Photovoltaic support column pile for expansive soil field

Abstract

The utility model discloses a photovoltaic support column pile for an expansive soil site, which comprises a column pile embedded in the ground, the upper end of the column pile is higher than the ground and is provided with a steel support member, and the steel support member is provided with an oblique beam for fixedly installing a photovoltaic assembly; the column pile is an integrated column body with the upper diameter and the lower diameter equal, the column pile is divided into three connected parts from top to bottom, namely a photovoltaic support stand column section, a pile foundation section influenced by expansive force and a pile foundation anchoring section in sequence, the photovoltaic support stand column section is located above the ground, and the pile foundation section influenced by the expansive force is located at the position from the ground to the atmospheric influence rapid layer bottom elevation. The pile foundation anchoring section is located below the atmospheric influence rapid layer bottom elevation; a coating made of industrial vaseline or residual oil is arranged on the outer side of the pile foundation section affected by expansive force. According to the scheme, measures are simple and convenient, material cost is low, engineering materials, construction labor and transportation cost are saved, meanwhile, the buried pile length of the column pile is greatly reduced, the length of the column pile is greatly optimized, and the construction period of expansive soil treatment is greatly shortened.

Description

Technical Field

[0001] This utility model belongs to the field of solar photovoltaic power generation technology, and specifically relates to a photovoltaic support column for expansive soil sites. Background Technology

[0002] In photovoltaic (PV) power plants, PV support structures are steel brackets used to support PV modules. The single-column type is one of the earliest forms of fixed PV support systems, and its proportion in fixed support systems has been increasing in recent years due to the large-scale implementation of agricultural-photovoltaic, forestry-photovoltaic, and fishery-photovoltaic complementary projects. A single-column PV support system consists of steel components such as purlins, diagonal beams, and diagonal braces that directly support the PV modules, as well as a single column.

[0003] The length of the exposed portion of the photovoltaic support column is generally determined by the process layout requirements and the connection requirements of the photovoltaic support, while its underground length is determined based on the load it bears and the soil and rock conditions of the site. For expansive soil sites, the underground pile length must not only resist external loads but also resist the effects of expansion and contraction forces generated by the soil and rock within the rapidly influencing atmospheric layer to avoid pile foundation instability.

[0004] Currently, it is generally necessary to increase the length of anchor piles, leading to a significant increase in pile length. For photovoltaic support pile foundations with low loads and short pile lengths, this increase is considerable. Therefore, in expansive soil sites, due to the influence of the expansive soil's expansion force, the pile length is usually controlled by the pile foundation's pull-out stability. Since photovoltaic supports are very lightweight, and the pull-out force in the main operating condition is large, and the combined external load of soil and rock at a rapidly increasing atmospheric depth has an adverse effect, the increase in pipe pile length after considering pull-out stability calculations is staggering. For piles numbering in the tens or hundreds of thousands, this will significantly increase the project cost.

[0005] Optimizing pile length can be achieved by replacing the pile perimeter with non-expansive materials such as sand and gravel, chemically modifying the soil, and setting up a moisture barrier layer. These methods are all quite complicated to implement. Taking the main method of replacing the pile perimeter with non-expansive materials as an example, the area around the pile needs to be excavated after the pile is driven. Considering the large number of piles, the workload is enormous. From the perspective of construction difficulty, excavation after construction can easily affect the pile body. Therefore, construction needs to be slow and meticulous, and the cycle will be long. Moreover, the amount of engineering work involved in purchasing replacement materials and transporting the replaced expansive soil is huge, especially in areas with a sharp impact on the atmosphere and deep layers, where the economic cost is enormous. Utility Model Content

[0006] The technical problem to be solved by this utility model is to provide a photovoltaic support column for expansive soil sites, which solves the problems of high cost and long construction period of photovoltaic support in expansive soil sites. It realizes the simple and effective optimization of the buried pile length of photovoltaic support column in expansive soil sites, thereby optimizing the total pile length. It is safe and reliable, and the construction is simple and fast, and can achieve better economic indicators.

