Shallow roadbed trenchless structure enhancement design method and construction process

Abstract

The invention discloses a shallow roadbed trenchless structure enhancement design method and a construction process. The method comprises the steps of structure checking calculation and reinforcement scheme design, construction process and process control. The structural checking calculation and reinforcement scheme design comprises the following steps: A1, collecting design parameters; a2, building a pavement structure finite element model consistent with reality; a3, drawing up a structure enhancement scheme, and embedding the pavement structure finite element model; a4, performing non-excavation reinforced structure simulation calculation on the shallow roadbed; a5, recommending a structure enhancement scheme; the construction process comprises the following steps: B1, preparing two down-the-hole drills; b2, a base layer is punched through by a drilling machine; b3, a chambering drilling machine is used for chambering the soil foundation; b4, grouting is conducted on the reamed hole; the process control comprises the following steps: C1, recording the hole depth and the reaming aperture; c2, recording pre-construction data and positions; c3, comparing and analyzing the slurry distribution state; and C4, analyzing deflection and inversely calculating the difference between the modulus of the soil base. According to the process, non-excavation structure enhancement is carried out on the shallow roadbed, and the road repairing and reconstruction cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of road engineering, and particularly relates to a non-excavation structural enhancement design method and construction technology for shallow roadbeds. Background Art

[0002] There is a certain imbalance between the road surface structures of early-built roads and the traffic loads of upgraded roads.

[0003] During the large-scale development of infrastructure in China, the soil foundation grouting technology and soft soil replacement enhancement have been very mature. Grouting reinforcement processes such as steel flower pipes and sleeve valves have been developed. And soil replacement processes such as jet grouting piles and dry jet mixing piles. Materials such as cement (including slightly expanded), fly ash-cement, and geopolymers have also been formed, which have solved the bearing capacity problems of the foundations of structures such as bridges and houses, but are not suitable for treating shallow soil layers.

[0004] In addition, the grouting reinforcement technology is also commonly used for repairing damaged road surface structures. When dealing with cracked bases and base bottom voids, materials such as cement slurry are injected under pressure to re-consolidate the fragmented base and fill the voids between the soil foundation and the base formed by the subsidence of the soil foundation under long-term traffic action, effectively restoring the bearing capacity of the road surface, but it cannot further enhance the bearing capacity of the road surface structure.

[0005] Due to reconstruction, expansion, or traffic planning adjustment, some roads that originally did not bear traffic volume or had only a small traffic volume need to increase traffic volume after transformation. The technical difficulties are specifically as follows:

[0006] 1. Under the action of light traffic, the road surface structure of the original road has no diseases, the base is intact, and there are few voids. The main goal of road surface reinforcement should be to improve the bearing capacity of the roadbed (soil base), and the traditional grouting repair mechanism for damaged road surface structures is not applicable.

[0007] 2. The soil body of the roadbed (soil base) is fully compacted, has high strength, is located at a high level, and has a thin overlying layer, so it is not suitable for high-pressure compaction grouting or soil replacement and solidification processes. Because the overlying structure is thin, processes such as dry jet mixing rotation and grouting extrusion cannot be implemented.

[0008] 3. The way of road damage is the fatigue fracture of the base, which is closely related to the bearing capacity of the shallow roadbed (soil base). In addition, there is no pile cap or capping beam to disperse and transfer the load, so the enhancement of deep soil is of little significance. The traditional soil foundation enhancement measures for structures are difficult to take effect.

[0009] On the other hand, the pavement structure design software adopted in the linear pavement design code is based on the elastic layered semi-infinite body design theory and can only analyze pavement structures that are completely homogeneous in the horizontal dimension. However, the widening and upgrading of the old road structure has the characteristic of asymmetry. The general structure design software cannot analyze the mechanical state of variable structure thickness and variable structure material types, nor can it analyze the influence of the grouting body distribution on key design parameters. There is a lack of theoretical calculation tools for trenchless reinforcement.

[0010] The grouting project is a concealed project, and process control is particularly crucial. Quite a number of grouting projects fail due to the lack of effective process control measures. At the same time, due to the adoption of new construction techniques and theoretical analysis models, the process control indicators and measures should also be matched with the techniques and design parameters. Summary of the Invention

[0011] In view of the deficiencies in the prior art, the present invention provides a trenchless structure enhancement design method and construction technique for shallow roadbeds. This technique can perform trenchless reinforcement on shallow roadbeds, improve construction efficiency, and reduce construction costs.

