CN112302030A - Foundation pit structure for reducing displacement of cantilever pile foundation pit supporting system and construction method - Google Patents
Foundation pit structure for reducing displacement of cantilever pile foundation pit supporting system and construction method Download PDFInfo
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- E02D17/00—Excavations; Bordering of excavations; Making embankments
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Abstract
The invention provides a foundation pit structure for reducing the displacement of a cantilever pile foundation pit supporting system and a construction method. The foundation pit structure comprises a long-strip foundation pit of which an enclosure structure adopts cantilever support piles, the length of a long edge of the foundation pit is far larger than that of a short edge, the depth of the foundation pit is not more than 8m, two long-edge support axes of the foundation pit enclosure structure arch towards the outer side of the foundation pit, the long-edge support axes after arching are changed into a parabola from an original straight line, the cantilever support piles on the long edge of the foundation pit enclosure structure are arranged along the long-edge support axes after arching, and armpit triangular plate strips are respectively arranged at four corners of the foundation pit enclosure structure. According to the invention, the load of the middle part of the long side of the foundation pit is transferred to the corner part by arching the cantilever pile, so that the stress mechanism of the supporting structure can be improved, the overlarge displacement of the middle part of the long side of the long strip-shaped foundation pit caused by the time-space effect is effectively limited, the reliability of the supporting structure is improved, the redundant supporting structure is not increased, and a large number of construction periods are saved.
Description
Technical Field
The invention relates to the field of foundation pit supporting engineering, in particular to a foundation pit structure for reducing displacement of a cantilever pile foundation pit supporting system and a construction method.
Technical Field
Along with the rapid development of the process of Chinese urbanization, available land in a city is less and less, the distance between the side line of a basement foundation pit and the side line of a land used is more and more tense, and the underground space outside the land used infrared line cannot be occupied randomly under the general condition, so that when the foundation pit generates large deformation, the influence on surrounding building structures is relatively greater. How to solve the problem becomes a new problem in the field of foundation pit supporting engineering. Under the situation, the foundation pit support is limited by the field or the surrounding environment, slope excavation cannot be used, the support structure cannot use members such as anchor cables and soil nails, and the cantilever pile soil retaining structure can adapt to a limited support space and achieve the effects of controlling displacement and maintaining the stability of the foundation pit, so that the cantilever pile support structure constitutes an effective method for overcoming the problem.
Generally speaking, when the surrounding environmental conditions of the foundation pit are simpler, the excavation depth of the foundation pit is not deep, and the main structure is a basement foundation pit top without a slope space; and secondly, when the main structure is a two-layer basement foundation pit with a slope space on the top, a cantilever pile supporting system can be selected, and the height of a cantilever of the cantilever pile is between 4m and 6 m.
Under most circumstances, the displacement of control foundation ditch lateral wall that cantilever pile supporting construction can be better, but in some special plane shape's foundation ditch support, for example the long limit length of foundation ditch is far greater than the foundation ditch of short length of side length, cantilever pile supporting construction is not enough to the displacement control on the long limit of foundation ditch, because the foundation ditch has the space-time effect, the displacement in the middle part of the long limit is the biggest behind the foundation ditch excavation, if there are important buildings such as building structures, road, pipeline in the middle part, can produce adverse effect. Particularly in the foundation pit of a soft soil area, after the foundation pit is excavated, the displacement of the cantilever pile is mainly limited by the soil resistance of a passive area, and if the foundation pit is immersed in water, the displacement of the cantilever pile is difficult to control. However, in the foundation pit design calculation, the calculation section is taken according to each linear meter, so that the space-time effect cannot be considered. Even if the profile calculation can be passed, because the foundation pit field construction can not be controlled in progress and quality, the displacement of the foundation pit always exceeds the calculated value in the construction process, and the displacement problem in the later stage of foundation pit excavation still needs to be considered. In this case, the following three solutions are available: (1) when the surrounding environment of the foundation pit allows, a row of anchor cables can be constructed on the top beam to achieve the purpose of controlling the displacement of the cantilever pile; (2) when the surrounding environment of the foundation pit is not allowed, a double-row pile supporting scheme can be adopted; (3) when the surrounding environment of the foundation pit is not allowed, the shear strength of the soil layer is high and the excavation depth of the foundation pit is large, an inner support supporting scheme can be adopted.
