CN215669631U - Deep overburden foundation structure - Google Patents
Deep overburden foundation structure Download PDFInfo
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- CN215669631U CN215669631U CN202121622335.9U CN202121622335U CN215669631U CN 215669631 U CN215669631 U CN 215669631U CN 202121622335 U CN202121622335 U CN 202121622335U CN 215669631 U CN215669631 U CN 215669631U
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Abstract
The utility model discloses a foundation structure with a deep and thick covering layer, which comprises an earth-rock cofferdam and a foundation covering layer positioned below the earth-rock cofferdam, wherein the foundation covering layer comprises an upper sand gravel layer or an artificial filling permeable layer, a middle lake-phase deposition covering layer and a lower ancient river bed sand gravel layer; an impervious wall is arranged at the upstream of the earth-rock cofferdam, and a downcomer well is arranged at the downstream of the earth-rock cofferdam; and a plurality of granular body piles are arranged in the foundation covering layer between the impervious wall and the downcomer well. The utility model mainly takes the acceleration of the drainage consolidation process of the weak soil body with weak water permeability as a main target, fully exerts the self bearing capacity and the shear strength of the soil body, improves the stability of the earth-rock cofferdam and the foundation and can greatly reduce the investment of foundation reinforcement engineering; by arranging the downcast pipe well, the occurrence of bursting damage accidents when the foundation pit excavation of the downstream dam of the earth-rock cofferdam is close to the bottom surface of the weak soil body with weak water permeability can be effectively prevented.
Description
Technical Field
The utility model belongs to the field of hydraulic and hydroelectric engineering, and particularly relates to a foundation structure with a deep covering layer.
Background
The large rivers of the great rivers in the southwest region of China are influenced by geological structures and earthquakes, historically mountain landslides often occur to form barrage dams and barrage lakes, the thickness of a weak clay covering layer formed by the deposition of the barrage lake is from dozens of centimeters to dozens of meters, the deep covering layer is a geological structure commonly encountered in the development of hydroelectric engineering in recent years in China, and the deep covering layer has the characteristics of loose structure, large stacking thickness, deposition layer which can reach hundreds of meters and even hundreds of meters generally, low permeability, low shear strength, low bearing capacity, high water content and the like. When a river dam is built on the foundation with the covering layer, the bearing capacity and the shear strength of the foundation are improved by adopting the treatment modes of direct excavation, pile foundation reinforcement, grouting reinforcement, drainage plates and the like according to the characteristics of the thickness, the burial depth, the properties and the like of the covering layer. However, for a deep and soft covering layer with the depth of more than 40m, when temporary buildings such as a high earth-rock cofferdam and the like are built on the covering layer, the construction conditions of excavation replacement are not provided, meanwhile, after the cofferdam is built, the dam foundation is excavated to form a comprehensive high slope, and in the cofferdam filling period and the cofferdam water retaining period, the cofferdam structure faces the technical problems of large settlement deformation, prominent slope stability and the like.
The earth-rock cofferdam is built on a natural riverbed covering layer, the stability safety coefficient of the upper slope and the lower slope of the cofferdam is less than 1, the safety requirement is not met, the covering layer can generate super-pore water pressure under the action of the gravity of the upper earth-rock cofferdam, the dissipation time of the super-pore water pressure is long, and the dissipation time of the super-pore water pressure can be dozens of years due to the low permeability, so that the effective stress in the soil body is greatly reduced, the shear strength of the soil body is further reduced, and the stability of the earth-rock cofferdam is reduced. Therefore, the middle lake phase deposition covering layer needs to be completely treated, and the treatment depths of a drainage plate, a sand pile, high-pressure jet grouting, a deep stirring pile and the like in the conventional soft foundation treatment mode can not meet the engineering requirements; the underground diaphragm wall structure is adopted, the engineering quantity is large, the structure stress is complex, the investment is large, and the construction is difficult.
For such situations, common treatment methods have technical bottlenecks, for example, a construction method is not suitable for a condition of deep covering layer, reinforcement measures are not suitable for physical characteristics of a foundation, a reinforcement effect cannot promote drainage consolidation of a soil body to improve bearing capacity, the reinforcement measures cannot be manufactured at high cost, and the like.
SUMMERY OF THE UTILITY MODEL
The utility model aims to provide a foundation structure with a deep covering layer, which aims to solve the technical problem of slow drainage and consolidation of a soil body.