[0007] According to the technical solution of this utility model, this utility model provides a photovoltaic support column for expansive soil sites, including a column buried in the ground, the upper end of the column being higher than the ground and equipped with a steel support member, and an inclined beam for fixing and installing photovoltaic modules on the steel support member; the column is a single column of equal diameter at both ends, and the column is divided into three connected parts from top to bottom, namely, a photovoltaic support column section, a pile foundation section affected by expansive force, and a pile foundation anchoring section. The photovoltaic support column section is located above the ground, the pile foundation section affected by expansive force is located from the ground to the bottom elevation of the layer with the steepest atmospheric influence, and the pile foundation anchoring section is located below the bottom elevation of the layer with the steepest atmospheric influence; an industrial petroleum jelly or residual oil coating is applied to the outside of the pile foundation section affected by expansive force.

[0008] In some implementations, the piles are prestressed concrete pipe piles.

[0009] In some implementations, the outer side of the photovoltaic support column section is in direct contact with the atmosphere.

[0010] In some implementations, the pile, steel support, and inclined beam form a single-column photovoltaic support system that integrates the pile and column.

[0011] In some implementations, the length of the pile segment affected by the expansion force is 1.35m to 2.25m.

[0012] Compared with the prior art, the beneficial technical effects of this utility model are as follows:

[0013] This utility model relates to photovoltaic support piles for expansive soil sites. Lubricating material is applied to the outer wall of the pile only at specific locations within the atmospheric impact zone. This coating reduces the expansion and contraction forces exerted on the pile by the soil and rock within the atmospheric impact zone, thereby reducing the required anchor pile length and optimizing the total pile length. The method is very simple, the materials are readily available and extremely low-cost, saving on engineering materials, labor, and transportation costs while significantly reducing the buried pile length and optimizing the pile length, thus greatly shortening the construction cycle for expansive soil treatment. The design calculations are reliable, the improvement in bearing conditions is clearly measurable, and the original force transmission mode and path of the photovoltaic support pile structure are not altered. It is safe, effective, and offers considerable economic benefits. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the photovoltaic support column structure provided by this utility model.

[0015] Explanation of reference numerals in the attached figures:

[0016] 1. Column piles; 2. Steel support components; 3. Photovoltaic modules; 4. Inclined beams; 5. Photovoltaic support column section; 6. Pile foundation section affected by expansion force; 7. Pile foundation anchorage section. Detailed Implementation

[0017] This utility model provides a photovoltaic support column for expansive soil sites, belonging to the field of solar photovoltaic power generation technology, specifically relating to photovoltaic support foundations in photovoltaic power stations. The purpose of this utility model is to find a simple and effective way to optimize the buried pile length of photovoltaic support columns in expansive soil sites, thereby optimizing the total pile length. The calculation method also needs to be simple and clear, with effective design basis, safe and reliable, while being easy and quick to construct and achieving good economic optimization results. The main concept of this utility model's typical solution is: in expansive soil sites, a coating is applied to the atmospheric influence layer of the single-column photovoltaic support pile body to reduce the pull-out force of the soil and rock acting on the pile foundation, thereby optimizing the pile length. This utility model adopts a photovoltaic support column design that is easy to process, uses readily available and conventional materials, and is extremely easy to construct with low labor costs. It effectively reduces the pile length of photovoltaic support columns in expansive soil sites, significantly saving project costs while reducing construction difficulty and shortening the construction period, achieving considerable economic benefits. It is particularly suitable for high-thickness expansive soil sites and large-capacity photovoltaic projects.

[0018] Please see Figure 1 This utility model discloses a photovoltaic support column for expansive soil sites, comprising a column 1 buried in the ground, the upper end of the column 1 being higher than the ground and equipped with a steel support member 2, and an inclined beam 4 for fixing and installing photovoltaic modules 3 on the steel support member 2. The column 1 is a single column with equal diameter at both ends, preferably a prestressed concrete pipe pile. The column 1 is divided into three connected parts from top to bottom (i.e., the single column 1 is divided into three sections): a photovoltaic support column section 5, a pile foundation section 6 affected by expansion force, and a pile foundation anchoring section 7. The photovoltaic support column section 5 is located above the ground (in other words, the exposed part), the pile foundation section 6 affected by expansion force is located from the ground to the bottom elevation of the layer with the steepest atmospheric influence, and the pile foundation anchoring section 7 is located below the bottom elevation of the layer with the steepest atmospheric influence. An industrial petroleum jelly or residual oil coating is applied to the outside of the pile foundation section 6 affected by expansion force to reduce the expansion and contraction force on the pile foundation, thereby reducing the length of the lower pile foundation anchoring section and ultimately optimizing the overall pile length.

