Rigidity progressive pile-soil composite foundation structure for widening roadbed and construction method

Abstract

The invention discloses a rigidity progressive pile-soil composite foundation structure for widening a roadbed and a construction method, the rigidity progressive pile-soil composite foundation structure comprises a stepped slope, a rigidity progressive member, a pile foundation assembly and a new roadbed filling layer, the stepped slope is arranged at the upper part of one side, close to a new roadbed base layer, of an original roadbed; the rigidity progressive component is arranged on the stepped slope surface; the pile foundation assembly comprises a plurality of evenly-buried pile bodies buried in a new road foundation base layer. The densities of the plurality of pile bodies are sequentially reduced from the original roadbed to the new roadbed base course; and the new roadbed filling layer is arranged above the pile foundation assembly and is in contact connection with the rigidity progressive component. The density of the pile bodies gradually increases from the original roadbed to the new roadbed base layer, so that the strength of the pile bodies is sequentially reduced, meanwhile, the rigidity gradual transition balance between the original roadbed and the new roadbed is realized in cooperation with the rigidity gradual components, and effective rigidity transition between the new roadbed and the old roadbed can be realized, so that the performance of the roadbed is optimized, improved and widened, and the construction period is shortened. And settlement caused by roadbed widening is prevented.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering construction, and in particular to a stiffness progressive pile-soil composite foundation structure for widening a roadbed and a construction method. Background Art

[0002] When reconstructing and expanding roads in coastal soft soil areas, there is often a difference in stiffness between the new and old roadbeds due to differences in materials, structures and stress conditions. However, most of the current traditional construction methods for widening the roadbed do not consider the gradual stiffness of the new and old roadbeds. After construction, due to the large difference in stiffness between the new and old roadbeds, the roadbed is prone to uneven settlement and longitudinal cracks, which in turn affects the flatness of the road surface and seriously threatens the safety and durability of the road. At the same time, the traditional construction method has a long construction period, which is not conducive to the rapid completion of the roadbed widening project and the goal of restoring traffic. Summary of the invention

[0003] In view of the above problems in the prior art, the present invention provides a progressive stiffness pile-soil composite foundation structure for widening a roadbed, which solves the problem of settlement caused by not considering the progressive stiffness of the new and old roadbeds in traditional roadbed widening.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] On the one hand, a stiffness progressive pile-soil composite foundation structure for widening a roadbed is provided, comprising:

[0006] Stepped slope: the stepped slope is set on the upper part of the original roadbed close to the base of the new roadbed;

[0007] A progressive stiffness member, wherein the progressive stiffness member is arranged on a stepped slope;

[0008] The pile foundation assembly includes a plurality of uniformly buried pile bodies buried in the base of the new road base; the density of the plurality of pile bodies decreases from the original road base to the base of the new road base;

[0009] The new roadbed filling layer is arranged above the pile foundation assembly and is in contact with and connected to the progressive stiffness member.

[0010] In the present invention, the density of the pile body gradually increases from the original roadbed to the base of the new roadbed, so that the strength of the pile body gradually decreases. At the same time, the stiffness progressive component is used to make the stiffness progressive transition balance between the original roadbed and the new roadbed, and an effective stiffness transition can be achieved between the new and old roadbeds, thereby optimizing and improving the performance of the widened roadbed and preventing settlement of the widened roadbed.

[0011] Furthermore, the progressive stiffness component includes ecological permeable transverse structures having the same number as the steps of the stepped slope, and adjacent ecological permeable transverse structures are connected by ecological permeable oblique structures;

[0012] In the horizontal structure of ecological permeable, the density of the base layer decreases from the original roadbed to the new roadbed, and permeable gaps are opened;

[0013] The ecological permeable oblique structure has permeable gaps with the density decreasing from high to low.

[0014] Furthermore, a supporting structure obliquely buried in the stepped slope is provided on the ecological permeable oblique structure.

[0015] Furthermore, the pile body comprises a pile tube buried in the base of the new road foundation, a steel cage is placed in the pile tube, and concrete is poured; the pile tops of adjacent pile tubes are connected by a cap.

[0016] Furthermore, the new roadbed filling layer includes a crushed stone cushion layer laid on top of the foundation, a plurality of filling layers are arranged on the crushed stone cushion layer, and geogrids are filled between adjacent filling layers.

[0017] Furthermore, it also includes a monitoring component, which includes a single-point displacement meter pre-buried in the filling layer, an earth pressure box buried in the gravel cushion layer, and a strain gauge arranged on the circumferential direction of the outer surface of the pile tube; the single-point displacement meter, the earth pressure box and the strain gauge are all connected to the host computer signal.

[0018] On the other hand, a construction method of a progressive stiffness pile-soil composite foundation structure for widening a roadbed is proposed, which comprises the following steps:

[0019] Step S1, surveying the original roadbed and the base of the new roadbed to obtain survey data between the original roadbed and the base of the new roadbed;

[0020] Step S2, prefabricating a progressive stiffness component according to the survey data obtained in step S1;

[0021] Step S3, excavating the shoulder of the original roadbed, and performing slope treatment on the shoulder of the original roadbed to form a stepped slope;

[0022] Step S4, determining the length of the pile body according to the survey data obtained in step S1; the arrangement density of the pile body is reduced from the connection point of the original roadbed and the base of the new roadbed to the edge direction, so as to determine the arrangement position and number of the pile body and obtain the arrangement plan of the pile body; the pile body is installed and constructed in sections according to the arrangement plan of the pile body, and when installing and constructing the pile body, the strain gauge is attached to the outer surface of the pile body;

[0023] Step S5, when the strength of the pile body meets the construction of the new roadbed filling layer, a cap is set on the pile top of the pile body, and adjacent pile bodies are connected through the cap to ensure that the load is evenly distributed on each pile body, and then a crushed stone cushion layer is laid on the cap, and an earth pressure box is buried when laying the crushed stone cushion layer;

[0024] Step S6, installing the progressive stiffness components on the stepped slope in layers; when installing a layer of progressive stiffness components, construct a filling layer, and after each filling layer is completed, lay the geogrid; bury the single-point displacement meter when constructing each filling layer;

[0025] Step S7: Monitor and measure during and after construction using single-point displacement meters, earth pressure cells, and strain gauges, record monitoring data, and analyze monitoring results.

