Advanced Materials Research Vols. 250-253

Abstract: Cone penetration test is a fast and efficient in-situ test technique. With the development of sensor technology and the use of new probes, such test is employed in more fields and reveals more soil parameters. Based on the advanced CPTU equipment, porewater pressure dissipation processes were measured at different depths, dissipation characteristics of the sandy soil and cohesive soil were analyzed respectively; Then, consolidation and permeability coefficients of the cohesive soil were calculated, the results are close to the laboratory test results. Undrained shear strength of soft clay were determined use theoretical and empirical methods, calculation accuracy of these methods were analyzed and the results show that the total cone tip resistance method is in good consistence with the measured values. CPTU is able to provide plenty of geotechnical parameters; therefore, more experience of regional tests should be drawn so as to produce more economic and technical benefit in the future.

Abstract: The soil and rock mixture is widely spread in the world， which is much different from homogeneous and continuous soil, it is hard to get the permeability of the soil and rock mixture by theories, and it is also hard to get that from the large lab test as the difficulty in sampling. The particle flow code (PFC) method is used to study the permeability character influenced by large rock particles. The result shows that the seepage of the soil and rock mixture obeys the linearity of Darcy’s law in low fluid velocity, but the large particles influence the local pore pressure evidently. The permeability increases while the ratio of rock to soil increase first, and decreases while the ratio enlarge to 0.5, then increases after the ratio enlarge to 0.7. The large rock particles jam the fluid path, but decrease the length of the pipe, the permeability is influenced by the two effects.

Abstract: This subject studies the mutual effect between the upper structure and the foundation of the long-span spatial structure in the process of construction, normal use and carrying capacity. It compares different foundation forms which can withstand relatively large levels of thrust. The internal force analysis models of the most common form-prestressed tie rod are established and a systemic design theory about the long-span spatial arch space structure is formed. This subject fills the research gap on the foundation design of the long-span spatial arch structure.

Abstract: Under the concentrated loads, the crack evolutions of reinforced concrete experimental beams (RCEB) with three different aggregate sizes are studied. Using fractal theory, the generation, development and distribution of the cracks on the RCEB are analyzed. The results show that the cracks on the RCEB have fractal characteristics obviously. By studying the fractal dimension of the cracks, the aggregate sizes have significant effect to the cracks on the RCEB. The relationships of the fractal dimensions of the crack evolution in loading processing and loads meet the power function laws. The researching results of this paper provide a new theoretical basis for selecting the appropriate aggregate size to improve the strength of reinforced concrete beams.

Abstract: The main feature of NATM is to utilize all available means to develop the maximum self-supporting capacity of the surrounding rock or soil itself, and to undertake investigation and monitoring during construction to provide the stability of the tunnel. If undetected worse ground condition is encountered, the strengthening works will be carried out to ensure safety. In this case study, taking the Wangkeng tunnel portal engineering of the Jiyuan-Shaoyuan Expressway in Henan Province as an example, the calculation and evaluation of landslide stability are performed by limit equilibrium method and FEM. Based on the results of stability analysis, the anti-slide piles and ground drainage are adopted as the harnessing measures of landslide. Comparison of stability analysis before/after landslide harnesses was made by FEM. The results show that these treatments can satisfy the design requirements. It could be a useful reference to the design and construction of tunnels with soil entrance.

Abstract: Problem of lateral driving stability of the automobiles passing by the vicinity of pylons of cable-supported bridges in condition of strong cross wind exists obviously because of the alternative wind environment above the deck due to complex flow fluid around the pylon and the deck. Based on numerical wind tunnel technology, the numerical simulation investigation of alternating wind environment above the girder near A-shaped pylon for main span of the steel truss girder cable-stayed bridge of Zhengxin Yellow River Highway-railway Bridge is carried out, considering wind barrier set up on the deck or not. The result shows that the original program has significant effect on wind speed amplification and mutation near the pylon domain in cross wind. Further investigation on wind barrier set up on both sides of the girder section or near the A-shaped pylon along the bridge gives that wind barrier near the A-shaped pylon is useful for reducing wind speed above the leeward deck near the pylon and weakening its mutation. Deeply, taken a medium-size commercial bus as an example, lateral driving stability of the automobiles passing by the leeward lane near A-shaped pylon is discussed through the dynamic response simulation of the vehicle controlled by ideal-driver under cross wind. The results confirms again that the wind barrier near the A-shaped pylon is good for driving safety of vehicles passing by the leeward lanes in vicinity of A-shaped pylon. In all, above work provides technical support for the final implementation of the wind barrier as an engineering measure.

