The treatment of soft ground with low vacuum preloading for Guangdong water conservancy and hydropower station Chen Guohua\Chen Xiaohui j (1. Zhuhai Senmao Engineering Supervision Co., Ltd., Zhuhai 519020, Guangdong, China; 2. The 3rd Engineering Bureau of Guangdong Water Resources and Hydropower, Dongguan 523710, Guangdong, China)1 Zhuhai Xiangzhou Science and Technology T Industry Park is located on the west side of the Zhuhai Free Trade Zone, southeast of Hongwan Power Plant, and the area of ​​the second phase of the park is 1.3 million m2. According to the plan, the Xiang T Road has a total length of 2585.89m, a width of 34m and a total area of ​​87920.26m2. The roadbed reinforcement area is 2 engineering geological conditions. The landform of the park is an intertidal zone. The original topography is the pre-peace shallow beach floodplain, followed by person T sandblasting and filling and leveling. The current site is sugarcane land. According to the geological exploration results of the T Cheng Exploration Institute of Zhuhai City, the soil along the road from the top of the block is: 1 person T-filled soil layer, with an average thickness of 2.59m; 2 sea layers, with an average thickness of 33.56m; Alternating sedimentary layer, with an average thickness of 2.9m; 4 residual layers; 5 fully weathered Erbtite feldspar.
The road municipal sewers and storm drains are located in the sea layer, and the silt is the main layer in this layer. The main physical and mechanical indexes are as follows: The layer has a large thickness, wide distribution, low strength, high compressibility, poor permeability, and poor T-geological properties. It belongs to the soft soil layer and cannot be used as a subgrade bearing layer. When the road is diverted, the foundation must be reinforced.
3 Xianggong Road Weak Foundation Treatment Plan Selection 3.1 Alternatives After on-site survey and investigation of the same nature of T-projects under construction in surrounding areas, at present, there are three main methods for processing weak foundations in Zhuhai: strengthening sand, plastic, and plastics. Drainage board plus pre-compression and deep mixing piles.
3.2 Comparison of alternatives 3.2.1 The depth of dynamic compaction with sand and gravel piles is about 10m, and the soft soil thickness of Dingcheng is 2242m. The fill height of roadbed is 3. 54.0m, and the depth of settlement is 2028m. Only pore water in the range of about 7m in soft soil layer was pressed out, and the settlement of the lower layer of 1321m occurred. The treatment effect was not satisfactory. In addition, the use of sandstone was more expensive and more expensive in the dynamic plan. Uneconomical. The most important thing is: Strong will produce strong vibrations and have a large range of influence. It will have an impact on Hongwan Power Plant and it is easy to break the plant and cause disputes over claims.
3.2.2 The concept of plastic drainage board plus pre-m drainage consolidation and preloading is simple and easy to construct. The cost is low, but the quality of the plastic drainage board itself is not stable. After the treatment, the board surface is more likely to produce smearing effect, which results in drainage effect. Greatly reduced.
3.2.3 Deep mixing pile The deep mixing pile is a quick and effective method to deal with soft ground. However, the processing cost is higher. According to the soft soil theory and the practical experience of the T process, the depth of treatment of deep mixing piles should not be more than 12m, and if it is more than 12m, it will be difficult to guarantee the quality of the piles and the results will not be satisfactory. In addition, the soft soil of the site has a large water content, and the amount of cement required is also expensive and more expensive.
In summary, after comparison, the drainage consolidation plus pre-pressurization scheme is more suitable for the T range.
However, due to the preloading of the heaped load, the D phase is longer. The use of surcharged materials is costly, and low-level vacuum preloading does not require stacking materials, and the application of T is simple, the construction period is short, the settlement is uniform, and the overall cost is low. Therefore, a low-level vacuum preloading method is used for the foundation treatment.
3.3 Low vacuum preloading reinforcement mechanism and characteristics Low vacuum preloading method is the vacuum vacuum system in the long-term under the silt to maintain a negative pressure of 80kPa, the vacuum suction caused by the huge suction and silt layer caused by the additional preload load Under the action, most of the pore water in the soft soil is discharged through the plastic drainage plate and the horizontal filter pipe network more quickly. The soft clay in the foundation will shrink and consolidate. At the same time, the silt layer will gradually complete its consolidation and reach the reinforcement foundation. The two main purposes of soft soil and backfill.