[0019] Photovoltaic (PV) support structures bear loads such as their own weight, wind, snow, and earthquakes. When assembled, these loads generate tensile or compressive forces and corresponding horizontal forces that act on the supporting piles. The exposed length of the PV support column is determined by the process layout requirements and the connection requirements of the PV support structure. Its underground length is determined based on the load it bears and the site's soil and rock conditions. In expansive soil sites, the buried pile length must resist not only external loads but also the expansion and contraction forces generated by the soil and rock within the abrupt atmospheric influence layer. That is, when the soil expands, the soil and rock generate pull-out forces. The soil within the abrupt atmospheric influence layer (e.g., 1.35m~2.25m) not only cannot resist external loads but also, together with the external load, pushes the pile foundation outwards. This pull-out force may cause pile instability. To counteract this effect, the anchor pile length needs to be increased, resulting in a significant increase in pile length. For PV support pile foundations with relatively low loads and short pile lengths, this increase is considerable. Therefore, in expansive soil sites, due to the influence of the expansive soil's expansion force, the pile length is usually controlled by the pile foundation's pull-out stability. Because photovoltaic (PV) support structures are very lightweight, and the pull-out force under the main operating conditions is large, coupled with the adverse effects of combined soil and rock loads at depths of the atmospheric influence layer, the increase in pile length after considering pull-out stability calculations is staggering. For piles numbering in the tens or hundreds of thousands, this would significantly increase project costs. Existing solutions, such as backfilling around the piles and soil improvement, are all quite complex and labor-intensive, especially in areas with deep atmospheric influence layers, where the economic costs are enormous.

[0020] The basic principle of this utility model is as follows: by applying industrial petroleum jelly or residual oil to the depth of the atmospheric influence layer (i.e., the area affected by the expansive force of the pile foundation), the surface state of the pile in this layer is altered, changing the friction conditions between the pile and the soil. This reduces the expansive shear force acting on the pile foundation, thereby reducing the expansive force of the expansive soil and thus minimizing the impact on the pile foundation. This reduces the required length of the lower anchorage section of the pile foundation, ultimately optimizing the total pile length. Preferably, when using this structure, no other auxiliary structures are needed; the outer side of the photovoltaic support column section 5 is directly in contact with the atmosphere, making it simpler and easier to implement.

[0021] In the specific implementation, the pile 1, steel support 2, and inclined beam 4 form a single-column photovoltaic support system integrating pile and column. The length of the pile foundation section 6, affected by expansion force, can be taken as 1.35m to 2.25m when no relevant professional data is available based on observation. The lengths of the photovoltaic support column section 5 and the pile foundation anchoring section 7 can be determined through design calculations.

[0022] In summary, the advantages of the photovoltaic support column of this utility model are: simple construction, low labor cost, short construction period, low cost, simple and reliable stress conditions, clear force transmission path, easy-to-obtain and inexpensive materials, and the ability to significantly optimize the buried pile length of photovoltaic support columns in expansive soil sites, especially in sites with deep atmospheric influence layers, thereby effectively reducing the total pile length, reducing the difficulty of pile driving construction, shortening the construction period, and significantly reducing project costs.

[0023] Based on the basic structure of the photovoltaic support column of this utility model, this utility model also provides a design method for photovoltaic support columns for expansive soil sites. The photovoltaic support column includes a column 1 buried in the ground. The column 1 is divided into three connected parts from top to bottom: a photovoltaic support column section 5, a pile foundation section 6 affected by expansive force, and a pile foundation anchoring section 7. The photovoltaic support column section 5 is located above the ground, the pile foundation section 6 affected by expansive force is located from the ground to the bottom elevation of the layer with the most rapid atmospheric influence, and the pile foundation anchoring section 7 is located below the bottom elevation of the layer with the most rapid atmospheric influence. Industrial petroleum jelly or residual oil is applied to the outside of the pile foundation section 6 affected by expansive force.

[0024] The design method for photovoltaic support columns for expansive soil sites includes the following steps.

