The bearing capacity of the former is mainly provided by the rock layer at the bottom of the pile, and the latter is provided by the vertical friction of the pile body passing through the soil layer.
Pier piles are buried 60m~66m into the soil and are buried by pre-drilling method.
Considering the serious scouring of the riverbed during the rainy season, the steel casing is provided at the upper part of the bored pile, and the steel casing of the pier pile is designed as the diameter φ 3.0m, and the pile casing is 52m long.
After the hole is formed, the reinforcement cage is placed, and then the casing is gradually pulled out when the pile body concrete is poured.
The role of the casing is to prevent the collapse of the hole, in which the heavy hammer grab is used for soil removal.
Pile foundation construction methods can be divided into two categories: cast-in-place pile and sunk pile.
The bridge foundation is cast-in-place concrete bored piles, 4 for each pier φ 3.0m bored piles, 10.0m in transverse direction, 9.0m in longitudinal direction, and 91.0m in length.
It is generally divided into four sections and delivered to the site by flat trailer or tractor.
6 pieces evenly distributed along the circumference inside the reinforcement cage φ 50mm steel pipe is used for ultrasonic inspection of the pouring quality of pile concrete.
.
Construction process 1 Construction process 2 Manufacturing and installation of steel casing The diameter of pier steel casing is 3.0m, the length is 52m, and the plate thickness is 25mm.
For geology that is not easy to be excavated, bored cast-in-place piles shall be used for construction.
Reinforcement cage manufacturing and installation Pier pile reinforcement cage length 94.5m, reinforcement cage weight about 150t main reinforcement φ 36mm, stirrup φ 20mm。 Some sections are double-layer reinforcement cages.
It can be constructed near existing buildings.
Reinforced concrete piles are mostly used for bridge pile foundations.
Pile bottom grouting: in order to keep the grouting pipeline at the bottom of the reinforcement cage as close to the hole bottom as possible without being damaged, the bottom contact indicator switch is installed at the bottom of the reinforcement cage.
Highway and bridge construction units should attach great importance to this.
Working procedure Positive and reverse circulation drilling machine hole forming: rely on the drill bit rotary drilling, use the mud to circulate in and out of the hole and float up, and take the drilling slag out of the hole to realize the mucking.
Impact drilling is applicable to a wide range of clay, silt and pebble layers.
The drill bit can be lifted out of the hole mouth and used for mucking out, or mud circulation method can be used for mucking out.
With the development of China’s economy and the acceleration of the pace of highway and bridge construction, a series of quality accidents have also occurred in highway and bridge projects, which are directly related to people’s property safety and become the focus of attention.
The number of reinforcement in the same section is up to 240, and the reinforcement is dense.
When the weak overburden at the pier and abutment is thick and the supporting rock stratum is deep, the pile foundation can be supported on the supporting rock stratum through the weak overburden.
Manual welding shall be adopted for splicing on site, and all welds shall be subject to ultrasonic flaw detection.
Install first φ 3.4m temporary casing, the depth of temporary casing into the soil is about 10m, and then the drilling rig is installed, and the diameter of the drill bit is φ 3.15m~ φ 3.22m, drill to the elevation of – 49m, the design elevation of the bottom of the steel casing is – 50m, and leave 1m to be knocked in place with APE vibration hammer.
It has good environmental protection and is applicable to clay, silt, sand, muddy soil and some pebble and gravel strata Hole forming by impact drilling machine: the impact drilling machine is to raise the heavy bit with a blade or grab with a winch and other equipment, then release the winch, the bit falls down, and cut and crush the rock and soil at the bottom of the hole.
The thickness of ballast at the hole bottom: the thickness of ballast at least 50% of the cross section at the hole bottom is<15mm, and the thickness of ballast at any position of the hole bottom section is ≯ 40mm.
Drilling pile hole forming methods mainly include: rotary drilling machine hole forming, positive and negative circulation drilling machine hole forming, casing drilling machine hole forming, impact drilling machine hole forming, etc.
Hole forming by casing drill: It is to press a steel casing with mechanical shaking while drilling.
The casing drilling method is applicable to the overburden layer of non-rock strata and has good protection effect on hole collapse.
The construction of cast-in-place bored pile is to make a pile hole in the soil manually or mechanically, then put the reinforcement cage of the pile body into the pile hole, pour concrete into the hole to form the pile, and finally pour the tie beam or bearing platform at the top of the pile.
Drilling pile hole forming methods mainly include: rotary drilling machine hole forming, positive and negative circulation drilling machine hole forming, casing drilling machine hole forming, impact drilling machine hole forming, etc.
The mud is composed of clay or expansive soil and additives, and its specific gravity is generally between 1.1 and 1.3.
The drill bit rotates to cut the soil or sand particles into ballast soil, and then quickly lift out of the hole.
The power drill bit can be rotated forward to drill at low speed, and the reverse rotation can be used to dump the soil at high speed.
The slag removal efficiency of reverse circulation method is higher than that of positive circulation method.
The construction of cast-in-place pile is to make the pile hole in the soil manually or mechanically, then put the reinforcement cage of the pile body into the pile hole, pour concrete into the hole to form the pile, and finally pour the tie beam or bearing platform at the top of the pile.
The pile foundation can be divided into end-bearing pile and friction pile according to the stress form.
The concealment of bridge pile foundation construction requires that the construction of bridge pile foundation should not only rely on advanced science and technology, but also deal with the problems arising in the construction in time according to rich construction experience to avoid the occurrence of engineering quality accidents.
According to the mud circulation method, it can be divided into two types: positive circulation and reverse circulation.
At the same time, the mud plays a role in protecting the wall (balancing the water pressure in the hole) and preventing hole collapse and floating ballast.
Because the bored pile in the bridge project is a concealed project, most of the work is carried out underwater, and the construction quality inspection is very difficult.
Features: from the drilling of the bottom of the permanent steel casing to the concrete filling to the bottom of the permanent steel casing, it shall not exceed 73 hours (39m pile length).
This method can realize dry construction without mud mucking.
The pile foundation is composed of several piles and pile caps, which is a common deep foundation.
Hole forming by rotary drilling rig: the drill pipe drives the drill bit to rotate.
If the pile hole is excavated manually, it is called a bored pile, and if the hole is excavated mechanically, it is called a bored pile.
According to the specific geological conditions of the project, the construction of pile foundation generally adopts the construction of hollowed-out piles.
The geological conditions at the typical example bridge site are silty, fine, medium and coarse sand layers and a small amount of gravel layers.
Therefore, it is of great significance to discuss the construction technology of bored piles in bridge engineering.
If the pile hole is excavated manually, it is called a bored pile, and if the hole is excavated mechanically, it is called a bored pile.
The casing is manufactured in a steel structure factory, formed by a plate rolling machine, and welded on a rotating jig frame by an automatic welding machine.
