CN110685286A - A deep foundation pit support construction technology adjacent to the road under complex geological conditions - Google Patents

Abstract

The invention discloses a deep foundation pit support construction process adjacent to a road under complex geological conditions, comprising the following steps: Step 1. Excavate the foundation pit beside the road to the rock layer, carry out grading construction, and form a first foundation pit ; Step 2, drive the first column pile along the edge of the pit bottom of the first foundation pit to form the first inclined column support; Step 3, excavate the rock layer at the pit bottom of the first foundation pit to form the second foundation pit, and carry out placement Slope construction, and then bolt support; step 4, driving a second column pile along the edge of the pit bottom of the second foundation pit to form a second inclined column support. The present invention supports the deep foundation pit by adopting the method of inclined column support + bolt support + inclined column support, so as to solve the difficulty of supporting the deep foundation pit adjacent to the road under complex geological conditions, high construction cost and easy In the event of safety hazards and other problems, the deep foundation pit support construction adjacent to the road under complex geological conditions has been realized, providing a successful practical experience for the field of support construction.

Description

A deep foundation pit support construction technology adjacent to the road under complex geological conditions

technical field

The invention relates to the technical field of foundation pit support construction, in particular to a deep foundation pit support construction technique adjacent to a road under complex geological conditions.

Background technique

The foundation pit support is a temporary measure of support, reinforcement and protection and groundwater control for the side wall of the foundation pit and the surrounding environment to ensure the safety of the construction of the underground structure and the surrounding environment of the foundation pit. The foundation pit support project is a temporary project. The design safety reserve is relatively small, but its high cost, large number of starts, and complex technology are the most challenging technical difficulties in construction projects, and it is also the focus of reducing project cost and ensuring project quality.

The forms of foundation pit support mainly include row pile support, cement retaining wall, soil nail wall, underground diaphragm wall support, reverse arch wall, etc. Generally, these foundation pit support forms are mainly based on the depth of the foundation pit. The application is different. However, for the deep foundation pit support under complex geological conditions, the geological conditions are basically the emergence of soft and hard geological layers, which has always been the focus and difficulty of the construction party. How to use these foundation pit support forms requires It is determined according to the specific and complex geological conditions of the deep foundation pit. Taking the CLZF-2 bid project of the Chengdu-Chuanzhusi section of the Chengdu-Lanzhou Railway undertaken by the applicant as an example, during the construction of the Huangshengguan and Chuanzhusi station buildings, the temporary site on site was relatively narrow, and the excavation line of the foundation pit was temporarily away from the site. The road is about 50cm, the depth of the foundation pit is more than 5m, and the geological conditions are complex. The upper part of the stratum is a loose, high-humidity soil layer, and the lower part is a hard and compact rock layer. It is not suitable for foundation pits with a depth of more than 5m), then because the soil layer is only 2-3m and the road is adjacent, the vertical retaining plate cannot effectively retain the soil, and the foundation pit wall is not suitable for vertical type. It is easy to deform and collapse under pressure. Correspondingly, if the existing pile supporting structure is used, due to the existence of the hard rock layer, the concrete cast-in-place pile is subjected to a large shear force and cannot form an effective supporting effect. . Therefore, the traditional single support form cannot form an effective support structure, and if the support form is used in combination, since there are no examples to draw on, according to the characteristics of each support form, the technician can think of using a continuous vertical However, the main disadvantage of this method is that the rock layer is not a vertical grading structure, resulting in a large gap between the rock layer slope and the row of piles, and a large amount of soil needs to be backfilled To fill, the construction volume is large, and the later cleaning is troublesome. At the same time, due to the deep depth, it is necessary to make high-height cast-in-place piles, and the construction cost is high. In addition, when the slope collapses and rolling stones occur, the piles intercept the shear force and are affected. If the force is too large, it is easy to cause potential safety hazards. Therefore, this method is not suitable. It is urgent to develop a construction technology suitable for deep foundation pit support under complex geological conditions, especially when the slope surface is close to the road.

SUMMARY OF THE INVENTION

The purpose of the present invention is to: in view of the above-mentioned problems, provide a deep foundation pit support construction technology near the road under complex geological conditions, the present invention adopts the mode of inclined column support + bolt support + inclined column support To support the deep foundation pit, it solves the problems of difficult support, high construction cost, and potential safety hazards for the deep foundation pit adjacent to the road under complex geological conditions.

