阅读说明：本技术 一种超大型沉井结构联合地基施工方法 (Combined foundation construction method for ultra-large open caisson structure ) 是由 黄建武 吴建国 金涛 汤旅军 李琪 孙斌斌 孙影杰 于 2020-12-21 设计创作，主要内容包括：本发明公开了一种超大型沉井结构联合地基施工方法,主要包括如下步骤：1)在准备新建大型循环水取水区域的滩涂上填筑中粗砂垫层；2)利用中粗砂垫层作为桩架持力层,进行嵌岩钻孔灌注桩施工；3)对钻孔灌注桩下部进行嵌岩施工,填筑钢筋混凝土,作为超大型沉井结构的永久支撑结构；4)将钻孔灌注桩的桩顶部位进行压密注浆,对桩头部位土体进行加固,使桩与土体成为一个整体；5)沉井分级制作分级下沉或分级制作整体下沉,待下沉至设计标高后进行素混凝土封底,浇筑钢筋混凝土底板,将嵌岩灌注桩与底板连接,形成整体；该施工方法有效解决了沉井在制作、下沉过程中的突沉、超沉问题,也解决了沉井就位后的工后沉降问题。(The invention discloses a combined foundation construction method of an ultra-large open caisson structure, which mainly comprises the following steps: 1) filling a medium coarse sand cushion layer on a mudflat of a large circulating water taking area to be newly built; 2) using the medium-coarse sand cushion layer as a pile frame bearing layer to carry out rock-socketed cast-in-situ bored pile construction; 3) carrying out rock embedding construction on the lower part of the cast-in-situ bored pile, and filling reinforced concrete to serve as a permanent support structure of the ultra-large open caisson structure; 4) compacting and grouting the pile top part of the cast-in-situ bored pile, and reinforcing the soil body at the pile head part to integrate the pile and the soil body; 5) the open caisson is made to sink in stages or the whole open caisson is made to sink in stages, plain concrete bottom sealing is carried out after the open caisson sinks to the designed elevation, a reinforced concrete bottom plate is poured, and the rock-socketed cast-in-place pile is connected with the bottom plate to form a whole; the construction method effectively solves the problems of sudden sinking and super sinking of the open caisson in the manufacturing and sinking processes, and also solves the problem of post-construction sinking after the open caisson is in place.)

1. A combined foundation construction method for an ultra-large open caisson structure is characterized by comprising the following steps: the method mainly comprises the following steps:

1) filling a medium coarse sand cushion layer on a mudflat of a large circulating water taking area to be newly built, wherein the thickness of the cushion layer can be determined according to the requirements of preloading and well sinking structure pouring;

2) the middle coarse sand cushion layer is used as a pile frame bearing layer to carry out rock-embedded cast-in-situ bored pile construction, the upper part of the cast-in-situ bored pile is subjected to air drilling, filled with middle coarse sand or broken stones and used as a sand well structure, and the sand cushion layer with the thickness of 3m at the upper part is piled, pre-pressed and becomes a drainage channel, so that a soft soil layer with the deep thickness at the upper part is subjected to pre-consolidation;

3) carrying out rock embedding construction on the lower part of the cast-in-situ bored pile, and filling reinforced concrete to serve as a permanent support structure of the ultra-large open caisson structure;

4) compacting and grouting the pile top part of the cast-in-situ bored pile, and reinforcing the soil body at the pile head part to integrate the pile and the soil body;

5) and (3) making the open caisson in a grading manner and sinking in a grading manner or making the open caisson in a grading manner and sinking integrally, sealing the bottom of the open caisson by plain concrete after sinking to a designed elevation, pouring a reinforced concrete bottom plate, and connecting the rock-embedded cast-in-place pile with the bottom plate to form an integral body.

2. The combined foundation construction method of the ultra-large open caisson structure according to claim 1, wherein: in the step 1), the filling thickness of the medium coarse sand cushion layer is 3m, the plane size of the medium coarse sand cushion layer is 3m larger than that of the open caisson structure, and a plain concrete cushion layer with the width of 1.5m and the thickness of about 0.4m is poured at the edge foot position of the open caisson to serve as a foundation for manufacturing the open caisson.

3. The combined foundation construction method of the ultra-large open caisson structure according to claim 1 or 2, wherein: in the step 4), the grouting range of the compaction grouting is 5m greater than that of the open caisson structure, the thickness of the grouting is 5m, the position is the position where the open caisson sinks to the designed elevation, and the pressure of the compaction grouting is not more than 0.3 Mpa.

