Rain-Taiwan-Wenzhou Expressway Vacuum-Heating-Loaded Combined Precompression Soft Foundation Treatment Wei Bo, He Huaijian (Wuhan Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, Hubei, China) The second generation method of reinforcement is vacuum-surcharge combined preloading. The method, observation results and treatment results all indicate that the method is effective and can be applied in similar projects.
l Project Overview The geological conditions of the DK0+32DK0+500 subgrade of the Ruan-Taiwan-Wenzhou Expressway in the Rui'an section are complex, and the soft ground is deep (about 25m), and the soft soil has large water content, poor permeability, and high compressibility. , low bearing capacity. In order to ensure the quality of the expressway, to meet the post-construction settlement requirements, to minimize the residual settlement during the use of the expressway, and to ensure the construction period, the command and design agencies decided to perform vacuum-surcharge combined preloading and soft foundation treatment on the base of the road section. The roadbed filling height of the road section is 3.03.7m, the length of the vacuum-surcharge combined preloading treatment is 188m, and the treated area is about 3582m2. The vacuum-surcharge combined preloading method is used to treat the expressway's soft foundation, and it is on the Yongtaiwen Expressway. It is the first time that it is applied and it is being constructed in a tunnel with a small width and a large camber. Therefore, it is necessary to organize the design meticulously, manage the construction scientifically, carry out the necessary experimental research, and adopt as complete design methods, construction techniques and specifications as possible to ensure the The combined vacuum preloading of the section meets the design requirements, and the experience in this paragraph summarizes the experience for the future design and other sections of the construction.
2 Engineering Geological Conditions According to the provided geological survey report, drilling data of 2 (Z2, KD0+292.1), the main soil layers are distributed from top to bottom: Plain fill: Mainly consists of rock, gravel, sand, and cohesive soil. Such as composition, layer thickness, shallow depth, digging should be excavated when the trench.
2.0m, the trench should be basically excavated when excavated.
%, porosity ratio e=1.993, low compression modulus s=l.40 MPa, depth of burial 2.0024.40 m, and soft soil layer and compression layer.
Pebbles, gravel: slightly dense and dense, clay soil content of less than 20%, buried depth of 24.4027.60m, a natural drainage layer, plastic drainage boards should avoid entering this layer.
Muddy clay: dark gray, saturated, soft plastic, containing a small amount of fine sand and charred, partially clay, layer thickness of about 5m. Pebbles: slightly dense and dense, clay soil content of less than 20%, buried depth 32.8035.30m For the natural drainage layer.
From the above geological data, there is no pervious layer in the main treatment soil, which is suitable for vacuum-surcharge combined preloading.
3 Principles and characteristics The vacuum-surcharge combined preloading method is a new technology for ground reinforcement developed in recent years. The vacuum preloading method is to set up a sand well or a drainage plate as a vertical drainage channel on the soft soil foundation that needs reinforcement. Then, a sand-cushion layer is laid on the ground as a horizontal drainage layer, and an airtight sealing film is overlaid on the ground to isolate it from the atmosphere. A suction device is used to evacuate the membrane through a suction channel embedded in the sand-cushion layer. The inner air is discharged so that a pressure difference occurs in the film. This part of the pressure difference becomes a load acting on the foundation. As the air in the membrane is continuously discharged, the pressure difference gradually increases, and the water and gas in the foundation are continuously eliminated and consolidated. The vacuum-surcharge combined preloading method is developed on the basis of vacuum preloading and surcharge preloading. It has the dual effects of vacuum preloading and surcharge preloading, although during the loading process, the ground soil will also occur. Lateral extrusion deformation, but due to the role of vacuum load, the lateral contraction and deformation caused by vacuum and lateral extrusion deformation caused by the load offset, on the other hand under vacuum load consolidation of the foundation soil, strength Growth, so that the speed of the heap can be made quickly without loss of stability. For highways and railways, the embankment itself is a very good surcharge.
Vacuum-surcharge combined precompression cross-section is shown in Fig. U 4 Vacuum-surcharge combined preloading Soft foundation construction Overview Vacuum pumping system is installed until December 25th, and vacuum is started on December 26, 2002. The vacuum degree on the day reached 80 kPa and remained in the range of 7585 kPa. Construction began on January 9 and reached the design elevation on May 8. From the point of view of the entire construction process, the sealing groove, membrane surface and membrane perimeter are well sealed, the vacuum degree under the membrane rises normally, the holding load is stable, and the vacuum-surcharge-loaded combined pre-compression construction is successful.
5 Observing results and analysis See the location of the exploration sites and the situation of the instrumentation. The vacuum-surcharge combined preloading is carried out according to the following procedures: construction preparation; preliminary exploration and instrument embedding; positioning and installation of main and branch pipes; sealing membranes and geotextiles; excavation and backfilling of sealing trenches; and connection between pumping pipelines and vacuum pumps. Vacuum pumping and soft ground monitoring; Paving the second layer of sealing film, geotextile, membrane equipment; Subgrade filling; Vacuum preload unloading acceptance. Vacuum preloading process flow chart see.
The construction of vacuum-heaped combined precompression and reinforcement of soft foundation works began on November 10, 2001. The surface settlement curves reflected by the drainage filter tube embedding, sealing film laying, and 5.1 surface settlement surface settling plates are as shown in the figure. The amount of sedimentation is as follows: BM1 is 1. Surface Settlement Graph From the period of April 25 to May 28, the daily sedimentation rate of the three-settling plates is shown in Table 1.
From Table 1 and Table 1, it can be seen that the sedimentation rate has apparently stabilized from May 22 to May 25. However, as a result of laying a protective layer of gravel on the embankment around May 25, The sedimentation rate has increased, but at this time the increased instantaneous settling velocity is not large, indicating that the soil consolidation due to drainage promotes the increase of the elastic modulus of the soil.
Table 1 Daily Surface Settlement Rate Table (Unit: m/d) Plate No. H Phase April 25æ›° May 4 May May 4 May May 6 May May 6 May 18 May 6 May May 11 May 18 May May 22 May May Day May 14 May 22 May May 25 May May 14 May 15 May 25 May 28 Pore pressure is maintained above 80 kPa to meet Design requirements.
DK0+400 section and DK0+455 section of the subgrade pore pressure in water on February 23, April 14th, June 3, suppressing all the time, such as SIG knows to read fi time/month-day. Harbin: Harbin Branch of China Civil Engineering Society, 1957. Tang Junsheng. Field Test and Application of Vacuum Preloading for Consolidation of Soft Soil Foundation . Vacuum preloading reinforcement soft soil foundation essays. :. Tianjin: Research Institute of the Aviation Bureau of the Ministry of Communications, 1984.
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