Concrete crack control method during manufacturing of immersed tube joint

Abstract

The invention relates to a concrete crack control method during manufacturing of an immersed tube joint, which is characterized in that a pre-cast section and a post-cast strip of the immersed tube joint are cast in a full-section casting manner, so that the construction efficiency can be improved, and meanwhile, cracks caused by vertical layering are reduced; the crack control requirement is obtained by obtaining the stress influence of the waterproof bottom steel plate on the two poured adjacent pre-pouring sections, then control indexes of control parameters are determined according to the crack control requirement, full-section pouring process construction organization arrangement is conducted, then immersed tube joints are manufactured, and the construction quality of the immersed tube joints is improved. According to the mode, the restraining effect of the post-cast strip waterproof bottom steel plate on the two adjacent pre-cast sections can be considered, the better crack control effect can be achieved, the full-section interval pouring immersed tube section concrete crack control method is provided, the whole-section pouring technology of the supporting integral type immersed tube section is provided, high-quality prefabrication of the immersed tube section is guaranteed, and the construction efficiency is improved. And meanwhile, the immersed tube joint prefabricating efficiency is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of immersed tube segment manufacturing, in particular to a method for controlling concrete cracks when manufacturing immersed tube segments. Background Art

[0002] Existing immersed tube sections are divided into segmental immersed tube sections and integral immersed tube sections. The length of segmental immersed tube sections is generally about 20m. Adjacent segmental immersed tube sections are connected by immersed tube joints, so there is no need to consider the problem of cracking at the joints of immersed tube sections too much; while the length of integral immersed tube sections is about 100m. At present, most immersed tube tunnels at home and abroad are integral immersed tube sections. Because the integral immersed tube sections are relatively long, the integral immersed tube sections are divided into several sections for prefabrication. The sections generally adopt a layered casting process, and post-cast strips are set between the sections. The problem of concrete cracking is a common problem of immersed tube tunnels, especially at the layered casting construction joints, post-cast strips and segment construction joints, so the concrete of the integral immersed tube sections is prone to cracking.

[0003] The existing segmental immersed tube segments adopt the full-section casting process, which effectively reduces the number of vertical construction joints and achieves better crack control effect. The full-section casting process can be promoted and applied to the prefabrication of integral immersed tube segments with its technical advantages to reduce the number of vertical construction joints, but there is little relevant technical experience.

[0004] The integral immersed tube segment adopts the full-section interval casting process and faces new technical problems. The bottom of the integral immersed tube segment is equipped with a waterproof bottom steel plate. Generally, a full-length continuous construction method is adopted, and the steel bars of the post-cast strip can be continuously disconnected, resulting in the restraint effect of the waterproof bottom steel plate and the steel bars of the post-cast strip between the first-cast sections, which can easily lead to concrete cracking in the first-cast section. At the same time, the crack control needs of the full-section casting of the first-cast section and the post-cast strip must also be considered. At present, there is no relevant research at home and abroad, and there is a lack of crack control methods for full-section interval casting of integral immersed tube segments. Summary of the invention

[0005] The purpose of the present invention is to provide a method for controlling concrete cracks when manufacturing immersed tube segments, in view of the fact that a waterproof bottom steel plate is provided at the bottom of the integral immersed tube segment in the prior art, and a continuous construction method is generally adopted, which results in the restraining effect of the waterproof bottom steel plate of the post-cast strip between the first-cast segments, and the problem of easily causing concrete cracks in the first-cast segments.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for controlling concrete cracks when manufacturing an immersed tube segment, wherein the immersed tube segment comprises a pre-cast section and a post-cast strip, wherein the pre-cast section is longer than the post-cast strip, and the post-cast strip is located between two adjacent pre-cast sections;

[0008] First, two adjacent pre-cast sections are cast. At this time, a waterproof bottom steel plate is arranged along the entire length of the bottom of the immersed tube section at the bottom of the area where the post-cast strip to be cast is located. Then, the post-cast strip between the two adjacent pre-cast sections that have been cast is cast.

[0009] The first pouring section and the post pouring strip of the immersed tube segment are cast by full section casting;

[0010] The concrete crack control method includes the following steps:

[0011] S1. Clarify the crack control requirements, which include controlling the stress effect of the waterproof bottom steel plate on the two adjacent pre-cast sections that have been cast;

[0012] S2. According to the crack control requirements, the control indicators of the control parameters are clarified through finite element and specification calculations;

[0013] S3. Arrange the construction organization of the full-section pouring process according to the control indicators of the control parameters;

[0014] S4. Produce immersed tube segments according to the construction organization arrangement of the full-section casting process.

[0015] The method for controlling concrete cracks when making immersed tube segments of the present invention adopts the full-section casting method to cast both the first pouring section and the post-pouring strip of the immersed tube segment, which can improve construction efficiency and reduce cracking caused by vertical stratification. The crack control requirement is obtained by obtaining the stress influence of the waterproof bottom steel plate on the two adjacent first pouring sections that have been cast, and then the control index of the control parameter is clarified according to the crack control requirement, and the full-section casting process construction organization arrangement is carried out, and then the immersed tube segment is made. This method can take into account the restraining effect of the waterproof bottom steel plate of the post-pouring strip on the two adjacent first pouring sections, and can achieve better crack control effect. A method for controlling concrete cracks of immersed tube segments by full-section interval casting is proposed, which supports the full-section casting process of the integral immersed tube segment, ensures high-quality prefabrication of the immersed tube segment, and greatly improves the prefabrication efficiency of the immersed tube segment.

