Construction method for partial sloping unloading retaining structure

Abstract

The invention provides a construction method for a partial sloping unloading retaining structure. The construction method comprises the steps that S1, the retaining structure and a staging wall of a foundation pit are constructed; s2, a first inner support of the foundation pit excavated firstly and a first inner support of the foundation pit excavated later are constructed synchronously; s3, the post-excavation side is subjected to first-time local sloping unloading, and the first-excavation side is excavated to the second supporting bottom; s4, second-time local sloping unloading is conducted on the later excavation side, and the first excavation side is excavated to the third supporting bottom; s5, the Nth-time local sloping unloading is conducted on the later excavation side in sequence till the first excavation side is excavated to the bottom face of the bottom plate; n is an integer greater than or equal to 3; s6, a foundation pit bottom plate of the foundation pit which is excavated firstly is constructed; s7, firstly excavating a side structure and performing layered backbuilding; s8, post-excavation side supports are constructed in sequence; and S9, layered backbuilding of the post-excavation side structure is carried out. Through the reasonable design of the construction process, the internal force of the staged wall on the post-excavation side can be reduced on the premise of not influencing a peripheral protection object, so that the post-excavation side of the staged wall meets the reinforcement requirement.

Description

Technical Field

[0001] The invention relates to the technical field of building construction, and in particular to a construction method of a local slope unloading enclosure structure suitable for an extra-large foundation pit with two ends close to protection objects. Background Art

[0002] In the construction of extra-large foundation pits that are adjacent to protected objects at both ends, the "phased construction" method is usually adopted, that is, the extra-large foundation pit is divided into several small pits no larger than 10,000 square meters with phased walls. All the surrounding structures are constructed first, and then the small pits are constructed in phases according to a certain order.

[0003] When constructing adjacent small pits, the other side of the foundation pit must be excavated after the basement structure is back-built on the first side of the foundation pit. The reinforcement design on both sides of the phased wall is usually based on the bending moment and shear force values ​​during the excavation process. The design is based on the steps that the later excavated foundation pit is now soil and the first excavated foundation pit is excavated in layers. The stress of the phased wall is tension on the first excavation side and compression on the second excavation side, and the bending moment on the first excavation side is greater than that on the second excavation side. In order to save materials, uneven reinforcement design is adopted on both sides of the phased wall, and the reinforcement on the first excavation side is greater than that on the second excavation side.

[0004] However, due to the long construction time, when the original excavation sequence is changed due to on-site construction conditions, the problem of the reinforcement of the phased wall on the back excavation side not meeting the requirements due to the change in the on-site foundation pit excavation sequence is changed to the first excavation side. The reinforcement bearing capacity originally designed according to the back excavation side is insufficient, and the phased wall has been completed and the reinforcement of the phased wall cannot be changed. It is urgent to adopt a local slope unloading enclosure structure construction method to reduce the internal force of the phased wall on the back excavation side without affecting the surrounding protection objects, so that it can meet the reinforcement requirements. Summary of the invention

[0005] The purpose of the present invention is to provide a local slope unloading enclosure structure construction method to solve the problem that the side reinforcement of the phased wall excavation does not meet the requirements due to the change of the on-site foundation pit excavation sequence.

[0006] In order to solve the above technical problems, the present invention provides a local slope unloading enclosure structure construction method, the local slope unloading enclosure structure construction method comprising:

[0007] S1. The retaining structure and phased walls of the construction pit are used to divide the pit adjacent to the protected objects at both ends into the first excavation pit and the second excavation pit; the area of ​​the first excavation pit and the second excavation pit is less than or equal to 10,000 square meters;

[0008] S2, simultaneous construction of the first excavation pit and the first internal support of the later excavation pit;

[0009] S3, the first local slope unloading on the rear excavation side, and the first excavation side is excavated to the second support bottom;

[0010] S4, the second local slope unloading on the rear excavation side, the first excavation side is excavated to the third support bottom;

[0011] S5, sequentially carry out the Nth local slope unloading on the later excavation side until the earlier excavation side is excavated to the bottom surface of the base plate; N is an integer greater than or equal to 3;

[0012] S6. During construction, the foundation pit bottom slab is excavated first;

[0013] S7, first excavate the side structure and build it back in layers;

[0014] S8, the rear excavation side support is constructed in sequence;

[0015] S9, back-building of the side structure after excavation in layers;

[0016] S10. After the foundation pit is backfilled, the phased walls above the foundation pit bottom plate are removed layer by layer, and the first excavation side structure is connected with the later excavation side structure.

