Traditional Culture Encyclopedia - Hotel reservation - What are the methods and procedures for optimization of earthwork excavation scheme and site management of ultra-deep foundation pit?

What are the methods and procedures for optimization of earthwork excavation scheme and site management of ultra-deep foundation pit?

Taking xxx building project as an example, this paper expounds the technical scheme optimization and site management in the earthwork excavation construction stage of ultra-deep foundation pit. Under the guidance of value engineering, through scientific organization and reasonable planning, the excavation task of ultra-deep foundation pit has been effectively completed, and good results have been achieved in realizing technical, economic, social and environmental benefits.

1 project overview

1. 1 project introduction

Xx building is located in the core of "America, Thailand and Heng" advanced business district on xxxxxx Road. The building is 6 1 floor, with a height of 24 1m and a total construction area of about 200,000 m2. It is a landmark building integrating the functions of a five-star luxury hotel and a super-5A intelligent office building. As a supporting project of Shanghai World Expo 20 10 planning function, the project will add a new urban landscape to xx after completion (Figure 1).

1.2 foundation and enclosure form

The project consists of a tower, a surrounding podium and a four-story basement. The design of foundation pit construction adopts the top-down construction of tower and the top-down construction of surrounding podium. Tower foundation adoption

For 800mm cast-in-place pile, the skirt building enclosure adopts 800 mm wide underground continuous wall except the south side, and the tower enclosure adopts 1000mm wide underground continuous wall, which is adopted in the design because the tower is constructed first.

1 100mm cast-in-place pile is used for pit enclosure, and triaxial cement mixing pile and compaction grouting are used for water stop curtain (as shown in Figure 2). The foundation pit of the tower is provided with three reinforced concrete supports (as shown in Figure 3).

1.3 engineering features

This project is located at the intersection of xxxxxxx Road, with complex surrounding environment and dense underground pipelines. The excavation depth of the foundation pit is 20. 1m, and the deepest part is 24.7m, which belongs to the ultra-deep foundation pit construction. The surrounding buildings have high protection requirements, tight construction period and great construction difficulty. The project started in July 2007, and the foundation pile and enclosure construction of the iron tower was completed in June 5438+ 10. In order to meet the time limit for pouring the large bottom plate before the Spring Festival in 2008, the site headquarters put forward the goal of completing the excavation and support tasks in three months. The earthwork volume of the iron tower is about 65,438+200,000 m3, and the average daily excavation is about 2000m3 to meet the schedule requirements. Completing such a large-scale excavation in the city center with urgent construction period puts forward higher requirements for excavation scheme and site management.

2 earthwork excavation scheme optimization

2. 1 Design excavation principle

"Layering, blocking, symmetry, quick excavation and quick support to keep the stress balance of foundation pit enclosure" is the principle of foundation pit excavation construction. The first floor is used to organize the excavation of the pool to complete the trestle, and it is used as the construction working face of the excavator. The design scheme of the second floor is island excavation (as shown in Figure 4). In the design scheme, the earthwork in the basin is excavated first, and then the earthwork on the east and west sides of the pit is excavated. The passive earth pressure formed by the soil in this scheme area is not fully utilized, and eventually braces are formed, so the curing time will affect the early excavation of the lower soil.

2.2 Optimized implementation of the second-floor earthwork excavation scheme.

Because the excavation period at the bottom of the trestle and the middle of the south and north pits is about 10 day (earthwork volume is about 20,000m3), the completion of the second support will be delayed by nearly 10 day compared with the original design scheme, so the current excavation method is adopted from the corners (northwest corner and southeast corner) to shorten the technical intermission time. (1) After the completion of partial excavation, the excavation of part (2) will be carried out immediately, and the four corners of the tower will be obliquely symmetrical in turn, thus reducing the bending moment of the mid-span enclosure. (4) Final excavation of regional earthwork. During this period, the secondary support has been completely completed and entered the maintenance period, which laid the foundation for the lower earthwork excavation in advance (Figure 5).

(1) When excavating, fully consider the space-time effect, that is, "digging" and "supporting" alternate construction.

(2) In order to improve the early strength of the stent, the stent is mixed.

Early strength agent is added to the concrete, so that the formwork can be removed in advance and the subsequent excavation can be carried out in time.

(3) Reasonably divide the construction joints, and avoid setting the construction joints in the weak parts and in the same direction. When there are different grades of concrete, the joints should be treated with mature steel mesh pieces at present, and at the same time, pay attention to the lap length of the main reinforcement in the support to meet the requirements.