[0012] A trenchless structure enhancement design method and construction technique for shallow roadbeds, including structural checking and reinforcement plan design, construction technique, and process control;

[0013] The structural checking and reinforcement plan design includes the following steps:

[0014] A1. Collect design parameters, obtain the distribution law of wheel traces in the lane, determine the lane position where the wheel trace belt is located, count the traffic load of each lane, and determine the positions that may need to be enhanced due to structural weakness;

[0015] A2. Build a finite element model of the pavement structure layer consistent with the actual pavement, and check whether the structural life under the existing structure thickness and structural parameters meets the requirements of traffic load;

[0016] A3. For the lane positions that cannot meet the traffic load requirements, conduct trenchless enhancement design of the shallow roadbed;

[0017] A4. Draw up several structural enhancement plans;

[0018] A5. Embed the enhancement model designed by the proposed structural enhancement plan into the finite element model of the existing structure, and check whether the structural life can meet the requirements of the actual traffic load. If not, replace the structural enhancement plan. If it meets the requirements, the structural enhancement plan passes the structural check;

[0019] The construction technique includes the following steps:

[0020] B1. According to the design plan, measure and mark the positions of all injection holes on-site;

[0021] B2. Prepare two down-the-hole drills, and install a structural perforating bit and a subgrade reaming bit respectively. Install multiple reaming claws at the head of the subgrade reaming bit;

[0022] B3. Use the down-the-hole drill installed with the structural perforating bit to drill holes in the weak structure, and drive the holes into the filled soil subgrade;

[0023] B4. Use the down-the-hole drill installed with the subgrade reaming bit to ream the holes in the filled soil subgrade;

[0024] B5. Use grouting equipment to grout the reamed holes. For perfusion grouting, it is necessary to ensure that the slurry fills the holes and the reamed holes densely. For split grouting, it is necessary to achieve that the slurry actively diffuses outward to fill the voids and loose parts;

[0025] Specifically, there are two hole layout and grouting methods.

[0026] (1) Reaming direct split grouting method:

[0027] A number of drill holes are divided into multiple rows, and each row of drill holes corresponds one by one. A number of drill holes form multiple columns.

[0028] (1) Insert a perforated steel pipe (Ф65 - 85mm) into the reamed hole. The bottom of the perforated steel pipe is closed, and the top of the perforated steel pipe is connected to an auxiliary connecting pipe. The auxiliary connecting pipe is located inside the drill hole. The side wall and the bottom wall of the perforated steel pipe are provided with grouting small holes (Ф6 - 8mm). The grouting small holes are sealed with tape or gel. The perforated steel pipe is positioned in the center of the reamed hole by a bracket;

[0029] (2) For the first grouting, the first grouting is external grouting of the pipe. Insert a Φ22mm PVC pipe into the reamed hole and inject cement slurry (water-cement ratio 60 - 100%), until the cement slurry fills all the spaces outside the perforated steel pipe. Wait for 6 - 10 hours and observe after the initial setting of the injected cement is completed;

[0030] (3) Insert a small-diameter grouting pipe (Ф60 - 70mm) into the perforated steel pipe, and lock the pipe under pressure. Start the second split grouting (water-cement ratio 40 - 60%). The second split grouting is grouting inside the perforated steel pipe. The second grouting is carried out in three sections. The first section is grouting at 20cm above the bottom of the reamed hole, the second section is grouting at 40cm above the bottom of the reamed hole, and the third section is grouting at 60cm above the bottom of the reamed hole. Continuously increase the pressure until the cement slurry breaks through the grouting small holes 3 and splits out (the split pressure is generally 4 - 6MPa). After splitting, maintain the pressure of 1 - 2MPa and grout for 2 - 4 minutes.

[0031] The interval time between the first grouting and the second split grouting should be 8 - 10 hours.

[0032] (2) Reaming non-pressure or low-pressure perfusion plus small-diameter grouting hole split grouting method:

[0033] A number of drill holes are divided into multiple rows, and the drill holes are arranged in a plum blossom shape.

[0034] (1) At the middle position between adjacent reaming holes, drill small-diameter grouting holes (Ф60 - 80mm). The depth of the grouting holes is slightly deeper than the reaming depth. Use a drill bit of the corresponding size to drill to the designed depth at one time.

[0035] (2) Insert a large-diameter grouting pipe into the reaming hole, and inject cement slurry (water-cement ratio 40 - 60%) into the reaming hole until it is full.