However, although the pile anchor scheme has a good restriction on the displacement of the cantilever pile, the construction period is long, the problem that an anchor cable passes through a red line is encountered, the construction period is limited by soil layer geological conditions, and the displacement of the cantilever pile cannot be restricted if the filled soil is thick; although the double-row pile scheme has good restriction on the displacement of the cantilever piles, the double-row pile scheme has high manufacturing cost and long construction period and does not have economy; although the inner support scheme has good restriction on the displacement of the cantilever pile, the construction period is long, the construction cost is high, and the construction of a main structure can be influenced. Under the background, aiming at the foundation pit with the length of the long side far greater than that of the short side and the depth not more than 8m, the invention provides the structure and the method for reducing the displacement of the cantilever pile support system, the cantilever pile is used for arching, and the load of the middle part of the long side of the foundation pit is transmitted to the corner part, so that the effect of reducing the displacement of the cantilever pile of the long side of the foundation pit is achieved, meanwhile, the method does not need to use other support structures, only needs to add an armpit at the corner part, and has very obvious economical efficiency.
Disclosure of Invention
The invention provides a foundation pit structure for reducing the displacement of a cantilever pile foundation pit supporting system and a construction method according to the defects of the existing supporting scheme.
In order to achieve the technical purpose, the invention provides a foundation pit structure for reducing the displacement of a cantilever pile foundation pit supporting system; the foundation pit structure comprises a long-strip foundation pit of which an enclosure structure adopts cantilever support piles, the length of a long edge of the foundation pit is far larger than that of a short edge, the depth of the foundation pit is not more than 8m, two long-edge support axes of the foundation pit enclosure structure arch towards the outer side of the foundation pit, the long-edge support axes after arching are changed into a parabola from an original straight line, the cantilever support piles on the long edge of the foundation pit enclosure structure are arranged along the long-edge support axes after arching, and armpit triangular plate strips are respectively arranged at four corners of the foundation pit enclosure structure.
The invention has the following excellent technical scheme: the length of the long side of the foundation pit is more than or equal to two times of the length of the short side, and the camber of the long side supporting axis is 1/100-6/100.
The invention has the following excellent technical scheme: and the long-edge crown beam and the short-edge crown beam of the foundation pit support structure are respectively constructed along a long-edge support axis and a short-edge support axis.
The invention has the following excellent technical scheme: the earthwork excavation of the foundation pit is carried out in a layered and sectional mode, and concrete is sprayed along with excavation of soil between piles.
The invention has the following excellent technical scheme: the triangular plate belt is arranged between the long-edge crown beam and the short-edge crown beam, the thickness of the triangular plate belt is 300-400 mm, and the length of the position, overlapped with the crown beam, of two sides of the triangular plate belt is 5.0-9.0 m.
Aiming at the condition that the length of a long side is far larger than that of a short side in the plane size of a foundation pit, the surrounding environment of the foundation pit is simpler, but the side line of an underground chamber is closer to a red line and does not have a slope space, the cantilever pile enclosure structure adopts a cantilever support pile with the cantilever length of 4-6 m, and the cantilever pile support structure can meet the calculation requirement and ensure the safety and the stability of the foundation pit.