[0016] Preferably, in step S1, the crack control requirement includes four control stages when the first pouring section is made, and the four control stages when the first pouring section is made are:

[0017] During the first concrete full-section pouring process of the first pouring section, the first concrete mix ratio and the first inter-layer pouring gap of the first pouring section are controlled to control the first concrete stress to be less than the concrete standard tensile strength;

[0018] In the early stage after the first concrete of the first pouring section is poured on the entire section, under the control of the first concrete mix ratio, by controlling the first curing temperature and humidity of the first pouring section, the stress generated by the temperature difference between the inside and outside of the first concrete is controlled to be less than the standard tensile strength of the concrete;

[0019] In the middle period after the first concrete of the first pouring section is poured on the whole section, under the control of the first concrete mix ratio and the first curing temperature and humidity, the first demoulding time of the first pouring section is controlled, and the first concrete stress is less than the standard tensile strength of concrete when the temperature difference between the inside and outside of the first concrete, the deadweight of the first concrete, and the constraint of the waterproof bottom steel plate at the bottom of the post-casting belt are controlled;

[0020] In the later stage after the first concrete of the first pouring section is poured in full section, by controlling the length design of the post-cast strip before the first concrete of the first pouring section is poured in full section and the first concrete mix ratio, the first concrete stress is controlled to be less than the specified tensile strength of concrete when the restraint effect of the waterproof bottom steel plate at the bottom of the post-cast strip is controlled.

[0021] Preferably, in step S2, the control parameters include the internal and external temperature difference required for the production of the first pouring section, the first concrete strength development curve, the first interlayer pouring gap, the restraint stress, the deadweight action node and the volume shrinkage; the control parameters also include the internal and external temperature difference required for the production of the post-casting strip, the second concrete strength development curve, the second interlayer pouring gap and the volume shrinkage;

[0022] In step S3, the first concrete mix ratio and the first curing temperature and humidity are designed according to the internal and external temperature difference required for the production of the first pouring section, the first concrete strength development curve and the control index of the volume shrinkage;

[0023] Design the first inter-layer pouring gap and the first demoulding time according to the first concrete mix ratio, and the first demoulding time is used as the deadweight action node;

[0024] Design the second concrete mix ratio and the second curing temperature and humidity according to the internal and external temperature difference required for the production of the post-casting strip, the second concrete strength development curve and the control index of the volume shrinkage;

[0025] Design the second inter-layer pouring gap and the second demoulding time according to the second concrete mix ratio;

[0026] The construction organization arrangement of the full-section pouring process is carried out according to the segmentation of immersed tube sections, the first concrete mix ratio, the second concrete mix ratio, the first inter-layer pouring gap, the second inter-layer pouring gap, the first curing temperature and humidity, the second curing temperature and humidity, the first demolding time and the second demolding time;

[0027] In step S4, the production of the immersed tube segment includes the installation of the waterproof bottom steel plate, the production of the pre-cast section and the production of the post-cast strip, and the casting area of ​​the pre-cast section and the post-cast strip is determined according to the length of the post-cast strip;

[0028] When making the immersed tube segment: first install the waterproof bottom steel plate, then make the pre-cast section on the waterproof bottom steel plate; make the post-cast strip after the two adjacent pre-cast sections are made;

[0029] The production of the first pouring section includes pouring, curing and demolding. The first concrete poured in the first pouring section adopts the first concrete mix ratio. The first concrete poured in the first pouring section adopts the full-section pouring method of layered advancement. The pouring time difference between layers is the first inter-layer pouring gap. The first pouring section is cured according to the first curing temperature and humidity. The first pouring section is demolded according to the first demolding time.

[0030] The production of the post-cast joint includes pouring, curing and demolding. The second concrete poured in the post-cast joint adopts the second concrete mix ratio. The second concrete poured in the post-cast joint adopts the full-section pouring method of layered advancement. The pouring time difference between layers is the second inter-layer pouring gap. The post-cast joint is cured according to the second curing temperature and humidity, and the post-cast joint is demolded according to the second demolding time.

[0031] Preferably, in step S3, the length of the post-cast strip is obtained, and the first stress of the waterproof bottom steel plate on the two adjacent pre-cast sections before the post-cast strip is cast is determined as the constraint stress according to the length of the post-cast strip, and the internal and external temperature difference, the first concrete strength development curve and the control index of the volume shrinkage required for the production of the pre-cast section and the internal and external temperature difference, the second concrete strength development curve and the control index of the volume shrinkage required for the production of the post-cast strip are determined according to the first stress.

[0032] Preferably, in step S3, after obtaining the length of the post-cast strip, the second stress of the waterproof bottom steel plate and the longitudinal steel bar as a whole on the two adjacent pre-cast sections before the post-cast strip is cast is determined as the constraint stress according to the length of the post-cast strip, and the internal and external temperature difference, the first concrete strength development curve and the control index of the volume shrinkage required for the production of the pre-cast section and the internal and external temperature difference, the second concrete strength development curve and the control index of the volume shrinkage required for the production of the post-cast strip are determined according to the second stress;

[0033] In step S4, before pouring the first concrete of the pre-cast section, the longitudinal reinforcements of the pre-cast section and the post-cast strip are stretched and arranged.

[0034] Preferably, the internal and external temperature difference, the second concrete strength development curve and the volume shrinkage required for the production of the post-cast strip are determined according to the measured volume shrinkage after the production of two adjacent pre-cast sections.

[0035] Preferably, the early period after the first concrete full section pouring is within 3 days after the first concrete full section pouring;

[0036] The mid-term period is 3-10 days after the first concrete full-section pouring;

[0037] The late period after the first concrete full section pouring is 10 days after the first concrete full section pouring.