[0017] Optionally, in the local slope unloading retaining structure construction method, in S3, the first local slope unloading on the rear excavation side is performed according to the first local slope unloading parameters on the rear excavation side; wherein the first local slope unloading parameters on the rear excavation side include: the depth, excavation slope and width of the first unloading soil on the rear excavation side.

[0018] Optionally, in the local slope unloading enclosure structure construction method, the process of determining the first local slope unloading parameters on the rear excavation side includes:

[0019] Determine the depth of the first unloading of soil on the rear excavation side;

[0020] The excavation slope and width are determined according to the depth of the first unloading of soil on the rear excavation side and the allowable slope ratio requirements for slope excavation in GB 51004.

[0021] Optionally, in the local slope unloading enclosure structure construction method, the determining the depth of the first unloading soil on the rear excavation side includes the following steps:

[0022] Select the 1m ground wall unit, first excavate the side soil to the top of the second support, when the second support has not yet been formed, assume that the unloading depth is h1, and use the equivalent beam method to calculate the maximum bending moment borne by the staged wall under the current working condition;

[0023] According to the reinforcement and section width of the staged wall, the maximum bending moment that a 1m ground wall unit can withstand is calculated;

[0024] The assumed unloading depth is continuously adjusted, and the maximum bending moment borne by the staged wall of the 1m ground wall unit under the current working condition is compared with the maximum bending moment that the 1m ground wall unit can withstand, until the maximum bending moment borne by the staged wall under the current working condition is equal to the maximum bending moment that the 1m ground wall unit can withstand. The unloading depth corresponding to the maximum bending moment borne by the staged wall under the current working condition is determined as the depth of the first unloading of soil on the rear excavation side.

[0025] Optionally, in the local slope unloading retaining structure construction method, the assumed unloading depth is continuously adjusted, and the maximum bending moment Mmax borne by the phased wall of the 1m ground wall unit under the current working condition is compared with the maximum bending moment Mu that the 1m ground wall unit can bear to determine the depth of the first unloading of the soil on the excavation side, and the process includes the following steps:

[0026] Consider Mmax as a function of the assumed unloading depth and compare Mmax(h1) with Mu;

[0027] When Mmax(h1)<M u When , the excavation condition is safe. At this time, assuming that the unloading depth is 2h1, continue to calculate Mmax(2h1);

[0028] When Mmax(2h1)>M u When , the excavation condition is unsafe and the excavation depth of the active zone needs to be reduced. At this time, assuming that the unloading depth is (2h1+h1) / 2=1.5h1, continue to calculate Mmax(1.5h1);

[0029] When Mmax(1.5h1)>M u When , the excavation condition is unsafe and the excavation depth of the active zone needs to be reduced. At this time, assuming that the unloading depth is (1.5h1+h1) / 2=1.25h1, continue to calculate Mmax(1.25h1);

[0030] Repeat the above steps until Mmax(h 1极 )=M u When the excavation condition is in the limit state, Mmax(h 1极 ) for the corresponding unloading depth h 1极 It is the depth of the first unloading of soil on the rear excavation side.

[0031] Optionally, in the local sloping and unloading retaining structure construction method, during the first local sloping and unloading process on the rear excavation side, when the excavation depth exceeds 2 meters, step sloping is adopted, and the step width is not less than 1.5m.

[0032] Optionally, in the local slope unloading retaining structure construction method, during the second local slope unloading process on the rear excavation side, the step width is greater than 1.5m and less than 3m.

[0033] Optionally, in the local slope unloading enclosure structure construction method, in S6, the construction sequence of the foundation pit bottom plate is as follows:

[0034] Follow the sequence of finishing excavation and construction of subsequent basement structures.