The invention also provides a construction method for reducing the displacement of the cantilever pile foundation pit supporting system, aiming at the long side of the foundation pit is far longer than the long side of the:
(1) determining a construction scheme of a foundation pit enclosure structure according to a geological survey report, surrounding environment conditions and the excavation depth of a foundation pit, wherein the foundation pit enclosure structure is supported by a cantilever pile, the cantilever length of the cantilever support pile is 4-6 m, the short-side support axis of the foundation pit is a design side line of the foundation pit, the long-side support axis arches towards the outer side of the design side line of the foundation pit along the direction perpendicular to the long side of the foundation pit, the arch camber is controlled to be 1/100-6/100, and the arch camber is calculated according to the arch camber;
(2) calculating construction parameters of cantilever piles of the enclosure structure by taking a calculation section per linear meter by adopting a classical Rankine soil pressure theory and a plane rod member elastic ground beam method;
(3) arranging support pile positions on the determined short-edge support axis and the arched long-edge support axis according to the cantilever pile construction parameters calculated in the step (2) in the step (1), extracting pile position coordinates on the short-edge support axis and the arched long-edge support axis, and extracting pile position coordinates when the long edge of the foundation pit is not arched to form a support pile construction file;
(4) in the construction stage, constructing cantilever support piles according to the construction parameters in the step (2) according to the pile position coordinates on the short-side support axis and the arched long-side support axis extracted in the step (3), excavating a pile top crown beam of the foundation pit construction after the support piles reach maintenance, wherein the excavation width of the foundation pit is not less than 10m, and the excavation elevation of the foundation pit is the same as the bottom elevation of the crown beam;
(5) when a pile top crown beam is constructed, an armpit triangular plate strip is arranged at the corner where the long side and the short side of the foundation pit are intersected to reinforce the corner of the foundation pit;
(6) after the construction of the crown beam is finished and the maintenance period is reached, carrying out foundation pit earthwork excavation; and excavating the earthwork of the foundation pit in a layered and sectional manner, spraying concrete along with excavation of the soil body between the fender piles, and immediately constructing a basement bottom plate after the foundation pit is excavated to the bottom.
The further technical scheme of the invention is as follows: when the construction scheme of the foundation pit support structure is determined in the step (1), calculating the camber of the long-side support axis of the foundation pit according to the camber deflection when the camber is zero, and calculating according to the following formula:
in the formula: q-horizontal soil pressure at the depth of the non-hinged arch calculation model, unit N/m;
f, arch height without a hinged arch, unit m;
l-the projection length of the arch length without the hinged arch in the x-axis direction, namely the length of the long side of the foundation pit, and the unit m;
delta-zero arch height is zero without middle deflection of the hinged arch, unit m;
e-hinge-arch-free arch body elastic die with unit of N/mm2；
I-moment of inertia of arch body without hinged arch, unit m4；
Gamma-arch camber without hinge arch;
[] -mathematically rounding the symbols.
The further technical scheme of the invention is as follows: the cantilever pile construction parameters in the step (2) comprise the pile spacing of the cantilever piles, the pile diameter, the pile length, the reinforcement, the size of the top crown beam of the pile and the reinforcement of the top crown beam of a single cantilever pile.
The invention has the following excellent technical scheme: and (3) welding the supporting steel bars of the axillary triangle plate band in the step (5) with the main bars of the crown beam, and integrally pouring concrete with the pile top crown beam to form the axillary triangle plate band, wherein the thickness of the triangle plate band is 300-400 mm, and the length of the position, overlapped with the crown beam, of two sides of the triangle plate band is 5.0-9.0 m.
The invention has the following excellent technical scheme: and (5) monitoring the displacement of the foundation pit while excavating the earthwork in the step (6), and feeding the displacement back to the construction of foundation pit supporting and earthwork excavation.
According to the foundation pit structure, along the long side of the foundation pit, in the plane where any cross section of the cantilever pile is located, a calculation model is established to perform theoretical analysis on the force distribution in the cantilever pile supporting structure system. The established calculation model is a hingeless arch, the arch body consists of cross sections of all cantilever piles on the long side, the arch foot support consists of support piles on the short side of the foundation pit and an armpit at the corner, and the borne external load is the horizontal soil pressure at the depth. The arch axis of the arch is a quadratic parabola in a hingeless arch calculation model, the bending moment of the arch body is minimum and close to zero, the maximum value of the bending moment of the middle part and the corner of the arch body and the deflection of the arch body can be obtained after analysis according to a building structure static calculation manual, and the corresponding arch height can be selected according to the deflection of the arch body when the arch height is zero.