[0038] Preferably, the concrete strength development curves of the first concrete strength development curve and the second concrete strength development curve: the compressive strength of the first concrete strength and the second concrete strength on the third day is controlled to be above 20 MPa, and the compressive strength of the first concrete strength and the second concrete strength on the seventh day is controlled to be above 35 MPa;

[0039] The temperature difference between the first concrete and the second concrete should be controlled within 15℃;

[0040] The first curing temperature and humidity and the second curing temperature and humidity: temperature ≥ 30°C, humidity ≥ 85%;

[0041] The gap between the first concrete layer and the second concrete layer should be controlled within 4 hours;

[0042] First, the transverse volume shrinkage of concrete: controlled within 400με;

[0043] Length of post-pouring strip: not less than 1.2m.

[0044] Preferably, the first concrete mix design includes: obtaining a first concrete mix design scheme by adjusting the water-cement ratio and the water reducing agent content, and conducting indoor and field tests according to the first concrete mix design scheme to verify whether the first concrete strength development curve, the internal and external temperature difference, and the lateral volume shrinkage meet the control index requirements;

[0045] Obtaining the volume shrinkage of two adjacent first-cast sections under the action of hydration heat and shrinkage of the first concrete as the second concrete volume deformation control amount of the post-cast zone;

[0046] The mix ratio of the second concrete is optimized according to the control amount of the second concrete volume deformation of the post-cast zone;

[0047] The second concrete mix design includes: obtaining a second concrete mix design scheme by adding an expansive agent, and conducting indoor and field tests based on the second concrete mix design scheme to verify whether the second concrete strength development curve, internal and external temperature difference, and lateral volume shrinkage meet the control index requirements.

[0048] Preferably, the second concrete mix design includes:

[0049] Determine the control requirements based on the transverse volume shrinkage of the first pouring section: the expansion agent’s 40-day deformation control capability is above 300με;

[0050] Carry out indoor tests to analyze the influence of expansion agent type and content on lateral volume shrinkage and select reasonable expansion agent.

[0051] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0052] The method for controlling concrete cracks when making immersed tube segments of the present invention adopts the full-section casting method to cast both the first pouring section and the post-pouring strip of the immersed tube segment, which can improve construction efficiency and reduce cracking caused by vertical stratification. The crack control requirement is obtained by obtaining the stress influence of the waterproof bottom steel plate on the two adjacent first pouring sections that have been cast, and then the control index of the control parameter is clarified according to the crack control requirement, and the full-section casting process construction organization arrangement is carried out, and then the immersed tube segment is made. This method can take into account the restraining effect of the waterproof bottom steel plate of the post-pouring strip on the two adjacent first pouring sections, and can achieve better crack control effect. A method for controlling concrete cracks of immersed tube segments by full-section interval casting is proposed, which supports the full-section casting process of the integral immersed tube segment, ensures high-quality prefabrication of the immersed tube segment, and greatly improves the prefabrication efficiency of the immersed tube segment. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a schematic diagram of the construction of full-section interval casting of integral immersed tube segments;

[0054] Figure 2 This is the elevation drawing of the full-section interval pouring construction of the integral immersed tube segment;

[0055] Figure 3 The stress of the first pouring section changes with time;

[0056] Figure 4 This is a schematic diagram of the layered advancement of full-section pouring;

[0057] Figure 5 This is the stress cloud diagram of the full-section cast bottom plate;

[0058] Figure 6 This is the analysis diagram of the influence of the inter-layer pouring gap on the stress of the first pouring section;

[0059] Figure 7 This is the stress cloud diagram of the first pouring section under the constraint of the waterproof bottom steel plate of the post-cast zone;

[0060] Figure 8 This is the stress diagram of the waterproof bottom steel plate of the post-cast zone on the pre-cast section;

[0061] Fig. 9 This is the demoulding time analysis chart;

[0062] Fig.10 This is the technical roadmap for controlling cracking of the first concrete in the first pouring section;

[0063] Fig.11 It is the development curve of transverse volume deformation of the first pouring section;

[0064] Fig.12 It is the volume deformation development curve of the post-cast zone concrete expansion agent;

[0065] Fig.13 This is an analysis diagram of the effect of curing temperature on the volume deformation of the expansion agent;

[0066] Fig.14 This is an analysis diagram of the effect of curing humidity on the volume deformation of the expansion agent;

[0067] Fig.15 It is a technical roadmap for crack control of post-cast concrete;

[0068] Fig.16 It is a schematic diagram of the crack control stage;

[0069] Fig.17 This is the experimental diagram of compressive strength of the first concrete of the first pouring section;

[0070] Fig.18 This is the temperature test diagram of the first concrete in the pouring section.

[0071] Icons: 1- immersed tube section; 2- first pouring section; 3- post pouring strip; 31- longitudinal reinforcement; 32- waterproof bottom steel plate. DETAILED DESCRIPTION

[0072] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0073] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0074] Example 1

[0075] The integral pipe segment full-section interlayer gap casting process is adopted to make the immersed pipe segment: the integral immersed pipe segment 1 is divided into several pre-casting sections 2, and a post-casting strip 3 is set between two adjacent pre-casting sections 2. The length of the pre-casting section 2 is greater than the post-casting strip 3. The longitudinal steel bars 31 at the post-casting strip 3 can be kept connected, and the waterproof bottom steel plate 32 is continuous throughout the length. The pre-casting section 2 and the post-casting strip are all cast in full section. Figure 1 , Figure 2 As shown. Casting sequence: first cast two adjacent precast sections 2, at this time, the bottom of the area where the postcast strip to be cast is located has a waterproof bottom steel plate 32 set along the bottom of the immersed tube segment 1, or a waterproof bottom steel plate 32 and a longitudinal steel bar 31; then cast the postcast strip 3 between the two adjacent precast sections 2 that have been cast; the precast section 2 and the postcast strip 3 of the immersed tube segment are cast by full-section casting;