2.3 the third layer earthwork excavation sequence optimization

In the original design scheme, the earthwork in area ① of the foundation pit was excavated first, and then the area ② of the east and west sides was excavated after the earthwork excavation in the north and south pit basins was completed, so as to complete the east-west lateral support construction and finally complete the corner support. However, according to the analysis, because the east side of the foundation pit of the iron tower is close to the temporary foundation, the nearest place is about 15m, and the buried depth of the temporary foundation is shallow (about 7m), if this design scheme is adopted for excavation, the east-west cross brace in the middle will be completed on the side of 15d after large-scale excavation of the foundation pit, and the maintenance body will be greatly deformed due to the squeezing effect of the temporary foundation. According to the observation data of temporary houses, the foundation settlement and inclination are obvious when the third layer of earthwork is excavated (settlement 14mm, inclination 15 mm, which is close to the design alarm value), which is the period of maximum deformation in the excavation stage. If we don't take corresponding measures, it will aggravate the original cracks in temporary houses and cause many adverse effects.

Key points of implementation of optimization scheme (as shown in Figure 6):

(1) After the excavation of area ① and area ② is completed, the third brace at the corner of the foundation pit will be completed.

(2) After the excavation of Area ③ is completed, the east-west support of the south and north pits will be formed.

(3) After the earthwork excavation in areas ④ and ⑤ is completed, the third diagonal brace at the four corners of the foundation pit is formed.

(4) Excavate the earthwork in Area 6, complete the supports at both ends of the trestle, and connect the north and south vertical supports.

(5) Finally, the central earthwork is excavated to complete the central support. Leaving soil in the middle until the final excavation can resist the uplift at the bottom of the foundation pit.

2.4 the fourth floor earthwork excavation sequence optimization

The original design scheme is the same as the third layer earthwork excavation sequence:

Key points of adjustment plan implementation (Figure 7):

(1) The fourth floor earthwork excavation takes the post-cast strip as the dividing line, first excavate the peripheral 1. 1m thick terrace area clockwise, and add cushion.

8 mm steel mesh, steel support is set in post-cast strip, so that the outer bottom plate of 1. 1m forms an inner hoop (support) system, which bears part of the lateral pressure of maintenance and reduces the supporting load of reinforced concrete in the previous road.

(2) After the peripheral bottom plate is formed, the deep earthwork of the foundation pit is excavated, and finally the large bottom plate with a thickness of 3.2m in the post-pouring zone is completed.

2.5 Analysis of foundation pit detection data

Table 1 Monitoring data of foundation pit

2. The design alarm value of envelope shape variable is 55 mm. ..

As can be seen from the table 1:

(1) The maximum deformation of foundation pit maintenance occurs when the internal 3.2m thick large bottom plate is poured. According to the large distance between the third support and the basement (up to 8.2m, as shown in Figure 3), there are certain hidden dangers in the safety of foundation pit. Therefore, when the foundation pit is excavated according to the original design scheme, additional reinforcement measures must be considered.

(2) First, the large floor area outside 1. 1m was excavated, and the annular floor was poured to form a rigid support system, which reduced the third support pressure, and the effect was obvious. According to the observation data, the deformation of the support is reduced to 52.85 mm; After pouring the annular 1. 1m thick bottom plate. The supporting axial force is basically stable, which increases slowly with the increase of the exposure time of the foundation pit, and decreases gradually after the completion of the bottom plate, indicating that the large bottom plate of the outer ring 1. 1m has played an effective supporting role.

(3) The data show that the earth excavation in the original 3.2m large floor area of the inner ring has obvious effect on resisting the uplift of the foundation pit. Through the steel transfer support set in the post-pouring zone, the whole concrete layer of the large bottom plate formed a balanced horizontal support. The later observation data showed that the deformation of the enclosure and the axial force of the support gradually eased after the completion of the large bottom plate.

(4) Due to the effective implementation of excavation measures, the deformation of the maintenance body and the axial force of the support failed to reach the design alarm value, and the safety performance of the foundation pit remained in good condition during the whole excavation process.

From the excavation of the fourth floor (65438+February 2007 16) to the completion of the pouring of the big bottom plate (65438+20081October 18), the total construction period is more than 30 days, which is 15d earlier than originally planned at this stage, giving full play to it.

3 Site management in earthwork excavation stage

3. 1 organization and management

(1) According to the characteristics of the project, establish the management system of the site project department headed by the owner, maximize the integration of resources and improve work efficiency.

(2) Establish a coordination system for earthwork excavation in the morning and evening to control the pace of construction progress in days.

(3) Establish a "comprehensive duty room" system, which is used as the excavation site headquarters at night, and the owner's representative, supervision department, general contractor, excavation, dewatering and monitoring units work together to improve the efficiency of site problem handling.

(4) Strengthen the effective implementation of on-site safety measures, such as foundation pit fence, horizontal safety net, foundation pit safety ladder, foundation pit lighting, distribution box setting and pavement anti-skid measures. The construction unit is required to prepare a detailed special plan and strictly implement it after approval.

(5) To speed up the lap construction of subsequent processes, such as broken piles and shuttering, and clear them in time to strive for the working face for the next process.

(6) Take reasonable shift-shifting measures, and stop the inspection and maintenance of earth-moving machinery and pumping equipment during night construction according to the regulation of "two stops and one stop" in Jing 'an District of Shanghai, so as to ensure normal construction and reduce the interference of objective factors.

