Underwater geotextile construction in seawall engineering
Geotextile has good toughness, good water permeability, filtration, isolation, reinforcement, protection and other properties, and is widely used in seawall engineering. Laying high-strength split-film silk woven geotextiles on the seabed surface outside the project mainly plays a reinforcing role. The geotextiles are used to enhance the tensile strength and deformation resistance of the soil. The geotextiles are buried in the soil. Diffusion of soil stress to increase the modulus of the soil, transfer tensile stress, and limit the lateral displacement of the soil; also increase the direct frictional resistance of the soil and other materials, improve the stability of the soil and related buildings, but the construction of the project The environment is poor, and some departments need to carry out underwater construction when laying geotextiles on the coating surface. Compared with inland rivers and lakes, the ocean has unfavorable factors such as tidal currents and undercurrents, and is easily disturbed by a series of factors such as wind and waves on the sea surface. , construction organization and other requirements are higher.
1 Pre-construction preparations
Due to the limitations of the seawall construction environment, the construction of geotextiles should be comprehensively arranged according to the actual tide level, sea surface wind force and other factors. The available construction time is short and the requirements for construction equipment are relatively high. The construction ship of this project is a civil barge. The advanced GPS satellite positioning system is installed, because manual positioning is affected by unfavorable factors such as tides, wind and waves, it is basically impossible to carry out reliable positioning, and it is difficult to carry out effective construction. The geotextiles laid each time are not 4 sheets of geotextiles with a single width of 6M and are seamed into one piece (J-shaped seams are selected among the 4 common seaming methods of flat joint, butt joint, J-shaped joint and butterfly joint), The cushion layer of the subsequent repression geotechnical work shall use fine gravel slag with a mud content of less than 5%.
2 Construction methods
2.1 Material preparation
The geotextile is rolled on the 5t heavy circular drum loaded by the construction ship. When the cloth is rolled, the edge of the geotextile is connected to the drum in the longitudinal direction with a number of fine iron wires (to ensure that the geotextile does not slide during the rolling process, and the rolling efficiency is improved. , The iron wire should not be too thick to prevent the geotextile from being effectively separated from the drum after construction is completed), and at the same time, the bamboo strips are fixed horizontally on the geotextile with thin iron wire every 5M (effectively ensure that the geotextile is spread when it encounters water. After undercurrent and vortex, it will not shrink laterally to ensure the quality of laying cloth), after loading sufficient qualified stone on the bed according to the requirements, the ship is equipped with an excavator to match the laying of the stone when the geotextile is laid.
2.2 Positioning of construction vessel
According to the original coordinates of the measurement points (generally no less than 3) provided by the construction site, the construction ship calculates and rechecks the initial and end positions of the construction ship, and inputs the construction coordinates into the loaded GPS positioning system. The construction ship drives into the predetermined construction position, uses the winches (generally no less than 4) loaded at both ends of the ship, anchors to fix the position of the hull, and waits for a favorable construction time for construction.
2.3 Construction time selection
The specific construction time should be based on the latest low tide time provided by the nearby tide level station, combined with the observation of the tide level in the project, select the available construction tide level, combine with the wind and wave conditions at the time of construction, make full use of the existing equipment conditions, and go as far as possible. Lay geotextiles.
Before construction starts, fix the initial position of the geotextile (cooperate with a small boat, press with large rocks on the shore, or anchor it on the coating surface), and the spreading boat will set the direction according to the GPS and sink the roller with the geotextile onto the coating surface. (If the geotextile is not constructed on the coated surface and exposed to the water surface, it will be affected by unfavorable factors such as sea wind, water buoyancy, etc., and the construction quality cannot be guaranteed at all), the two ends of the central axis of the geotextile roller and the 2 steel cables dragged by the tractor The connection should be firm, and the hull should be laid in an orderly manner in the vertical direction of the water flow. During the laying process, if the drum is stuck, it should not be forcibly dragged. The positioning boat should be started, and slowly move to the drum through the twisted rope. After lifting the drum, reposition and pull to complete the laying; the excavator on the ship moves with the hull. Keep a certain distance from the drum, and evenly lay the stones on the geotextile (if conditions permit, the belt conveyor can be loaded on the ship for automatic laying) to prevent the geotextile from being overturned or rolled. After the geotextile is laid, follow-up stone loading should be carried out in time to prevent the geotextile from being overturned or folded after the cushion is washed by excessive wind and waves. shift.
After the construction is completed, the relevant personnel can use the boat to drive the boat into the edge of the geotextile, and use a certain length of thin bamboo poles on the boat to probe the edge of the geotextile to determine whether the geotextile is laid in place. If the water depth is too deep to make a simple determination, a shallow water survey should be carried out to determine the laying quality.
(1) The underwater construction of geotextiles in seawall projects has particularly high requirements for equipment. Only reliable construction equipment can be used for effective construction. Especially in the special construction environment of the ocean, the requirements for positioning systems are particularly important.
(2) During the construction, pay attention to selecting favorable construction time, pay special attention to the time of the lowest tide level and the highest tide level during the construction period, and then observe the wind and waves on the sea surface during the construction period, make full use of the limited construction time, and operate in the tide as much as possible. Carry out downstream construction.
(3) Reasonable construction organization should be carried out during construction. In the process of material preparation, especially in key processes such as geotextile seaming, rolling, and spreading, a reasonable construction organization should be carried out, and a comprehensive construction plan should be formulated. Ensure the smooth progress of construction and ensure construction quality.