[0026] Furthermore, the prefabrication method of the progressive stiffness component of the progressive stiffness type in step S2 is:

[0027] Step S21, material preparation, the main materials are ordinary cement, fine aggregate and coarse aggregate, and the admixture is a foaming agent.

[0028] The additive is a water reducing agent or an air entraining agent;

[0029] Step S22: base concrete ratio, according to the actual stiffness difference between the original roadbed and the new roadbed, determine the base concrete ratio;

[0030] Step S23, preparing a bubble generating agent, wherein the concentration of the bubble generating agent is 0.5%-2%;

[0031] Step S24, mixing base concrete and bubble generating agent;

[0032] In the initial mixing, add 0.5% of the bubble generator to the base concrete and mix well;

[0033] In the mid-term mixing, based on the initial mixing, gradually add a bubble generator with a concentration of 1%, and continue stirring until it is evenly mixed;

[0034] In the final mixing, add a bubble generator with a concentration of 2% based on the mid-term mixing, and finally stir to mix evenly.

[0035] Step S25, pouring in layers, pouring the mixed concrete in step S24 in layers into a mold of a progressive stiffness component, the pore density of each layer is from sparse at the bottom to dense at the top, and the stirring time and vibration intensity of each layer of concrete can be adjusted according to actual conditions to ensure uniform distribution of the bubble generating agent and gradual change of the pore structure;

[0036] Step S26, curing treatment: after the pouring in step S25 is completed, a standard curing treatment is performed to maintain appropriate humidity and temperature to ensure the strength of the concrete and the stability of the pore structure;

[0037] Step S27: After the solidification is completed, a progressive stiffness component is obtained, and then the concrete specimen of the progressive stiffness component is subjected to a porosity test, a strength test, and a uniformity test to ensure that the pore distribution meets the design requirements.

[0038] Furthermore, in step S4, the pile arrangement scheme needs to be evaluated and measured by a load-settlement test, and the load-settlement test evaluation and measurement method is:

[0039] Step S41, determining the evaluation and measurement area;

[0040] Step S42, performing local installation work in the evaluation and measurement area according to the pile installation plan; burying the settlement meter and displacement sensor at the same time during the installation work;

[0041] Step S43, performing a load-settlement test, applying multiple levels of predetermined load increments to the pile body step by step through a static load test device, and recording the settlement data of the pile body under each level of load;

[0042] Step S44, data analysis, plotting the applied load and recorded settlement data into a graph, calculating the initial slope of the load-settlement curve, evaluating the stiffness of the foundation, and analyzing the stiffness change.

[0043] Step S45, evaluating the design effect, comparing the load-settlement curves of different areas, and confirming whether the pile arrangement has achieved the progressive stiffness effect of the original roadbed and the new roadbed.

[0044] The invention discloses a progressive stiffness pile-soil composite foundation structure for widening a roadbed, and its beneficial effects are:

[0045] 1. In the present invention, the density of the pile body gradually increases from the original roadbed to the base of the new roadbed, so that the strength of the pile body decreases gradually. At the same time, the stiffness progressive component is used to make the stiffness progressive transition balance between the original roadbed and the new roadbed, and an effective stiffness transition can be achieved between the new and old roadbeds, thereby optimizing and improving the performance of the widened roadbed and preventing the widened roadbed from causing settlement.

[0046] 2. The progressive stiffness component of the present invention introduces an optimized combination of rigid and flexible elements to effectively improve the bearing capacity of the foundation and even out the stress distribution, which not only enhances the bearing capacity of the roadbed, but also reduces the maintenance requirements in long-term use. In addition, the design fully considers geological conditions and environmental factors to ensure the adaptability and reliability of the structure under complex geological conditions, and ensures the long-term stability and safety of the project.

[0047] 3. The progressive stiffness component of the present invention adopts ecological permeable concrete as a transition layer, which can not only adapt to the hydrological characteristics of coastal soft soil and reduce the impact of moisture on the stability of the roadbed, but also gradually add bubble generators to achieve the distribution of ecological concrete pores from sparse to dense, and then naturally adjust the stiffness by its pore structure, and finally achieve an eco-friendly gradual stiffness transition. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The schematic diagram of the structure of a progressive stiffness pile-soil composite foundation structure for widening a roadbed according to the present invention.

[0049] Figure 2 It is a schematic structural diagram of the progressive stiffness component of the present invention.

[0050] Figure 3 It is a structural schematic diagram of the ecological permeable horizontal structure of the present invention.

[0051] Figure 4 It is a structural schematic diagram of the ecological permeable oblique structure of the present invention.

[0052] Figure 5 It is a structural schematic diagram of the pile body of the present invention.

[0053] Figure 6 It is a structural schematic diagram of the transverse arrangement of the support platform of the present invention.

[0054] Figure 7 It is a structural schematic diagram of the vertical arrangement of the pedestal of the present invention.

[0055] Figure 8 The present invention is a construction flow chart of a progressive stiffness pile-soil composite foundation structure for widening a roadbed.