[0036] (3) After the cement slurry poured into the reaming hole has completed initial setting, conduct pressure grouting on the grouting holes. Insert a small-diameter grouting pipe (Ф60 - 70mm) and apply pressure to lock the pipe. Start grouting (water-cement ratio 40 - 60%), maintain the pressure at 0.6 - 1.2MPa, and grout for 2 - 4 minutes. If the pressure continuously exceeds 1MPa, terminate the pressure grouting.

[0037] The process control includes the following steps:

[0038] C1. After the hole marking is completed, use FWD and 3D ground penetrating radar for structural strength testing and structural scanning, and record the pre-construction data and the testing positions.

[0039] C2. During the reaming process, record the hole depth and reaming hole diameter hole by hole before grouting. During the grouting process, randomly extract the slurry according to the workload, form test specimens, conduct strength testing, and record the grouting quantity and grouting pressure of each hole at the same time.

[0040] C3. 1 - 2 days after the grouting operation is completed, conduct 3D radar structural scanning, compare and analyze the slurry distribution state, judge the post-construction slurry filling state, and conduct small-hole slurry replenishment if the filling is insufficient.

[0041] C4. 7 - 28 days after the grouting operation is completed, conduct FWD strength testing, compare and analyze the differences in deflection and back-calculated subgrade modulus before and after, and if the design requirements are not met, there is an opportunity for small-diameter slurry replenishment once.

[0042] Preferably, the diameter of the drill hole is 110 - 200mm, and the reaming hole diameter is 250 - 500mm.

[0043] Preferably, a number of drill holes are divided into multiple rows, and the distance between the centers of adjacent drill holes in one row is 100 - 150cm.

[0044] Preferably, the distance between the centers of adjacent rows of drill holes is 35 - 130cm.

[0045] The effects of the present invention are reflected in that: in this technical solution, by constructing a simulation structure and a finite element design model for trenchless reinforced structures, a theoretical checking tool for shallow structure reinforcement is provided to design and check the shallow trenchless reinforcement plan. Through the construction technology of shallow soil base reaming, a rigid large column support for the soil base is formed, and by adopting a multiple grouting technology, full combination and compaction of the rigid column and the soil body are realized. By using a controllable and verifiable process control method, the effective implementation of shallow roadbed trenchless reinforcement is ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally denoted by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0047] Figure 1 Schematic diagram of the borehole distribution of the splitting grouting method in the present invention;

[0048] Figure 2 Side sectional view of the borehole and reaming of the splitting grouting method in the present invention;

[0049] Figure 3 Schematic diagram of the borehole and grouting hole distribution of the reaming non-pressure or low-pressure perfusion plus small-diameter grouting hole splitting grouting method in the present invention;

[0050] Figure 4 Side sectional view of the borehole and reaming of the reaming non-pressure or low-pressure perfusion plus small-diameter grouting hole splitting grouting method in the present invention.

[0051] Reference numerals: 1 - perforated steel pipe, 2 - auxiliary connecting pipe, 3 - small grouting hole, 4 - grouting hole. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] The following will describe in detail the embodiments of the technical solutions of the present invention in conjunction with the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and thus are only examples and should not be used to limit the protection scope of the present invention.

[0053] It should be noted that unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meanings understood by those skilled in the art to which the present invention belongs.

[0054] Embodiment 1

[0055] In this embodiment, a design method and construction technology for shallow roadbed trenchless structure reinforcement are provided, including structural checking and reinforcement plan design, construction technology and process control;

[0056] The structural check and reinforcement plan design includes the following steps:

[0057] A1. Collect design parameters, obtain the distribution law of wheel paths in the lane, determine the lane position where the wheel path belt is located, count the traffic load of each lane, and determine the positions that may need to be strengthened due to structural weakness;

[0058] In this embodiment, conventional pavement design parameters are collected according to the requirements of the "Code for Design of Highway Asphalt Pavements" (JTG D50), including: traffic volume, load composition, climate, etc.

[0059] The structural and cross-section parameters of the project, including: the structural cross-section of the new and old roads, the structural parameters of the old road, the structural parameters of the new road, the lane distribution of the new and old roads, etc.

[0060] According to the investigation and research results, obtain the distribution law of wheel paths in the lane, and determine the lane position where the wheel path belt is located according to the peak value of the lateral distribution probability of the traffic load in the wheel path belt.

[0061] A2. Build a finite element model of the pavement structure layer consistent with the actual pavement, and check whether the structural life under the existing structural thickness and structural parameters meets the requirements of the traffic load;

[0062] Here, the structural life includes the flexural fatigue life at the bottom of the base layer, which is calculated according to the calculation method of JTG D50 and the equivalent cumulative number of action axle loads of the traffic load during the design period to calculate the flexural fatigue life at the bottom of the base layer.

