A variable stiffness stepped foundation structure and method of construction

Abstract

The application discloses a variable-rigidity stepped foundation structure and a construction method, and is applied to the fields of building structure engineering and foundation treatment technology, and comprises a stepped foundation part and an abutment foundation part, wherein the abutment foundation part is arranged on the top of the stepped foundation part, the stepped foundation part comprises a plurality of layers of stepped foundations, all the layers of stepped foundations extend to the outer edge of a mountain foundation, all the layers of stepped foundations form a stepped shape on the side facing the mountain foundation, and the end of each layer of stepped foundation corresponds to a primary step; the construction method comprises the steps of excavating the mountain foundation, layer-by-layer pouring the stepped foundation part, and pouring the abutment foundation part; the stepped abutment foundation is combined with the mountain foundation, the foundation stress has a better coordination relationship along the transverse bridge direction, uneven settlement of the foundation can be effectively controlled, and stress distribution is optimized; meanwhile, the method can be suitable for different foundation conditions, construction is convenient, and the engineering cost is reduced.

Description

Technical Field

[0001] This invention relates to the fields of building structure engineering and foundation treatment technology, and in particular to a variable stiffness stepped foundation structure and its construction method. Background Technology

[0002] With the advancement of transportation infrastructure, the need to address complex geological engineering environments is becoming increasingly urgent. Constructing large-span arch bridges in mountainous and canyon areas with complex geological conditions presents a significant challenge in foundation stability. Ensuring foundation stability to meet engineering requirements in terms of load-bearing capacity and deformation is crucial. The arch abutment foundation is the main load-bearing component of an arch bridge structure, playing a decisive role in its stability. The form of the arch abutment foundation is determined comprehensively based on the topographical and geological conditions of the arch bridge. In arch bridge design, to improve system stability, the foundation typically adopts an enlarged foundation form acting on the rock strata. For large-span arch bridge structures, large-volume arch abutments are required. However, large-volume arch abutments present many problems, as their actual stress characteristics and mechanisms are complex. Common issues include insufficient load-bearing capacity estimation and excessively large foundation dimensions. Furthermore, excessively large volumes are prone to shrinkage cracking and other defects during construction due to concrete hydration reactions, posing significant risks to the bridge's later operation. Conventional foundations provide tension to the superstructure through excavation into platforms or ground anchors. For platform-type foundations, due to the structural stress characteristics of bridges, the direction of the bearing reaction force is mainly along the arch axis, resulting in uneven stress distribution in the foundation, stress concentration, and subsequent foundation cracking and other damage, seriously threatening the safety of the superstructure. In the stress system of arch bridge structures, the stiffness of the foundation is one of the main factors affecting the magnitude and distribution of its internal forces. Greater and constant stiffness results in greater and more uniform internal forces, and higher bearing capacity. Traditional methods calculate the base stress as long as it is less than the allowable bearing capacity of the foundation, neglecting the influence of the back-side reaction force on the foundation stress. In reality, stress concentration exists between the back of the foundation and the ground, which does not reflect the actual structural stress conditions, and the calculation results are conservative, leading to high engineering costs. For old bank arch abutment foundations, because they are built on a hillside and the foundation is a bedding rock foundation, the load of the superstructure has a significant impact on the overall stability of the slope. From a planar perspective, the closer the base projection area is to the slope (i.e., the side facing the water), the worse the slope stability. Therefore, shifting the high-stress area of ​​the foundation to a deeper part of the mountain is more beneficial to the overall stability of the slope. Optimizing the force transmission path and stress distribution of the arch-foundation-ground becomes essential.

[0003] Traditional foundations, due to limitations in technology and construction conditions, require site leveling beforehand, and the foundations are typically arranged in a strip-like, regular pattern. They are laid out according to the principle of equal stiffness, assuming a uniform distribution of base reaction forces. However, in actual engineering, mountain slope excavation is difficult, and foundation deformation is uneven. Uneven settlement easily occurs when the foundation acts on the ground, leading to an unstable force transmission path between the foundation and the ground, significantly impacting the service life and safety of the bridge structure. According to the "Code for Design of Building Foundations," the stress distribution of the foundation under superload is related to its stiffness. For uneven foundations, even with uniform foundation stiffness, inconsistent deformation coordination will occur, leading to brittle foundation failure and affecting the stability of the superstructure. To minimize differential settlement and improve structural stability, the stiffness characteristics of the foundation need to be optimized. In summary, the shortcomings of existing technologies include: 1. Large concrete pouring volume; 2. Large foundation leveling and excavation volume, resulting in high project costs; 3. Inconsistent deformation coordination between the foundation and the ground, making differential settlement difficult to control. The key to solving the above problems lies in improving the variable stiffness adjustment capability between the foundation and the subgrade, a problem that current technologies have not yet solved.