[0056] Among them, 1. original roadbed; 2. new roadbed base; 3. new roadbed filling layer; 31. crushed stone cushion layer; 32. filling layer; 33. geogrid; 4. stepped slope; 5. progressive stiffness component; 51. ecological permeable lateral structure; 52. ecological permeable oblique structure; 53. permeable gap; 54. supporting structure; 6. pile foundation assembly; 61. pile body; 62. pile tube; 63. steel cage; 64. pedestal; 71. single-point displacement meter; 72. earth pressure box; 73. strain gauge. DETAILED DESCRIPTION

[0057] The specific embodiments of the present invention are described to facilitate those skilled in the art to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0058] Example 1

[0059] refer to Figure 1-Figure 7 , which is a structural schematic diagram of a progressive stiffness pile-soil composite foundation structure for widening a roadbed in this embodiment. Its purpose is to solve the problem that the traditional roadbed widening does not take into account the progressive stiffness of the new and old roadbeds and thus causes settlement. The specific structure in this embodiment will be described in detail below.

[0060] A progressive stiffness pile-soil composite foundation structure for widening a roadbed comprises a stepped slope 4, a progressive stiffness component 5, a pile foundation assembly 6 and a new roadbed filling layer 3.

[0061] Among them, the stepped slope 4 is arranged on the upper part of the original roadbed 1 close to the new roadbed base layer 2; the progressive stiffness component 5 is arranged on the stepped slope 4; the pile foundation assembly 6 includes a plurality of uniformly buried pile bodies 61 buried in the new roadbed base layer 2; the density of the plurality of pile bodies 61 decreases successively from the original roadbed 1 to the new roadbed base layer 2; the new roadbed filling layer 3 is arranged above the pile foundation assembly 6 and is in contact and connected with the progressive stiffness component 5.

[0062] In this embodiment, a plurality of pile bodies 61 are arranged in the base layer 2 of the new road base, and the density of the plurality of pile bodies 61 decreases successively from the original road base 1 to the base layer 2 of the new road base, so that the strength of the pile bodies 61 decreases successively, the stiffness of the new and old road bases is transitioned, the uneven settlement and deformation of the overall structure under load is controlled, and the stability of the road base is significantly improved.

[0063] At the same time, a progressive stiffness component 5 is used to connect the original roadbed 1 and the new roadbed filling layer 3, so that the progressive stiffness transition between the new and old roadbeds is balanced, and an effective stiffness transition can be achieved between the new and old roadbeds, thereby optimizing and improving the performance of the widened roadbed and preventing settlement of the widened roadbed.

[0064] Specifically, the progressive stiffness component 5 includes an ecological permeable transverse structure 51 with the same number of steps as the stepped slope 4, and adjacent ecological permeable transverse structures 51 are connected by an ecological permeable oblique structure 52; wherein, the ecological permeable transverse structure 51 is divided into two parts, namely the first ecological permeable transverse structure and the second ecological permeable transverse structure, and the first ecological permeable transverse structure and the second ecological permeable transverse structure are connected by a mortise and tenon structure, and the first ecological permeable transverse structure is laid on the stepped slope 4, and with the ecological permeable oblique structure 52, it is intended to adjust the stiffness difference between the new and old roadbeds. This section of structural materials is precisely proportioned and processed efficiently to ensure its mechanical properties and durability. At the same time, the ecological permeable oblique structure 52 makes the structure more in line with the actual foundation stress state and improves the overall stability.

[0065] The second ecological permeable transverse structure is laid in the new roadbed filling layer 3 to further gradually adjust the roadbed stiffness. The porosity of the permeable concrete in this section is moderate, ensuring sufficient support and buffering when transitioning to the new roadbed.

[0066] A plurality of permeable gaps 53 are provided on both the ecological permeable transverse structure 51 and the ecological permeable oblique structure 52. The density of the permeable gaps 53 provided on the ecological permeable transverse structure 51 decreases from the original roadbed 1 to the new roadbed base 2.

[0067] The density of the ecological permeable oblique structure 52 decreases from high to low, and the functional effect of the permeable gaps 53 needs to be supplemented. The distribution of the permeable gaps 53 from sparse to dense can naturally adjust the stiffness by its gap structure to achieve the function of gradual transition, and also has a significant positive effect on water circulation, ecological environment and structural sustainability. Specifically, the efficacy of the permeable gaps can be detailed from the following aspects:

[0068] 1. Naturally adjust the stiffness

[0069] The distribution of permeable voids can be changed from sparse to dense, and the stiffness can be naturally adjusted through the change of its void structure. This gradual transition of stiffness distribution helps to adapt to different external forces, reduce local stress concentration, and avoid excessive fatigue or damage of the material. At the same time, the gradual transition of stiffness contributes to the stability and durability of the overall structure, reduces the formation of cracks, and thus increases the service life of the material.

[0070] 2. Water penetration and drainage regulation

[0071] The design of permeable gaps allows natural water such as rainwater to effectively penetrate into the ground or the lower layer of the structure, reducing surface runoff, reducing the burden on the drainage system, and preventing water accumulation on the road surface. At the same time, through the permeable gaps, water can gradually penetrate into the soil, which is conducive to the replenishment of groundwater, improves soil moisture conditions, helps regulate local water circulation, and improves the quality of the ecological environment.

[0072] 3. Eco-friendly stiffness transition

[0073] The gradual transition of the stiffness design of the permeable gap not only meets the engineering requirements, but also plays a positive role in the ecological environment. The structure with gradual transition of stiffness allows plant roots to penetrate and grow better, providing a foundation suitable for plant growth. The permeable gap can also provide a habitat for microorganisms, insects, etc., which helps to maintain and promote biodiversity in the soil and improve the health of the ecosystem.