[0063] A3. For the lane positions that cannot meet the requirements of the traffic load, carry out trenchless reinforcement design for the shallow roadbed;

[0064] A4. Draw up several structural reinforcement plans;

[0065] A5. Embed the reinforcement model designed by the proposed structural reinforcement plan into the finite element model of the existing structure, and check whether the structural life can meet the requirements of the actual traffic load. If not, replace the structural reinforcement plan. If it meets the requirements, the structural reinforcement plan passes the structural check;

[0066] The construction process includes the following steps:

[0067] B1. According to the design plan, measure and mark the positions of all injection holes on site;

[0068] B2. Prepare two down-the-hole drills, and install a structural perforation bit and a subgrade reaming bit respectively. Multiple reaming claws are installed at the head of the subgrade reaming bit;

[0069] B3. Use the down-the-hole drill installed with the structural perforation bit to drill holes in the weak structure, and the drilled holes penetrate into the filled soil subgrade layer;

[0070] Since the object of hole expansion is the compacted roadbed (earth-filled road base course), the soil contains more crushed stones. The hole-expanding claws and their main rod connectors should be made of high-strength steel, and the anti-torsion and wear-resistant indicators should be met. When the hole-expanding claws are retracted, the diameter is Фmin, and when fully opened, the diameter is Фmax. The design of the soil base hole-expanding drill bit should consider minimizing damage to the road surface structure, and a structural mode with Фmax:Фmin not less than 2 should be adopted. Фmax is generally 200 - 400 mm.

[0071] B4. Use a down-the-hole drill equipped with a soil base hole-expanding drill bit to expand the drilled hole in the earth-filled road base course;

[0072] B5. Use a grouting device to grout the expanded hole. For perfusion grouting, ensure that the grout fills the drilled hole and the expanded hole densely. For split grouting, ensure that the grout actively diffuses outward to fill the voids and loose parts;

[0073] The process control includes the following steps:

[0074] C1. After the hole marking is completed, use FWD and 3D ground-penetrating radar for structural strength testing and structural scanning, and record the pre-construction data and the testing positions;

[0075] C2. During the hole-expanding process, record the hole depth and the expanded hole diameter hole by hole before grouting. During the grouting process, randomly extract the grout according to the workload, form test specimens, conduct strength testing, and record the grouting quantity and grouting pressure of each hole at the same time;

[0076] C3. 1 - 2 days after the grouting operation is completed, conduct 3D radar structural scanning, compare and analyze the slurry distribution state, judge the post-construction slurry filling state, and conduct small-hole supplementary grouting if the filling is insufficient;

[0077] C4. 7 - 28 days after the grouting operation is completed, conduct FWD strength testing, compare and analyze the differences in deflection and back-calculated subgrade modulus before and after, and if the design requirements are not met, there is one opportunity for small-hole diameter supplementary grouting.

[0078] Embodiment 2

[0079] This embodiment is further described based on Embodiment 1, where

[0080] The grouting equipment is as follows:

[0081] (1) Sensors for grouting pressure and grouting quantity are equipped at the grouting outlet position, and the control cabinet is equipped with a display screen, an automatic recorder, and a function of connecting to the cloud;

[0082] (2) A split-type slurry-making and grouting equipment, with intermittent stirring (water volume control) in the upper layer and continuous grouting in the lower layer under the stirring state;

[0083] (3) The grouting head is equipped with an airbag-type automatic hole-locking device, which can achieve sealing at a pressure above 1.2 MPa. With the extension rod, layered grouting can be realized.

[0084] There are two specific hole layout and grouting methods.

[0085] Such as Figure 1 - Figure 2 shown, the direct splitting grouting method for hole enlargement:

[0086] A number of drill holes are divided into multiple rows, and each drill hole in each row corresponds one by one. A number of drill holes form multiple columns.