[0004] On the other hand, conventional foundation construction focuses on whether the stress at the foundation base can meet the bearing capacity requirements. Therefore, common bridge arch abutment foundations are typically constructed by excavating and leveling the ground and building an integrated box foundation. However, the stress in a cast-in-place box foundation primarily acts on the underlying ground. Considering that the stress distribution of an arch bridge abutment is mainly along the arch axis, the outer side of the abutment experiences a greater load from the upper structure, while the inner side experiences a smaller load. This results in uneven stress distribution between the inner and outer sides of the abutment foundation, making it prone to brittle fracture and other problems. Simultaneously, the excessively high stiffness on the inner side of the abutment fails to function effectively and further exacerbates foundation failure—a phenomenon that conventional foundation construction cannot avoid. Research on improving foundation structures to better adapt to mountainous terrain is scarce. Therefore, utilizing the characteristics of mountainous terrain and rationally designing foundation types to achieve continuous deformation coordination between the foundation and the ground, and avoiding localized stress concentration leading to abutment foundation failure and subsequent superstructure insecurity, is crucial. Based on this, the innovative foundation type, which is suitable for different foundation conditions, easy to construct, and has continuous foundation settlement and stress distribution, has great engineering significance and practical value.

[0005] Therefore, based on years of experience and practice in related industries, the inventor proposes a variable stiffness stepped foundation structure and construction method to overcome the shortcomings of existing technologies. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies, such as uneven stress in the arch foundation leading to difficulty in controlling differential settlement, and to provide a variable stiffness stepped foundation structure and construction method. The stepped arch foundation has better consistency in the overall stiffness change with the mountain foundation, thereby eliminating uneven foundation stress, and has better anti-slip and anti-overturning capabilities. It can effectively control uneven foundation settlement and optimize stress distribution, and the foundation stress has a better coordination relationship along the transverse bridge direction. At the same time, this method can be applied to different foundation conditions, is convenient to construct, and also reduces engineering costs.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] A variable stiffness stepped foundation structure is disclosed, wherein the stepped foundation structure matches the side surface shape of the mountain foundation. It includes a stepped foundation part and an arch foundation part. The arch foundation part is located on top of the stepped foundation part and is block-shaped. The top of the arch foundation is used to provide a horizontal support surface for the arch. The stepped foundation part includes several layers of stepped foundations. All layers of stepped foundations extend to the outer edge of the mountain foundation. The stepped foundations increase in length layer by layer in the direction of increasing height. All layers of stepped foundations form a stepped shape on the side facing the mountain foundation. The end of each layer of stepped foundations corresponds to a step.

[0009] Because the thickness of the stepped foundation gradually decreases from the side edge of the mountain foundation to the center of the mountain, this stepped structure creates a variable stiffness foundation that corresponds to the deformation of the mountain. The foundation is evenly stressed internally, has a simple structure, and plays a significant role in regulating foundation deformation. The layered stepped foundation has good anti-slip properties. Due to the different lengths of each layer of the stepped foundation, the thickness of each layer in the height direction is different, resulting in different stiffness. The layered design results in uneven resistance to horizontal forces, with the top layer playing a major role. In actual construction, the strength of the material on the back of the top layer is ensured to guarantee the structural strength. When each step foundation bears external loads, it will not only experience downward and backward translational motion, but also, through foundation stress transfer, determine the effective foundation size in contact with the bedrock surface. The entire load borne by the arch foundation is converted into lateral forces and moments at the foundation's center of gravity, resulting in the stress distribution of each step base and the horizontal resistance on the back side. Considering the contribution of the horizontal resistance on the base stress redistribution, differential settlement can be reduced through variable stiffness leveling. If the mountain foundation stiffness is distributed with softness near the center and hardness near the edge, the high-stress zone shifts towards the edge, which is beneficial to the overall stability of the slope. The main mechanism is to counteract the uneven stiffness distribution caused by different parts by changing the support stiffness of the step foundation, thereby adjusting and reducing differential settlement, thus eliminating uneven foundation stress. This results in better anti-slip and anti-overturning capabilities, effectively controlling uneven foundation settlement and optimizing stress distribution. The foundation stress has a better coordination relationship along the transverse direction, avoiding local brittle cracking failure. Furthermore, this method is applicable to different foundation conditions, is easy to construct, and reduces project costs.