[0025] Step S1: Determine the photovoltaic support structure layout based on site policy conditions and process layout, and calculate the external load on the pile foundation according to the actual layout of the photovoltaic support structure based on the site's natural climate conditions and site conditions. This step is existing technology, and relevant provisions exist in current specifications. In short, sites typically have policy requirements restricting the row and column spacing of piles and the lowest point of the modules. The pile spacing is determined based on these policy requirements. The structural layout is determined according to the wind and snow pressure conditions with a 50-year return period, based on the string arrangement of the modules in the process, and the external load on the pile foundation is obtained through software calculation.

[0026] Step S2: Determine the length L1 of the photovoltaic support column section 5 exposed above the ground of the pile 1 according to the arrangement of the photovoltaic support. This step is also an existing design step. Considering factors such as economy and construction convenience, and combining the actual arrangement of the support steel components determined in step S1 with the calculation results, determine the length L1 of the photovoltaic support column section 5, that is, the height of the column part of the upper structure that is also the exposed part of the pile foundation.

[0027] Step S3: Determine the depth of the atmospheric impact layer based on the actual site conditions, specifically provided by geological survey data, thereby determining the length L2 of the pile foundation segment 6 affected by expansion force that needs to be coated with industrial petroleum jelly or residual oil, so that the required coating can be formed during construction.

[0028] Step S4: In section 6 of the pile foundation affected by expansion force, consider the shear stress of the soil and rock after applying industrial petroleum jelly or residual oil to the pile. Refer to the "Code for Design of Building Foundations in Frozen Soil Areas." The shear stress can be reduced to 40% of the original shear stress on the pile foundation surface after application. The ultimate shear stress of each layer of soil and rock in the original site's atmospherically affected layer is q. ei After application, the ultimate shear stress of each layer of soil and rock can be reduced to 0.4q. ei Therefore, the total pull force generated in the original L2 range changes from the original uΣq ei l ei It becomes 0.4uΣq after reduction. ei l ei Among them, the depth of the atmospheric influence layer is numerically equal to L2, which is equal to Σl. ei .

[0029] Step S5: The length L3 of the pile foundation anchorage section 7 is initially determined, thereby initially determining the overall pile length of the column pile 1. The overall pile length is the sum of L1, L2, and L3.

[0030] Based on the aforementioned determined external loads, shear stress, and actual soil and rock conditions, the length of the conventional pile foundation anchorage section is determined according to the foundation bearing capacity calculation. Photovoltaic support structures have many different working condition combinations. When calculating the foundation bearing capacity, the loads determined for different combinations are calculated separately based on the maximum pressure and maximum pull-out force. Due to the contribution of end bearing during compression and the fact that the soil's side friction compressive strength is greater than its pull-out strength, and given the relatively large pull-out force on the photovoltaic support structure, the pull-out condition usually plays a controlling role. Unlike general light buildings, photovoltaic support structures frequently experience upward wind loads. Based on the structural characteristics of the photovoltaic support structure and the aforementioned actual reduction conditions, corresponding calculations of the pull-out foundation bearing capacity of the photovoltaic pile foundation are required. The photovoltaic support piles are all considered as non-integral failures; once the layout is determined, the numerical values ​​of the parameters used in the calculations are unique. The physical and mechanical properties of each soil and rock layer on site are also fixed. Therefore, the reduction of the ultimate shear stress in the layer with the most significant atmospheric influence can significantly reduce uΣλ. i q sik l i The value of Σl is used to reduce the pile length Σl below the layer of abrupt atmospheric influence. i The length L3 is determined based on the load and actual site soil and rock conditions. For photovoltaic support pile foundations, in general, when calculating the bearing capacity of the foundation in expansive soil sites, the tensile bearing capacity is more likely to be controlled than the compressive bearing capacity. However, the compressive bearing capacity of the foundation is also necessary to be calculated as a step. The combined pressure is usually greater than the tensile force because the tensile force is only generated by wind load, while self-weight, snow load, maintenance load, etc. are all compressive forces. Due to the coating of section L2, the effect on the side friction of the foundation is bidirectional, and the corresponding compressive bearing capacity calculation formula needs to be adjusted (refer to the negative skin friction formula for soil shrinkage conditions).