[0076] This embodiment provides a method for controlling concrete cracks when manufacturing immersed tube segments. Fig.10 As shown, the concrete crack control method includes the following steps:

[0077] S1. Clarify the crack control requirements, which include controlling the stress influence of the waterproof bottom steel plate 32, or the waterproof bottom steel plate 32 and the longitudinal steel bar 31 on the two adjacent pre-cast sections 2 that have been cast;

[0078] For the first pouring section 2, it is divided into 4 stages according to the first concrete pouring time. The causes of cracks in each stage are considered as follows:

[0079] ① During the full-section pouring of the first concrete in the first pouring section 2: the first concrete is poured in a full-section manner in layers, and the pouring time difference between layers is the first inter-layer pouring gap. The first inter-layer pouring gap and the first concrete mix ratio affect the crack generation at this stage.

[0080] ② In the early stage after the first concrete of the first pouring section 2 is poured on the entire section: the formwork is not removed, the strength of the first concrete develops rapidly, and the hydration heat reaction is intense, resulting in a large temperature difference between the inside and outside. The temperature difference between the inside and outside affects the formation of cracks at this stage.

[0081] ③ In the middle period after the first concrete of the first pouring section 2 is poured, the template is removed, the strength growth rate of the first concrete gradually decreases, and the temperature difference between the inside and outside gradually decreases. The deadweight of the first pouring section 2, the temperature difference between the inside and outside of the first concrete, and the constraint of the waterproof bottom steel plate 32 at the post-casting zone to be poured all affect the crack generation at this stage;

[0082] ④ In the later stage after the first concrete of the first pouring section 2 is poured in full section, the formwork has been removed, the first concrete has a relatively large strength, and the constraint of the waterproof bottom steel plate 32 at the pouring zone becomes the main factor affecting the cracking of the concrete.

[0083] In a preferred embodiment, in step S1, crack control requirements include four control stages when the first casting section 2 is made, such as Fig.16 As shown, the four control stages during the production of the first pouring section 2 are:

[0084] Stage ①: During the first concrete full-section pouring process of the first pouring section 2, the first concrete mix ratio and the first inter-layer pouring gap of the first pouring section 2 are controlled, and the first concrete stress is controlled to be less than the standard tensile strength of concrete to ensure that the concrete does not crack;

[0085] Stage ②, in the early stage after the first concrete of the first pouring section 2 is poured, under the control of the first concrete mix ratio, by controlling the first curing temperature and humidity of the first pouring section 2, the stress generated by the temperature difference between the inside and outside of the first concrete is controlled to be less than the standard tensile strength of the concrete, so as to ensure that the concrete does not crack; preferably, the early stage after the first concrete is poured is within 3 days after the first concrete is poured;

[0086] Specifically: adjusting the water-cement ratio can change the first concrete strength development curve and hydration heat temperature, and combined with the control of the first curing temperature and humidity, the temperature difference between the surface and the center of each part of the immersed tube segment can be controlled;

[0087] Stage ③, in the middle period after the first concrete full section pouring of the first pouring section 2, under the control of the first concrete mix ratio and the first curing temperature and humidity, the first demoulding time of the first pouring section 2 is controlled, and the first concrete stress is less than the standard tensile strength of the concrete when the temperature difference between the inside and outside of the first concrete, the deadweight of the first concrete, and the constraint of the waterproof bottom steel plate 32 at the bottom of the post-casting belt act together, so as to ensure that the concrete does not crack; preferably, the middle period after the first concrete full section pouring is 3-10 days after the first concrete full section pouring;

[0088] Stage ④, the later period after the first concrete full section of the first pouring section 2 is poured, by controlling the length design of the post-casting strip 3 before the first concrete full section of the first pouring section 2 and the first concrete mix ratio, the first concrete stress is controlled to be less than the concrete standard tensile strength when the restraining effect of the waterproof bottom steel plate 32 at the bottom of the post-casting strip is controlled, ensuring that the concrete does not crack. In this process, the lateral volume shrinkage of the first pouring section 2 is controlled by the first concrete mix ratio. Specifically, the admixture content, such as the water reducing agent content, is adjusted to control the volume shrinkage of the first concrete. Preferably, the later period after the first concrete full section is poured is 10 days after the first concrete full section is poured.

[0089] S2. According to the crack control requirements, the control indicators of the control parameters are clarified through finite element and specification calculations;

[0090] In step S2, the control parameters include the internal and external temperature difference required for the production of the first pouring section 2, the first concrete strength development curve, the first interlayer pouring gap, the restraint stress, the deadweight action node and the volume shrinkage; the control parameters also include the internal and external temperature difference required for the production of the post-casting strip 3, the second concrete strength development curve, the second interlayer pouring gap and the volume shrinkage;

[0091] In the early stage after concrete pouring, the strength gradually increases with the hydration heat reaction. The hydration heat reaction will cause the internal and external temperature difference of each part of the immersed tube segment. When the internal and external temperature difference is high and the concrete strength is insufficient, it is easy to cause concrete cracking. The concrete strength development curve is selected as a concrete crack control parameter; the concrete strength development curve is a curve in which the strength of the first concrete gradually increases with the hydration heat reaction in the early stage after the pouring of the first concrete. The first concrete strength development curve and the second concrete strength development curve are the concrete strength development curves of the first concrete and the second concrete, respectively.