[0087] (1) Insert the perforated steel pipe 1 (Ф65 - 85mm) into the enlarged hole. The bottom of the perforated steel pipe 1 is sealed. The top of the perforated steel pipe 1 is connected to the auxiliary connecting pipe 2. The auxiliary connecting pipe 2 is located inside the drill hole. The side wall and bottom wall of the perforated steel pipe 1 are provided with grouting small holes 3 (Ф6 - 8mm). The grouting small holes 3 are sealed with tape or gel. The perforated steel pipe 1 is positioned in the center of the enlarged hole by a bracket;

[0088] (2) First grouting, the first grouting is external grouting of the pipe. Insert a Φ22mm PVC pipe into the enlarged hole and inject cement slurry (water-cement ratio 60 - 100%) until the entire space outside the perforated steel pipe is filled with cement slurry. Wait for 6 - 10 hours and observe after the initial setting of the injected cement is completed;

[0089] (3) Insert a small-diameter grouting pipe (Ф60 - 70mm) into the perforated steel pipe, and lock the pipe under pressure. Start the secondary splitting grouting (water-cement ratio 40 - 60%). The secondary splitting grouting is internal grouting of the perforated steel pipe. The secondary grouting is carried out in three sections. The first section is grouting at 20 cm above the bottom of the enlarged hole, the second section is grouting at 40 cm above the bottom of the enlarged hole, and the third section is grouting at 60 cm above the bottom of the enlarged hole. Continuously increase the pressure until the cement slurry breaks through the grouting small holes and splits out (the splitting pressure is generally 4 - 6 MPa). After splitting, maintain the pressure at 1 - 2 MPa for grouting for 2 - 4 minutes.

[0090] The interval time between the first grouting and the secondary splitting grouting should be 8 - 10 hours.

[0091] Such as Figure 3 - Figure 4 shown, the hole enlargement non-pressure or low-pressure perfusion plus small-diameter grouting hole splitting grouting method:

[0092] A number of drill holes are divided into multiple rows, and a number of drill holes are arranged in a plum blossom shape.

[0093] (1) At the middle position between adjacent enlarged holes, drill small-diameter grouting holes 4 (Ф60 - 80mm). The depth of the grouting holes 4 is slightly deeper than the depth of the enlarged holes. Use a drill bit of the corresponding size to drill to the designed depth at one time;

[0094] (2) Insert a large-diameter grouting pipe into the enlarged hole and inject cement slurry (water-cement ratio 40 - 60%) until it is full;

[0095] (3) After the cement slurry poured in the reaming has initially set, pressure grouting is carried out on the grouting hole 4. Insert a small-diameter grouting pipe (Ф60 - 70mm) and lock the pipe under pressure. Start grouting (water-cement ratio 40 - 60%), maintain the pressure at 0.6 - 1.2 MPa, and grout for 2 - 4 minutes. If the pressure continuously exceeds 1 MPa, terminate the pressure grouting.

[0096] Final grouting standard:

[0097] a) The grouting pressure exceeds 1.2 MPa;

[0098] b) The grouting pressure cannot reach the designed pressure range. After 1.5 minutes of continuous grouting, stop grouting. After a period of time, supplementary grouting may be required;

[0099] c) In case of slurry leakage and serious slurry running, stop grouting;

[0100] d) When the grouting pressure reaches the designed pressure and the single-hole grouting flow rate is less than 1 L / min, the pressure should be stabilized for 10 minutes. If the pressure does not drop or the drop does not exceed 10%, stop grouting;

[0101] e) When the pavement lifting amount exceeds 10 mm or micro-cracks appear, stop grouting.

[0102] Example 3

[0103] This example is further described based on Example 1. As Figure 1 - Figure 2 shown, in this example, the diameter of the drilled hole is 110 - 200 mm, and the reaming diameter is 250 - 500 mm. In this example, the diameter of the drilled hole is 170 mm, and the reaming diameter is 300 mm.

[0104] In this example, several drilled holes are divided into multiple rows, and the distance between the centers of adjacent drilled holes in one row is 100 - 150 cm.

[0105] In this example, the distance between the centers of adjacent rows of drilled holes is 35 - 130 cm.

[0106] By setting the distance between the drilled holes, the diameter of the drilled holes, and the diameter of the reaming in this example, the flexural fatigue life of the base layer can be significantly improved, meeting the requirements of the flexural fatigue life, while meeting the construction requirements of the construction space and reducing the construction cost.

[0107] The specific design standard principle is as follows:

[0108] 1. Flexural fatigue life calculated by traffic volume

[0109] 1.1 Pavement overlay on old roads

[0110] This project is located in Guangdong Province and belongs to an expressway. The starting mileage is K3534+000, and the ending mileage is K3594+896. The designed service life is 15.0 years. According to the traffic volume OD survey and analysis, the traffic volume of large buses and trucks in the cross-section is 4,224 vehicles per day (calculated with 30% of small trucks with 2 axles and 6 wheels), the annual growth rate of traffic volume is 2.8%, the direction coefficient is taken as 55.0%, and the lane coefficient is taken as 78.0%. Based on the traffic historical data, it is determined that this designed highway belongs to TTC Class 4, and the vehicle type distribution coefficients are shown in Table 1.1-1.