[0035] Optionally, in the local slope unloading enclosure structure construction method, in S6, the pouring construction of the foundation pit bottom plate is as follows:

[0036] The base slab pouring is carried out in zones. Each area adopts the mature technology of pouring from the center to the surrounding areas. The pouring is carried out in layers and sufficient construction personnel are equipped to vibrate each layer into place.

[0037] Optionally, in the local slope unloading retaining structure construction method, the earth in the foundation pit is excavated using a basin-type excavation method.

[0038] The local slope unloading enclosure structure construction method provided by the present invention has at least the following beneficial effects:

[0039] 1) The present invention implements the local slope unloading enclosure structure construction method of the present invention on an extra-large foundation pit whose two ends are adjacent to the protection objects. Based on its designed construction process, it can reduce the internal force of the phased wall on the rear excavation side without affecting the surrounding protection objects, so that the rear excavation side of the phased wall meets the reinforcement requirements.

[0040] 2) The construction method of the present invention can form a situation where the foundation pits on both sides of the phased wall are constructed synchronously under the premise of ensuring safety, the on-site traffic is organized in an orderly manner, and there is no overlap in the working procedures, which significantly improves the construction efficiency and the on-site green construction effect.

[0041] 3) The construction method of the present invention is easy to operate, saves costs, speeds up construction progress, shortens construction period, is easy to promote and popularize on a large scale, and has high applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The above and other objects, features and advantages of the present disclosure will become more apparent through a more detailed description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present disclosure.

[0043] Figure 1 It is a flow chart of a construction method of a local slope unloading enclosure structure according to an embodiment of the present invention;

[0044] Figure 2 It is the underground continuous wall construction flow chart;

[0045] Figure 3 It is the flow chart of base plate construction;

[0046] Figure 4 It is the construction flow chart of the basement structure concrete project;

[0047] Figure 5 It is a schematic diagram of the construction process of demolishing a single floor wall during the execution of S10;

[0048] Figure 6a and Figure 6b It is a schematic diagram of executing step S1 in the construction method of a local slope unloading enclosure structure in one embodiment of the present invention;

[0049] Figure 7 It is a schematic diagram of executing step S2 in the construction method of a local slope unloading enclosure structure in one embodiment of the present invention;

[0050] Figure 8 It is a schematic diagram of executing step S3 in the construction method of a local slope unloading enclosure structure in one embodiment of the present invention;

[0051] Figure 9a It is a schematic diagram of the intensity distribution of active earth pressure on the rear excavation side during the execution of step S3 in the local slope unloading enclosure structure construction method in one embodiment of the present invention;

[0052] Figure 9b It is a schematic diagram of the distribution of the passive earth pressure intensity on the rear excavation side during the execution of step S3 in the local slope unloading enclosure structure construction method in one embodiment of the present invention;

[0053] Fig.9c It is a mechanical analysis schematic diagram of the maximum bending moment borne by the phased wall under the current working condition during the execution of step S3 in the local slope unloading enclosure structure construction method in one embodiment of the present invention;

[0054] Fig.10 It is a schematic diagram of executing step S4 in the construction method of the local slope unloading enclosure structure in one embodiment of the present invention;

[0055] Fig.11 It is a schematic diagram of executing step S5 in the construction method of a local slope unloading enclosure structure in one embodiment of the present invention;

[0056] Fig.12 It is a schematic diagram of executing step S6 in the construction method of a local slope unloading enclosure structure in one embodiment of the present invention;

[0057] Fig.13 It is a schematic diagram of executing step S7 in the construction method of a local slope unloading enclosure structure in one embodiment of the present invention;

[0058] Fig.14 It is a schematic diagram of executing step S8 in the construction method of a local slope unloading enclosure structure in one embodiment of the present invention;

[0059] Fig.15 It is a schematic diagram of executing step S9 in the construction method of a local slope unloading enclosure structure in one embodiment of the present invention;

[0060] Fig.16 It is a schematic diagram of executing step S10 in the local slope unloading enclosure structure construction method in one embodiment of the present invention. DETAILED DESCRIPTION

[0061] The following is a further detailed description of the construction method of the local slope unloading enclosure structure proposed by the present invention in combination with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer according to the following description and claims. It should be noted that the accompanying drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0062] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0063] In the description of the invention, it is necessary to understand that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention.

