet hole provided on a side of the first drill frame facing the impact teeth; The reaming head used for reaming comprises a second connecting rod connected to the drilling machine at one end, a second drill bit skeleton fixedly connected to the other end of the second connecting rod at one end, and a plurality of reaming wings radially slidably connected to the other end of the second drill bit skeleton, wherein the plurality of reaming wings are arranged in an annular array on the circumferential side of the second drill bit skeleton; A second air inlet hole is provided at the center of the second connecting rod, and the second air inlet hole is connected to a second air outlet hole provided at one end of the second drill frame close to the hole-expanding wing; It is achieved that during punching and expanding, air is blown toward the first air outlet hole and the second air outlet hole through the first air inlet hole and the second air inlet hole to blow out dust, and the dust is removed by using the dust suction equipment.

3. A method for reinforcing a shoulder of a highway based on micro-pile construction and expansion according to claim 1, characterized in that: The bottom end of the steel flower tube in step S3 is provided with a plurality of connecting holes, and the plurality of connecting holes provided at the bottom end of the steel flower tube are arranged linearly, and the plurality of connecting holes provided at the top end of the side wall of the steel flower tube and the plurality of connecting holes at the bottom end are arranged in a circular array; The production steps are as follows: Take a pipe section with the same height as the expanded hole section as the basic pipe section, open connecting holes at the bottom end of the steel flower pipe, the bottom end of the side wall and the top end of the side wall respectively, plug the connecting holes, and tap the internal thread on the inner wall of the top end of the steel flower pipe to connect the auxiliary pipe.

4. A method for reinforcing a road shoulder with micro piles based on the reconstruction and expansion of a highway according to claim 3, characterized in that: The plug is made of water glass.

5. The method for reinforcing a road shoulder with micro piles based on the reconstruction and expansion of a highway according to claim 1, characterized in that: Step S4 specifically includes the following steps: Extend the catheter into the bottom of the external grouting cavity and inject cement into the catheter. Inject cement into the external grouting cavity from bottom to top. The cement uses PO42.5 cement with a water-cement ratio of 0.4 to 0.6 and solidifies after 7 to 10 hours.

6. The method for reinforcing a road shoulder with micro piles based on the reconstruction and expansion of a highway according to claim 1, characterized in that: Step S5 specifically includes the following steps: S51, wrapping an elastic water injection cavity outside the grouting pipe, and the elastic water injection cavity is connected with a water injection pipe; S52, placing the grouting pipe with the elastic water injection cavity into the steel flower pipe until the grouting port at the bottom end of the grouting pipe is aligned with the connecting hole at the bottom end; S53, injecting water into the elastic water injection cavity through the water injection pipe, and the elastic water injection cavity expands until it fits with the inner wall of the steel flower tube; S54, grouting the bottom of the steel flower pipe through the grouting pipe, the cement at the bottom is flushed down and sealed, and then penetrates into the external grouting cavity through the connecting hole at the bottom, and waits for a set time until the grouting at the bottom solidifies; S55. Drain the water in the elastic water injection cavity, lift the grouting pipe upward until the grouting pipe is aligned with the connecting hole at the top, and inject grout into the steel flower pipe again through the grouting pipe. The cement at the top is flushed down and sealed, and then penetrates into the external grouting cavity from the connecting hole at the top, and penetrates into the contact zone between the water-stabilizing layer and the roadbed layer until the cement is flush with the top of the pavement layer, pull out the grouting pipe and seal the auxiliary pipe.

7. A method for reinforcing a shoulder of a highway based on micro-pile construction and expansion according to claim 6, characterized in that: In step S53, the water injection pressure is 3.5MPa to 4.5MPa; In step S54 and step S55, the water-cement ratio of the grouting cement used is 0.8-1.1, the grouting splitting pressure is 3.8MPa-5.0MPa, and the grouting pressure after flushing and plugging is 0.8MPa-1.3MPa.

8. The method for reinforcing a road shoulder with micro piles based on the reconstruction and expansion of a highway according to claim 1, characterized in that: In step S6, wait for 8 to 12 hours and use cement slurry with a water-cement ratio of 0.4 to 0.6 for plugging and leveling.

9. A structure used in the method for reinforcing the shoulder of a highway based on micro-pile reinforcement according to any one of claims 1 to 8, characterized in that: It includes a micro pile and a steel flower tube concentrically inserted into the micro pile, wherein the micro pile includes an insertion hole section and an expansion hole section which are connected up and down and arranged concentrically, wherein the insertion hole section sequentially penetrates the pavement layer and the water-stable layer, the expansion hole section is arranged on the side of the road base layer facing the water-stable layer, and a contact zone is left between the water-stable layer and the road base layer; The bottom end of the steel flower pipe contacts the inner wall of the bottom end of the expansion section, the top end of the steel flower pipe is flush with the top end of the expansion section, and the top end of the steel flower pipe extends out of the insertion section through the auxiliary pipe; the steel flower pipe is provided with connecting holes at positions corresponding to the bottom end and the top end of the expansion section, and there is a blockage in the connecting holes; Cement is filled in layers inside the steel flower tube at positions corresponding to the communicating holes at the bottom and the communicating holes at the top, and the cement corresponding to the communicating holes at the top is flushed out of the communicating holes and then penetrates into the contact zone; The space between the outside of the steel flower tube and the micro piles is filled by external grouting.

10. The structure of the micro-pile reinforcement method for the shoulder of a highway based on reconstruction and expansion according to claim 9, characterized in that: A plug is clamped in the communicating hole and is made of water glass.

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