Technical Field

The invention relates to the field of open caisson construction, in particular to a combined foundation construction method for an ultra-large open caisson structure.

Background

At present, the southeast coastal economy of China develops rapidly, and the demand of electricity is large. In consideration of convenience and economy of coal transportation and water taking and drainage of circulating water, a large-scale thermal power plant is generally arranged along a coastline; meanwhile, in order to save precious land resources, a plurality of coastal large-scale thermal power plants adopt a method of building land by enclosing the sea, and a building is arranged on the mudflat. The circulating water system is an important component of a thermal power plant, and coastal power plants generally adopt a seawater direct-flow cooling mode, and a large amount of seawater is used as cooling water to cool a condenser. The water intake requirement of a large-scale thermal power plant can be met only by constructing a large-scale seawater intake pump house on the mudflat and adopting an oversized reinforced concrete open caisson structure on the lower part of the pump house.

The mud flat silt has the characteristics of low foundation bearing capacity, large compressibility, small permeability coefficient, low consolidation speed and the like, and a natural foundation cannot meet the requirement of building the foundation bearing capacity of a large water intake pump house, so that a proper foundation treatment method must be adopted. The current commonly used treatment scheme is the adoption of pile foundations, and the scheme has the following disadvantages: 1. the stability requirements of open caisson manufacturing and sinking stages cannot be met, the open caisson is easy to deflect during pouring, and suddenly sinks and super sinks during sinking; 2. when the open caisson is used for taking soil, soil around the open caisson is easy to gush into the open caisson body, so that the open caisson structure is inclined, and especially the ultra-large open caisson is difficult to correct; 3. disturbance of a foundation soil body easily causes extrusion deflection of a foundation pile, and a pile breaking accident is caused; 4. after the pile foundation deflects, the well body, the blade foot and the engineering pile foundation are generated to be placed, and the sinking difficulty of the open caisson is caused. For the above reasons, there is an urgent need to find better ground treatment methods.

Disclosure of Invention

The invention aims to solve the technical problem that the defects of the prior art are overcome, and the combined foundation construction method of the ultra-large open caisson structure is provided, so that the construction method can effectively solve the problems of sudden sinking and ultra sinking of the ultra-large open caisson structure in the construction process, and avoids the phenomenon that the lower pile foundation is laterally extruded due to the inflow of the surrounding soil body when soil is taken in the well body, and the pile is broken and the whole foundation is unstable.

The invention aims to complete the construction method of the combined foundation of the ultra-large open caisson structure by the following technical scheme, which mainly comprises the following steps:

1) filling a medium coarse sand cushion layer on a mudflat of a large circulating water taking area to be newly built, wherein the thickness of the cushion layer can be determined according to the requirements of preloading and well sinking structure pouring;

2) the middle coarse sand cushion layer is used as a pile frame bearing layer to carry out rock-embedded cast-in-situ bored pile construction, the upper part of the cast-in-situ bored pile is subjected to air drilling, filled with middle coarse sand or broken stones and used as a sand well structure, and the sand cushion layer with the thickness of 3m at the upper part is piled, pre-pressed and becomes a drainage channel, so that a soft soil layer with the deep thickness at the upper part is subjected to pre-consolidation;

3) carrying out rock embedding construction on the lower part of the cast-in-situ bored pile, and filling reinforced concrete to serve as a permanent support structure of the ultra-large open caisson structure;

4) compacting and grouting the pile top part of the cast-in-situ bored pile, and reinforcing the soil body at the pile head part to integrate the pile and the soil body;

5) and (3) making the open caisson in a grading manner and sinking in a grading manner or making the open caisson in a grading manner and sinking integrally, sealing the bottom of the open caisson by plain concrete after sinking to a designed elevation, pouring a reinforced concrete bottom plate, and connecting the rock-embedded cast-in-place pile with the bottom plate to form an integral body.

Further, in the step 1), the filling thickness of the medium coarse sand cushion layer is 3m, the plane size of the medium coarse sand cushion layer is 3m larger than that of the open caisson structure, and a plain concrete cushion layer with the width of 1.5m and the thickness of about 0.4m is poured at the edge foot position of the open caisson to serve as a foundation for manufacturing the open caisson.

Further, in the step 4), the grouting range of the compaction grouting is 5m greater than that of the open caisson structure, the thickness of the grouting is 5m, the position is the position where the open caisson sinks to the designed elevation, and the pressure of the compaction grouting is not more than 0.3 Mpa.