[0010] In a preferred embodiment of the present invention, the aforementioned stepped foundation is formed by pouring concrete in layers sequentially. Based on the characteristics of the arch bridge and the foundations of the mountains on both sides, the stress distribution of the arch abutment is calculated. The number of steps is adjusted according to the slope of the mountain foundation and the layering situation. Based on the stress characteristics of the arch abutment, the layered pouring situation is determined, thereby adapting to different mountain foundations.

[0011] In a preferred embodiment of the present invention, in each of the aforementioned stepped foundations, low-strength concrete is used on the side closer to the mountain foundation, and high-strength concrete is used on the side closer to the outer edge of the mountain foundation. Considering that the mountain foundation is also a stepped structure, this method of setting different concrete strengths at different locations can effectively avoid uneven stress at the arch abutment and the inability of the inner concrete to exert its compressive effect effectively. At the same time, the project cost is significantly reduced due to the reduction in the amount of concrete used.

[0012] In a preferred embodiment of the present invention, the strength grade of the concrete ranges from C40 to C80. Based on the stress characteristics of the arch abutment, the strength grade of the poured concrete is adjusted, and finally, concrete of different strength grades is poured in layers to adapt to different structural stresses, thus making it suitable for different foundation conditions.

[0013] In a preferred embodiment of the present invention, the step angle of each of the aforementioned step foundations is 90–150°. The angle value and the concrete material grade work together to achieve this. The step angle value is determined based on the slope of the mountain foundation. By changing the material strength at different locations within the step foundation, the step foundation structure achieves different lateral stiffnesses. Once the angle value and concrete material parameters are determined, the step foundation structure possesses only a unique stiffness characteristic. However, by varying the angle value, a variable stiffness characteristic can be achieved, allowing for flexible adjustment of the step foundation stiffness during construction.

[0014] In a preferred embodiment of the present invention, the side slope of the first-level step at the end of all layers of the stepped foundation structure is 90-150°. The mountain features include the type of rock and soil and the slope angle. The arch bearing features include the arch bridge configuration and the position of the arch bearing center of gravity. Based on the mountain features and the arch bearing features, the stress distribution of each step is calculated, and the rotation angle value of each layer is determined. Specifically, the stress distribution of the stepped foundation structure is obtained through numerical simulation. The stepped foundations with different side slopes form an integral stepped foundation part and provide horizontal resistance and bearing capacity. The variable stiffness characteristics can be adjusted according to the size of the step rotation angle value.

[0015] In a preferred embodiment of the present invention, the aforementioned stepped foundation structure is further equipped with a data monitoring component, which includes several stress sensors and several settlement monitoring sensors. The stress sensors and settlement monitoring sensors are located at the bottom of the stepped foundation portion, between the mountain foundation and the stepped foundation structure. Stress sensors are installed on the sides of the stepped foundation portion, and settlement monitoring sensors are installed on the surface of the mountain foundation. The data monitoring component is connected to a data acquisition system and a PC. The PC monitors the data from each sensor, the stress sensors monitor the base stress at the bottom of the stepped foundation structure, and the settlement monitoring sensors monitor the structural deformation values. Based on the feedback from these findings, the stress distribution of the structure is determined, thereby analyzing the stress level and vertical settlement at each monitoring point and accurately assessing the actual bearing capacity of the stepped foundation structure.

[0016] A construction method for a variable stiffness stepped foundation structure, used for casting and forming the aforementioned variable stiffness stepped foundation structure, includes the following steps:

[0017] S1. Excavate the mountain foundation to form a stepped foundation structure;

[0018] S2. Support formwork, concrete is poured into the space corresponding to the step foundation part through grouting equipment to form the first layer of concrete foundation. After hardening and shaping, the next layer of concrete foundation is poured, and so on to form the multi-layer concrete foundation step foundation part, with each layer of concrete foundation corresponding to one layer of step foundation.

[0019] S3. Finally, pour the arch foundation on top of the stepped foundation.

[0020] This construction method requires that the terrain of the mountain foundation should not be too steep, and that slope cutting work can be carried out. The arch bridge force borne by the stepped foundation structure generally extends along the arch axis. For a homogeneous and regularly shaped arch seat, the stress point is inclined downward along the center of gravity. However, under this condition, the pressure area on the side of the arch seat near the mountain foundation is large, while the pressure area on the side near the water is small, resulting in uneven stress distribution in the arch seat. This construction method forms a multi-layered concrete foundation by pouring concrete in layers. According to the structural form of the steps, the concrete is poured in layers. When pouring concrete in layers, each layer of the step foundation forms a good horizontal surface, so that the force transmission path of each layer does not change. This changes the influence of the weight of the arch seat and realizes the adjustable lateral stiffness of the arch seat, thereby achieving a better force (bending moment) transmission mechanism between the arch seat and the mountain foundation. This allows the mountain foundation and the stepped foundation structure to transition well, and the mountain foundation and the stepped foundation structure form a good coordination effect, reducing differential settlement, saving construction materials, and reducing project costs.