The technical scheme adopted in the present invention is as follows: a deep foundation pit support construction technology adjacent to a road under complex geological conditions, is characterized in that, comprises the following steps:

Step 1. Carry out foundation pit excavation beside the road until the bottom of the foundation pit reaches the rock layer, and at the same time carry out grading construction on the formed foundation pit to form the first foundation pit;

Step 2. Drive a first column pile along the edge of the pit bottom of the first foundation pit, support a retaining plate inside the first column pile and support the top with a first diagonal brace, and fill and compact the inner side of the retaining plate to form a first inclined column support;

Step 3. Excavate the rock layer at the bottom of the first foundation pit to form the second foundation pit. The excavation starting point is 0.5-2m away from the support of the first inclined column, and the excavation depth reaches the design depth. Grading construction, and then perform bolt support for the rock slope of the second foundation pit according to the existing bolt support construction standards;

Step 4: Drive a second column pile along the edge of the bottom of the second foundation pit, support a stone block on the inner side of the second column pile, and use a second inclined support to support the top to form a second inclined column support.

In the above method, first, for the construction of deep foundation pits with soft and hard geological structures, the method of excavating foundation pits in layers is used for support, and the problems of different geological conditions are solved by the method of layered support. To avoid the defect that the same support structure cannot be applied to different geological conditions, further, through the design of inclined column support + bolt support + inclined column support, inclined column support is used in the uppermost geological layer to provide lateral support for the roadbed At the same time, it avoids the collapse of the loose foundation soil around the subgrade under the action of heavy pressure and rain, reduces the influence of the foundation pit on the strength of the road subgrade, and also prevents the collapsed foundation soil from rolling down into the second foundation pit. Affect the construction and provide good construction conditions for the formation of the supporting structure of the second foundation pit. The rock layer (hard layer) is supported by bolts, mainly to prevent the collapse of the rock layer and the rolling of large rocks. The inclined column support at the bottom of the second foundation pit not only solves the problem of the second foundation pit support, but also avoids the use of row pile support with a high column pile structure, which greatly reduces the amount of backfill and construction cost, eliminates potential safety hazards, at the same time, it also solves the problem that the supporting structures cannot be effectively cooperated when using various supporting structures in combination, and realizes the deep foundation pit support adjacent to the road under complex geological conditions. It provides successful practical experience in the field of support construction.

Further, considering that the crushed stone rolled from the rock layer side slope will impact the column pile supported by the second inclined column, especially the connection between the second column pile and the bottom of the foundation pit, the degree of stress concentration formed is relatively large. Fill soil between the stone retaining plate and the rock layer slope to form a buffer soil layer to solve the problem of stress concentration at the connection caused by the impact of the crushed stone on the second column pile.

Further, considering the problems of rammed earth backfill in the early stage and the convenience of site clearance in the later stage, the backfill height of the buffer soil layer is between 2/5-3/5 of the height of the second column and pile, and the amount of backfill rammed earth should be reduced as much as possible. At the same time, the basic role that the buffer soil layer can play is ensured.

In the present invention, since it belongs to the deep foundation pit support construction, there will be a problem of rock water seepage in the rock layer. A drainage ditch is excavated, the drainage ditch forms an annular shape along the connection, a cover plate with through holes or through grooves is laid on the top of the drainage ditch, and the buffer soil layer is located on the cover plate. The seepage water of the rock layer slope penetrates into the drainage ditch through the buffer soil layer, and then drains to the drainage place through the drainage ditch, which solves the adverse effect of rock seepage on the foundation pit.

Further, in order to better perform the grading construction of the second foundation pit, the grading slope of the grading construction of the second foundation pit is 1:0.25.

Further, in step 4, the bolt construction is preferably as follows: drilling a hole on the rock vertical wall to the design depth, putting a tie rod in the hole, pouring cement mortar into the rock to combine with the rock to form a strong tensile bolt, and one end of the bolt is fixed at the On the rock wall, the other end is anchored in the rock layer, and is supported by this shaped bolt.

To sum up, due to the adoption of the above technical solutions, the beneficial effects of the present invention are: the present invention supports the deep foundation pit by adopting the method of inclined column support + bolt support + inclined column support, which solves the problem of solving the problem of deep foundation pit support. Under complex geological conditions, the deep foundation pit support near the road is difficult to support, the construction cost is high, and it is prone to potential safety hazards. Experience.

