PERBANDINGAN METODE PRELOADING DENGAN VAKUM KONSOLIDASI TANAH PADA PEMODELAN DI LABORATORIUM

ABSTRACT This study aims to determine the parameter comparison of the magnitude of the primary reduction and consolidation time in the preloading method using PVD and vacuum method using PVD with modeling in the laboratory. The benefit of this research is that it can provide a comparison of the preloading method and the vacuum method in terms of accelerating the consolidation time as well as contributing to science in the field of soil improvement. Primary consolidation theory is used in this research. Quantitative descriptive research method with testing data collection techniques by means of modeling in the laboratory. The modeling of the vacuum method used a test tub measuring (1.2 × 0.6 × 0.9) m, the vacuum pump suction capacity of 5 Pa, the air hose as PHD and geomembrane cloth as PVD material. The preloading method with PVD uses a test tub measuring (0.8 × 0.6 × 0.9) m, preloading load in the form of bangka sand (ɣ = 1.532 t / m³) with a thickness of 10 cm and a geomembrane cloth as PVD material. In each test basin filled with soil and water with a soil volume weight of 1.3 t / m³, a ground surface height of 0.5 m and a groundwater level of 0.42 m. The results showed that with the same amount of reduction, namely 7.26 mm preloading method using PVD took 81 hours while in the vacuum method the time needed was 41 hours. Thus it can be concluded that the reduction in the vacuum method is faster than the preloading method with PVD. Keywords: Primer settelment, PVD, Vacum, consolidation time

Laboratory and Field Experimental Study on the Vacuum Preloading Method with Pumping and Discharging

Negative vacuum pressure hardly reaches deep soils due to the drain board bending and serious blockage with the existing vacuum preloading methods (VPMs), thus resulting in poor reinforcement relative to practical engineering applications. To address this issue, this paper proposes a vacuum preloading method with pumping and discharging (a new dredger filling foundation processing technique based on vacuum preloading). This new VPM is developed through technological improvement and plastic drain board innovations in traditional VPMs. The new VPM uses a plastic vertical drainage board with double drainage channels, and the core board is in a “tic-tac-toe” shape with a hollow centre and square pipeline channels. It can execute air and water drainage. Vacuum transfer holes were set at two grooves, every 2-3 m from the central pipeline of the core board. Grooves at two sides of the core board and filter membrane were rolled together to improve drainage. In addition, the vacuum pipe, tube connector, and core board centre of the vertical plastic drainage board were connected directly and securely. A stereoscopic vacuum transmission system composed of a horizontal and vertical drainage system was built. In this vacuum transmission system, the transfer route was shortened, and the loss of vacuum along the route was decreased. The negative vacuum pressure was transferred to different soil depths through the central pipeline of the core board to accelerate the dissipation of pore pressure in soil mass and prevent vacuum pressure loss caused by drainage board bending, thus improving the reinforcement effect. Dredger filling silt foundation reinforcement by VPM and VPM with pumping and drainage were compared in laboratory simulations and field tests with different drainage boards. Test results show that the loss of vacuum pressure along the drainage path was relatively smaller in the new physical vapor deposition (PVD), and the pressure transfer efficiency was increased. Deep soil mass was reinforced effectively by using the new PVD. After reinforcement, the physical and mechanical properties of soil layers were improved. Moreover, soil strengths were remarkably improved, with sharp reductions in natural moisture content and porosity. Then, the transfer law of vacuum on different drainage boards and the reinforcement mechanism of VPM with pumping and drainage were analysed. Research conclusions show the superiority of VPM with pumping and drainage in terms of effectiveness and soft foundation reinforcement. This study provides a theoretical basis for the application and development of the new VPM.

Design Method and Verification of Electroosmosis-Vacuum Preloading Method for Sand-Interlayered Soft Foundation

The design method of electroosmosis-vacuum preloading for soft foundation treatment is not systematic and complete, thereby restricting the application of the technology in engineering. A design method for the electroosmosis-vacuum preloading treatment of sand-interlayered soft foundation is therefore presented. A compressible electrical prefabricated vertical drain is developed, and a vacuum sealing and draining system is designed for the application of the electroosmosis-vacuum preloading in sand-interlayered soft foundation. Calculation formulas of site resistance considering the interlayer and interface resistivity of the electrode are established to design the power supply and electrical circuit. A simple numerical simulation method is proposed to predict the ground settlement treated by electroosmosis-vacuum preloading. A field test of electroosmosis-vacuum preloading is designed using the suggested method, and comparison tests between the electroosmosis-vacuum preloading and the vacuum preloading are performed to verify the proposed technique. The test results show that the proposed design method is reasonable for the design of electroosmosis-vacuum preloading in engineering.

Analysis of the Effectiveness of the Step Vacuum Preloading Method: A Case Study on High Clay Content Dredger Fill in Tianjin, China

As a solution to avoid the blockage of the drainage pipe by traditional vacuum preloading, step vacuum preloading (SVP) has been progressively studied. However, the effectiveness of this technique has yet to be systematically analyzed. In this study, an indoor model test was conducted in which vacuum pressure was applied in five stages (10, 20, 40, 60, and 80 kPa) to dredger soil with high clay content at a reclamation site in Binhai New Area, Tianjin, China. The extent of the consolidation effect of the soil was determined, and the effectiveness of the step vacuum preloading method to address drainage pipe blockage was evaluated. The results indicate that soil settlement increases at each stage of vacuum pressure treatment and the degree of vertical consolidation at each stage exceeds 90%. At the end of the treatment stage with vacuum pressure of 80 kPa, the weakly bound water was discharged. Dissipation of pore water pressure occurred in all stages. On the basis of these results, it is shown that SVP can efficiently reinforce dredger fill. Moreover, after SVP, the grain size of the soil and void ratio are still uniformly distributed. Regardless of their location from the drainage pipe, soil exhibits permeability coefficients within the same order of magnitude. The consolidation effect of soil in each stage and the increased drainage rate in the initial stage of vacuum preloading with 80 kPa indicate that the test in the current study can decrease the horizontal displacement of fine particles and can avoid drainage pipe blockage.

Damage evolution analysis of rock under Uniaxial compression and Brazilian splitting based on discrete element method

In order to better analyze the mechanical behavior of rock in uniaxial compression and Brazilian splitting, numerical model was established according to laboratory test by PFC2D particle flow program, and the simulation results were compared with the experimental results. The results show that when the rock reaches the peak stress, the failure curve of cement appears an obvious turning point, and the failure rate of cement increases.The compressive strength of rock is much greater than the tensile strength under compression condition. The preloading method is more detailed for experimental restoration, and it provides certain reference significance for rock simulation in the future.