[0074] 4. Structural buffer and seismic performance

[0075] The gradual transition design of the permeable voids can also provide a certain buffer function, especially when subjected to impact or vibration. The internal void structure of the permeable material can absorb and disperse stress, making the structure more flexible when responding to earthquakes or other sudden forces, reducing the risk of damage to the surface structure.

[0076] The ecological permeable oblique structure 52 is provided with a supporting structure 54 which is obliquely buried in the stepped slope 4. The supporting structure 54 provides additional vertical supporting force for the ecological permeable oblique structure 52 to form a continuous and stable supporting system. The connection method thereof can be a plug-in connection in which a card block is inserted into a card slot, or a threaded connection can be achieved by passing a fixing bolt through the threaded hole on the ecological permeable transverse structure 51 and the ecological permeable oblique structure 52, or a threaded connection can be achieved by passing a fixing bolt through the threaded hole on the ecological permeable oblique structure 52 and the supporting structure 54.

[0077] Specifically, the pile body 61 includes a pile tube 62 buried in the base layer 2 of the new road foundation, a steel cage 63 is placed in the pile tube 62, and concrete is poured; by placing a steel cage 63 in each pile tube 62, the bearing capacity of the pile body 61 is increased, and the pile tops of adjacent pile tubes 62 are connected by a pedestal 64, which is a reinforced concrete structure, to ensure that the load is evenly distributed on each pile body 61.

[0078] Optionally, the cap 64 may be arranged horizontally to connect the pile barrels 62 in the horizontal direction, or the cap 64 may be arranged vertically to connect the pile barrels 62 in the vertical direction.

[0079] Specifically, the new roadbed filling layer 3 includes a crushed stone cushion layer 31 laid on the top of the cap 64, and multiple filling layers 32 are arranged on the crushed stone cushion layer 31. Geogrids 33 are filled between adjacent filling layers 32. The crushed stone cushion layer 31 usually has a thickness of 30-50 cm. The crushed stone cushion layer 31 can improve the drainage performance of the base and increase the bearing capacity of the foundation. Optionally, the crushed stone cushion layer 31 can be wrapped with geotextile to form a pillow cushion layer, which can better diffuse the stress of the upper roadbed fill.

[0080] After each layer of filling layer 32 is filled, it is compacted using compaction equipment to ensure the density and stability of the filling material. The geogrid 33 is made of high-strength, corrosion-resistant geogrid material to enhance the rigidity and stability of the filling layer 32. After each layer of filling layer 32 is completed, the geogrid 33 is laid to ensure that the geogrid 33 is flat and wrinkle-free. The coverage area must exceed the edge of the filling layer 32, and special connectors are used to connect and fix the geogrid 33 to the ecological permeable transverse structure 51 to ensure the stability and continuity of the overall structure.

[0081] Specifically, it also includes a monitoring component, which includes a single-point displacement meter 71 pre-buried in the filling layer 32, an earth pressure box 72 buried in the gravel cushion layer 31, and a strain gauge 73 arranged on the circumference of the outer surface of the pile tube 62; the single-point displacement meter 71, the earth pressure box 72 and the strain gauge 73 are all connected to the host computer signal.

[0082] The single-point displacement meter 71, the earth pressure box 72 and the strain gauge 73 are used to carry out monitoring and measurement during and after the construction, record the monitoring data and analyze the monitoring results.

[0083] Example 2

[0084] refer to Figure 1 and Figure 8 Based on Example 1, this embodiment provides a construction method for a progressive stiffness pile-soil composite foundation structure for widening a roadbed, the purpose of which is to solve the problem of settlement caused by not considering the progressive stiffness of the new and old roadbeds in traditional roadbed widening. The specific steps of the construction method in this embodiment will be described in detail below.

[0085] A construction method for a progressive stiffness pile-soil composite foundation structure for widening a roadbed, comprising the following steps:

[0086] Step S1, survey the original roadbed 1 and the new road base 2 to obtain survey data between the original roadbed 1 and the new road base 2; specifically, before construction, high-precision monitoring technology, such as ground penetrating radar and GPS positioning, is used to measure the original roadbed 1 and the new road base 2 in detail, evaluate the stiffness difference between the two, evaluate the physical and mechanical properties of the roadbed, and obtain survey data.

[0087] Step S2, based on the survey data obtained in step S1, prefabricate a progressive stiffness component 5 with progressive stiffness, the progressive stiffness component 5 includes an ecological permeable lateral structure 51, an ecological permeable oblique structure 52 and a supporting structure 54, and selects recycled permeable concrete with progressive pore distribution as the main material, and gradually adds a bubble generating agent to realize the distribution of pores of the ecological concrete from sparse to dense.

[0088] The prefabrication method of the progressive stiffness component in step S2 is:

[0089] Step S21, material preparation, the main materials are ordinary cement, fine aggregate and coarse aggregate, the fine aggregate can be sand, the coarse aggregate can be recycled aggregate crushed from building demolition waste, the admixture is a foaming agent, the admixture can be a foaming agent suitable for bubble generation, and the additive is a water reducer or an air entraining agent;

[0090] Step S22, base concrete mix ratio, according to the actual stiffness difference between the original roadbed 1 and the new roadbed base 2, determine the base concrete mix ratio; the standard mix ratio includes the ratio of cement, fine aggregate and recycled coarse aggregate.

[0091] The specific proportion of permeable concrete (based on 1 cubic meter): cement: 300-400kg, fine aggregate (sand): 600-700kg, recycled coarse aggregate: 1000-1200kg, water: 120-160L, bubble generator: 0.5%-2% of the cement weight per cubic meter of concrete, that is, 1.5-8kg (adjusted according to foaming requirements) water reducer or air entraining agent: 0.3%-0.6% of the cement weight per cubic meter of concrete, about 0.9-2.4kg.