[0092] In the early stage after concrete pouring, the concrete has not yet reached sufficient strength, and the large temperature difference between inside and outside can easily cause concrete cracking, such as Figure 3As shown. The internal and external temperature difference is selected as a concrete crack control parameter; the internal and external temperature difference is the internal and external temperature difference of each part of the immersed tube segment 1 when the concrete has not yet reached sufficient strength in the early stage of the first concrete pouring;

[0093] The first pouring section 2 and the post-pouring zone 3 both adopt the full-section pouring method of "slope layering, natural flow, continuous advancement, and one-time top". Figure 4 As shown in the figure, the interlayer casting gap makes the interlayer contact surface have a certain restraint stress. At this time, the concrete strength is low, and the interlayer casting gap is large, which is easy to cause concrete cracking. Figure 5 , Figure 6 As shown. The interlayer pouring gap is selected as a concrete crack control parameter; the interlayer pouring gap is the time gap for the layered pouring of the first pouring section 2; the first interlayer pouring gap is the interlayer pouring gap of the first pouring section 2, and the second interlayer pouring gap is the interlayer pouring gap of the post-casting zone 3;

[0094] The volume of the immersed tube segment is generally shrunk by the shrinkage of concrete and the temperature drop of hydration heat. The first pouring section 2 is prone to cracks when it is constrained by the waterproof bottom steel plate of the post-casting belt, or the waterproof bottom steel plate and the unbroken steel bars 32. The restraint stress of the post-casting belt is determined by the volume shrinkage of the immersed tube segment and the degree of restraint of the post-casting belt, such as Figure 7 , Figure 8 As shown. The post-casting belt restraint stress is selected as a concrete crack control parameter; the post-casting belt restraint stress is jointly determined by the volume shrinkage of the immersed tube segment 1 and the restraint degree of the post-casting belt 3, and the post-casting belt 3 restraint includes the waterproof bottom steel plate 32 set along the bottom of the immersed tube segment 1; the post-casting belt 3 restraint may also include the unbroken steel bar 31 of the post-casting belt 3, and the unbroken steel bar 31 is set along the length of the immersed tube segment 1.

[0095] When the immersed tube segment is demolded, its own weight begins to affect the stress of the immersed tube segment. If the demolding is too early and the concrete has not yet reached sufficient strength, the combined effect of the self-weight and hydration heat can easily cause the top plate of the immersed tube segment to crack. Fig. 9 The self-weight action time point is selected as a concrete crack control parameter; the self-weight action time point is the time point of demoulding after the first concrete pouring.

[0096] S3. Arrange the construction organization of the full-section pouring process according to the control indicators of the control parameters;

[0097] According to the control index of the restraint stress of the post-casting belt, the length of the post-casting belt 3 is selected to control the restraint effect of the post-casting belt 3 on the pre-casting section 2;

[0098] In step S3, the length of the post-cast strip 3 is obtained, and the first stress of the waterproof bottom steel plate 32 on the two adjacent pre-cast sections 2 before the post-cast strip 3 is cast is determined as the constraint stress according to the length of the post-cast strip 3. The internal and external temperature difference, the first concrete strength development curve and the control index of the volume shrinkage required for the production of the pre-cast section 2 and the internal and external temperature difference, the second concrete strength development curve and the control index of the volume shrinkage required for the production of the post-cast strip 3 are determined according to the first stress. In this embodiment, the pre-cast section 2 and the post-cast strip 3 do not use the longitudinal steel bars 31 set through;

[0099] In step S3, the first concrete mix ratio and the first curing temperature and humidity are designed according to the internal and external temperature difference required for the production of the first pouring section 2, the first concrete strength development curve and the control index of the volume shrinkage; that is, the first concrete strength development curve is fast, the hydration heat temperature is low and the volume shrinkage is low; that is, through the design of the first concrete mix ratio, a concrete mix ratio with fast strength development, low hydration heat temperature and low volume shrinkage is sought.

[0100] Optionally, the first concrete mix design includes: obtaining a first concrete mix design scheme by adjusting the water-cement ratio and the water reducing agent content, and conducting indoor and field tests according to the first concrete mix design scheme to verify whether the strength development curve, the internal and external temperature difference, and the lateral volume shrinkage of the first concrete meet the control index requirements;

[0101] After obtaining the first concrete mix ratio, design the first inter-layer pouring gap and the first demolding time according to the first concrete mix ratio, and use the first demolding time as the node for deadweight action; full-section pouring process: make reasonable construction organization arrangements, shorten the full-section pouring time, optimize the pouring sequence, and control the pouring gap between layers, especially the pouring intervals between the bottom plate, side wall, and top plate.

[0102] like Fig.15 As shown, the second concrete crack control method of the post-cast zone includes the following steps:

[0103] Design the second concrete mix ratio and the second curing temperature and humidity according to the internal and external temperature difference required for the production of the post-casting strip 3, the second concrete strength development curve and the control index of the volume shrinkage;

[0104] The volume shrinkage of the two adjacent first-cast sections 2 under the action of the first concrete hydration heat and shrinkage is obtained as the second concrete volume deformation control amount of the post-cast zone 3, such as Fig.11 As shown;

[0105] The mix ratio of the second concrete is optimized and designed according to the second concrete volume deformation control amount of the post-cast zone 3. The second concrete mix ratio design includes: obtaining a second concrete mix ratio design scheme by adding an expansion agent, and conducting indoor and field tests according to the second concrete mix ratio design scheme to verify whether the second concrete strength development curve, the internal and external temperature difference, and the lateral volume shrinkage meet the control index requirements.

[0106] Preferably, the second concrete mix design includes:

[0107] Determine the control requirements based on the transverse volume shrinkage of the first pouring section: the expansion agent’s 40-day deformation control capability is above 300με;

[0108] Carry out indoor tests to analyze the influence of expansion agent type and content on lateral volume shrinkage and select reasonable expansion agent.

[0109] Adding expansion agent to the second concrete can inhibit shrinkage, and the volume of the second concrete in the post-cast zone can be regulated by optimizing the expansion agent, such as Fig.12 shown.

