Essentials of Vacuum Preloading Method for Construction of Freeway Soft Soil Foundation

The vacuum preloading method is used to deal with the technical points of Tian Yaojuan's pressure installation and so on. The corresponding construction monitoring and project acceptance methods are proposed.

Through the use of a number of expressway engineering practices, it has been found that the method of vacuum preloading for soft soil foundation in the area of ​​expressway embankment is effective and has the characteristics of low cost, good effect and short construction period.

1 Overview Vacuum preloading method is used to test soil consolidation by testing changes in the physical and mechanical properties of the original soil before and after consolidation, in-situ “slab” tests, undrained shear strength tests, in-situ pore water pressure tests, and magnetic layered sedimentometers. Degree of change, through the total settlement and stability of the slope, determine the reinforcement effect.

2 Construction preparations The positioning of the reinforcement zone boundaries shall be carried out in accordance with the soft foundation treatment design drawings of the roadbed. The allowable deviation is *10cm. The debris and accumulated water in the reinforcement zone must be cleaned, and the allowable height difference between the sites shall not exceed 15cm. The test: Before drilling the plastic plate, sampling and in-situ testing of foundation drilling were performed to obtain data.

Hydropower system: The water supply system is rich in water resources. The drainage is drained by an open ditch or submersible pump, and the water is drained into the sealing membrane on the cofferdam to increase the sealing degree and load. The power supply system shall ensure the safe and normal operation of the plastic panel installation and the jet pump, as well as the normal use of lighting and other ancillary facilities. At the same time when the network power is collected, sufficient power should be provided for emergency use.

3 sand cushion and plastic plate construction sand cushion sand should be used in the construction of coarse sand, mud and other impurities content should be less than 5%, is strictly prohibited sand mixed with sharp stone, iron and other edge hard objects. The thickness of the sand cushion is 40cm, the allowable deviation is *4cm, and every 100m2 is an inspection point during the inspection. The sand cushion shall be covered with the entire reinforcement area, and light mechanical construction or manual laying may be adopted.

The quality of the plastic board construction plastic drainage board should comply with the relevant specifications and regulations, the allowable deviation of the plane position is *10cm, the verticality is 1.5%, the exposed length of the plastic board on the sand cushion is not less than 30cm, and the length of the return belt is strictly controlled. The band rate is not more than 5%, and the length of the band is not more than 50cm. Otherwise, compensation should be made nearby. The soft soil layer to be reinforced shall be pierced when the plastic panel is set. Kinking is forbidden and lapping is not allowed. Plastics are buried in the sand mat after acceptance.

4Preload Installation 41 Sealing film processing The sealing film should be polyvinyl chloride film with a thickness of 0. The shape must be the same as the reinforced area after processing. The area of ​​the processed film should not be smaller than the designed area. The length of each side of the sealing film should be greater than the reinforcement area. Corresponding side 3m ~ 4m. Each reinforced area with 2 to 3 layers of sealing film, the specific number of layers can be determined according to the performance of the sealing film. Thin film processing can be hot-legal, hot-forging and heat-sealing are strictly prohibited, and cross-sealing seams are not suitable. The material of the filter tube can be a 60mm70mm hard plastic tube, and the perforated non-woven filter water layer should be perforated. The position of the laying filter tube is positioned according to the design drawing line. The filter tube can be connected with a hose with a length of about 30cm to 40cm. The length of the filter tube inserted into the hose should be 10cm. Then, the length of the filter tube should be tightly tied with the lead wire, and the lead wire should not be turned upwards.

42 Installation of filter tube The filter tube should be buried in the middle of the sand cushion. The distance from the top surface of the mud surface to the sand cushion should be more than 5cm. The filter tube must be filled with sand around it. After the filter tube is buried, the sand surface should be smoothed to remove debris such as stones and rubble.

43 Measure Elevation Measure the ground elevation before and after the plastic drain plate is set and before the vacuum pre-filter to determine the amount of subsidence that occurs before the pre-press.

44 The sealing groove and the cofferdam seal groove shall be excavated along the reinforced boundary. The depth shall reach the groundwater and cut off the permeable layer. The internal and external slopes shall be smooth and free of sand. The width of the bottom of the groove should be 0.4 m or more to ensure that the sealing film is in full contact with the clay at the bottom of the groove to meet the sealing requirements. Sealing ditch backfill should be pure clay, free of impurities, backfill should avoid backfill directly hit the sealing film, so as not to break the leak. The location of the built-in concrete shall be along the outer edge of the sealed trench, and the soil shall be layered and compacted or covered with straw. Before laying the film, it is necessary to connect the film elbow with the filter tube, and cultivate the sand. The surface of the export pressure plate and the sand cushion should be flush with the rubber mat. After the film is finished, it should be along the film bend. The nozzle cut the film, and then the application of good rubber pad Bonieve in repair pits Yang Ruiping and construction process flow are elaborated, and the relevant precautions in the construction are put forward.