[0092] For example: If you plan to use higher strength concrete and choose a medium coarse aggregate ratio, the ratio is as follows: cement: 350kg, sand: 650kg, recycled coarse aggregate: 1100kg, water: 140L, bubble generator: 1.75kg (about 0.5% of the weight of cement), water reducer: 1.4kg (about 0.4% of the weight of cement).

[0093] This ratio can be used for roadbed structures with medium strength requirements. If the porosity needs to be further adjusted, the pore gradient effect can be achieved by adjusting the proportion of the bubble generator or the aggregate content. These specific values ​​can be further optimized according to the survey data and material properties in actual construction to ensure that they meet the construction needs. That is, by adjusting the proportion of aggregate, cement, water and the concentration of the foaming agent, the pore distribution from sparse to dense can be gradually achieved to ensure a gradual transition in stiffness.

[0094] Step S23, prepare a bubble generator. A composite foaming agent (such as Sika Lightcrete) can be used for large-area construction. The recommended foaming multiple is: the foaming multiple is usually required to be 20-30 times in concrete, that is, the volume of the foaming agent can be expanded by 20-30 times, so that a uniform bubble structure can be formed in the concrete. Foam stability: The foam should have good stability to prevent the bubbles from breaking or disappearing during the concrete curing process. The concentration of the bubble generator is 0.5%-2%.

[0095] Step S24, mixing the base concrete and the bubble generator; gradually adding the bubble generator to the base concrete during mixing.

[0096] Initial mixing: prepare the basic concrete ingredients by mixing cement, aggregate and water according to the designed proportions, add a bubble generator with a concentration of 0.5% into the basic concrete and mix well.

[0097] In the mid-term mixing, based on the initial mixing, gradually add a bubble generator with a concentration of 1% and continue stirring until it is evenly mixed.

[0098] In the final mixing, add a bubble generator with a concentration of 2% based on the mid-term mixing, and finally stir to mix evenly.

[0099] Step S25, layered pouring, pouring the mixed concrete in step S24 in layers into the mold of the progressive stiffness component 5, the pore density of each layer is from sparse at the bottom to dense at the top, the stirring time and vibration intensity of each layer of concrete can be adjusted according to actual conditions to ensure the uniform distribution of the bubble generator and the gradual change of the pore structure; for ease of pouring, the mold is placed upright during pouring, that is, the bottom corresponds to the left side of the ecological permeable concrete, and the top corresponds to the right side of the ecological permeable concrete, the stirring time and vibration intensity of each layer of concrete can be adjusted according to actual conditions to ensure the uniform distribution of the bubble generator and the gradual change of the pore structure.

[0100] Step S26, curing treatment: after the pouring in step S25 is completed, a standard curing treatment is performed to maintain appropriate humidity and temperature to ensure the strength of the concrete and the stability of the pore structure;

[0101] Step S27, after the solidification is completed, the progressive stiffness component 5 is obtained, and then the concrete specimen of the progressive stiffness component 5 is subjected to a porosity test, a strength test and a uniformity test to ensure that the pore distribution meets the design requirements.

[0102] Through the above method, the distribution of pores in the eco-concrete specimen can be changed from sparse to dense, which is manifested in the gradual transition of the pore structure inside the specimen. This gradual structure can effectively improve the performance of concrete in the transition of stiffness between the new and old roadbeds.

[0103] Step S3, excavate the shoulder of the original roadbed 1, and perform slope treatment on the shoulder of the original roadbed 1 to form a stepped slope 4; excavate the steps layer by layer to ensure that each layer meets the design requirements and ensures the stability of the steps. Basic requirements: Each step is 80 cm high and 200 cm wide, with a bottom surface with a slope of 2-4%, and no water accumulation. Rolling and impact rolling must be pressed to the root of the step.

[0104] Step S4, determining the length of the pile body 61 according to the survey data obtained in step S1; the arrangement density of the pile body 61 decreases from the connection between the original roadbed 1 and the new roadbed base 2 toward the edge to determine the arrangement position and number of the pile body 61, and obtain the arrangement plan of the pile body 61; the pile body 61 is installed and constructed in sections according to the arrangement plan of the pile body 61, and when installing the pile body 61, the strain gauge 73 is attached to the outer surface of the pile body 61.

[0105] Based on the early detection of geological data, the depth of the bedrock area is determined to determine the length of the pile body 61. A uniform length can be selected, or the length can be progressively reduced.

[0106] During construction, drilling: Use drilling equipment to drill holes at the marked position, and the hole diameter and depth are determined according to design requirements.

[0107] Drilling sequence: Drill holes gradually from the junction of the original roadbed 1 and the new road base 2 toward the new road base 2 to form a foundation structure with gradually changing stiffness.

[0108] Drilling density: The density of drilling holes gradually decreases from the junction of the original roadbed 1 and the new road base base 2 toward the new road base base 2.

[0109] Pile installation: Soil-cement rock solidified recycled aggregate is selected as the pile body 61, and the material strength is gradually increased according to the progressive stiffness requirements.

[0110] Installation in sections: The first section of pile body: a pile body 61 with a higher density is installed at one end close to the original roadbed 1 to form a pile body 61 with a higher strength to provide basic support.

[0111] The second section of pile body: after the first section of pile body, a pile body 61 with moderate density is installed to form a pile body 61 with moderate strength, and the installation continues in the direction of the base layer 2 of the new road base, gradually reducing the strength of the pile body 61.

[0112] The third and subsequent piles: According to the design requirements, continue to install piles 61 with lower strength until the edge of the new roadbed to ensure a gradual transition in stiffness. The subsequent steps are carried out in the same way.