[0031] Specifically, the length L3 of the pile foundation anchorage section 7 is initially determined through the following steps S51 to S54.

[0032] Step S51: Determine the length L31 of the pile anchorage section under the maximum pull-out force calculation condition using the following formula:

[0033] ,

[0034] ,

[0035] ,

[0036] ;

[0037] In the formula, u is the circumference of the pile body. In this scheme, u = πd, where d is the diameter of the uniform-diameter pile (the pre-determined pile diameter), and q ei For the ultimate shear stress of the i-th soil layer in the layer of rapid atmospheric influence, l ei N represents the thickness of the i-th soil layer in the layer of rapid atmospheric influence. wk T represents the standard value of the upward wind load. Uk The standard value of the ultimate tensile bearing capacity of a column pile in a stable soil layer below a layer of soil with rapidly increasing atmospheric influence when the failure is not integral. (N) G For the weight of the photovoltaic support structure and its components borne by the foundation pile, G P For the self-weight of the foundation pile, λ i q is the pull-out coefficient. sik The standard value of the ultimate compressive lateral resistance of the i-th soil layer on the pile side surface below the layer with rapid atmospheric influence is given by l. i The thickness of the i-th soil layer below the pile side, which is affected by atmospheric conditions.

[0038] The maximum pressure is further divided into two cases: normal working conditions and soil shrinkage working conditions.

[0039] Step S52, determine the length L32 of the pile anchorage section under normal compression conditions using the following formula:

[0040] ,

[0041] ,

[0042] ,

[0043] ;

[0044] In the formula, N k Let Q be the average vertical force of the pile under the standard combination of load effects and axial vertical force. Uk Q represents the standard value of the vertical ultimate bearing capacity of a single pile. skQ is the standard value of the total ultimate lateral resistance of a single pile. pk q represents the standard value of the total ultimate end resistance of a single pile. pk A is the standard value of the limiting end resistance. P This represents the area at the pile tip.

[0045] Step S53: Determine the length L33 of the pile anchorage section under the soil shrinkage condition under compression using the following formula:

[0046] ,

[0047] ,

[0048] ,

[0049] ;

[0050] In the formula, q esi Q represents the limiting contraction tangential force of the atmospheric influence layer. UUk Q represents the standard value of the vertical ultimate bearing capacity of a single pile under a layer with rapid atmospheric influence. sUk This represents the standard value of the total ultimate side resistance of a single pile in a layer with abrupt atmospheric influence.

[0051] Step S54: Based on the pile foundation anchorage section lengths L31, L32, and L33 calculated in steps S51 to S53 under the three working conditions, the maximum value is taken (i.e., the longest length calculated under the three working conditions) and determined as the initially determined length L3 of the pile foundation anchorage section 7.

[0052] Step S6: The overall pile length determined in Step S5 is checked based on the stability and deformation conditions of the pile foundation. If the conditions are not met, the length L3 of the pile foundation anchorage section 7 is adjusted (generally by increasing the length L3 of the pile foundation anchorage section 7), and Step S6 is repeated until the overall pile length that meets the specifications is determined. The specific verification method is based on existing technology. In short, the pile foundation length calculation includes bearing capacity calculation (compression and pull-out) (Step S5), stability calculation (mainly for horizontal forces), and deformation calculation. After stability and deformation calculations, the pile length may be increased. In areas without special soil conditions, the pile length determined by the foundation bearing capacity usually does not determine the final pile length.

[0053] Step S7: Based on the overall pile length determined after review in Step S6, further calculate the pile strength using the load design value to determine the appropriate pile type, thus completing the column-pile design work. This step is existing technology, where pile type refers to the model, such as the specific amount of reinforcing steel.