The invention can be obtained according to the influence of shear deformation on the integral stability in the plane of the large-span lattice arch, the parabola hingeless arch under the action of the full-span uniformly distributed load belongs to a pressure arch, and the arch body can not generate displacement before the load reaches the buckling load of the arch. Therefore, near the middle section of the hingeless arch, the displacement of the cantilever pile is greatly reduced, and the purpose of reducing the displacement of the middle part in the long side of the cantilever pile is achieved.
Aiming at the foundation pit with the length of the long side far greater than that of the short side and the depth not more than 8m, the invention utilizes the arching of the cantilever piles to transfer the load in the middle of the long side of the foundation pit to the corner part and improve the stress mechanism of the supporting structure, thereby achieving the effect of reducing the overlarge displacement of the cantilever piles on the long side of the foundation pit due to the space-time effect. The support system not only utilizes the arching of the cantilever piles to effectively control the displacement of the cantilever piles on the long side of the foundation pit, but also utilizes the corner haunches of the foundation pit to resist the transmitted concentrated stress, thereby greatly reducing the displacement of the cantilever piles in the cantilever pile support system, ensuring the stability of the foundation pit enclosure structure and having great popularization and application values.
Drawings
FIG. 1 is a schematic plan view of an elongated foundation pit of the present invention;
FIG. 2 is a model diagram for analyzing and calculating the arch camber internal force of the long side of the elongated foundation pit according to the present invention;
FIG. 3 is a non-hinge-arch limit instability curve in the computational model of the present invention;
FIG. 4 is a plan view of an elongated foundation pit according to an embodiment of the present invention;
fig. 5 is a long-side section calculation result diagram of the cantilever pile supporting structure according to the embodiment of the invention.
In the figure: 1-long side, 1-long side supporting axis, 1-2-long side crown beam, 2-short side, 2-1-short side supporting axis, 2-short side crown beam, 3-cantilever supporting pile, 4-triangular plate strip and 5-strip foundation pit.
Detailed Description
The invention is further illustrated by the following figures and examples. Fig. 1 to 5 are drawings of embodiments, which are drawn in a simplified manner and are only used for the purpose of clearly and concisely illustrating the embodiments of the present invention. The following claims presented in the drawings are specific to embodiments of the invention and are not intended to limit the scope of the claimed invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it is to be understood that the terms "upper", "lower", "inner", "outer", "left", "right", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, or the orientations or positional relationships that the products of the present invention are conventionally placed in use, or the orientations or positional relationships that are conventionally understood by those skilled in the art, and are used for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the equipment or elements referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
In the embodiment, the foundation pit structure for reducing the displacement of the cantilever pile foundation pit supporting system is shown in fig. 1, and comprises a long strip foundation pit 5 with a support structure adopting cantilever support piles 3, wherein the length of a long side 1 of the foundation pit 5 is more than or equal to two times of the length of a short side, the cantilever length of the cantilever support piles 3 is 4 m-6 m, and the depth of the foundation pit 5 is not more than 8 m; the two long-side support axes 1-1 of the enclosure structure of the foundation pit 5 arch towards the outer side of the foundation pit, the arch camber of the long-side support axis 1-1 is 1/100, the original long side supporting axis and the short side supporting axis of the foundation pit 5 are both straight lines, the long side supporting axis 1-1 after arching is changed into a parabola from the original straight line, the short side supporting axis 2-1 is still a straight line, the cantilever supporting piles 3 on the long side of the foundation pit enclosure structure are arranged along the long side supporting axis 1-1 after arching, the long-side crown beam 1-2 and the short-side crown beam 2-2 of the enclosure structure of the foundation pit 5 are respectively constructed along a long-side support axis 1-1 and a short-side support axis 2-1, and four corners of the foundation pit enclosure structure are respectively provided with an armpit triangular plate strip 4 for resisting concentrated stress transmitted from the middle part. The triangular plate strip 4 is arranged between the long-side crown beam 1-2 and the short-side crown beam 2-2, the thickness of the triangular plate strip 4 is 300mm, and the length of the position, overlapped with the crown beam, of the two sides of the triangular plate strip 4 is 5 m. The earthwork excavation of the foundation pit 5 is carried out in a layered and sectional manner, and the concrete is sprayed along with the excavation of the soil between piles.