[0113] Pile reinforcement: a steel cage 63 is placed in the pile tube 62 of each pile body 61 to increase the bearing capacity of the pile body 61. Secondary pouring: secondary concrete pouring is performed to ensure a firm connection between the steel cage 63 and the pile tube 62.

[0114] In step S4, the layout scheme of the pile body 61 needs to be evaluated and measured by a load-settlement test, and the load-settlement test evaluation and measurement method is:

[0115] Step S41, determine the evaluation and measurement area; select representative areas for load-settlement tests. These areas should cover different parts of the old and new roadbeds to ensure the comprehensiveness of the data; and select the test type to decide whether to conduct a static load test or an in-situ test. Static load tests are suitable for stiffness determination of a single point or a local area, while in-situ tests can cover a larger range; determine the target load, and set the range and classification of the load according to the design requirements and foundation conditions. The load should cover normal use loads as well as ultimate loads to comprehensively evaluate foundation performance.

[0116] Step S42, local installation is performed in the evaluation and measurement area according to the installation plan of the pile body 61; during the installation, a settlement meter and a displacement sensor are buried simultaneously;

[0117] Step S43, perform a load-settlement test, apply multiple levels of predetermined load increments to the pile body 61 step by step through a static load test device, and record the settlement data of the pile body 61 or the foundation under each level of load. Ensure the accuracy of the measurement, and record the time for data analysis;

[0118] If necessary, the test can be repeated to test different areas (old roadbed and new roadbed) to obtain load-settlement curves for different areas. The test can be performed on different piles 61, or different loads can be applied to the same pile 61 to obtain a complete curve.

[0119] Step S44, data analysis, plotting the applied load and recorded settlement data into a graph, calculating the initial slope of the load-settlement curve, evaluating the stiffness of the foundation, and analyzing the stiffness change. For a progressive stiffness design, the curve in the old roadbed area should be steeper, and the curve in the new roadbed area should be gentler.

[0120] Step S45 , evaluating the design effect, comparing the load-settlement curves of different areas, and confirming whether the arrangement of the piles 61 has achieved the progressive stiffness effect of the original roadbed 1 and the new roadbed base 2 .

[0121] If the curve shows that the stiffness change does not meet the design requirements, it is necessary to adjust the pile foundation layout, optimize the design, and adjust the pile foundation parameters: according to the analysis results of the load-settlement curve, adjust the design parameters of the pile foundation (such as pile length, diameter, density, etc.) to achieve the ideal stiffness distribution. Then retest and perform another load-settlement test on the adjusted design to ensure that the modified layout meets the stiffness progressive requirements.

[0122] Implementation example:

[0123] Assuming that a load-settlement test is planned for a project, the steps are as follows:

[0124] 1. Design stage: set the pile layout, select the test area, and set the load level (such as 50kN increase per level).

[0125] 2. Construction phase: Arrange piles in the test area, install settlement meters, and prepare static load test equipment.

[0126] 3. Test phase: gradually apply loads (such as 100kN, 150kN, 200kN) and record the settlement data under each level of load.

[0127] 4. Data analysis: Plot load-settlement curves to evaluate whether the stiffness distribution meets the progressive design requirements.

[0128] 5. Optimize the design: adjust the pile layout according to the analysis results, make necessary design adjustments, and conduct tests again to verify the results.

[0129] Through these implementation steps, it can be ensured that the pile layout can achieve a progressive stiffness effect from the old roadbed to the new roadbed, thereby improving the stability and bearing capacity of the project.

[0130] A load-settlement curve that meets the stiffness progression criterion should reflect the gradual change in stiffness from the old embankment to the new embankment. Specifically, such a curve usually has the following characteristics:

[0131] 1. Changes in the slope of the curve. The load-settlement curve is usually steeper in the old roadbed area, indicating that the stiffness of this area is higher. In other words, the settlement produced by a unit load is small and the stiffness is large. The load-settlement curve gradually flattens in the new roadbed area, indicating that the stiffness of this area is low. In other words, the settlement produced by a unit load is relatively large and the stiffness is small.

[0132] 2. The shape of the curve. The load-settlement curve should show a gradual change from the old embankment to the new embankment. Specifically, the slope of the curve should transition smoothly rather than suddenly change. This means that the curve should be steep in the middle area and gradually become flatter at the edges. The transition of the curve should be as smooth as possible, avoiding sharp changes in slope. You can ensure that the change in stiffness is gradual rather than sudden by performing consecutive tests on different areas.

[0133] 3. Regional comparison: Compare the load-settlement curves of the old and new roadbeds. The curves in the old roadbed area should show a higher initial slope (stiffness), while the curves in the new roadbed area should gradually decrease in slope. In the diagram, two or more load-settlement curves (representing different areas) can be drawn and checked to see if the slope and shape of these curves meet the design requirements for stiffness progression.

[0134] 4. Numerical indicators: Calculate the stiffness (K) of different areas, which can be estimated by the initial slope of the load-settlement curve.

[0135]

[0136] Where ΔP and ΔS are the change in load and the corresponding change in settlement, respectively.

[0137] In addition, a stiffness progressive index is set to measure the change of stiffness. For example, define an index To express the stiffness ratio between the original roadbed 1 and the new roadbed base 2:

[0138]

[0139] In the formula, K1 represents the stiffness of the original roadbed 1, and K2 represents the stiffness of the base layer 2 of the new roadbed.