[0021] In a preferred embodiment of the present invention, step S1 specifically comprises:

[0022] Based on geological survey data, the excavation and leveling surface of the mountain foundation was determined, and multiple layers to be excavated were divided. The mountain foundation was excavated layer by layer from top to bottom, forming a multi-level stepped structure of the mountain foundation side surface. The top surface of each step structure is horizontal and flat, and the side slope of each step structure is 90-150°. The mountain foundation includes the canyon mountain body, as well as foundation soil with high strength and hardness, or rock foundation. The number of multi-level stepped structures is determined according to the characteristics of the mountain, the slope of the mountain, and the stress area. When there are more layers, the corresponding stepped foundation structure has better variable stiffness control capability.

[0023] In a preferred embodiment of the present invention, the above construction method further includes the step of: arranging stress sensors and settlement monitoring sensors at the bottom of the step foundation portion and between the mountain foundation and the step foundation structure.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This stepped foundation structure compensates for uneven stiffness distribution caused by different parts by changing the support stiffness of the stepped foundation, thereby adjusting and reducing differential settlement, eliminating uneven foundation stress, effectively reducing stress concentration inside the stepped foundation structure, and having better anti-slip and anti-overturning capabilities. It can effectively control uneven foundation settlement and optimize stress distribution, and the foundation stress has a better coordination relationship along the transverse bridge direction, avoiding differential settlement and brittle failure. At the same time, this method can be applied to different foundation conditions, is convenient to construct, and also reduces project costs.

[0026] 2. This construction method forms a multi-layered concrete foundation through layered pouring. Based on the structural form of the steps, the concrete is poured in layers. During layered pouring, each layer of the step foundation forms a good horizontal plane, ensuring that the force transmission path remains unchanged. This alters the influence of the arch abutment's weight and allows for adjustable lateral stiffness of the arch abutment, thereby achieving a better force (bending moment) transmission mechanism between the arch abutment and the mountain foundation. This enables a smooth transition between the mountain foundation and the step foundation structure, resulting in good coordination between them. It also reduces differential settlement, saves construction materials, and lowers project costs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the variable stiffness stepped foundation structure of the present invention.

[0028] Figure 2 This is a schematic diagram of another structural form of the variable stiffness stepped foundation structure of the present invention.

[0029] Figure 3 This is a diagram showing the stress distribution at the bottom of the variable stiffness stepped foundation structure of the present invention, obtained from a numerical simulation.

[0030] Figure 4 This is a schematic diagram showing the stress distribution at the bottom of the variable stiffness stepped foundation structure of this invention compared to that of a traditional box-shaped arch foundation.

[0031] Figure 5 This is a schematic diagram illustrating the construction process of the variable stiffness stepped foundation structure of the present invention.

[0032] Marked in the diagram: 1-Slope foundation, 2-First step foundation, 3-Second step foundation, 4-Third step foundation, 5-Arch base foundation, 6-Step corner, 7-Grouting equipment, 8-Data monitoring components, 9-Step foundation, 10-Load application area for arch ribs and junction piers. Detailed Implementation

[0033] The present invention will be further described in detail below through specific embodiments. In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. They should not be construed as limiting the scope of the above subject matter of the present invention to the following embodiments, and should not be used to limit the protection scope of the present invention. All technologies implemented based on the content of the present invention belong to the scope of the present invention.

[0034] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0035] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" or "several" means two or more, unless otherwise explicitly specified.

[0036] Example 1

[0037] Please refer to Figure 1This embodiment provides a variable stiffness stepped foundation structure. The stepped foundation structure matches the side surface shape of the mountain foundation 1. The stepped foundation structure includes a stepped foundation part 9 and an arch foundation part 5. The stepped foundation part 9 includes multiple stepped foundations, and the arch foundation part 5 is located on top of the stepped foundation part 9. The mountain foundation 1 is leveled according to the stepped structure, and then the stepped foundation structure is poured layer by layer from bottom to top along the height direction of the mountain foundation 1. The pouring thickness of each stepped foundation is determined according to the characteristics of the mountain. The sides of each stepped foundation are fitted into the mountain foundation 1 to form the arch foundation. This structure changes the support stiffness of the stepped foundation. This method compensates for uneven stiffness distribution caused by different parts, thereby adjusting and reducing differential settlement, and eliminating uneven foundation stress. It has better resistance to slippage and overturning, effectively controls uneven foundation settlement and optimizes stress distribution. The foundation stress has a better coordination relationship along the transverse direction of the bridge, and can flexibly adjust the stress transfer path between the foundation and the ground. It significantly improves the horizontal force resistance without changing the vertical bearing capacity. The variable stiffness system reduces the stress concentration phenomenon in the foundation and inhibits potential foundation damage and cracking. At the same time, this method is applicable to different foundation conditions, is easy to construct, and reduces project costs.