[0064] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0065] In the invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to the specific circumstances.

[0066] Please refer to Figures 1 to 16 The local slope unloading enclosure structure construction method includes:

[0067] First, please refer to Figure 2 , Figure 6a and Figure 6b , execute step S1, construct the retaining structure and phased wall of the foundation pit, so as to divide the foundation pit adjacent to the protection object at both ends into the first excavation pit and the later excavation pit; wherein the area of ​​the first excavation pit and the later excavation pit is less than or equal to 10,000 square meters. Among them, the whole pit adopts the sequential construction method to construct all the retaining structures of the foundation pit. For the specific underground continuous wall construction process, please refer to Figure 2 .

[0068] Next, please refer to Figure 7 , execute step S2, and simultaneously construct the first inner support of the first excavation pit and the second excavation pit.

[0069] Determine a reasonable and efficient earthwork excavation method during earthwork excavation: The excavation of the foundation pit is strictly carried out in the order of design requirements, following the principles of "layering and block, retaining soil and protecting walls, limited time symmetry, and timely support" to reduce the impact on the surrounding construction / operation stations, pipelines and surrounding projects under construction. In this embodiment, the earthwork in the foundation pit is excavated using a basin excavation method, which effectively speeds up the excavation speed of the earthwork and reduces the exposure time of the ground wall in an unsupported state.

[0070] Strengthen foundation pit monitoring and use information technology to guide construction: During the construction period, we will work closely with the third-party monitoring unit entrusted by the owner, focusing on monitoring data such as support axial force, deformation of retaining walls, changes in pressure head, settlement and displacement of underground pipelines, so as to provide information technology to guide construction.

[0071] Next, please refer to Figures 8 to 9c , execute step S3, the first local slope unloading is performed on the rear excavation side, and the first excavation side is excavated to the second support bottom.

[0072] Further, in S3, the first local slope unloading of the rear excavation side is performed according to the first local slope unloading parameters of the rear excavation side; wherein the first local slope unloading parameters of the rear excavation side include: the depth h of the first unloading soil body of the rear excavation side 1极 , excavation slope m and width L.

[0073] Specifically, the process of determining the first local slope unloading parameters on the rear excavation side includes:

[0074] Determine the depth h of the first unloading of soil on the rear excavation side 1极 ;

[0075] According to the depth h of the first unloading of soil on the rear excavation side 1极The excavation slope m and width L are determined based on the allowable slope ratio requirements for slope excavation in GB 51004 (i.e., Code for Construction of Building Foundation Engineering).

[0076] Among them, please refer to Figures 9a to 9c , the depth h of the first unloading of soil on the excavation side is determined 1极 The following steps are involved:

[0077] Select the 1m ground wall unit, first excavate the side soil to the top of the second support, when the second support has not yet been formed, assume that the unloading depth is h1 (that is, the initial value of the unloading depth), and use the equivalent beam method to calculate the maximum bending moment Mmax borne by the staged wall under the current working condition;

[0078] Specifically, Figure 9a As shown, the active earth pressure E on the excavation side is calculated based on the following formula: a :

[0079]

[0080] Where γ is the soil weight, kN / m 3 ; c is soil cohesion, kPa; is the internal friction angle of soil, °; Z0 is the depth of the calculation point from the soil surface, m; h is the depth from the bottom of the retaining wall to the top of the soil, m; K a is the active earth pressure coefficient.

[0081] Specifically, Figure 9b As shown, the passive earth pressure E on the first excavation side is calculated based on the following formula p :

[0082]

[0083] Where γ is the soil weight, kN / m 3 ; c is soil cohesion, kPa; is the internal friction angle of soil, °; Z0 is the depth of the calculation point from the soil surface, m; h is the depth from the bottom of the retaining wall to the top of the soil, m; K p Passive earth pressure series.

[0084] Please refer to Fig.9c , Pa is the active earth pressure along the depth, which is a distributed force and its unit is kPa; Ea is the resultant force of Pa and its unit is kN / m; Pp is the passive earth pressure along the depth, which is a distributed force and its unit is kPa; Ep is the resultant force of Pp and its unit is kN / m.