[0140] Select any two areas, calculate the stiffness ratio between the new original roadbed 1 and the new road base 2, and get the degree of stiffness difference between the two. For example, the stiffness difference between area 1 and area 2 can also be calculated between area 2 and area 3, and between area 3 and area 4. After the calculation, you can know how the stiffness of the original roadbed 1 and the new road base 2 changes within the entire cross-section. Moreover, the finer the area, the more precise the calculation of stiffness change process! The stiffness progression index should show a reasonable stiffness difference, indicating the effect of stiffness progression.

[0141] Step S5, laying of pile top and cushion layer: when the strength of the pile body 61 meets the requirements for the construction of the new roadbed filling layer 3, a cap 64 is set on the pile top of the pile body 61, and adjacent pile bodies 61 are connected through the cap 64 to ensure that the load is evenly distributed on each pile body 61, and then a crushed stone cushion layer 31 is laid on the cap 64, and an earth pressure box 72 is buried when laying the crushed stone cushion layer 31.

[0142] Step S6, install the progressive stiffness components 5 on the stepped slope 4 in layers; when installing a layer of progressive stiffness components 5, build a filling layer 32, and after each filling layer 32 is completed, lay the geogrid 33; when filling each filling layer 32, bury the single-point displacement meter 71.

[0143] Installation of the progressive stiffness component 5: The first section of the ecological permeable transverse structure 51 is installed on the table top of the stepped slope 4 to ensure that it is closely integrated with the roadbed.

[0144] The second section of the ecological permeable transverse structure 51 is installed on the filling layer 32 and connected to the first section of the ecological permeable transverse structure 51 through a mortise and tenon structure to gradually adjust the roadbed stiffness.

[0145] The ecological permeable oblique structure 52 is installed on the inclined surface of the stepped slope 4, connecting the ecological permeable transverse structure 51 and the supporting structure 54, and adopts an oblique design to adapt to the stress state of the foundation.

[0146] Support rod structure 54: buried in the stepped slope 4 and connected to the ecological permeable oblique structure 52 to provide additional vertical support to ensure the stability of the overall structure.

[0147] Fixed bolt connection: Use fixed bolts to connect the sections of the structure together to ensure the stability and continuity of the overall structure.

[0148] Roadbed filling of the filling layer 32: laying the geogrid 33 on the crushed stone cushion layer 31, and filling the first filling layer 32.

[0149] Compacting treatment: After each filling layer 32 is filled, compacting equipment is used to perform compacting treatment to ensure the density and stability of the filling material.

[0150] Filling layer by layer: Filling shall be carried out layer by layer according to the design requirements. The thickness of each layer shall be strictly implemented according to the design standards to ensure the stability of the overall structure.

[0151] Step S7: Monitor and measure during and after construction using the single-point displacement meter 71, the earth pressure box 72 and the strain gauge 73, record the monitoring data, and analyze the monitoring results.

[0152] The subgrade settlement monitoring of the widening test section is carried out by arranging measuring points in the original subgrade 1, the base layer 2 of the new subgrade and the filling layer 3 of the new subgrade, and burying displacement sensors, strain gauges and earth pressure cells. Figure 1 During construction, monitoring sections are selected for the test section, monitoring data are recorded, and monitoring results are analyzed. The settlement monitoring frequency is determined according to the roadbed settlement rate. If the roadbed settlement rate is found to be accelerated during the construction period, monitoring should be strengthened and the number of monitoring times should be appropriately increased, as shown in Table 1. It is ensured that problems are discovered through monitoring and timely remediation is carried out to ensure the construction quality of the roadbed reconstruction and expansion.

[0153] After the construction is completed, the overall structure is inspected for quality, including material strength, connection stability, and roadbed flatness. Ensure that the construction quality meets the design requirements and technical standards. Continue to check the stability of the expanded roadbed and the settlement of the roadbed in the future, and perform necessary maintenance and reinforcement. Record maintenance data to provide reference for future roadbed expansion projects.

[0154] Table 1 Frequency of observation of roadbed settlement during reconstruction and expansion

[0155]

[0156] Although the specific implementation of the invention is described in detail in conjunction with the drawings, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A progressive stiffness pile-soil composite foundation structure for widening a roadbed, characterized in that: include: A stepped slope (4), wherein the stepped slope (4) is arranged on the upper part of the original roadbed (1) close to the base layer (2) of the new roadbed; A progressive stiffness component (5), wherein the progressive stiffness component (5) is arranged on the stepped slope (4); A pile foundation assembly (6), the pile foundation assembly (6) comprising a plurality of evenly buried pile bodies (61) buried in a new road base layer (2); the density of the plurality of pile bodies (61) decreases from the original road base (1) to the new road base layer (2); A new roadbed filling layer (3) is arranged above the pile foundation assembly (6) and is in contact and connected with the progressive stiffness component (5).

2. The progressive stiffness pile-soil composite foundation structure for widening a roadbed according to claim 1, characterized in that: The progressive stiffness component (5) comprises ecological water-permeable transverse structures (51) having the same number as the steps of the stepped slope (4), and adjacent ecological water-permeable transverse structures (51) are connected via ecological water-permeable oblique structures (52); The ecological permeable transverse structure (51) is provided with permeable gaps (53) with a decreasing density from the original roadbed (1) to the new roadbed base (2); The ecological permeable oblique structure (52) is provided with permeable gaps (53) with a density decreasing from high to low.

3. The stiffness progressive pile-soil composite foundation structure for widening the roadbed according to claim 2, characterized in that: The ecological permeable oblique structure (52) is provided with a supporting structure (54) obliquely buried in the stepped slope surface (4).

4. The progressive stiffness pile-soil composite foundation structure for widening a roadbed according to claim 1, characterized in that: The pile body (61) comprises a pile tube (62) buried in the base layer (2) of the new road foundation, a steel cage (63) is placed in the pile tube (62) and concrete is poured; the pile tops of adjacent pile tubes (62) are connected via a cap (64).