[0038] In this embodiment, one side of the stepped foundation structure matches the side surface of the mountain foundation 1. The following description uses the cross-section of the mountain foundation 1 as an example. The mountain foundation 1 is a foundation with good conditions, such as a canyon mountain, where the soil strength and hardness are high, or the foundation is made of rock. The side surface of the mountain foundation 1, that is, the side from the center of the mountain foundation 1 to the side edge, is a semi-pit-shaped stepped foundation. This forms a multi-level stepped structure on the side of the mountain foundation 1. The top of each step of the multi-level stepped structure is a horizontal plane, and the slope of the side of each step is 90° to 150°, which can be 90°, 120°, or 150°. This slope is matched with the stepped foundation part 9.

[0039] In this embodiment, the stepped foundation 9 includes several layers of stepped foundations. This embodiment has three layers of stepped foundations. The number of layers is related to the mountain characteristics and structural stress. The maximum shear force and bending moment of the box foundation are at the bottom and boundary positions. By setting a segmented stepped foundation, stress concentration is avoided, and the horizontal shear force sharing ratio is reduced. Therefore, variable stiffness stepped foundations are feasible to a certain extent. However, how to effectively improve the shear force sharing ratio and make the stress transfer between the foundation and the ground more reasonable is still a problem that needs to be studied. Generally, the more steps there are, the stronger the horizontal lateral resistance, but too many steps increase the construction process. The thickness of the above three stepped foundation layers is equal. In other embodiments, this thickness can also be set to non-equal thickness. The top and bottom surfaces of each stepped foundation layer are horizontal planes. One end of all stepped foundation layers extends to the outer edge of the mountain foundation 1, while the other end of all stepped foundation layers matches the multi-level stepped structure on the side surface of the mountain foundation. Because the thickness of the stepped foundation 9 gradually decreases from the side edge of the mountain foundation 1 to the center of the mountain, the stepped foundation structure gradually changes thickness from the center to the edge through the ends of all the stepped foundations, forming a variable stiffness foundation form that corresponds to the deformation shape of the mountain. The internal stress of the foundation is uniform, the structure is simple, and it plays a significant role in regulating the deformation of the foundation. The layered stepped foundation has a good anti-slip effect. Since its resistance to horizontal forces is uneven, the top step plays the main role. In actual construction, the strength of the material on the back of the top step is ensured to ensure the structural stress.

[0040] In this embodiment, the specific configuration of the stepped foundation is as follows: the stepped foundation part 9 includes a first stepped foundation 2, a second stepped foundation 3, and a third stepped foundation 4. The first stepped foundation 2 is located at the bottom of the second stepped foundation 3, and the second stepped foundation 3 is located at the bottom of the third stepped foundation 4. The first stepped foundation 2, the second stepped foundation 3, and the third stepped foundation 4 are progressively longer in the direction of increasing height. The length of each stepped foundation is equal. In other embodiments, the length of the length may be unequal. Since all the stepped foundations extend horizontally on the side facing the edge of the mountain foundation 1, all the stepped foundations form a stepped shape on the side facing the mountain foundation 1. The concave part formed by the stepped structure matches the stepped part of the multi-level stepped structure on the side surface of the mountain foundation. The stepped part formed by the stepped structure matches the concave part formed by the multi-level stepped structure on the side surface of the mountain foundation. They fit together in this way, and the end of each stepped foundation corresponds to a step. When each step foundation bears external loads, it will not only generate downward and backward translational motions, but also determine the effective foundation size in contact with the bedrock surface through foundation stress transfer. The entire load borne by the arch foundation is converted into forces and moments at the center of gravity of the foundation, and the stress distribution of each step base and the horizontal resistance on the back side are obtained. Considering the contribution of the horizontal resistance on the redistribution of base stress, the settlement difference can be reduced by adjusting the stiffness. If the stiffness of the mountain foundation 1 is distributed as soft in the front and hard in the back, the high stress zone of the foundation will shift backward, which is beneficial to the overall stability of the slope.

