A new technology of vacuum preloading with prefabricated radiant drain (PRD), including prefabricated vertical drain (PVD) and prefabricated horizontal drains (PHD), was proposed in this paper. The validity of numerical model parameter was verified by comparative analysis of deformation development of numerical simulation results and field tests. In addition, two influence factors of PHD spacing and PHD length for vacuum preloading with PRD technique were systematically studied by finite element method. The results show that vacuum preloading with PRD can obviously improve the reinforcement effect of dredged fill ground. Compared with the conventional vacuum preloading, the maximum settlement of vacuum preloading with PRD respectively is increased by 88.94 % and the maximum lateral displacement is 110.4 % at the PHD spacing of 0.5 m. Moreover, reducing the PHD spacing can improve the ground treatment effect. Compared with the PHD spacing of 1.5 m, the maximum settlement respectively is enlarged by 39.93 % and the maximum lateral displacement is increased by 49.4 % for the PHD spacing of 0.5 m. Increasing the PHD length can boost settlement and lateral displacement for the PHD length range of 0.2 m~0.4 m. The settlement and lateral displacement are 38.98 % and 50.3 % higher for the PHD length of 0.4 m than those for a PHD length of 0.2 m.
Recently, construction of GRS (Geosynthetic reinforced soil) structures with closely spaced layers of geosynthetic reinforcement has been increased significantly. In order to achieve direct comparison between GRS structures and the conventional mechanically stabilized earth structures using geosynthetic (GMSE) under the same working condition, three model tests with a bridge abutment as a prototype were designed in this research. Under the vertical load of 100 kPa in simulating the weight of the bridge deck, important parameters such as stresses and deformations of the model abutment were measured, and the effect of reinforcement spacing on the performance of different reinforced soil structures was evaluated. According the test results, the overall better performance of GRS abutment was proved in terms of measured strains and stresses. In addition, comparisons were made between the measurements and the analytical predictions following solutions available in literature, and the accuracy as well as limitations of different calculation methods was discussed.
Wooden architecture sites are important archaeological objects in southern China. Existing archaeological studies generally believe that the settlement architecture of the Hemudu period is single-story pile-dwelling. Because of its unique geological conditions, a large number of well-preserved wooden pillars have been unearthed in the Tianluoshan site, Zhejiang province, China. Based on the huge settlement founded under wooden pillars at this site, the historical load on the wooden pillar was calculated in reverse according to the calculation method of foundation settlement. Then the tribal architectural form at that time can be inferred according to the layout map of the wooden pillar at the Tianluoshan site. The results show that the Hemudu culture could build multistory buildings already, which presumed to be sacrificial buildings.
The secondary design of building is not mandatorily required in Japan. However, to rationally design the building and minimize the earthquake damage, it is important to consider the secondary design of not only the foundation structure, but also the interaction between the ground and the superstructure. Therefore, as the first step to understand the response of the foundation structure during L2 earthquake motion, we focused on the ground improvement for liquefaction countermeasures. In this research, in order to clarify the mechanical behavior and effect of the liquefaction mitigation subjected to L1 and L2 earthquake ground motions, centrifuge model tests using the soil-cement grid with assumed thickness, area replacement ratio and interval corresponding to the construction site were conducted. The test results show that even if the soil-cement gird is damaged such as cracks, the shear deformation of the improved ground due to subsequent earthquake motion could be partially reduced.
Damage caused by liquefaction has been confirmed in various parts of Japan due to the recent large earthquake. The permeable grouting method is mentioned as the effective liquefaction countermeasure technical method in a limited space. Chemical grouting materials and cement-based solidifying materials are often used in the permeable grouting method. Although permeable grouting used chemical grouting material has high permeability, the long-term durability is not sufficiently secured and there are many constructor would not introduce it. On the other hand, with in regard to cement-based solidifying materials, although sufficient long-term strength is exerted, permeability is low, and injection into sand having fine particles is insufficient. In recent years, ultra-fine particle cement has been developed to solve these problems of cement-based solidifying materials .Ultra-fine particle cement is a material in which cement particles are very finely divided. The c cement-based solidifying materials using ultra-fine particle cement has been confirmed to have the same permeability as chemical grouting materials. The authors used the ultra-fine particle cement to change the water-cement ratio and investigate the dynamic deformation coefficient using a bender element test device. From the results, the influence of water-cement ratio on the improved sand was investigated.
Most of the earthen sites in coastal areas of South China are rescue excavations. According to the statistics, the main environmental geological hazards of the protection of original earthen sites is the water seepage caused by groundwater damages, especially during typhoon season (Jun.-Sep.). The article takes the Jingtoushan site of Zhejiang province, China as an example to establish a hydrogeological model, which was formally started excavation on June 3, 2018. The average depth of Neolithic remains in this site is 7m and the scheme is to design a rectangular foundation pit with row pile supporting structure. By collecting and analyzing the local meteorological data (precipitation, evaporation, etc.) and geological conditions of the site, the study simulates Jingtoushan site using the finite difference code of Visual MODFLOW to calculate the distribution of original groundwater and the variation law of seepage field in site area during construction period. The models are calibrated and verified through survey data using permeability and seepage model. The new numerical simulation method can be used to guide the excavation and construction of other earthen sites.
The soft soil treatment is one of the hot issues needed to be solved in many constructions including tunnels, freeways, etc. In this paper, a prefabricated pipe pile with side openings and wrapped geotextile is first proposed aiming to realize both the effect of pile foundation and composite foundation for soft soil treatment, which could be capable of draining and increasing frictional resistance. It combines fast drainage consolidation and high bearing capacity, which could be used under different engineering conditions with different designs. Small holes on pipe pile provide the drainage channel for vacuum to accelerate the consolidation and reduce the squeezing effect. The geotextile wrapped outside reduces the friction in pile-driven process and has the anti-filtering effect to ensure the long-term stability of the drainage channel. After the consolidation, the drainage pipe pile is grouted to form a composite foundation with high bearing capacity, which has good time, economy and environmental benefits. The drainage pipe pile can be developed to some special designs for dam filling and reclamation of islands. The proposed innovative designs of pipe pile could satisfy the demand of high bearing capacity and quick consolidation on soft soil, which combine both the effect of pile foundation and composite foundation.