The test technology requires that the test area is located behind the multi-purpose berth of the overall plan layout of the feasibility stage. According to the spacing of the plastic drainage plate, the two cell areas A and B are simultaneously carried out. The distance between the plastic drainage plate in Area A is 0.8 m and the area is 1750 m2. The area of ​​the plastic drainage plate is 1.0m and the area is 1750m2. The depth of the plastic drainage board is set to an average of 12.5m. The vacuum preloading load is 80kPa, and the consolidation degree of the foundation is more than 85%.
Geological conditions According to the results of on-site exploration, the thickness of silt in the test area is approximately 10.0m, and the dredging mud thickness is approximately 6.0m. The physical and mechanical properties of the soil in the test area are shown in the table. The shear strength of the crosshead plate on the site is shown. Statistical tables of soil physical and mechanical properties in the test area (before and after consolidation) No. Depth m Water content X (%) Natural density Q/gcm-3 Porosity ratio e Plasticity index Ip (%) Liquidity index IL Three-axis shearing Cuu/ Reinforced before kPa Reinforcement before reinforcement Reinforcement before reinforcement Reinforcement before reinforcement Reinforcement before reinforcement Reinforcement before reinforcement 5 Test area shear strength curve of test area Siltation in the test area is a shallow layer of mud in the basin and channel, Therefore, compared with other sludges, the particles are fine, the strength is low, the sedimentation speed is slow, and the consolidation time is longer. Particle analysis results.
It can be seen from the above that Tianjin Port has a high siltation rate, so the lime mud for reinforcement and treatment of Lianyungang is longer than the construction period of Tianjin Port, and the reinforcement effect is better than Tianjin Port. For the two test areas A and B, the clay content is also very different. In the two grades below 0.075mm, the difference is more than 10%. This corresponds to the permeability coefficient of the dredged mud listed in the description. There is a big difference in the soil properties between the two test areas A and B. Monitoring items and inspection contents Monitoring contents include: pore water pressure, surface settlement, deep layered settlement, deep horizontal displacement of soil outside the reinforcement area, and water level observation. The results of the monitoring are shown in Fig.
Test Results Analysis Consolidation Analysis Ground Settlement Analysis Predicted Degree of Consolidation Ground surface settlement is the sum of the settling during the installation of the plastic drainage plate and the settlement caused by the vacuum preloading. According to the measurement results, the average settlement of the board in Area A is 16.6cm, the average surface settlement after preloading is 145.0cm, the total average settlement is St=161.6cm, the average ground surface settlement in Area B is 112.1cm, and the average settlement in boarding period is 16.8cm. The total average settlement is St=128.9 cm.
According to the surface settlement curve, the average final settlement of the reinforced area is calculated using the three-point method proposed by Zeng Guoxi: S ∞: After calculation, the final settlement in area A is S∞=172.8 cm, and the average consolidation degree of the foundation in the consolidation area is Ut=93.5. The final settlement in zone %.B is S∞=137.6cm, and the average degree of consolidation in the consolidation zone is Ut=93.7%.
Calculate the degree of consolidation of layered settlement According to the observation results of layered settlement meter, calculate the final settlement of each soil layer S∞ and the degree of soil consolidation, the results. The pore water pressure dissipation is calculated by using the effective stress formula to calculate the consolidation degree of the foundation, and the degree of consolidation at different depth points in the soil layer is calculated and calculated.
After the residual settlement preloading is completed, under the effect of the design load (80kPa), the foundation will still produce a certain settlement. This part of the settlement is customarily referred to as residual settlement, and the residual settlement in the test area. Calculate the consolidation coefficient According to the measured settlement curve, apply the theory of balun consolidation to calculate the average radiation to consolidation coefficient, Cr. After calculation, the average radiation to consolidation coefficient in area A is 4.11×10-4cm2/sB. The knot coefficient is 6.69×10-4cm2/s.
Using the measured pore water pressure curve, the Cr value at each pore water measuring point was deduced. Analysis of soil change after reinforcement After reinforcement, a hole drilling and two cross-board strength tests were performed in each test area. After reinforcement, one hole and two crosses were drilled in each reinforcement area. Plate strength test, 1 load test per test area. The following analysis of the test results is based on drill inspection data.
Cross-slab strength results before and after reinforcing the soil in various soil layers after reinforcement. After consolidation, the strength of the soil layers in the reinforced area has been greatly increased, and the soil strength growth is very significant, increasing by 1.2 to 12.5 times. The statistical results of physical and mechanical indexes of various soil layers after reinforcement are shown. The shear strength curve of the cross plate in the area B of the shear strength curve of the cross plate in the cross section of zone A can be seen from the statistical results in the table. After consolidation, the moisture content of the silt in zone A decreases by 24.3%, the void ratio decreases by 27.7%, and the liquidity index decreases. 36.1%; the water content of the dredged mud in the B-zone was reduced by 21.1%, the void ratio was reduced by 16.5%, the liquidity index was reduced by 40.6%, and the cross-board strength was increased from 3 to 24 kPa to 25 to 52 kPa, an increase of 1.2 to 12.5 times. The reinforcement effect is very significant. The basic values ​​of foundation bearing capacity were determined by field load tests: area A f0 = 150 kPa, area B f0 = 130 kPa. After consolidation, the physical and mechanical parameters of the foundation soil were significantly improved, meeting the design requirements and achieving the intended test objectives.
The load test test point is located on the sand cushion in the center of the test area. The load plate size is 0.707m×0.707m≈0.5m2. The test is in accordance with the relevant provisions of the foundation load test in the “Code for the Design of Foundations for Building Foundations†(GBJ7-89). Request to proceed. Test result: The load value corresponding to s/b=0.01 is the basic value of bearing capacity.
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