[0041] In this embodiment, the step angle 6 is the included angle formed by the end of the protruding part of each step structure of the step foundation. The size of the step angle 6 of each step foundation is 90 to 150°. This angle value is achieved in conjunction with the concrete material grade. The step angle value is determined according to the slope of the mountain foundation. By changing the material strength at different locations of the step foundation structure, the step foundation structure has different lateral stiffness. Once the angle value and concrete material parameters are determined, the step foundation structure has only a unique stiffness characteristic. However, according to the change in the size of the angle value, the variable stiffness characteristic can be achieved, and the stiffness of the step foundation can be flexibly adjusted during the construction process. The side slope of the steps and the step turning angle 6 are two different concepts. The step turning angle 6 is the turning angle on the plane, while the slope refers to the inclination of the steps. The side slope of the first step at the end of all layers of the step foundation structure is 90-150°. This slope setting matches the multi-level step structure of the mountain foundation 1, ensuring that each layer of the step foundation fits snugly with the corresponding step structure of the mountain foundation 1, that is, the slope of the step foundation matches the slope of the mountain foundation. The setting of this side slope is related to the characteristics of the mountain, including the type of rock and soil, slope angle, and the stress characteristics of the arch abutment, including the arch bridge configuration and the position of the center of gravity of the arch abutment. Based on the characteristics of the mountain and the stress characteristics of the arch abutment, the stress distribution of each step is calculated, and the turning angle value of each layer is determined. Specifically, the stress distribution of the step foundation structure is obtained through numerical simulation. The step foundations with different side slopes form the overall step foundation part 9 and provide horizontal resistance and bearing capacity. The variable stiffness characteristics can be adjusted according to the size of the step turning angle value.

[0042] In this embodiment, the arch base portion 5 is located on top of the step base portion 9. The arch base portion 5 is block-shaped. One end of the arch base portion 5 fits into the side surface of the mountain foundation. Since the mountain foundation in this embodiment has a vertical surface in the middle, one end of the arch base portion 5 is designed to be vertically flush and perfectly matches the aforementioned middle part of the mountain foundation. The other end of the arch base extends to the end of the uppermost step foundation. This end of the arch base is designed as an inclined surface, and the top of the arch base is designed as a horizontal plane, which provides a horizontal support surface for the arch base. In other embodiments, the arch base portion 5 can be designed as a structure that is wide at the bottom and narrow at the top, such as when the longitudinal section of the arch base is trapezoidal. Figure 2 .

[0043] In this embodiment, the foundation is made of concrete. The stepped foundation 9 is formed by pouring concrete in layers, with each stepped foundation constituting one layer. The arch abutment foundation 5 is a separate layer. Based on the characteristics of the arch bridge and the foundations 1 of the mountains on both sides, the stress distribution of the arch abutment can be calculated. The number of steps can be adjusted according to the slope and layering of the foundation 1 of the mountains. The layering pouring situation can be determined according to the stress characteristics of the arch abutment, thus adapting to different foundations 1 of the mountains. The strength grade of the concrete ranges from C40 to C80. If concrete with strengths of C40, C50, C60, C70, and C80 is used, each strength grade is determined according to the stress characteristics of the arch abutment. Different strength grades are used for different arch abutments. Then, the strength grade of the poured concrete is adjusted, and finally, concrete of different strength grades is poured in layers to adapt to different structural stresses, thus making it suitable for different foundation conditions. In this embodiment, low-strength concrete is used on the side closer to the mountain foundation in each stepped foundation, while high-strength concrete is used on the side closer to the outer edge of the mountain foundation. Specifically, three grades of concrete, C40, C60, and C80, are used: C40 on the side closer to the mountain foundation, C80 on the side closer to the outer edge of the mountain foundation, and C60 in the middle. In this embodiment, each stepped foundation is divided into three equal sections, each using one of the three different strengths of concrete. Considering that the mountain foundation 1 is also a stepped structure, this method of setting different concrete strengths at different locations can effectively avoid uneven stress at the arch abutment and the inability of the inner concrete to exert its compressive effect effectively. At the same time, the project cost is significantly reduced due to the reduction in concrete usage.

[0044] In this embodiment, a data monitoring component 8 is also provided. The data monitoring component 8 includes several stress sensors and several settlement monitoring sensors. The stress sensors are stress-sensitive sensors, and the settlement monitoring sensors are displacement-sensitive sensors. The stress sensors and settlement monitoring sensors are located at the bottom of the step foundation 9, between the mountain foundation 1 and the step foundation structure. Stress sensors are installed on the sides of the step foundation 9, and settlement monitoring sensors are installed on the surface of the mountain foundation. The data monitoring component 8 is connected to a data acquisition system and a PC. The PC monitors the data from each sensor, the stress sensors monitor the base stress at the bottom of the step foundation structure, and the settlement monitoring sensors monitor the structural deformation values. Based on the feedback from these findings, the stress distribution of the structure is determined, thereby analyzing the stress level and vertical settlement at each monitoring point and accurately assessing the actual bearing capacity of the step foundation structure.