5. The progressive stiffness pile-soil composite foundation structure for widening a roadbed according to claim 4, characterized in that: The new roadbed filling layer (3) comprises a crushed stone cushion layer (31) laid on top of a cap (64), a plurality of filling layers (32) are arranged above the crushed stone cushion layer (31), and geogrids (33) are filled between adjacent filling layers (32).

6. The stiffness progressive pile-soil composite foundation structure for widening the roadbed according to claim 5, characterized in that: The invention also comprises a monitoring component, which comprises a single-point displacement meter (71) pre-buried in the filling layer (32), an earth pressure box (72) buried in the crushed stone cushion layer (31), and a strain gauge (73) arranged on the circumferential direction of the outer surface of the pile tube (62); the single-point displacement meter (71), the earth pressure box (72) and the strain gauge (73) are all connected to the upper computer signal.

7. A construction method for a progressive stiffness pile-soil composite foundation structure for widening a roadbed based on any one of claims 1 to 6, characterized in that: The following steps are involved: Step S1, surveying the original roadbed (1) and the base layer of the new roadbed (2), and obtaining survey data between the original roadbed (1) and the base layer of the new roadbed (2); Step S2, prefabricating a progressive stiffness component (5) with progressive stiffness according to the survey data obtained in step S1; Step S3, excavating the shoulder of the original roadbed (1), and performing slope treatment on the shoulder of the original roadbed (1) to form a stepped slope surface (4); Step S4, determining the length of the pile body (61) according to the survey data obtained in step S1; the arrangement density of the pile body (61) is gradually reduced from the connection point between the original roadbed (1) and the base layer (2) of the new roadbed toward the edge, so as to determine the arrangement position and number of the pile body (61) and obtain the arrangement scheme of the pile body (61); the pile body (61) is installed and constructed in sections according to the arrangement scheme of the pile body (61), and when installing and constructing the pile body (61), the strain gauge (73) is attached to the outer surface of the pile body (61); Step S5, when the strength of the pile body (61) meets the requirements for the construction of the new roadbed filling layer (3), a cap (64) is arranged on the top of the pile body (61), and adjacent pile bodies (61) are connected via the cap (64) to ensure that the load is evenly distributed on each pile body (61), and then a crushed stone cushion layer (31) is laid on the cap (64), and an earth pressure box (72) is buried when the crushed stone cushion layer (31) is laid; Step S6, installing the progressive stiffness components (5) on the stepped slope (4) in layers; when installing a layer of progressive stiffness components (5), constructing a layer of filling layer (32), and after each layer of filling layer (32) is completed, laying the geogrid (33); burying the single-point displacement meter (71) when constructing each layer of filling layer (32); Step S7: Monitor and measure during and after construction using the single-point displacement meter (71), the earth pressure box (72) and the strain gauge (73), record the monitoring data, and analyze the monitoring results.

8. The construction method of the stiffness progressive pile-soil composite foundation structure for widening the roadbed according to claim 7, characterized in that: The method for prefabricating the progressive stiffness component (5) of the progressive stiffness type in step S2 is as follows: Step S21, material preparation, the main materials are ordinary cement, fine aggregate and coarse aggregate; the admixture is a foaming agent; the additive is a water reducing agent or an air entraining agent; Step S22, the base concrete ratio is determined according to the actual stiffness difference between the original roadbed (1) and the new roadbed base (2); Step S23, preparing a bubble generating agent, wherein the concentration of the bubble generating agent is 0.5%-2%; Step S24, mixing base concrete and bubble generating agent; In the initial mixing, add 0.5% of the bubble generator to the base concrete and mix well; In the mid-term mixing, based on the initial mixing, gradually add a bubble generator with a concentration of 1%, and continue stirring until it is evenly mixed; Final mixing: add 2% bubble generator based on the mid-term mixing, and finally stir to mix evenly; Step S25, pouring in layers, pouring the concrete mixed in step S24 in layers into the mold of the progressive stiffness component (5), the pore density of each layer is from sparse at the bottom to dense at the top, and the stirring time and vibration intensity of each layer of concrete can be adjusted according to actual conditions to ensure uniform distribution of the bubble generating agent and gradual change of the pore structure; Step S26, curing treatment: after the pouring in step S25 is completed, a standard curing treatment is performed to maintain appropriate humidity and temperature to ensure the strength of the concrete and the stability of the pore structure; Step S27: After the solidification is completed, a progressive stiffness component (5) is obtained, and then a porosity test, a strength test and a uniformity test are performed on the concrete specimen of the progressive stiffness component (5) to ensure that the pore distribution meets the design requirements.

9. The construction method of the stiffness progressive pile-soil composite foundation structure for widening the roadbed according to claim 8, characterized in that: In step S4, the arrangement scheme of the pile body (61) needs to be evaluated and weighed by a load-settlement test, and the load-settlement test evaluation and weighing method is: Step S41, determine the evaluation measurement area, select the test type, and determine the target load; Step S42, performing local installation work in the evaluation and measurement area according to the installation plan of the pile body (61); burying the settlement meter and displacement sensor at the same time during the installation work; Step S43, performing a load-settlement test, applying multiple levels of predetermined load increments to the pile body (61) step by step through a static load test device, and recording the settlement data of the pile body (61) under each level of load; Step S44, data analysis, plotting the applied load and recorded settlement data into a graph, calculating the initial slope of the load-settlement curve, evaluating the stiffness of the foundation, and analyzing the stiffness change; Step S45, evaluating the design effect, comparing the load-settlement curves of different areas, and confirming whether the arrangement of the pile body (61) has achieved the progressive stiffness effect of the original roadbed (1) and the new roadbed base (2).

Images