The main technical features of the low vacuum preloading method are: high efficiency, energy saving, economy, and environmental protection.
4 Low-level vacuum preloading method for reinforcement design and calculation 4.1 Division of T cycle units According to the conditions of the strengthening site, taking into account the application of T and the reinforcement effect and the technical requirements of the reinforcement system, the actual ground consolidation area of ​​Xiang T Road is divided into 17 rectangular reinforced zones. The width of all rectangular reinforcement partitions is 40m, in which the length of the reinforcement E is 185.89m, and the area is 7435.6m2. The length of the reinforcement two partitions to the seventeen reinforcement partitions is 150m and the area is 6000m2. 4.2 The consolidation calculation The plastic drainage board of T-Range is arranged in an equilateral triangle with a distance of 1.0m. It is a three-dimensional consolidation problem to use the vertical plastic drainage board for ground reinforcement. The three-dimensional axisymmetrical consolidation theory of Taishaji can be used to calculate the D drainage plate pJ. According to equivalent sand well simplification, when the influence of smearing and well resistance is not considered, the formula for calculating the degree of consolidation is as follows: Directional consolidation coefficient; H is the maximum drainage distance. When double-sided drainage, H is half of the soil thickness, single When the surface is drained, H is the total thickness of the soil layer; 6 is the width of the plastic drainage plate; "' is the thickness of the plastic drainage plate; GE is the equivalent conversion diameter of the plastic drainage plate; especially the diameter of the effective drainage circle; h is the plastic drainage plate Distance to diameter ratio.
After calculation, it is expected that the consolidation degree value is 85%, and the vacuum preloading time is calculated as 58 days. 4.3 Settlement calculation The final settlement of the foundation soil is calculated according to the total unidirectional compression layering law. The formula is as follows: the empirical coefficient of settlement calculation; Calculate the number of soil layers divided within the depth z*; P. as the additional pressure at the bottom of the foundation; 迳 as the base; the compressive modulus of the soil under the floor; Z, Z, y are the bottom and top of the fth soil layer. The base distance from the base; the average additional stress coefficient at the bottom and top of the soil.
Select the XG-1 and XG-5 drilling data to calculate the settlement; the average settlement at the time of completion is 56cm, and the settlement after T is 14cm. 5 The laying of the construction site is smooth and sand cushions are set up. Lateral Air Leakage) * Constructing Water Retaining Cofferdams and Isolation Ditches - Setting Up a Vacuum Pipe Network System - Laying a Sealing Membrane - Placing a Monitoring System - Vacuum Preloading and Overlaying - Site Shaping.
6 Construction Monitoring Construction engineering monitoring can not only find problems in the reinforcement process in time, and can be resolved in time, but also can be used to judge whether or not to achieve the intended purpose based on the monitored data, thus determining the suppression of reinforcement work and the start of follow-up T-dows.
6.1 Vacuum degree monitoring During vacuum pump operation. The vacuum level is measured once every 2 h, and once the vacuum level has been achieved, it is read every 6 h.
6.2 Negative Pore Water Pressure Monitoring When the probe of the pore water pressure gauge is adjusted to the required elevation, an initial reading is taken immediately. After the reinforcement is started, it is observed once a day (at the same time).
6.3. Settlement observations are observed once a day after obtaining the initial observation value. When the sedimentation rate is less than 2.0 mm/d, they are measured once every 3 days. When the sedimentation rate is less than 1.0 mm/d, they are measured once every 5 days. After the reinforcement is completed, The amount of ground rebound is measured.
6.4. Inclinometer monitoring Observe the lateral deformation once every 5 days until the end of the reinforcement process.
6.5. Groundwater level monitoring A groundwater level observation is performed once a day until the end of the strengthening process.
7 Reinforcement effect inspection and acceptance standards During the construction process, sampling indoor tests and on-site in-situ tests (mainly application of cross-plate shears and light static penetrators to determine the shear strength of the soil and the bearing capacity of the foundation), Analyze the reinforcement effect so as to adopt appropriate measures to ensure that T. Cheng completes on schedule.
T-pass acceptance standards adopt dual-control standards: 1 The load test of the foundations for flat load tests reaches 80 kPa; 2 Settlement reaches 60 cm or more.
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