In order to achieve the purpose, the specific technical scheme of the utility model is as follows:
a deep overburden foundation structure including an earth-rock cofferdam and a foundation overburden beneath the earth-rock cofferdam;
the foundation covering layer comprises an upper sand gravel layer or an artificial filling permeable layer, a middle lake phase deposition covering layer and a lower ancient river bed sand gravel layer;
an impervious wall is arranged at the upstream of the earth-rock cofferdam, and a downcomer well is arranged at the downstream of the earth-rock cofferdam;
and a plurality of granular body piles are arranged in the foundation covering layer between the impervious wall and the downcomer well.
Further, the lower part of the granular material pile extends into the sand gravel layer of the ancient river bed.
Further, the granular body piles communicate the upper layer and the lower layer of the foundation covering layer.
Further, the granular material pile is a gravel pile.
In addition, the impervious wall penetrates through the earth-rock cofferdam and the foundation covering layer and is perpendicular to the flowing direction of river water.
In addition, the bottom of the downcomer well is communicated with the ancient river bed sand gravel layer.
Therefore, the method adopts the gravel pile to reinforce the deep dammed lake phase sedimentary clay layer, accelerates the drainage consolidation of the soil body, can improve the shearing strength of the soil between the piles and improve the bearing capacity of the composite foundation; the top of the gravel pile is connected with a riverbed sand gravel layer or an artificial filling stone slag layer to form a top horizontal drainage channel, so that the drainage channel is solved when the soil body is solidified and drained; the bottom of the gravel pile is connected with the ancient river bed sand gravel layer to form a bottom horizontal drainage channel, so that a vertical drainage two-way channel of the gravel pile is solved, and the drainage consolidation speed of soil among piles is accelerated; the slope toe of the earth-rock cofferdam is provided with a downcast pipe well, water is continuously pumped by a water pump, the underground water level line in the gravel pile is reduced, the effective stress of the gravel pile and the soil between the piles can be improved, and the shear strength and the slope stability of the foundation are improved.
The utility model mainly takes the acceleration of the drainage consolidation process of the weak soil body with weak water permeability as a main target, fully exerts the self bearing capacity and the shear strength of the soil body, improves the stability of the earth-rock cofferdam and the foundation and can greatly reduce the investment of foundation reinforcement engineering; by arranging the downcast pipe well, the occurrence of bursting damage accidents when the excavation of the dam foundation pit is close to the bottom surface of the weak soil body with weak water permeability can be effectively prevented.
Drawings
FIG. 1 is a cross-sectional view of a deep overburden foundation structure of the present invention;
FIG. 2 is a schematic view of an embodiment of the present invention;
the notation in the figure is: 1. an earth-rock cofferdam; 2. a foundation overlay; 21. a layer of sand gravel; 22. lake deposition overburden; 23. an ancient riverbed sand gravel layer; 5. granular pile; 6. a downcomer well; 7. excavating a side slope in a dam foundation pit; 8. and (4) a seepage-proofing wall.
Detailed Description
For a better understanding of the objects, structure and function of the utility model, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.
As shown in fig. 1, a deep overburden foundation structure of the present invention includes an earth-rock cofferdam 1 and a foundation overburden 2 located at a lower portion of the earth-rock cofferdam 1; the foundation covering layer 2 comprises an upper sand gravel layer 21 or an artificial filling permeable layer, a middle lake phase deposition covering layer 22 and a lower ancient river bed sand gravel layer 23; the depth of the foundation covering layer 2 is H, the thickness of the upper sand gravel layer 21 or artificial filling permeable layer is H1, the thickness of the middle lake-phase deposition covering layer 22 is H2, and the 23-degree of the lower ancient river bed sand gravel layer is H3.
An impervious wall 8 is arranged at the upstream of the earth-rock cofferdam 1, and the impervious wall 8 penetrates through the earth-rock cofferdam 1 and the foundation covering layer and is vertical to the horizontal plane; a downcomer well 6 is arranged at the downstream of the earth-rock cofferdam 1, the upper part of the downcomer well 6 is opened on the ground, and the bottom of the downcomer well 6 is communicated with a riverbed sand gravel layer 23, is arranged vertical to the horizontal plane and is arranged vertical to the horizontal plane; a plurality of granular-body-dispersing piles 5 are arranged in the foundation covering layer between the impervious wall 8 and the downcomer well 6, the granular-body-dispersing piles 5 are gravel piles, the length of each gravel pile is larger than the thickness H2 of the lake-phase deposition covering layer 22, and the upper parts of the gravel piles are required to extend into the gravel layer 21 to a certain depth and extend into the gravel layer 23 at the lower parts to a certain depth, so that vertical and horizontal water permeable channels of the gravel piles are formed. The downcomer well 6 ensures that underground water in the gravel pile area seeps downwards through the water pumping, and the underground water is pumped into the downcomer well 6 through the ancient river bed sand gravel layer 23 and is discharged.