[0054] In summary, this utility model has the following beneficial technical effects: The application of lubricating material to the outer wall of the photovoltaic support piles is simple, requiring only a specific location within the depth range of the atmospheric impact layer. It eliminates the need for excavation and backfilling, and avoids the large-scale purchase of various materials to improve soil properties, such as backfill materials and waterproofing materials. The materials are readily available and extremely low-cost, saving on engineering materials, labor, and transportation costs while significantly reducing the buried pile length (depth of penetration), greatly optimizing pile length, drastically shortening the construction cycle for expansive soil treatment, and significantly reducing project costs. Furthermore, the design calculations are based on reliable, standardized verification of material performance, and the improvement in bearing capacity is clearly measurable. It does not alter the original force transmission mode and path of the photovoltaic support pile structure, ensuring safety, effectiveness, and considerable economic benefits. It is particularly suitable for photovoltaic power station projects with limited site conditions, tight schedules, and a large number of piles, especially for large-capacity photovoltaic projects with deep atmospheric impact layers and high expansion levels.

[0055] In particular, the present invention has the following key features.

[0056] Key point 1: By setting the coating, the pulling force of the soil and rock within the layer on the pipe pile is reduced due to the influence of the atmosphere, thereby reducing the anchor pile length required for pull-out resistance and achieving the goal of optimizing the total pile length.

[0057] Key Point 2: The only measures required are to apply industrial petroleum jelly or residual oil to specific locations on the piles. The materials used are inexpensive, readily available, and easy to procure. The process is simple, requires little labor, and has low construction costs.

[0058] Key Point 3: The measures taken are the changes to the contact surface between concrete and soil recommended by relevant structural codes, which are proven surface treatment methods, and the surface condition correction factors used are effective and reliable.

[0059] Key Point 4: The depth of the atmospheric influence layer is usually 1.35m~2.25m. In this range, the soil and rock in the soil expansion state have a harmful effect on the pile foundation. Reducing this range to 40% means that the harmful effect that needs to be resisted has been reduced by 60% of the original value. This can effectively optimize the effective anchor pile length required for stability, thereby significantly reducing the construction difficulty of pile driving and reducing the construction period while reducing the project cost.

[0060] Key Point 5: This solution does not change the original force transmission mode and path of the photovoltaic support column structure. It only appropriately reduces the soil and rock friction within the scope of the measures. The calculation method is simple, clear and measurable.

[0061] Key point 6: No post-excavation is required, which greatly reduces the amount of excavation work and avoids the possibility of damage to the pile foundation during construction after pile driving.

[0062] Key Point 7: No need to purchase large quantities of replacement materials, significantly reducing backfilling workload and shortening construction period.

[0063] Key Point 8: No need for a large amount of replacement fill material and transportation of the replaced expansive soil for soil improvement.

[0064] Key Point 9: Significantly reduces the construction period and cost of expansive soil treatment measures.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and not to limit it; obviously, the described embodiments are some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model; for ease of description, only the parts related to the utility model are shown in the accompanying drawings. In the absence of conflict, the embodiments and features in the embodiments of this utility model can be combined with each other; modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions for some of the technical features, do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model.

Claims

1. A photovoltaic support column for expansive soil sites, characterized in that, It includes a pile (1) buried in the ground, the upper end of the pile (1) is higher than the ground and is equipped with a steel support (2), and the steel support (2) is equipped with an inclined beam (4) for fixing the photovoltaic module (3); the pile (1) is a column with equal diameter at the top and bottom, and the pile (1) is divided into three connected parts from top to bottom, namely the photovoltaic support column section (5), the pile foundation section affected by expansion force (6) and the pile foundation anchoring section (7). The photovoltaic support column section (5) is located above the ground, the pile foundation section affected by expansion force (6) is located at the ground level to the bottom elevation of the layer with rapid atmospheric influence, and the pile foundation anchoring section (7) is located below the bottom elevation of the layer with rapid atmospheric influence; an industrial petroleum jelly or slag oil coating is provided on the outside of the pile foundation section affected by expansion force (6).

2. The photovoltaic support column for expansive soil sites according to claim 1, characterized in that, The column pile (1) is a prestressed concrete pipe pile.

3. The photovoltaic support column for expansive soil sites according to claim 1, characterized in that, The outer side of the photovoltaic support column section (5) is in direct contact with the atmosphere.

4. The photovoltaic support column for expansive soil sites according to claim 1, characterized in that, The column pile (1), steel support member (2) and inclined beam (4) form a single-column photovoltaic bracket integrating the pile and column.

5. The photovoltaic support column for expansive soil sites according to claim 1, characterized in that, The length of the pile foundation segment (6) affected by the expansion force is 1.35m to 2.25m.

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