The camber of the long-side supporting axis of the foundation pit is calculated according to the camber deflection when the camber is zero, and the camber is calculated according to the following formula:
in the formula: q-horizontal soil pressure at the depth of the non-hinged arch calculation model, unit N/m;
f, arch height without a hinged arch, unit m;
l-the projection length of the arch length without the hinged arch in the x-axis direction, namely the length of the long side of the foundation pit, and the unit m;
delta-zero arch height is zero without middle deflection of the hinged arch, unit m;
e-hinge-arch-free arch body elastic die with unit of N/mm2；
I-moment of inertia of arch body without hinged arch, unit m4；
Gamma-arch camber without hinge arch;
[] -mathematically rounding the symbols.
According to the foundation pit structure, along the long side of the foundation pit, in the plane where any cross section of the cantilever pile is located, a calculation model is established to perform theoretical analysis on the force distribution in the cantilever pile supporting structure system. The established calculation model is a hingeless arch, the arch body consists of cross sections of all cantilever piles on the long side, the arch foot support consists of support piles on the short side of the foundation pit and an armpit at the corner, and the borne external load is the horizontal soil pressure at the depth. In the non-hinged arch calculation model, the arch axis is a quadratic parabola, as shown in figure 2, the bending moment of the arch body is minimum and close to zero, and the maximum value of the bending moment of the middle part and the corner part of the arch body and the deflection of the arch body can be obtained after analysis according to the building structure static calculation manual:
in the formula: mCThe value of the bending moment in the middle of the arch body after arching is in kN.m;
MBthe bending moment value of the corner of the arch body after arching is in kN.m;
q is horizontal soil pressure at the depth of the non-hinged arch calculation model, and the unit is N/m;
f is the arch height without hinged arch, unit m;
l is the projection length of the arch length without the hinged arch in the x-axis direction, namely the length of the long side of the foundation pit, and the unit m;
the bending moments of the middle part and the corner part of the arch after arching are shown in the formulas III to IV respectively, and the bending moments of the middle part and the corner part of the arch before arching are shown in the formulas III to IV respectively. After the cantilever piles are arched, the bending moment of the support piles in the middle of the long edge is greatly reduced, and the bending moment value of the cantilever piles in the middle of the long edge is obviously reduced by comparing with a fixed supporting beam model at two ends before arching, which shows that the displacement value of the cantilever piles at the position is obviously reduced. The formula shows that the corresponding arch height can be selected according to the arch body deflection when the arch height is zero.
Example (b): the invention is specifically implemented for a certain engineering strip foundation pit, and the general engineering is as follows: the field is located in a western-style mountainous area in Kunming city, a planning project plans total floor area of 44734.8 square meters, the perimeter of a vertical excavation line of the foundation pit is about 861.3m, a layer of basement is arranged, the excavation depth of the foundation pit is 4.8-7.3 m, the length of the long side of the foundation pit is about 104.0m, and the length of the short side of the foundation pit is about 39.0 m. The east surface of the foundation pit is the Xihua road, the south-east corner foundation pit excavation line distance keeps the clear distance of the construction huayuan to be 8.3m, the excavation depth of the foundation pit is smaller, if the foundation pit supporting structure fails, the soil body is excessively deformed to have more serious influence on the surrounding environment of the foundation pit, and therefore the safety level of the supporting structure is two levels. According to the geological survey report, the surrounding environmental conditions and the excavation depth of the foundation pit, preliminarily drawing up a cantilever pile supporting scheme for the foundation pit, wherein the supporting scheme is as follows: (1) a cantilever pile supporting scheme; (2) pile top slope putting and cantilever pile supporting scheme.