[0111] Table 1.1-1 Vehicle Type Distribution Coefficients

[0112] Vehicle type Category 2 Category 3 Category 4 Category 5 Category 6 Category 7 Category 8 Category 9 Category 10 Category 11 Vehicle type distribution coefficient (%) 28.9 43.9 5.5 0.0 9.4 2.0 4.6 3.4 2.3 0.1

[0113] According to the investigation and analysis of the full-load situation of vehicles on adjacent roads in the road network and historical data, the ratios of unloaded to fully-loaded vehicles for various vehicle types are obtained, as shown in Table 1.1-2.

[0114] Table 1.1-2 Proportions of Unloaded Vehicles and Fully-loaded Vehicles (%)

[0115] Vehicle type Category 2 Category 3 Category 4 Category 5 Category 6 Category 7 Category 8 Category 9 Category 10 Category 11 Proportion of under - loaded vehicles (%) 85.0 90.0 65.0 75.0 55.0 70.0 45.0 60.0 55.0 65.0 Proportion of fully - loaded vehicles (%) 15.0 10.0 35.0 24.0 45.0 30.0 55.0 40.0 45.0 35.0

[0116] The corresponding design indicators for this designed road surface are the permanent deformation of the asphalt mixture layer and the fatigue cracking of the inorganic binder layer. The equivalent design axle load conversion coefficients for unloaded and fully-loaded vehicles of each vehicle type under different design indicators are obtained, as shown in Table 1.1-3.

[0117] Table 1.1-3 Equivalent Design Axle Load Conversion Coefficients for Unloaded and Fully-loaded Vehicles

[0118]

[0119] According to the formula calculation, the cumulative number of equivalent design axle load applications corresponding to the permanent deformation of the asphalt mixture layer is 19,702,681, and the cumulative number of equivalent design axle load applications corresponding to the fatigue cracking of the inorganic binder layer is 1,366,239,791. The cumulative traffic volume of large buses and trucks in the design lane within the designed service life of this highway is 12,122,825, and the traffic grade belongs to heavy traffic.

[0120] 1.2 Widening and Newly-built Road Surface

[0121] Highway Grade: Expressway

[0122] Target Reliability Index: 1.65

[0123] Annual Average Daily Two-way Traffic Volume of Large Buses and Trucks in the Initial Year (vehicles / day): 6467

[0124] Designed Service Life of Road Surface (years): 15

[0125] Period (years) from opening to traffic to the first rut repair: 8

[0126] Annual average growth rate of traffic volume: 2.82%

[0127] Direction coefficient: 0.55

[0128] Lane coefficient: 0.8

[0129] Proportion of integral trucks: 68%

[0130] Proportion of semi-trailer trucks: 22%

[0131] Annual average daily traffic volume (vehicles / day) of large buses and trucks on the designed lane in the initial year: 2845

[0132] Cumulative traffic volume of large buses and trucks on the designed lane within the design service life (vehicles): 1.906074E+07, and the pavement design traffic load level is extremely heavy traffic load level.

[0133] When checking the fatigue cracking of the asphalt mixture layer, the cumulative number of equivalent design axle load applications on the designed lane within the design service life is 4.370466E+07.

[0134] When checking the fatigue cracking of the inorganic binder stabilized layer, the cumulative number of equivalent design axle load applications on the designed lane within the design service life is 3.27842E+09.

[0135] When checking the permanent deformation of the asphalt mixture layer, the cumulative number of equivalent design axle load applications on the designed lane during the period from opening to traffic to the first rut repair is 2.103807E+07.

[0136] When checking the vertical compressive strain at the subgrade top surface, the cumulative number of equivalent design axle load applications on the designed lane within the design service life is 7.680584E+07.

[0137] 2. Flexural fatigue life of various structures and grouting methods

[0138] Table 2.1 shows the case of the flexural tensile stress at the bottom of the inorganic binder layer calculated when the shoulder is reserved at 1.25 m and 1.75 m and the load is applied on the wheel path of the third lane. Since the reserved shoulder position is far from the wheel path, when the shoulder is reserved at 1.25 m, the flexural tensile stress at the bottom of the inorganic binder layer is even significantly lower than that at the bottom of the inorganic binder layer of the new road under the right wheel, and the flexural tensile life of the bottom layer reserved at 1.75 m is equivalent to the flexural tensile life under the left wheel of the old road.