[0110] Conduct indoor tests to analyze the influence of expansion agent type and content on lateral volume shrinkage and select a reasonable expansion agent. Assume that the three calcium-magnesium composite expansion agents in Table 1 below are selected. 3 ,

[0111] Table 1: Proportion of expansion agent

[0112]

[0113] The test results show that all three types of expansion agents meet the requirement of 40-day deformation control capacity above 300με. CHJ6 and CHJ7 have a large surplus. Considering the economy, CHJ5 is selected.

[0114] The curing process of the second concrete is optimized, and the influence of the curing temperature and humidity of the second concrete of the post-casting strip 3 on the volume deformation of the second concrete of the post-casting strip 3 is controlled, so as to finally realize the regulation of the volume of the second concrete of the post-casting strip 3. The curing temperature and humidity have a great influence on the volume shrinkage of the second concrete. It is preferred to control the volume shrinkage of the post-casting strip concrete by curing temperature and humidity, such as Fig.13 , Fig.14 shown.

[0115] After obtaining the second concrete mix ratio, designing the second inter-layer pouring gap and the second demoulding time according to the second concrete mix ratio;

[0116] The construction organization arrangement of the full-section pouring process is carried out according to the segmentation of immersed tube sections, the first concrete mix ratio, the second concrete mix ratio, the first inter-layer pouring gap, the second inter-layer pouring gap, the first curing temperature and humidity, the second curing temperature and humidity, the first demolding time and the second demolding time;

[0117] Furthermore, the internal and external temperature difference, the second concrete strength development curve and the volume shrinkage required for the production of the post-cast strip 3 are determined according to the measured volume shrinkage after the production of the two adjacent pre-cast sections 2. The internal and external temperature difference, the second concrete strength development curve and the volume shrinkage required for the production of the post-cast strip 3 are determined according to the actual volume shrinkage after the first concrete pouring, which is more in line with reality.

[0118] For example, ① the length design of the post-pouring strip 3: the length of the first pouring section is 15m, and the length of the post-pouring strip is 1.6m, which meets the requirement that the length of the post-pouring strip is not less than 1.2m.

[0119] ② Design of the first concrete mix ratio: By adjusting the water-cement ratio, water reducing agent content, etc., the concrete mix ratio design scheme is obtained, and indoor and field tests are carried out to verify whether the strength development curve, internal and external temperature difference, and lateral volume shrinkage of the first concrete meet the control index requirements. Assume that the first concrete mix ratio is as shown in Table 2 below:

[0120] Table 2: First concrete mix ratio

[0121]

[0122] When the curing temperature is ≥30℃ and the curing humidity is ≥85%, the measured results of the first concrete strength development curve, the internal and external temperature difference, and the lateral volume shrinkage are as follows: Fig.17 , Fig.18 , meeting the requirements of control indicators.

[0123] S4. Produce immersed tube segments according to the construction organization arrangement of the full-section casting process.

[0124] Construction organization arrangement of full-section casting process: the casting time of the first casting section is controlled within 24 hours, and the casting interval between the first layers of the first casting section is controlled within 2 hours, meeting the control requirement of less than 4 hours.

[0125] In step S4, the production of the immersed tube segment 1 includes the installation of the waterproof bottom steel plate 32, the production of the pre-casting section 2 and the production of the post-casting strip 3, and the casting areas of the pre-casting section 2 and the post-casting strip 3 are determined according to the length of the post-casting strip 3;

[0126] When manufacturing the immersed tube segment 1: first install the waterproof bottom steel plate 32, then manufacture the pre-cast segment 2 on the waterproof bottom steel plate 32; manufacture the post-cast strip 3 after the manufacture of two adjacent pre-cast segments 2 is completed;

[0127] The production of the first pouring section 2 includes pouring, curing and demolding. The first concrete poured in the first pouring section 2 adopts the first concrete mix ratio. The first concrete poured in the first pouring section 2 adopts a layered full-section pouring method. The pouring time difference between layers is the first inter-layer pouring gap. The first pouring section 2 is cured according to the first curing temperature and humidity. The first pouring section 2 is demolded according to the first demolding time.

[0128] The production of the post-cast strip 3 includes pouring, curing and demolding. The second concrete poured in the post-cast strip 3 adopts the second concrete mix ratio. The second concrete poured in the post-cast strip 3 adopts a layered full-section pouring method. The pouring time difference between layers is the second inter-layer pouring gap. The post-cast strip 3 is cured according to the second curing temperature and humidity, and the post-cast strip 3 is demolded according to the second demolding time.

[0129] In another embodiment, in step S3, after obtaining the length of the post-cast strip 3, the second stress of the waterproof bottom steel plate 32 and the longitudinal steel bar 31 before the post-cast strip 3 is poured is determined as the constraint stress, and the internal and external temperature difference, the first concrete strength development curve and the control index of the volume shrinkage required for the production of the pre-cast section 2 and the internal and external temperature difference, the second concrete strength development curve and the control index of the volume shrinkage required for the production of the post-cast strip 3 are determined according to the second stress; in this embodiment, the longitudinal steel bar 31 set through the pre-cast section 2 and the post-cast strip 3 is used;

[0130] Design the first concrete mix ratio and the first curing temperature and humidity according to the internal and external temperature difference required for the production of the first pouring section 2, the first concrete strength development curve and the control index of the volume shrinkage;

[0131] Design the first inter-layer pouring gap and the first demoulding time according to the first concrete mix ratio, and the first demoulding time is used as the deadweight action node;

[0132] Design the second concrete mix ratio and the second curing temperature and humidity according to the internal and external temperature difference required for the production of the post-casting strip 3, the second concrete strength development curve and the control index of the volume shrinkage;

[0133] Design the second inter-layer pouring gap and the second demoulding time according to the second concrete mix ratio;

[0134] The construction organization arrangement of the full-section pouring process is carried out according to the segmentation of immersed tube sections, the first concrete mix ratio, the second concrete mix ratio, the first inter-layer pouring gap, the second inter-layer pouring gap, the first curing temperature and humidity, the second curing temperature and humidity, the first demolding time and the second demolding time;

[0135] In step S4 , before pouring the first concrete of the precast section 2 , the longitudinal reinforcements 31 of the precast section 2 and the postcast strip 3 are pulled through and arranged.