[0085] Using the equivalent beam method, the maximum bending moment Mmax borne by the staged wall under the current working condition is calculated. First, it is assumed that the point where the earth pressure Pa-Pp = 0 is the inflection point D. The bending moment M at the inflection point D isD =0; then according to M D =0, calculate the first support axial force R1; take the staged wall as a simply supported beam, the staged wall top as the free end, the first support as simply supported beam support 1, the inflection point D as support 2, the active earth pressure Pa as the distributed load, and calculate the position where the shear force Q=0, which is the maximum bending moment Mmax.

[0086] Furthermore, according to the reinforcement and section width of the staged wall, the maximum bending moment M that a 1m ground wall unit can withstand is calculated. u , M is calculated according to the following formula u :

[0087] M u =f y 'A s '(h0-a' s )+(A s -A s ')f y γ s h0;

[0088] γ s =1-0.5ξ;

[0089]

[0090] h0=ha s ;

[0091] Among them, γ s Internal force arm coefficient, ξ is the relative height of the compression zone; ρ is the reinforcement ratio; f y f is the design value of tensile strength of steel bars in the tension zone; y ' is the design value of tensile strength of steel bars in compression zone; f t is the design value of concrete tensile strength; α1 is a coefficient. When the concrete strength grade does not exceed C50, α1 is taken as 1.0; when the concrete strength grade is C80, α1 is taken as 0.94. The linear interpolation method is used in between. A s ' is the steel bar area in the compression zone; A s is the steel bar area in the tension zone; h is 1m; a s 'The distance from the steel bar in the compression zone to the compression edge; a s It is the distance from the steel bar in the tension zone to the tension edge.

[0092] The assumed unloading depth is continuously adjusted, and the maximum bending moment Mmax of the phased wall under the current working condition of the 1m ground wall unit is compared with the maximum bending moment M that the 1m ground wall unit can bear. u Until the maximum bending moment Mmax of the phased wall under the current working condition is equal to the maximum bending moment M that the 1m ground wall unit can bear uWhen the maximum bending moment Mmax borne by the phased wall under the current working condition is determined as the first unloading depth h of the soil on the rear excavation side, 1极 .

[0093] Among them, the assumed unloading depth is constantly adjusted, and the maximum bending moment Mmax borne by the 1m ground wall unit under the current working condition is compared with the maximum bending moment M that the 1m ground wall unit can withstand. u Determine the depth h of the first unloading of soil on the rear excavation side 1极 The process includes the following steps:

[0094] Since Mmax increases with the increase of h1, Mmax is considered as a function related to the assumed unloading depth h1, and Mmax(h1) is compared with M u ;

[0095] When Mmax(h1)<M u When , the excavation condition is safe. At this time, assuming that the unloading depth is 2h1, continue to calculate Mmax(2h1);

[0096] When Mmax(2h1)>M u When , the excavation condition is unsafe and the excavation depth of the active zone needs to be reduced. At this time, assuming that the unloading depth is (2h1+h1) / 2=1.5h1, continue to calculate Mmax(1.5h1);

[0097] When Mmax(1.5h1)>M u When , the excavation condition is unsafe and the excavation depth of the active zone needs to be reduced. At this time, assuming that the unloading depth is (1.5h1+h1) / 2=1.25h1, continue to calculate Mmax(1.25h1);

[0098] Repeat the above steps until Mmax(h 1极 )=M u When the excavation condition is in the limit state, Mmax(h 1极 ) for the corresponding unloading depth h 1极 is the depth of the first unloading of soil on the rear excavation side h 1极 ,h 1极 Related to h1.

[0099] In this embodiment, during the first local sloping and unloading process on the rear excavation side, when the excavation depth exceeds 2 meters, step sloping is adopted, and the step width is not less than 1.5m.

[0100] Next, please refer to Fig.10, execute step S4, the second local slope unloading on the rear excavation side, and the first excavation side is excavated to the third support bottom. In the second local slope unloading process on the rear excavation side, the step width is greater than 1.5m and less than 3m.