Abstract: Rainfall-induced landslides are of frequent occurrence in the south of China. One of the most effective methods to stabilize landslides is to lower the groundwater table by installing horizontal drain. A shallow landslide caused by typhoon Morakot happened along Shangyu - Sanmen Expressway in Zhejiang. Horizontal drains were installed and served as an important part of the slope stabilization scheme. The relationship among rainfall intensity, groundwater level, and slope stability was indicated by field monitoring data. Using software GeoStudio, the stability states of the original slope under rainfall are simulated, based on Fredlund’s Unsaturated Soil Strength Theory. After the rain ceases, the draining processes of the original slope and the slope with horizontal drains are compared. It is obvious that the factor of safety recovers rapidly in the slope with drains. The simulated discharge rate of drain and slope surface, and the change of groundwater table also prove the benefits of the drains, which agree well with the field monitoring data.

Abstract: The measured coefficient of consolidation can have a substantial degree of variation even in a uniform clay layer. The probability characteristic values for such parameters as consolidation coefficient and compression modulus are analyzed from local engineering data. This paper, through a probabilistic analysis, examines the variability of one-dimensional consolidation solutions. The multilayer models are evaluated. Then the Monte Carlo method is used to develop solutions for one dimensional consolidation. It identified the influence of the parameter uncertainty on the probability characteristic of the consolidation degree. The uncertainty of consolidation coefficient has a great impact on the probabilistic characteristics of the consolidation degree, but for compression modulus it is opposite true. It proposed a simplification analysis method that considers only the uncertainty of consolidation coefficient without consideration of the uncertainty of compression modulus, and its erroneous precision can meet the engineering requirements.

Abstract: Silt is widely distributed in coast area. Its consolidation is a popular geotechnical engineering issue. Coast silt is always under seasonal wave and tide, which made great influence on the consolidation process. Abundant lab and in-situ tests are used to study on the physical-mechanical properties of Xiamen coast silt. The engineering characteristic of the coast silt taken from Xiamen is evaluated and the relationships between physics and mechanics indexes such as compression coefficient, water content, void ratio, cohesion and internal friction angle are analyzed, and the linear regression equations between silt parameter is established. Then two in-situ tests cone penetration test (CPT) and flat dilatometer test (DMT) are applied to study the properties of coast silt, abundant in-situ test data obtained.

Abstract: The micro pore structure of isotropic consolidated clay was studied by using a scanning electron microscope (SEM). A digital imaging technique was applied to analyze the evolution of size, number of pores and their distributions in the process of isotropic consolidation according to the SEM images. Based on the fractal concepts of Koch curve and Sierpinski carpet, the Koch fractal dimension Dk and the Sierpinski fractal dimension D_s of soil pores are obtained from the measured data. The variations of both D_k and D_s following the change of micro pore parameters and mechanical properties of clay are investigated. The results show that the porosity and pore size decreases as the consolidation pressure increases, and the range of pore size becomes narrower. D_k reflects the degree of irregularity of the pore-solid interface in soil, and the larger the D_k the more irregular the soil pore profile. The distribution of D_k was found in agreement with a total normal distribution in soil pore. The magnitude of D_s reflects the variation of porosity of clay under isotropic consolidation. Large fractal corresponds to large consolidation pressure and small porosity. D_s displays a significant linear regression relationship with porosity, consolidation pressure, consolidation deformation of clay and an exponential growth relationship with permeability coefficient of clay. Both Dk and D_s is sensitive to isotropic consolidation of soil and they may be cited as useful indicators for soil consolidation.