[0136] The method for controlling concrete cracks when making immersed tube segments of the present invention, the first pouring section 2 and the post-pouring strip 3 of the immersed tube segment are cast by full-section casting, which can improve construction efficiency and reduce cracking caused by vertical stratification. The crack control requirement is obtained by obtaining the stress influence of the waterproof bottom steel plate 32 on the two adjacent first pouring sections 2 that have been cast, and then the control index of the control parameter is clarified according to the crack control requirement, and the full-section casting process construction organization arrangement is carried out, and then the immersed tube segment is made. This method can take into account the restraining effect of the waterproof bottom steel plate of the post-pouring strip on the two adjacent first pouring sections, and can achieve better crack control effect. It proposes a method for controlling concrete cracks of immersed tube segments by full-section interval casting, supports the full-section casting process of the integral immersed tube segment, ensures high-quality prefabrication of the immersed tube segment, and greatly improves the prefabrication efficiency of the immersed tube segment.

[0137] 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 in the protection scope of the present invention.

Claims

1. A method for controlling concrete cracks when manufacturing an immersed tube segment, wherein the immersed tube segment (1) comprises a pre-cast section (2) and a post-cast strip (3), wherein the pre-cast section (2) is longer than the post-cast strip (3), and the post-cast strip (3) is located between two adjacent pre-cast sections (2); First, two adjacent pre-cast sections (2) are cast, and at this time, a waterproof bottom steel plate (32) arranged along the entire length of the bottom of the immersed tube section (1) is present at the bottom of the area where the post-cast strip to be cast is located; and then, the post-cast strip (3) between the two adjacent pre-cast sections (2) that have been cast is cast; It is characterized in that The first pouring section (2) and the post pouring zone (3) of the immersed tube segment are both poured by a full-section pouring method; The concrete crack control method includes the following steps: S1. Clarify crack control requirements, which include controlling the stress influence of the waterproof bottom steel plate (32) on the two adjacent pre-cast sections (2) that have been cast; S2. According to the crack control requirements, the control indicators of the control parameters are clarified through finite element and specification calculations; S3. Arrange the construction organization of the full-section pouring process according to the control indicators of the control parameters; S4. Produce immersed tube segments according to the construction organization arrangement of the full-section casting process.

2. The method for controlling concrete cracks when manufacturing immersed tube segments according to claim 1 is characterized in that: In step S1, the crack control requirements include four control stages when the first pouring section (2) is made. The four control stages when the first pouring section (2) is made are: During the first concrete full-section pouring process of the first pouring section (2), the first concrete mix ratio and the first inter-layer pouring gap of the first pouring section (2) are controlled to control the first concrete stress to be less than the concrete standard tensile strength; In the early stage after the first concrete of the first pouring section (2) is poured on the entire section, under the control of the first concrete mix ratio, the first curing temperature and humidity of the first pouring section (2) are controlled to control the stress generated by the temperature difference between the inside and outside of the first concrete to be less than the standard tensile strength of the concrete; In the middle period after the first concrete of the first pouring section (2) is poured on the entire section, under the control of the first concrete mix ratio and the first curing temperature and humidity, the first demoulding time of the first pouring section (2) is controlled, and the first concrete stress is controlled to be less than the concrete standard tensile strength when the temperature difference between the inside and outside of the first concrete, the deadweight of the first concrete, and the constraint of the waterproof bottom steel plate (32) at the bottom of the post-casting zone act together; In the later stage after the first concrete full section of the first pouring section (2) is poured, by controlling the length design of the post-casting strip (3) before the first concrete full section of the first pouring section (2) is poured and the first concrete mix ratio, the first concrete stress is controlled to be less than the concrete standard tensile strength when the restraining effect of the waterproof bottom steel plate (32) at the bottom of the post-casting strip is controlled.