[0101] Next, please refer to Fig.11 , execute step S5, and perform local slope unloading for the Nth time on the later excavation side in sequence until the earlier excavation side is excavated to the bottom surface of the base plate; N is an integer greater than or equal to 3.

[0102] It can be understood that, whether in S4 or S5, before performing the local slope unloading on the rear excavation side, it is necessary to first calculate the local slope unloading parameters of the rear excavation side (for example, the depth h of the second unloading of the soil on the rear excavation side). 2极 ,h n极 ), the specific determination process can be obtained by referring to the process of determining the first local slope unloading parameters on the rear excavation side.

[0103] Next, please refer to Figure 3 and Fig.12 , execute step S6, and first excavate the foundation pit bottom plate of the foundation pit.

[0104] The construction of the base plate should strictly follow the sequence of excavation and the subsequent construction sequence of the basement structure, especially the construction sequence of the entire site ±0.00. The entire base plate construction plane should be constructed as far as possible under the premise of ensuring the construction conditions, and then the podium base plate should be constructed. The large base plate is poured by zone, and each area adopts the mature technology of pouring from the center to the surroundings, pouring in layers and equipped with sufficient construction personnel to vibrate each layer in place.

[0105] Next, please refer to Figure 4 and Fig.13 , execute step S7, first excavate the side structure and rebuild it in layers.

[0106] Next, please refer to Fig.14 , execute step S8, and then excavate the side supports and construct them in sequence.

[0107] Next, please refer to Fig.15 , execute step S9, and the structure on the rear excavation side is rebuilt in layers.

[0108] Next, please refer to Figure 5 and Fig.16 , execute step S10, after the foundation pit is backbuilt, the phased walls above the foundation pit bottom plate are removed layer by layer, and the first excavation side structure is connected with the later excavation side structure.

[0109] It should be noted that, for the aforementioned method embodiments, for the sake of simplicity, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the described order of actions, because according to the present application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present application.

[0110] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0111] The present invention has the following advantages:

[0112] 1) The present invention implements the local slope unloading enclosure structure construction method of the present invention on an extra-large foundation pit whose two ends are adjacent to the protection objects. Based on its designed construction process, it can reduce the internal force of the phased wall on the rear excavation side without affecting the surrounding protection objects, so that the rear excavation side of the phased wall meets the reinforcement requirements.

[0113] 2) The construction method of the present invention can form a situation where the foundation pits on both sides of the phased wall are constructed synchronously under the premise of ensuring safety, the on-site traffic is organized in an orderly manner, and there is no overlap in the working procedures, which significantly improves the construction efficiency and the on-site green construction effect.

[0114] 3) The construction method of the present invention is easy to operate, saves costs, speeds up construction progress, shortens construction period, is easy to promote and popularize on a large scale, and has high applicability.

[0115] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A method for constructing a local slope unloading enclosure structure, suitable for an extra-large foundation pit with two ends close to the protected object, characterized in that: include: S1. The retaining structure and phased walls of the construction pit are used to divide the pit adjacent to the protected objects at both ends into the first excavation pit and the second excavation pit; the area of ​​the first excavation pit and the second excavation pit is less than or equal to 10,000 square meters; S2, simultaneous construction of the first excavation pit and the first internal support of the later excavation pit; S3, the first local slope unloading on the rear excavation side, and the first excavation side is excavated to the second support bottom; S4, the second local slope unloading on the rear excavation side, the first excavation side is excavated to the third support bottom; S5, sequentially carry out the Nth local slope unloading on the later excavation side until the earlier excavation side is excavated to the bottom surface of the base plate; N is an integer greater than or equal to 3; S6. During construction, the foundation pit bottom slab is excavated first; S7, first excavate the side structure and build it back in layers; S8, the rear excavation side support is constructed in sequence; S9, back-building of the side structure after excavation in layers; S10. After the foundation pit is backfilled, the phased walls above the foundation pit bottom plate are removed layer by layer, and the first excavation side structure is connected with the later excavation side structure.

2. The construction method of the local slope unloading enclosure structure according to claim 1 is characterized in that: In S3, the first local slope unloading of the rear excavation side is performed according to the first local slope unloading parameters of the rear excavation side; wherein the first local slope unloading parameters of the rear excavation side include: the depth of the first unloading soil body of the rear excavation side (h 1极 ), excavation slope and width.