[0139] Table 2.1 Fatigue cracking check of the inorganic binder layer loaded on the wheel path of the third lane

[0140]

[0141] To study the influence of various grouting schemes on the pavement life, the most unfavorable loading method of loading in the middle of the reserved 1.25 m old road shoulder (such loading does not exist when actually reserving 1.25 m) was adopted, and the fatigue cracking life of the inorganic binder layer under different reinforcement schemes was compared. The calculation results are shown in Table 2.2. As shown in the table, the scheme with a 300 mm hole expansion and a row spacing of 40 cm recorded the minimum bottom flexural tensile stress of the base layer and the maximum flexural tensile fatigue life. After the spacing was adjusted to 80 cm, the flexural tensile fatigue life decreased significantly.

[0142] Table 2.2 Calculation results of the fatigue cracking life of the inorganic binder layer

[0143]

[0144] To further compare the influence of the grouting scheme on the bottom flexural tensile stress of the road shoulder base layer at the most unfavorable position under the actual loading state, the case of retaining 225 cm of the road shoulder, arranging four rows of holes, with a spacing of 40 cm for the right three rows and a spacing of 65 cm for the leftmost row was calculated. The calculation situation is as follows in the table. It can be seen from the table that the effect of hole expansion is more obvious than that of reducing the spacing for reinforcement.

[0145] At the 2.25 m lapping position, it is exactly under the double wheels of the third lane wheel path. If not reinforced, the bottom flexural tensile stress is very large, and the flexural tensile life is less than half of the design life. Among all the reinforcement schemes, the 300 mm hole expansion has the greatest effect on reducing the flexural tensile stress. Although its spacing is much larger than other schemes, it is still the scheme that can reach the design life requirement for displacement. The small-spacing reinforcement scheme with a 70 mm small hole diameter has little influence on the flexural tensile stress, and the flexural tensile life is only 2 / 3 of the design life. For the scheme with a 200 mm hole expansion, although the spacing is smaller than the 300 mm hole expansion scheme, the flexural tensile life is still less than that of the 300 mm expansion scheme, but it is significantly larger than the 70 mm hole diameter scheme.

[0146] Bottom tensile stress of the 2.25 m inorganic binder layer

[0147]

[0148] During the actual engineering implementation process, considering eliminating the edge weakness of the base layer, a scheme of retaining 200 cm was adopted for lapping. According to the previous calculation results and the results of the test road in Huizhou West Service Area, considering the comprehensive cost, according to Figure 1 the hole arrangement method, the hole arrangement calculation was carried out for the 300 mm hole expansion scheme. As the FWD back-calculation result shows, the subgrade modulus increases by 100 - 200% after grouting. Therefore, three subgrade moduli of 60 MPa, 120 MPa, and 180 MPa were set for calculation.

[0149] As shown in the following table, the unstrengthened road surface cannot meet the requirements of the design flexural tensile life of the subbase bottom. All three 300mm schemes can meet the requirements of the design flexural tensile life. When the subgrade modulus increases, the flexural tensile life increases by 12 - 25%. The grouting reinforcement scheme shown in the figure is recommended.

[0150] Retain the bottom tensile stress of the inorganic binder layer loaded on the wheel path of the third lane with a width of 2m

[0151]

[0152] 3. Scheme design

[0153] (1) From the perspective of the retained width, a width of 1.25m is far from the wheel path of the third lane, and the flexural tensile stress is very small, and the life exceeds the level of the new road. The edge of the 1.75m width is close to the wheel path, and the flexural tensile stress increases significantly. The flexural tensile stress is close to that of the new road, but the life is reduced, approaching the level of the full-structure old road.

[0154] (2) The edge of the 2.25m width is directly below the wheel path, and the flexural tensile stress increases significantly. The life has a large gap from that of the new and old roads. If no measures are taken, it does not meet the requirements of the flexural tensile fatigue life. In comparison, the reduction of the flexural tensile stress of the 300mm grouting with hole expansion is the most obvious, followed by the 200mm hole expansion scheme. The flexural tensile stress of the 70mm non-hole expansion scheme is very close to that without grouting. The 200mm and 70mm hole expansion schemes cannot reach the design fatigue flexural tensile life, and the 70mm gap is far.

[0155] (3) The bottom consolidation body is relatively important, affecting the life by about 20 - 30%. It is necessary to grout in layers at the bottom and use relatively high-pressure grouting.