The invention has the beneficial technical effects that: compared with the prior art, the invention has the advantages that: firstly, consolidation treatment of shallow foundation soil is carried out through a preloaded sand cushion layer and a sand well, so that surface layer software has certain bearing capacity, the prefabrication and pouring of a first section of open caisson are facilitated, and accidents such as well body cracking and deflection caused by surface layer soil deformation are prevented; secondly, the pile head soft soil is compacted and grouted for reinforcement, so that the super-sinking accident of the super-large open caisson structure due to the huge self weight is prevented; meanwhile, the pile breaking accident caused by pile squeezing of the engineering pile due to soil taking in the sinking well can be avoided.

Drawings

FIG. 1 is a schematic plan view of an underground open caisson structure of a circulating water pump house;

FIG. 2 is a schematic sectional view of foundation treatment during open caisson fabrication;

fig. 3 is a schematic sectional view of foundation treatment when the open caisson is in place.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clearly understood by those skilled in the art, the present invention is further described with reference to the accompanying drawings and examples.

As shown in fig. 1 to 3, the combined foundation construction method for the ultra-large open caisson structure mainly comprises the following steps:

1) filling a medium coarse sand cushion layer on a mudflat of a large circulating water taking area to be newly built, wherein the thickness of the cushion layer can be determined according to the requirements of preloading and well sinking structure pouring; the filling thickness of a common medium coarse sand cushion layer is 3m, the plane size of the medium coarse sand cushion layer is generally 3m larger than that of the open caisson structure, and a plain concrete cushion layer with the width of 1.5m and the thickness of about 0.4m is poured at the edge foot part of the open caisson to be used as a foundation for manufacturing the open caisson;

2) the construction of the rock-socketed cast-in-situ pile is carried out by using the medium coarse sand cushion as a pile frame bearing layer, because the self weight of the well body is huge, the pile foundation generally adopts the rock-socketed cast-in-situ pile, the pile top elevation of the rock-socketed cast-in-situ pile is determined according to the sinking depth of the open caisson structure, an air drill is adopted at the part above the pile top elevation, then medium coarse sand or broken stone is filled as a sand well structure, the sand well structure becomes a drainage channel under the preloading of the sand cushion layer 3m above the sand cushion layer, the upper soft soil body is subjected to drainage consolidation through the combined action of the ground filling sand cushion layer, the bearing capacity and the shear strength of the soil body are enhanced, the lateral friction resistance of the well body and the limit end resistance of the soil body at the blade foot position when.

3) Carrying out rock embedding construction on the lower part of the cast-in-situ bored pile, and filling reinforced concrete to serve as a permanent support structure of the ultra-large open caisson structure;

4) after the construction of the rock-socketed cast-in-place pile is completed, soil bodies near the sinking design elevation of the open caisson are subjected to compaction grouting reinforcement treatment, the pile top part of the cast-in-place pile is subjected to compaction grouting, the grouting range of the compaction grouting is 5m larger than that of the open caisson structure, the thickness of the grouting is 5m, the part is the position where the open caisson sinks to the design elevation, and the compaction grouting pressure is not more than 0.3 Mpa; the soil body at the pile head part is reinforced, so that the pile and the soil body form a whole, the bearing capacity of the soil body in the area is increased, finally, the blade foot of the open caisson can be supported in the reinforced soil body, the open caisson is prevented from being over-sunk, and simultaneously, the soil body around the open caisson can be prevented from flowing into the open caisson due to soil taking in the open caisson body, so that the pile squeezing and pile breaking accidents of the pile foundation at the lower part can be prevented;

5) and (3) making the open caisson in a grading manner and sinking in a grading manner or making the open caisson in a grading manner and sinking integrally, sealing the bottom of the open caisson by plain concrete after sinking to a designed elevation, pouring a reinforced concrete bottom plate, and connecting the rock-embedded cast-in-place pile with the bottom plate to form an integral body.

Example (b):

the Thunberg Leqing power plant is built in a Yuanqing bay, the general installation is 2 multiplied by 600MW +2 multiplied by 660MW, a large circulating water pump house is built on a deep soft soil layer, the lower part of the pump house adopts an ultra-large open caisson structure, mud at the position of the pump house is deep and thick, and the average mud thickness reaches 40 m-60 m. The mud flat sludge has the outstanding characteristics of high water content, low foundation bearing capacity and strong compressibility. If an effective foundation treatment scheme is not adopted, the construction becomes very difficult, and the construction is smoothly completed after the project adopts the combined foundation treatment scheme, so far, the project is operated safely for many years.

The specific embodiments described herein are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.