1 Overview Pit repair on the asphalt concrete pavement (bridge deck) of the expressway is not only the focal point of conservation operations, but also a difficult point in maintenance work. How to make repaired pits, especially deck pits, to maintain their durability under heavy loads is one of the difficulties in maintenance operations.

The introduction of BoniFibers asphalt concrete repair pit construction technology can increase the toughness of asphalt concrete, improve durability, and effectively improve the quality of asphalt concrete pavement. Pit repair has the characteristics of small area, scattered, long line length and large randomness. It is not suitable to use the mixing method of asphalt concrete mixing station, and it is suitable for the construction method of artificial field mixing. The following introduces artificial mixing and repair of Bonig asphalt concrete. Pit construction process.

2 Boniwi basic situation Bonivi is 100% poly-cool fiber, in a * C temperature, pressure plate, in the meantime grease evenly, and finally should tighten the two nuts, rubber, pad and film is strictly prohibited sand Material exists.

45 The laying of sealing film should be stretched from the wind to the wind when laying. The amount of slanting around the reinforcement area should be basically the same. The construction personnel should wear the shoes on the soft bottom shoes. It is strictly forbidden to wear shoes with nails and each layer should be covered. Personnel inspection, if there is a hole, in time to make up, in the inner side of the sealing groove should be paved the film, the film is too long, it can be folded at the bottom of the trench, can not be laid on the outer slope. After the sealing film is laid, the ground settlement observation disc can be applied to the membrane. The specific location should meet the requirements of the design drawings.

5 test vacuum jet pump should be commissioned before installation, if the vacuum pressure can not reach 0.09MPa should be maintained until the requirements are met.

Before replenishing the water, a vacuum test shall be conducted. At the same time, the operation of each jet pump and the tightness of the membrane shall be carefully inspected, and problems shall be discovered and dealt with promptly. Vacuum test should be 10d film vacuum pressure should reach 0. 08MPa If it is lower than this value is not normal, should immediately find the reasons for timely treatment. At the beginning of the test, the parameters such as vacuum pressure and settlement should be observed.

Not embrittlement, no softening and deformation, is a patented product of Capella Corporation in the United States.

Its characteristics are: raw materials using polymerization poly cool color is natural color (white), length: 6mm disabilities 1.36 persons 0.04 melting point greater than 250C burning point greater than 540C tensile strength greater than 517MPa elongation at break of 50%. The advantages of using Boniwei are: It can reduce road maintenance costs, improve road quality, prolong service life, prevent rutting, canalization and crowding, reflect cracks and temperature cracks on the road surface, prevent pitting and peeling of road surface, and protect bridge deck reinforcement or steel plates from corrosion. Simple.

3 Materials, mix ratios and design consumption 31 Materials The requirements for raw materials for asphalt mixtures are exactly the same as when no Bonneville was added.

That is, according to the material of the original asphalt concrete road, Bonbonvi.

6 After the normal vacuum pumping test meets the requirements, it can be transferred to the normal vacuum stage. This stage is the main stage of the vacuum preloading reinforcement foundation and can last for 2 to 5 months.

~40cm, after the water is covered, the vacuum pressure under the membrane should be gradually stabilized above 0.08MPa.

7 Construction monitoring 1) Pre-pressure parameters include pore water pressure, vacuum pressure, deep settlement and horizontal displacement. 2) The vacuum pressure observation (vacuum degree under the membrane) is observed once every 4 hours, and the surface settlement is measured once every two days in the first month, and then once a week.

8 Project Acceptance When the measured ground settlement is less than 2mm/d for four consecutive days and nights, or when the measured soil strength is increased to meet the upper continuous load, or the degree of consolidation of the foundation has reached 85% of the design requirements, the inspection is accepted by the supervisor. The pre-pressure can be terminated, the pump stopped, and the unloading stops the pump unloading. After 24hi, the surface rebound is measured.

After terminating the preloading, the site shall be leveled, and the various equipment and pipe used shall be removed in advance so that the work will be completed.

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