According to the geological survey report, the detailed geological condition information of the region of the foundation pit in the table 1 can be obtained.
Table 1 example soil layer geological shear strength parameter table
In the embodiment, the distance between the underground outer wall line of the structure and the ground red line is close, the surrounding roads need to be protected, the anchor cable cannot be used, but the pile top has a slope space, so that the long side of the foundation pit adopts a supporting scheme (2). The calculation of the displacement and the internal force of the cantilever pile in the supporting scheme (2) still adopts the channelThe typical method takes each linear meter as a calculation section to determine the height and the slope ratio of the slope, the pile diameter of the support pile, the pile length, the reinforcement and other parameters. In the supporting scheme (2), the height of the slope is 2.0m, the slope ratio is 1:1.0, the supporting pile parameter is phi 800@1100, the pile length is 17.0m, the height of the cantilever is 4.3m, the length of the long side of the foundation pit is l ═ 104m, the length of the short side of the foundation pit is 39m, the excavation depth of the foundation pit is H ═ 6.3m, and the elastic modulus E is 3.0 multiplied by 105N/mm2The soil pressure is taken as q is 100 kPa; taking the cross section of the arch body calculation model, wherein the width of the cross section is 0.8m, the height is 1.0m, and obtaining the inertia moment of the cross section
According to the two-end clamped concrete beam model, the deflection of the clamped beam model when the camber is 0 can be calculated:
and also by camber
The camber after rounding was 1/100. Therefore, the arch is raised according to the camber of 1/100, and the arch height of the long side of the foundation pit is 1.04 m.
During specific construction, firstly, arranging pile positions of support piles on the determined short-edge support axis 2-1 and the arched long-edge support axis 1-1 according to the calculated cantilever pile construction parameters, extracting the coordinates of the pile positions on the short-edge support axis and the arched long-edge support axis, and simultaneously extracting the coordinates of the pile positions when the long edge of the foundation pit is not arched to form a support pile construction file; then, constructing cantilever support piles according to the pile position coordinates on the determined support axis, excavating a foundation pit construction pile top crown beam after the support piles reach a maintenance period, wherein the excavation width of the foundation pit is not less than 10m, the excavation elevation of the foundation pit is the same as the bottom elevation of the crown beam, and arranging an haunching triangular plate strip at the corner where the long edge and the short edge of the foundation pit intersect to reinforce the corner of the foundation pit when constructing the pile top crown beam; after the construction of the crown beam is finished and the maintenance period is reached, carrying out foundation pit earthwork excavation; and excavating the earthwork of the foundation pit in a layered and sectional manner, spraying concrete along with excavation of the soil body between the fender piles, and immediately constructing a basement bottom plate after the foundation pit is excavated to the bottom. And after the foundation pit is excavated to the bottom, the basement bottom plate is constructed in time so as to reduce the exposure time of the foundation pit as much as possible and reduce the displacement of the foundation pit.
Under the working condition that the foundation pit is excavated to the depth of 6.3m in a distributed manner, calculating by adopting regular and deep foundation pit software, listing the calculation results of displacement, bending moment and shearing force of the cantilever pile supporting structure in FIG. 5, and listing the monitoring data of the displacement of the cantilever pile on site in the table 2;
table 2 example middle long side cantilever pile top crown beam displacement monitoring recording meter
And the settlement result shows that the supporting structure can meet the requirements of the safety and the stability of the foundation pit. As can be seen from the displacement monitoring and recording table of the top beam of the long-side cantilever pile of the foundation pit, the maximum displacement of the cantilever pile is 25.1mm, the standard requirement is met, and the maximum displacement is smaller than the displacement value of 28.74mm obtained by non-arching calculation, which indicates the effectiveness and superiority of the method provided by the invention.
For comparison, the added costs of the scheme provided by the invention, the pile anchor scheme, the double-row pile scheme and the inner support scheme are calculated respectively.