Description of drawings

FIG. 1 is a schematic diagram of a deep foundation pit supporting structure near a road under complex geological conditions of the present invention. Labels in the figure: 1 is the road subgrade, 2 is the first foundation pit, 3 is the second foundation pit, 4 is the rock layer, 5 is the first inclined column support, 501 is the first column pile, 502 is the retaining plate, 503 is the first diagonal brace, 504 is the wooden support pile, 6 is the backfill layer, 7 is the diagonal bracing platform, 8 is the bolt support, 9 is the second diagonal column support, 901 is the second column pile, 902 is the stone retaining plate, 903 is the second diagonal brace, 10 is the buffer soil layer, 11 is the drainage ditch, and 12 is the base soil layer.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings.

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example

Taking the CLZF-2 bid project of the Chengdu-Chuanzhusi section of the Chengdu-Lanzhou Railway undertaken by the applicant as an example, the project includes a total of 5 stations including Maoxian Station, Zhenjiangguan Station, Songpan Station, Chuanzhusi Station and Huangshengguan Station , Among them, during the construction of Huangshengguan and Chuanzhusi station buildings, the temporary site on site was relatively narrow, the excavation line of the foundation pit was about 50cm away from the temporary road on site, the depth of the foundation pit was more than 5m, the geological conditions were complex, and the upper stratum was loose and humid. In a very high soil layer, the lower part is a hard and compact rock layer, and the traditional support structure cannot be applied. In order to solve this problem, the present invention, as shown in Figure 1, adopts the deep foundation pit support construction technology including the following steps:

Step 1. Excavate the foundation pit next to the road subgrade 1 until the bottom of the foundation pit reaches the rock layer 5, that is, dig 2-3m first until the relatively soft foundation soil layer is dug through, and at the same time carry out grading construction for the formed foundation pit , the first foundation pit 2 is formed, and the slope and slope coefficient in the grading construction are selected according to the original design requirements, for example, 1:0.5 can be used in this embodiment;

Step 2. Drive a first column pile 501 along the edge of the first foundation pit, support a retaining plate 502 inside the first column pile 501 and support the top with a first diagonal brace 503, and fill the inner side of the retaining plate to form a first The inclined column supports 5, and the rammed earth layer forms the backfill layer 6;

Step 3. Excavate the rock layer 5 at the bottom of the first foundation pit 2 to form the second foundation pit 3, and the excavation starting point is 0.5-2m away from the first diagonal brace (in this embodiment, the excavation starting point is 1.5m away from the most suitable) to form a diagonal support platform 7, and the excavation depth of the second foundation pit 3 reaches the design depth of 3m. When excavating the second foundation pit 3, it is necessary to carry out grading construction on the second foundation pit 3, and the grading construction of the grading construction The slope is 1:0.25;

Step 4. According to the existing bolt support construction standards, perform bolt support 8 on the rock vertical wall of the second foundation pit, that is, drill holes on the rock vertical wall to the design depth, put a tie rod in the hole, pour cement mortar and The rock is combined into a strong tensile steel anchor, one end of the steel anchor is fixed on the rock wall, and the other end is anchored in the rock layer, and the stability of the rock slope is protected by the anchor support (the steel anchor supports As a preferred example, it can also use other bolt support structures, such as wire rope mortar bolt support or pipe-slot bolt support);

Step 5: Drive a second column pile 901 along the bottom edge of the second foundation pit 3 , support a stone blocking plate 902 inside the second column pile 901 and use a second diagonal brace 903 to support the top to form a second diagonal column support 9 .

In the above construction process, the first inclined column support 5 used in the first foundation pit 2 is an existing common inclined column support structure, and its construction requirements and construction operations can be implemented according to the existing standards, that is, the retaining plate 902 is set at the The inner side of the first pillar 501 and the outer side of the first pillar 501 are supported by a first diagonal brace 503, the bottom end of the first diagonal brace 503 is on the wooden brace 504, and the inner side of the retaining plate 502 is backfilled with soil, which will not be described in detail here. . Correspondingly, the second inclined column support used in the second foundation pit 3 is also an existing common inclined column support structure, which can be implemented according to the existing construction standards. In order to better enable the second inclined column support to play the role of supporting the stone, the soil retaining plate 502 is replaced with a concrete or steel stone retaining plate 902 with stronger material strength, which does not need to be backfilled inside the stone retaining plate 902 to form the backfill layer 6 .