[0156] (4) When 2.0m is retained, the flexural tensile stress is significantly affected by the change of the subgrade modulus. If the subgrade modulus increases by 1 - 2 times as the result of FWD back calculation, the life increases by 12 - 25%. <>

[0157] Suggestions:

[0158] (1) Retaining a 1.25m earthen shoulder is very safe, and it is only necessary to simply grout to seal the interface.

[0159] (2) The wider the retention, the closer it is to the wheel path of the third lane, and the greater the impact on the life of the subbase.

[0160] (3) When the width reserved is more than 2 meters, without reinforcement treatment, the flexural-tensile life of the base course cannot meet the requirements. When using small-diameter dense piles with a diameter of about 70 mm, the improvement of the flexural-tensile life of the base course is limited and still cannot meet the needs of the flexural-tensile life of the base course. When taking 170-mm drilling, expanding the hole to 300 mm, arranging the holes in three rows, with the row spacing (the distance between the centers of adjacent drilled holes in the same row) being 40 - 50 cm and the longitudinal spacing (the distance between the centers of adjacent drilled holes in the same row) being 1.1 meters, the flexural-tensile life of the base course is significantly improved and can meet the needs of the flexural-tensile life.

[0161] (4) Limited by cost and construction space, it is difficult to implement denser 300-mm hole expansion. It is more difficult to further improve the life of the shoulder base course.

[0162] 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 foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention.

Claims

1. A non-excavation structural enhancement design method and construction technology for shallow roadbeds, characterized in that: It includes structural checking and reinforcement plan design, construction technology and process control; The structural checking and reinforcement plan design includes the following steps: A1. Collect design parameters, obtain the distribution law of wheel paths in the lane, determine the lane position where the wheel path belt is located, count the traffic load of each lane, and determine the positions that may need to be strengthened due to structural weakness; A2. Build a finite element model of the pavement structure layer consistent with the actual pavement, and check whether the structural life under the existing structural thickness and structural parameters meets the requirements of traffic load; A3. For the lane positions that cannot meet the requirements of traffic load, carry out trenchless strengthening design of the shallow roadbed; A4. Draw up several structural strengthening plans; A5. Embed the strengthening model designed by the proposed structural strengthening plan into the finite element model of the existing structure, and check whether the structural life can meet the requirements of the actual traffic load. If the requirements are not met, replace the structural strengthening plan. If the requirements are met, the structural strengthening plan passes the structural check; The construction technology includes the following steps: B1. According to the design plan, measure and mark the positions of all injection holes on site; B2. Prepare two down-the-hole drills, and install a structural perforating bit and a subgrade reaming bit respectively. A plurality of reaming claws are installed at the head of the subgrade reaming bit; B3. Use the down-the-hole drill installed with the structural perforating bit to drill holes in the weak structure, and drive the holes into the fill subgrade layer; B4. Use the down-the-hole drill installed with the subgrade reaming bit to ream the holes in the fill subgrade layer; B5. Use grouting equipment to grout the reamed holes. During the perfusion grouting, it is necessary to ensure that the slurry fills the drilled holes and the reamed holes densely. During the fracturing grouting, the slurry should actively spread outwards to fill the voids and loose parts; The process control includes the following steps: C1. After the injection hole marking is completed, use FWD and 3D ground penetrating radar to conduct structural strength testing and structural scanning, and record the pre-construction data and testing positions; C2. During the reaming process, record the hole depth and reaming hole diameter for each hole one by one before grouting. During the grouting process, randomly extract slurry according to the workload, form specimens, conduct strength testing, and record the grouting quantity and grouting pressure of each hole at the same time; C3. 1-2 days after the grouting operation is completed, conduct 3D radar structural scanning, compare and analyze the slurry distribution state, judge the post-construction slurry filling state, and conduct small-hole supplementary grouting if the filling is insufficient; C4. 7-28 days after the grouting operation is completed, conduct FWD strength testing, compare and analyze the differences in deflection and back-calculated subgrade modulus before and after, and if the design requirements are not met, there is one opportunity for small-hole diameter supplementary grouting.

2. The enhanced design method and construction technology for a shallow roadbed trenchless structure according to claim 1, characterized in that, The diameter of the drilled hole is 110-200 mm, and the reaming hole diameter is 250-500 mm.

3. A design method and construction technology for enhancing the trenchless structure of a shallow roadbed according to claim 1, characterized in that A number of drilled holes are divided into multiple rows, and the distance between the centers of adjacent drilled holes in one row is 100-150 cm.

4. The enhanced design method and construction technology for a shallow roadbed trenchless structure according to claim 1, characterized in that, The distance between the centers of adjacent rows of drilled holes is 35-130 cm.

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