(1) In the scheme provided by the invention, the supporting piles are arched, because the arch camber is smaller, the number of the supporting piles is not increased, the increased workload is that the corner portion is provided with the axillary triangle, and the increased manufacturing cost is 0.75 ten thousand yuan;
(2) in the pile anchor scheme, the workload is increased by 94 anchor cables, the length of each anchor cable is calculated according to 24m, and the manufacturing cost is increased by 40.2 ten thousand yuan;
(3) in the scheme of double-row piles, the workload is increased by 96 supporting piles and connecting beams, the length of each supporting pile is 17.0m, and the construction cost is increased by 130.6 ten thousand yuan;
(4) in the internal support scheme, the internal support scheme can interfere the construction of a main body structure, and construction procedures such as replacement, disassembly, support, breaking and the like exist, so that the construction period can be greatly prolonged, and the increased construction cost is over 130 ten thousand yuan. Comparing with four theoretically feasible methods, the proposal of the invention can be found to increase the cost far less than the other three proposals.
In summary, the supporting structure system provided by the invention utilizes the cantilever pile to arch and transmit the load in the middle of the long side of the foundation pit to the corner part aiming at the foundation pit with the length of the long side far greater than that of the short side and the depth not greater than 8m, so that the stress mechanism of the supporting structure can be improved, the excessive displacement of the middle of the long side of the long strip-shaped foundation pit caused by the space-time effect can be effectively limited, the reliability of the supporting structure is improved, the redundant supporting structure can not be added, a large number of construction periods can be saved, and the scheme provided by the invention has the. The scheme provided by the invention only increases a small workload, can reduce a large amount of construction cost compared with other supporting schemes, has very obvious economical efficiency and extremely has popularization and application values.
Claims (10)
1. The utility model provides a reduce foundation ditch structure of cantilever pile foundation pit supporting system displacement which characterized in that: the foundation pit structure comprises a long-strip foundation pit (5) with a cantilever support pile (3) and an enclosure structure, wherein the length of a long edge (1) of the foundation pit is far larger than that of a short edge (2), the depth of the foundation pit is not more than 8m, two long-edge support axes (1-1) of the enclosure structure of the foundation pit (5) arch towards the outer side of the foundation pit, the long-edge support axes (1-1) after arch arching are changed into a parabola from an original straight line, the cantilever support piles (3) on the long edge of the enclosure structure of the foundation pit are arranged along the long-edge support axes (1-1) after arch arching, and haunching triangular plate strips (4) are respectively arranged at four corners of the enclosure.
2. The foundation pit structure for reducing displacement of a cantilever pile foundation pit supporting system according to claim 1, wherein: the length of the long side (1) of the foundation pit (5) is more than or equal to two times of the length of the short side, the length of a cantilever of the cantilever support pile (3) is 4-6 m, and the camber of the long side support axis (1-1) is 1/100-6/100.
3. A foundation pit structure for reducing displacement of a cantilever pile foundation pit supporting system according to claim 1 or 2, wherein: and the long-side crown beam (1-2) and the short-side crown beam (2-2) of the enclosure structure of the foundation pit (5) are respectively constructed along a long-side support axis (1-1) and a short-side support axis (2-1).
4. A foundation pit structure for reducing displacement of a cantilever pile foundation pit supporting system according to claim 1 or 2, wherein: the earthwork excavation of the foundation pit (5) is carried out in a layered and sectional manner, and the concrete is sprayed along with excavation of soil among piles.
5. A foundation pit structure for reducing displacement of a cantilever pile foundation pit supporting system according to claim 3, wherein: the triangular plate strip (4) is arranged between the long-edge crown beam (1-2) and the short-edge crown beam (2-2), the thickness of the triangular plate strip (4) is 300-400 mm, and the length of the position, overlapped with the crown beam, of the two sides of the triangular plate strip (4) is 5.0-9.0 m.