3.2 Technical management

(1) Requires the construction party to timely feedback the deformation observation data of temporary buildings, supports, enclosures, floors and pipelines.

(2) The precipitation level should be observed once in the morning and once every 6 hours when necessary, and the groundwater level should be closely monitored.

(3) Organize a special meeting on deep foundation pit excavation, conduct safety expert argumentation on the excavation scheme, and require the construction unit to effectively fulfill the procedures of quality and safety technical disclosure.

(4) Require the construction unit to complete the testing and approval of equipment and materials in time, and handle relevant contracts, safety agreements and engineering insurance in time.

(5) When designing the trestle, the load capacity is designed considering that four excavators are standing on the trestle to borrow soil at the same time (the design load of the trestle surface is 25KN/m2). In addition, the width of the trestle can meet the turning radius of earthwork vehicles; The foundation piles of the trestle site should be constructed in advance to ensure that they can be used in time after reaching the design strength, so as to carry out earthwork immediately.

(6) Require the construction party to prepare the emergency plan and accident treatment plan for foundation pit excavation in advance.

(7) Grasp the principle of "survey recheck, slope excavation and prevention of overbreak" and return the slope or overbreak in time as required.

(8) To strengthen the concrete curing of supporting beams, it is necessary to track the 3d and 7d strength pressure test reports in time to provide data support for scheme implementation.

(9) During the earthwork excavation of South and North Pits, two excavators will work at the same time in the longer part of the dump line and turn over the soil by relay.

(10) Minimize the workload of secondary excavation and speed up earthwork shipment.

(1 1) Increase the number of observation points, improve the monitoring density of foundation pit, and shorten the observation period in time.

(12) Take effective remedial measures for local leakage of enclosure, such as using plugging agent, building retaining dam and pumping water. Drainage operation, and make full use of pumped wastewater after precipitation treatment, such as maintenance, dust-proof spraying on site, flower bed watering, etc.

(13) The examination and approval of monitoring, excavation, precipitation, environmental protection and energy saving were completed ahead of schedule, which created technical conditions for excavation.

3.3 Coordinated management

(1) Establish an external coordination system for complaints against nuisance, visit regularly, and deal with residents' concerns in a timely manner.

(2) Establish an inspection system that actively cooperates with the urban management supervision department.

(3) Establish the goal of "Ensuring Magnolia Officinalis and Striving for Luban Prize", and declare "Shanghai Standard Chemical Site and Observing Construction Site"; Strive for the support of the district office and other government departments to create a good external environment.

(4) The muck certificate, night certificate, disposal certificate and underground structure construction permit shall be handled in declare in advance.

(5) Inform major hazard sources in time, and announce information such as daughter's notice in advance for night construction.

(6) Strengthen night patrol, strictly monitor noise and light pollution, and clean up vehicles and sprinkle soil in time.

(7) Set up the Node Target Award, No Safety Accident Competition Award, etc. , do a good job of mobilization for pre-holiday safety construction, and take measures to prevent cold and keep warm.

(8) The district trade union organized a conference on migrant workers' rights protection to stabilize their emotions.

(9) Actively prepare the pouring scheme for the large bottom plate, including the blue prints.the design and scheme confirmation, so as to realize the "seamless connection" of working procedures as far as possible; Set up a "countdown card for pouring large bottom plate" and implement incentive measures to catch up with work.

(10) According to the adjustment of the construction scheme, communicate with the design in time, and complete the change and improvement of the construction technology under the guidance of the design.

4. Effect of program implementation

This case is guided by value engineering, and the comprehensive benefits reflected in the project implementation process are as follows:

(1) After the optimization of the excavation scheme, the construction period of this project is shortened by nearly 50 days compared with the original design scheme, which shows the benefits of shortening the construction period and reducing the cost.

(2) The safety performance in the process of foundation pit excavation is improved. After the implementation of the scheme, the replacement of the support is completed in the shortest time, which makes the pouring time of the big bottom plate advance. The monitoring data show that the stress changes of the envelope structure are balanced, which proves that the optimization scheme is feasible.

(3) The plan pays attention to the space-time effect, organizes scientific flow construction, reduces the workload of secondary earth moving, improves the digging efficiency, and embodies good technical benefits.

(4) By strengthening the site management led by the owner, noise, dust and light pollution are immediately controlled. The monitoring data show that the settlement and inclination of surrounding buildings are controlled during the excavation stage, and good environmental benefits are achieved.

(5) Strengthen the coordination and communication with all parties in the construction process, organize the activity of "Building a Civilized Community in the Street of the Construction Site", and establish the concept of "building quality products, being honest and trustworthy, and serving the society", which embodies good social effects.

5 conclusion

The completion of Huamin Hao Di Building will add a new urban landscape to Shanghai's "Meihengtai" business circle. Starting with the design scheme, this case puts forward the adjustment measures of the super high-rise building in the earthwork excavation stage according to local conditions, and adopts the site management led by the owner, which has achieved good results and provided reference experience for the earthwork construction of deep foundation pit in complex urban environment.

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