As shown in fig. 2, the foundation structure with deep overburden according to the present invention can be applied to a certain project in the southwest region of our country, the height of the upstream earth-rock cofferdam 1 of the project is 60m, the depth H of the foundation overburden 2 is 71m, wherein the thickness H1 of the upper sand gravel layer 21 is about 6m, the middle lake phase deposition overburden 22 is a low liquid limit clay layer, the thickness H2 is about 50m, and the thickness H3 of the lower ancient river bed sand gravel layer 23 is about 15 m. The downstream of the cofferdam is a concrete faced rockfill dam, the rockfill dam foundation excavation bottom elevation G3, and the total height of the foundation pit excavation side slope 7 of the dam at the upstream of the foundation pit is about 75 m.
The middle lake-phase sediment covering layer 22 is reinforced by gravel piles, the diameter of the pile body of each gravel pile is 1m, the row spacing of the gravel piles is 3m in the upstream area L1 range, and the row spacing of the gravel piles is 2.5m in the downstream area L2 range. When in use, the upper pile head of the gravel pile extends into the sand gravel layer for 0.5m, and the lower pile bottom extends into the ancient river bed sand gravel layer 23 for 0.5 m. Two rows of five downcomer wells 6 are arranged at the downstream slope foot of the cofferdam, the diameter of each downcomer well 6 is 0.8m, the upper part of each downcomer well is opened on the ground, and the bottom of each downcomer well is communicated with the ancient river bed gravel layer 23.
According to the utility model, after the lake-phase deposition covering layer 22 is reinforced by the gravel pile with good water permeability, the gravel pile, the upper horizontal water-permeable gravel layer 21 and the downstream horizontal water-permeable ancient river bed gravel layer 23 form continuous vertical and horizontal water-permeable channels, and under the action of vertical pressure, saturated water in the soil body is extruded into the gravel pile, vertically flows to the upper sand gravel layer and the lower sand gravel layer along the gravel pile and is discharged out of the soil-rock cofferdam 1.
If the water pressure in the lower ancient river bed sand gravel layer 23 is large and the horizontal seepage channel is too far, the underground water in the gravel pile is not easy to be discharged to the lower part. Meanwhile, when the excavation depth of the dam foundation pit at the downstream of the cofferdam is close to the lower limit of the lake-facies deposition covering layer 22, the excavation slope surface of the foundation pit is influenced by the water pressure jacking in the bottom ancient river bed gravel layer 23, and the foundation pit is easy to damage. Consequently need set up downcomer well 6, draw water through the water pump in succession, realize that groundwater passes through bottom ancient river bed gravel layer 23 and flows to the tube-well in the gravel pile, can improve the effective stress of gravel pile and inter-pile soil, improve ground shear strength and side slope stability, reduce or release bottom ancient river bed gravel layer 23 water pressure simultaneously. After the gravel pile replaces the soil body, the composite foundation has the beneficial effects of improving the bearing capacity and the deformation modulus of the composite foundation.
The utility model has the following use effects:
the natural permeability coefficient of the lake deposit overlay 22 is about 2.9 x 10-6cm/s, consolidation coefficient of about 0.4MPa-1And when the upper cofferdam is filled, the maximum excess pore water pressure in the covering layer is about 1.5MPa, and the dissipation time required for the consolidation degree to reach 80% is more than 10 years. After the gravel pile with the diameter of 1m is adopted to reinforce the foundation, the gravel pile is used for vertical bidirectional drainage, the consolidation degree reaches more than 95%, and only 90 days are needed, so that the engineering use requirement is completely met.