6. A construction method for reducing the displacement of a cantilever pile foundation pit supporting system is provided, aiming at a long-edge foundation pit with the length of the long edge far larger than that of the short edge, the method is characterized by comprising the following specific construction steps:
(1) determining a construction scheme of a foundation pit enclosure structure according to a geological survey report, surrounding environment conditions and the excavation depth of a foundation pit, wherein the foundation pit enclosure structure is supported by a cantilever pile, the cantilever length of the cantilever support pile is 4-6 m, the short-side support axis of the foundation pit is a design side line of the foundation pit, the long-side support axis arches towards the outer side of the design side line of the foundation pit along the direction perpendicular to the long side of the foundation pit, the arch camber is controlled to be 1/100-6/100, and the arch camber is calculated according to the arch camber;
(2) calculating construction parameters of cantilever piles of the enclosure structure by taking a calculation section per linear meter by adopting a classical Rankine soil pressure theory and a plane rod member elastic ground beam method;
(3) arranging support pile positions on the determined short-edge support axis and the arched long-edge support axis according to the cantilever pile construction parameters calculated in the step (2) in the step (1), extracting pile position coordinates on the short-edge support axis and the arched long-edge support axis, and extracting pile position coordinates when the long edge of the foundation pit is not arched to form a support pile construction file;
(4) in the construction stage, constructing cantilever support piles according to the construction parameters in the step (2) according to the pile position coordinates on the short-side support axis and the arched long-side support axis extracted in the step (3), excavating a pile top crown beam of the foundation pit construction after the support piles reach maintenance, wherein the excavation width of the foundation pit is not less than 10m, and the excavation elevation of the foundation pit is the same as the bottom elevation of the crown beam;
(5) when a pile top crown beam is constructed, an armpit triangular plate strip is arranged at the corner where the long side and the short side of the foundation pit are intersected to reinforce the corner of the foundation pit;
(6) after the construction of the crown beam is finished and the maintenance period is reached, carrying out foundation pit earthwork excavation; and excavating the earthwork of the foundation pit in a layered and sectional manner, spraying concrete along with excavation of the soil body between the fender piles, and immediately constructing a basement bottom plate after the foundation pit is excavated to the bottom.
7. The construction method for reducing the displacement of the cantilever pile foundation pit supporting system according to claim 6, wherein when the construction scheme of the foundation pit enclosure structure is determined in the step (1), the camber of the long-side supporting axis of the foundation pit is calculated according to the camber deflection when the camber is zero, and the calculation is performed according to the following formula:
in the formula: q-horizontal soil pressure at the depth of the non-hinged arch calculation model, unit N/m;
f, arch height without a hinged arch, unit m;
l-the projection length of the arch length without the hinged arch in the x-axis direction, namely the length of the long side of the foundation pit, and the unit m;
delta-zero arch height is zero without middle deflection of the hinged arch, unit m;
e-hinge-arch-free arch body elastic die with unit of N/mm2；
I-moment of inertia of arch body without hinged arch, unit m4；
Gamma-arch camber without hinge arch;
[] -mathematically rounding the symbols.
8. The construction method for reducing the displacement of the cantilever pile foundation pit supporting system according to claim 6, wherein the construction method comprises the following steps: the cantilever pile construction parameters in the step (2) comprise the pile spacing of the cantilever piles, the pile diameter, the pile length, the reinforcement, the size of the top crown beam of the pile and the reinforcement of the top crown beam of a single cantilever pile.
9. The construction method for reducing the displacement of the cantilever pile foundation pit supporting system according to claim 6, wherein the construction method comprises the following steps: and (3) welding the supporting steel bars of the axillary triangle plate band in the step (5) with the main bars of the crown beam, and integrally pouring concrete with the pile top crown beam to form the axillary triangle plate band, wherein the thickness of the triangle plate band is 300-400 mm, and the length of the position, overlapped with the crown beam, of two sides of the triangle plate band is 5.0-9.0 m.
10. The construction method for reducing the displacement of the cantilever pile foundation pit supporting system according to claim 6, wherein the construction method comprises the following steps: and (5) monitoring the displacement of the foundation pit while excavating the earthwork in the step (6), and feeding the displacement back to the construction of foundation pit supporting and earthwork excavation.
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