Further, considering that the crushed stones rolled from the side slope of the rock layer 4 will impact the second column pile 901 of the second inclined column support 9, especially the connection between the second column pile 901 and the bottom of the foundation pit, the formed The degree of stress concentration is relatively large. As shown in FIG. 1 , the buffer soil layer 10 is formed by filling and compacting between the stone retaining plate 902 and the slope of the rock layer 4 to solve the problem of stress concentration at the connection caused by the impact of the crushed stone on the column pile.

Further, considering the convenience of backfilling with rammed earth in the early stage and site clearance in the later stage, the backfill height of the buffer soil layer 10 is between 2/5 and 3/5 of the height of the second pile 5, 5/10 or 3/5, the specific value is selected according to the actual situation. This setting method can reduce the amount of backfill rammed earth as much as possible, and at the same time ensure the basic role that the buffer soil layer 10 can play.

In the present invention, since it belongs to the deep foundation pit support construction, there will be a problem of rock water seepage in the rock layer 4 part. A drainage ditch 11 is excavated at the bottom connection, and the drainage ditch 11 forms a ring shape along the connection. The top of the drainage ditch 11 is laid with a cover plate with a through hole or a through groove (not shown in the figure), and the buffer soil layer 10 on the cover. The seepage water on the slope of the rock layer 4 penetrates into the drainage ditch 11 through the buffer soil layer 10, and then drains to the drainage place through the drainage ditch 11, which solves the adverse effect of the rock seepage on the foundation pit.

In the above-mentioned construction technology, it is suitable for the deep foundation pit support construction in which there are two kinds of stratum structure, soft and hard when excavating the deep foundation pit, that is to say, when the rock layer in the above-mentioned embodiment is replaced with a harder soil layer, It is also applicable. The support of deep foundation pit is realized by adopting inclined column support + bolt support + inclined column support, which solves the difficulty of supporting and constructing deep foundation pit adjacent to roads under complex geological conditions. Due to the high cost and potential safety hazards, the deep foundation pit support construction adjacent to the road under complex geological conditions has been realized, providing a successful practical experience for the field of support construction.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (6)

1. a deep foundation pit support construction technique near road under complex geological conditions, is characterized in that, comprises the following steps: Step 1. Carry out foundation pit excavation beside the road until the bottom of the foundation pit reaches the rock layer, and at the same time carry out grading construction on the formed foundation pit to form the first foundation pit; Step 2. Drive a first column pile along the edge of the pit bottom of the first foundation pit, support a retaining plate inside the first column pile and support the top with a first diagonal brace, and fill and compact the inner side of the retaining plate to form a first inclined column support; Step 3. Excavate the rock layer at the bottom of the first foundation pit to form the second foundation pit. The excavation starting point is 0.5-2m away from the support of the first inclined column, and the excavation depth reaches the design depth. Grading construction, and then perform bolt support for the rock slope of the second foundation pit according to the existing bolt support construction standards; Step 4: Drive a second column pile along the edge of the bottom of the second foundation pit, support a stone block on the inner side of the second column pile, and use a second inclined support to support the top to form a second inclined column support. 2 . The deep foundation pit support construction process adjacent to the road under complex geological conditions as claimed in claim 1 , wherein the buffer soil layer is formed by filling and compacting between the stone retaining plate and the rock layer side slope. 3 . 3. The deep foundation pit support construction technique near the road under complex geological conditions as claimed in claim 2, wherein the backfill height of the buffer soil layer is 2/5-3 of the height of the second column pile /5. 4. the deep foundation pit support construction technique near road under complex geological conditions as claimed in claim 1 or 3, is characterized in that, a drainage ditch is dug at the junction of the rock layer side slope and the pit bottom of the second foundation pit, A cover plate with through holes or through grooves is laid on the top of the drainage ditch, and the buffer soil layer is located on the cover plate. 5 . The deep foundation pit support construction technique adjacent to the road under complex geological conditions as claimed in claim 1 , wherein the grading gradient of the grading construction of the second foundation pit is 1:0.25. 6 . 6. the construction technique of deep foundation pit support near road under complex geological conditions as claimed in claim 1, is characterized in that, drilling to design depth on rock vertical wall, putting tie rod in hole, pouring cement mortar and rock Combined into a strong tensile strength bolt, one end of the bolt is fixed on the rock wall, and the other end is anchored in the rock layer, so as to be supported by the shaped bolt.

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