And (II) the natural shear strength effective stress index cohesion c of the lake phase deposition covering layer 22 is 42kPa, the internal friction angle is 20 degrees, the compressive stress is basically converted into the excess pore water pressure after the cofferdam is loaded, the effective stress of the foundation soil body is still the natural state soil body stress, and the shear strength cannot be improved. After the gravel pile is adopted for reinforcement, the effective stress index cohesion c of the composite foundation is 34.69kPa, the internal friction angle is 23.59 degrees, and the compressive stress is basically converted into the effective stress of the soil body after the cofferdam is loaded. The safety coefficient of the cofferdam downstream slope in the cofferdam construction period shown in figure 1 is improved to 1.51 from less than 1 in a natural state. The slope stability safety factor after the excavation of the dam foundation pit shown in figure 2 is also improved to 1.368.
And (III) when the foundation is treated only by using the gravel piles, the arrangement distance of the gravel piles in the cofferdam pressing occupying area L2 needs 2 m. By applying the technical scheme, after the downcast pipe well is arranged at the toe of the slope, the gravel piles and the underground water level of soil among the piles are further reduced, the effective stress is further improved, the arrangement distance of the gravel piles in the cofferdam compressed area L2 is adjusted from 2m to 2.5m, the number of the gravel piles is reduced by about 36%, and the engineering investment is greatly saved.
It is to be understood that the present invention has been described with reference to certain embodiments, and that various changes in the features and embodiments, or equivalent substitutions may be made therein by those skilled in the art without departing from the spirit and scope of the utility model. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the utility model without departing from the essential scope thereof. Therefore, it is intended that the utility model not be limited to the particular embodiment disclosed, but that the utility model will include all embodiments falling within the scope of the appended claims.
Claims (6)
1. A deep overburden foundation structure including an earth-rock cofferdam (1) and a foundation overburden (2) below the earth-rock cofferdam (1), the foundation overburden (2) including an upper gravel layer (21) or a man-made water permeable layer, a middle lake-deposited overburden (22) and a lower ancient river bed gravel layer (23); the method is characterized in that:
an impervious wall (8) is arranged at the upstream of the earth-rock cofferdam (1), and a downcomer well (6) is arranged at the downstream of the earth-rock cofferdam (1);
a plurality of granular piles (5) are arranged in the foundation covering layer between the impervious wall (8) and the downcomer well (6).
2. The deep overburden foundation structure as recited in claim 1, characterised in that said lower part of said granular ballast piles (5) is extended into said layer of ancient river bed sand gravel (23).
3. Deep overburden foundation structure as claimed in claim 1, characterized in that said granular piles (5) communicate the upper and lower layers of said foundation overburden (2).
4. Deep overburden foundation structure as claimed in any of the claims 1 to 3, characterized in that said granular material piles (5) are gravel piles.
5. Deep overburden foundation structure as claimed in claim 1, characterized in that said cut-off wall (8) extends through the earth-rock cofferdam (1) and the foundation overburden and is perpendicular to the flow direction of the river water.
6. The deep overburden foundation structure as claimed in claim 1, wherein said downcomer well (6) is in communication at its bottom with a layer of ancient river bed gravel (23).
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| Application Number | Priority Date | Filing Date | Title |
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| CN202121622335.9U CN215669631U (en) | 2021-07-16 | 2021-07-16 | Deep overburden foundation structure |
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| CN202121622335.9U CN215669631U (en) | 2021-07-16 | 2021-07-16 | Deep overburden foundation structure |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116522823A (en) * | 2023-05-22 | 2023-08-01 | 中国水利水电科学研究院 | Fluid-solid coupled slope stability analysis method |
| CN116556264A (en) * | 2023-06-06 | 2023-08-08 | 中国水利水电科学研究院 | Slope reinforcement method combining vertical drainage body with drainage |
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2021
- 2021-07-16 CN CN202121622335.9U patent/CN215669631U/en active Active
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116522823A (en) * | 2023-05-22 | 2023-08-01 | 中国水利水电科学研究院 | Fluid-solid coupled slope stability analysis method |
| CN116522823B (en) * | 2023-05-22 | 2023-10-20 | 中国水利水电科学研究院 | Fluid-solid coupled slope stability analysis method |
| CN116556264A (en) * | 2023-06-06 | 2023-08-08 | 中国水利水电科学研究院 | Slope reinforcement method combining vertical drainage body with drainage |
| CN116556264B (en) * | 2023-06-06 | 2023-09-22 | 中国水利水电科学研究院 | Slope reinforcement method combining vertical drainage body with drainage |
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