3. The construction method of the local slope unloading enclosure structure according to claim 2 is characterized in that: The process of determining the first local slope unloading parameters on the rear excavation side includes: Determine the depth of the first unloading of soil on the rear excavation side (h 1极 ); According to the depth of the first unloading soil on the rear excavation side (h 1极 ) and the allowable slope ratio requirements for slope excavation in GB 51004 to determine the excavation slope and width.

4. The construction method of the local slope unloading enclosure structure according to claim 3 is characterized in that: The depth of the first unloading of soil on the rear excavation side is determined (h 1极 ) comprises the following steps: Select the 1m ground wall unit, first excavate the side soil to the top of the second support, when the second support has not yet been formed, assume that the unloading depth is h1, and use the equivalent beam method to calculate the maximum bending moment (Mmax) borne by the staged wall under the current working condition; According to the phased wall reinforcement and section width, the maximum bending moment (M) that a 1m ground wall unit can withstand is calculated. u ); The assumed unloading depth is continuously adjusted, and the maximum bending moment (Mmax) of the 1m ground wall unit under the current working condition is compared with the maximum bending moment (Mmax) that the 1m ground wall unit can withstand. u ) until the maximum bending moment (Mmax) borne by the phased wall under the current working condition is equal to the maximum bending moment (Mmax) that the 1m ground wall unit can withstand. u ), the unloading depth corresponding to the maximum bending moment (Mmax) borne by the phased wall under the current working condition is determined as the depth of the first unloading of the soil on the rear excavation side (h 1极 ).

5. The construction method of the local slope unloading enclosure structure according to claim 4 is characterized in that: The assumed unloading depth is continuously adjusted, and the maximum bending moment (Mmax) of the 1m ground wall unit under the current working condition is compared with the maximum bending moment (Mmax) that the 1m ground wall unit can withstand. u ) Determine the depth of the first unloading of soil on the rear excavation side (h 1极 ) process includes the following steps: Consider Mmax as a function of the assumed unloading depth (h1) and compare Mmax(h1) with Mu; When Mmax(h1)<M u When , the excavation condition is safe. At this time, assuming that the unloading depth is 2h1, continue to calculate Mmax(2h1); When Mmax(2h1)>M u When , the excavation condition is unsafe and the excavation depth of the active zone needs to be reduced. At this time, assuming that the unloading depth is (2h1+h1) / 2=1.5h1, continue to calculate Mmax(1.5h1); When Mmax(1.5h1)>M u When , the excavation condition is unsafe and the excavation depth of the active zone needs to be reduced. At this time, assuming that the unloading depth is (1.5h1+h1) / 2=1.25h1, continue to calculate Mmax(1.25h1); Repeat the above steps until Mmax(h 1极 )=M u When the excavation condition is in the limit state, Mmax(h 1极 ) for the corresponding unloading depth h 1极 is the depth of the first unloading of soil on the rear excavation side (h 1极 ).

6. The construction method of the local slope unloading enclosure structure according to claim 3 is characterized in that: During the first local slope unloading process on the rear excavation side, when the excavation depth exceeds 2 meters, step slope is adopted, and the step width is not less than 1.5m.

7. The construction method of the local slope unloading enclosure structure according to claim 1 is characterized in that: During the second local slope unloading process on the rear excavation side, the step width is greater than 1.5m and less than 3m.

8. The construction method of the local slope unloading enclosure structure according to claim 1 is characterized in that: In S6, the construction sequence of the foundation pit bottom plate is as follows: Follow the sequence of finishing excavation and construction of subsequent basement structures.

9. The construction method of the local slope unloading enclosure structure according to claim 1, characterized in that: In S6, the pouring construction of the foundation pit bottom plate is as follows: The base slab pouring is carried out in zones. Each area adopts the mature technology of pouring from the center to the surrounding areas. The pouring is carried out in layers and sufficient construction personnel are equipped to vibrate each layer into place.

10. The construction method of the local slope unloading enclosure structure according to claim 1, characterized in that: The earthwork in the foundation pit is excavated using basin-type excavation method.

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