3. The method for controlling concrete cracks when manufacturing immersed tube segments according to claim 2 is characterized in that: In step S2, the control parameters include the internal and external temperature difference required for the production of the first pouring section (2), the first concrete strength development curve, the first interlayer pouring gap, the restraining stress, the deadweight action node and the volume shrinkage; the control parameters also include the internal and external temperature difference required for the production of the post-casting strip (3), the second concrete strength development curve, the second interlayer pouring gap and the volume shrinkage; In step S3, the first concrete mix ratio and the first curing temperature and humidity are designed according to the internal and external temperature difference required for the production of the first pouring section (2), the first concrete strength development curve and the control index of the volume shrinkage; Design the first inter-layer pouring gap and the first demoulding time according to the first concrete mix ratio, and the first demoulding time is used as the deadweight action node; Design the second concrete mix ratio and the second curing temperature and humidity according to the internal and external temperature difference required for the production of the post-casting strip (3), the second concrete strength development curve and the control index of the volume shrinkage; Design the second inter-layer pouring gap and the second demoulding time according to the second concrete mix ratio; The construction organization arrangement of the full-section pouring process is carried out according to the segmentation of immersed tube sections, the first concrete mix ratio, the second concrete mix ratio, the first inter-layer pouring gap, the second inter-layer pouring gap, the first curing temperature and humidity, the second curing temperature and humidity, the first demolding time and the second demolding time; In step S4, the production of the immersed tube segment (1) includes the installation of the waterproof bottom steel plate (32), the production of the pre-cast section (2) and the production of the post-cast strip (3), and the casting areas of the pre-cast section (2) and the post-cast strip (3) are determined according to the length of the post-cast strip (3); When manufacturing the immersed tube segment (1), the waterproof bottom steel plate (32) is first installed, and then the precast section (2) is manufactured on the waterproof bottom steel plate (32); the postcast strip (3) is manufactured after the two adjacent precast sections (2) are manufactured. The production of the first pouring section (2) includes pouring, curing and demolding. The first concrete poured by the first pouring section (2) adopts a first concrete mix ratio. The first concrete poured by the first pouring section (2) adopts a layered full-section pouring method. The pouring time difference between layers is a first inter-layer pouring gap. The first pouring section (2) is cured according to a first curing temperature and humidity. The first pouring section (2) is demolded according to a first demolding time. The production of the post-cast strip (3) includes pouring, curing and demolding. The second concrete poured in the post-cast strip (3) adopts the second concrete mix ratio. The second concrete poured in the post-cast strip (3) adopts a layered full-section pouring method. The pouring time difference between layers is the second inter-layer pouring gap. The post-cast strip (3) is cured according to the second curing temperature and humidity. The post-cast strip (3) is demolded according to the second demolding time.

4. The method for controlling concrete cracks when manufacturing immersed tube segments according to claim 3 is characterized in that: In step S3, the length of the post-cast strip (3) is obtained, and the first stress of the waterproof bottom steel plate (32) before the post-cast strip (3) is cast on the two adjacent pre-cast sections (2) is determined as the constraint stress according to the length of the post-cast strip (3). The internal and external temperature difference, the first concrete strength development curve and the control index of the volume shrinkage required for the production of the pre-cast section (2) and the internal and external temperature difference, the second concrete strength development curve and the control index of the volume shrinkage required for the production of the post-cast strip (3) are determined according to the first stress.

5. The method for controlling concrete cracks when manufacturing immersed tube segments according to claim 4, characterized in that: In step S3, after obtaining the length of the post-cast strip (3), the second stress of the waterproof bottom steel plate (32) and the longitudinal steel bar (31) before the post-cast strip (3) is cast on the two adjacent pre-cast sections (2) is determined as a constraint stress according to the length of the post-cast strip (3), and the internal and external temperature difference, the first concrete strength development curve and the control index of the volume shrinkage required for the production of the pre-cast section (2) and the internal and external temperature difference, the second concrete strength development curve and the control index of the volume shrinkage required for the production of the post-cast strip (3) are determined according to the second stress; In step S4, before pouring the first concrete of the pre-cast section (2), the longitudinal steel bars (31) of the pre-cast section (2) and the post-cast strip (3) are pulled through and arranged.

6. The method for controlling concrete cracks when manufacturing immersed tube segments according to claim 5, characterized in that: The internal and external temperature difference, the second concrete strength development curve and the volume shrinkage required when making the post-casting strip (3) are determined according to the measured volume shrinkage after the two adjacent pre-casting sections (2) are made.

7. The method for controlling concrete cracks when manufacturing immersed tube segments according to any one of claims 2 to 6, characterized in that: The early period after the first concrete full section pouring is within 3 days after the first concrete full section pouring; The mid-term period is 3-10 days after the first concrete full-section pouring; The late period after the first concrete full section pouring is 10 days after the first concrete full section pouring.

8. The method for controlling concrete cracks when manufacturing immersed tube segments according to claim 7, characterized in that: Concrete strength development curve of the first concrete strength development curve and the second concrete strength development curve: the compressive strength of the first concrete strength and the second concrete strength on the 3rd day is controlled above 20MPa, and the compressive strength of the first concrete strength and the second concrete strength on the 7th day is controlled above 35MPa; The temperature difference between the first concrete and the second concrete should be controlled within 15℃; The first curing temperature and humidity and the second curing temperature and humidity: temperature ≥ 30°C, humidity ≥ 85%; The gap between the first concrete layer and the second concrete layer should be controlled within 4 hours; First, the transverse volume shrinkage of concrete: controlled within 400με; Length of post-cast strip (3): not less than 1.2m.

9. The method for controlling concrete cracks when manufacturing immersed tube segments according to claim 8, characterized in that: The first concrete mix design includes: obtaining the first concrete mix design scheme by adjusting the water-cement ratio and the water reducing agent content, and conducting indoor and field tests according to the first concrete mix design scheme to verify whether the first concrete strength development curve, the internal and external temperature difference, and the lateral volume shrinkage meet the control index requirements; Obtaining the volume shrinkage of two adjacent first-cast sections (2) under the action of the hydration heat and shrinkage of the first concrete as the second concrete volume deformation control amount of the post-cast zone (3); performing an optimal design of the mix ratio of the second concrete according to the second concrete volume deformation control amount of the post-cast zone (3); The second concrete mix design includes: obtaining a second concrete mix design scheme by adding an expansive agent, and conducting indoor and field tests based on the second concrete mix design scheme to verify whether the second concrete strength development curve, internal and external temperature difference, and lateral volume shrinkage meet the control index requirements.

10. The method for controlling concrete cracks when manufacturing immersed tube segments according to claim 9, characterized in that: The second concrete mix design includes: Determine the control requirements based on the transverse volume shrinkage of the first pouring section: the expansion agent’s 40-day deformation control capability is above 300με; Carry out indoor tests to analyze the influence of expansion agent type and content on lateral volume shrinkage and select reasonable expansion agent.

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