[0045] In this embodiment, the stepped foundation structure is analyzed using ABAQUS numerical simulation. Considering the worst-case scenario, only the rear 1 / 3 of the mountain foundation 1 rests on moderately weathered rock, while the remaining portion rests on strongly weathered rock. Since the mountain foundation and loads are both symmetrical, to simplify the calculation, only the left side is modeled and calculated, with a symmetrical boundary set for the cross-section. Rock mass parameters are referenced from geological survey data, concrete parameters from relevant specifications, and loads are applied to the arch ribs and junction piers in area 10 based on data provided in the structural design. The stress distribution at the bottom of the stepped foundation structure in this embodiment is obtained based on the numerical simulation as follows: Figure 3 As shown in the figure, the left side of the figure represents the center of the mountain foundation, and the right side represents the edge of the mountain foundation. The high-stress zone (the area with base stress greater than 1 MPa) has shifted approximately 5 meters backward, and the range of the high-stress zone has decreased. The stress distribution at the bottom of the traditional box-shaped arch foundation and the stepped arch foundation of this invention are shown below. Figure 4 As shown, the stress distribution characteristics of the traditional box-shaped arch foundation are: the stress gradually increases from the front end to the rear end of the arch foundation, and the stress distribution of the base is uneven. However, the stress distribution of the base of the stepped foundation structure in this embodiment is more consistent from front to back along the steps. The calculation results show that the base stiffness has a deformation coordination effect on the base stress, and the stress distribution characteristics between the mountain foundation 1 and the stepped foundation structure can be well transitioned. In addition, the reduction in foundation thickness leading to the reduction in foundation weight and the change in the center of gravity is also one of the reasons for the change in base stress distribution. The stress distribution at the bottom of the stepped foundation structure in this embodiment is more uniform. This result is beneficial to the static and dynamic stability requirements of the arch, and the stability of the structure is also better under dynamic (earthquake) conditions.

[0046] Example 2

[0047] Please refer to Figure 5 This embodiment provides a construction method for a variable stiffness stepped foundation structure, used for casting and forming the variable stiffness stepped foundation structure in Embodiment 1. The construction method includes the following steps:

[0048] S1. Excavation of the mountain foundation 1, which includes the canyon mountain and the foundation soil with high strength and hardness, or the rock foundation. This construction method requires that the terrain of the mountain foundation 1 should not be too steep, and that the slope cutting work can be carried out, so as to form a foundation that matches the stepped foundation structure. First, the excavation level surface of the mountain foundation 1 is determined according to the geological survey data, and multiple layers to be excavated are divided. Then, the mountain foundation 1 is excavated layer by layer from top to bottom to form the side surface of the mountain foundation 1 with a multi-level stepped structure. The number of layers in the multi-level stepped structure is determined according to the characteristics of the mountain, the slope of the mountain, the stress area, etc. When there are more layers, the corresponding stepped foundation structure has better variable stiffness control ability. The top surface of each stepped structure is horizontal and flat, and the side slope of each stepped structure is 90 to 150°.

[0049] S2. Support formwork, concrete is poured into the space corresponding to the step foundation 9 through grouting equipment 7 to form the first layer of concrete foundation. After hardening and forming, the next layer of concrete foundation is poured, and so on to form the multi-layer concrete foundation step foundation 9. Each layer of concrete foundation corresponds to one layer of step foundation. Under the condition of meeting the bearing capacity of the foundation, by setting a reasonable number of step foundations and controlling the angle of the step turn 6, the stress sharing coefficient of each layer of foundation is changed, which is a variable stiffness means to realize the stress transfer between the step foundation structure and the mountain foundation 1. The arch bridge forces borne by the stepped foundation structure generally extend along the arch axis. For a homogeneous and regularly shaped arch seat, the stress point is inclined downward along the center of gravity. However, under this condition, the pressure area on the side of the arch seat near the mountain foundation is large, while the pressure area on the side near the water is small, resulting in uneven stress distribution in the arch seat. This construction method forms a multi-layered concrete foundation by pouring concrete in layers. According to the structural form of the steps, the concrete is poured in layers. When pouring concrete in layers, each layer of the step foundation 9 forms a good horizontal plane, so that the force transmission path of each layer does not change, thereby changing the influence of the weight of the arch seat and realizing the adjustable lateral stiffness of the arch seat.

[0050] S3. Finally, the arch foundation 5 is poured on top of the step foundation 9. The arch foundation 5 plays a key role as the direct support part of the arch. After the pouring is completed, stress sensors and settlement monitoring sensors are placed at the bottom of the step foundation 9 and between the mountain foundation 1 and the step foundation structure. Specifically, settlement monitoring sensors are set at the bottom of the step foundation 9, and stress sensors are set at the contact position between the mountain foundation 1 and the step foundation structure. The sensors can be inserted into the structural gaps. The arrangement of the sensors is the existing conventional method.

[0051] The above process uses a grouting device 7 for pouring concrete. The grouting device 7 is the main part for controlling the thickness of the layered step foundation. The through-hole support formwork acts as a retaining element. Concrete is poured into the space enclosed by the support formwork. After hardening, a layer of step foundation is formed. Then, the next layer of step foundation and the final arch foundation 5 are poured.

[0052] This construction method enables a better force (bending moment) transmission mechanism between the arch abutment and the mountain foundation 1, allowing for a smooth transition between the mountain foundation 1 and the step foundation structure. The mountain foundation 1 and the step foundation structure form a good coordination effect, reducing differential settlement. This construction method is particularly effective in regulating the deformation of the mountain foundation 1, avoiding differential settlement and brittle failure of the foundation, while also saving construction materials and reducing project costs.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A variable stiffness stepped foundation structure, wherein the stepped foundation structure matches the side surface shape of the mountain foundation, characterized in that, It includes a stepped foundation section and an arch base section. The arch base section is located on top of the stepped foundation section. The arch base section is block-shaped, and the top of the arch base is used to provide a horizontal support surface for the arch base. The stepped foundation section includes several layers of stepped foundations. All layers of stepped foundations extend to the outer edge of the mountain foundation. The stepped foundations increase in length layer by layer in the direction of increasing height, and all layers of stepped foundations form a step shape on the side facing the mountain foundation. The end of each layer of stepped foundations corresponds to a step. The thickness of the foundation of the steps gradually decreases from the side edge of the mountain foundation to the center of the mountain; The thickness of the entire stair base varies at each step along the height.

2. The variable stiffness stepped foundation structure according to claim 1, characterized in that, The foundation of the steps is formed by pouring concrete in layers.

3. The variable stiffness stepped foundation structure according to claim 2, characterized in that, In each of the aforementioned step foundations, low-strength concrete is used on the side closer to the mountain foundation, and high-strength concrete is used on the side closer to the outer edge of the mountain foundation.

4. The variable stiffness stepped foundation structure according to claim 3, characterized in that, The strength grade range of the concrete is C40 to C80.

5. The variable stiffness stepped foundation structure according to claim 1, characterized in that, The step angle of each step foundation is 90~150°.

6. The variable stiffness stepped foundation structure according to claim 1, characterized in that, The side slope of the first step at the end of the foundation of all layers of the steps is 90~150°.

7. The variable stiffness stepped foundation structure according to any one of claims 1-6, characterized in that, It also includes a data monitoring component, which includes several stress sensors and several settlement monitoring sensors. The settlement monitoring sensors and the stress sensors are respectively located at the bottom of the step foundation and between the mountain foundation and the step foundation structure.

8. A construction method for a variable stiffness stepped foundation structure, used for casting and forming the variable stiffness stepped foundation structure according to any one of claims 1-7, characterized in that, Including the following steps: S1. Excavate the mountain foundation to form the foundation of the stepped foundation structure; S2. Support formwork, concrete is poured into the space corresponding to the step foundation part through grouting equipment to form the first layer of concrete foundation. After hardening and shaping, the next layer of concrete foundation is poured, and so on to form the multi-layer concrete foundation step foundation part, with each layer of concrete foundation corresponding to one layer of step foundation. S3. Finally, pour the arch foundation portion on top of the step foundation portion.

9. The construction method for the variable stiffness stepped foundation structure according to claim 8, characterized in that, S1 includes: The excavation and leveling surface of the mountain foundation is determined, and multiple layers to be excavated are divided. The mountain foundation is excavated layer by layer from top to bottom to form a multi-level stepped structure of the mountain foundation side surface. The top surface of each step structure is horizontal and flat, and the side slope of each step structure is 90~150°.

10. The construction method of the variable stiffness stepped foundation structure according to claim 8, characterized in that, The method also includes the step of: placing the settlement monitoring sensor and the stress sensor at the bottom of the step foundation and between the mountain foundation and the step foundation structure, respectively.

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