Qian Su

Models for Strength Prediction of High-Porosity Cast-In-Situ Foamed Concrete

A study was undertaken to develop a prediction model of compressive strength for three types of high-porosity cast-in-situ foamed concrete (cement mix, cement-fly ash mix, and cement-sand mix) with dry densities of less than 700 kg/m3. The model is an extension of Balshin’s model and takes into account the hydration ratio of the raw materials, in which the water/cement ratio was a constant for the entire construction period for a certain casting density. The results show that the measured porosity is slightly lower than the theoretical porosity due to few inaccessible pores. The compressive strength increases exponentially with the increase in the ratio of the dry density to the solid density and increases with the curing time following the composite function for all three types of foamed concrete. Based on the results that the compressive strength changes with the porosity and the curing time, a prediction model taking into account the mix constitution, curing time, and porosity is developed. A simple prediction model is put forward when no experimental data are available.

Construction Technique of Pile-Board Subgrade Crossing Over-Shallow-Embedded Metro in Deep Soft Ground

Subway shield lining segments are highly sensitive to peripheral soil disturbance. Shield displacement may destroy the whole structure which can not be repaired, and directly affects the subway operation safety at the worst. Therefore, it is necessary to reasonably determine the construction technology, in order to avoid the unfavorable influences caused by construction disturbance. According to the pile-board subgrade scheme which is adopted by the comparison of schemes, also considering the high risk of over-shallow-embedded metro construction, we put forward the key construction technique of pile-board subgrade, including: technique of casing tube bored pile, construction process of pile-board structure and monitoring of settlement and deformation which are important to guide the similar projects.

Ultimate Capacity Analysis and Determination of the Position of Failure Surface for Uplift Piles

Ultimate capacity and failure surface position of uplift piles are dependent on soil parameters. In this paper, the horizontal slice method is used to discuss the relation among the ultimate uplift capacity, the failure surface position, and soil parameters with Mohr-Coulomb failure criterion. According to the limit equilibrium analysis, the ultimate uplift capacity is calculated by dividing soil around the pile into slices with considering the potential failure surface as a group of several sectional planes. Then the multivariate function used to calculate ultimate capacity is established and optimized by the sequential quadratic programming. Through the numerical calculation and comparison with the previous research, the results show that the method is reasonable and effective and can be used to determine the failure surface and the magnitude of the ultimate capacity of uplift piles.

Seismic Stability Analysis of High-Fill Embankment

Three problems remained to be solved in the analysis of the seismic stability of high-fill embankment: the pseudo-static method was defective, the embankment damage model was not clear, and the stability evaluation index was still to be discussed. It analyzed the dynamic response of a typical transect of high embankment with FEM to find out its instability mechanism. Then it chose the most dangerous sliding surface and analyzed its stability. The selection of the evaluation index of the seismic stability of high-fill embankment was discussed at last. The results show that the upper embankment, especially the shoulder is easily to be damaged. It is too conservative to use the safety factor as the involution index of the seismic stability of high-fill embankment, and the permanent displacement is a better choice.

The Load Carrying Mechanism of Plate-Chair Type Retaining Structure

The plate-chair type retaining structure, which developed from h type anti-slide pile, has the characteristics of high stiffness and small deformations, and is suitable for subgrade retaining engineering on high slopes. The difficulty is that the landslide thrust distribution is not clear and the action of soil between the front and back row piles is not definite. First, a theoretical method of calculating the earth pressure acting on the structure is presented based on analyzing its carrying mechanism. Then an example is analyzed using the method. Finally, on the base of constructing a three-dimensional numerical simulation model of soil-structure interaction using ABAQUS, a validation and comparison between the theoretical calculation and numerical simulation is carried out. The result shows that the method is simple, safer, suitable for designing and can be used in the similar engineering.

Analysis on Genesis of Frost Damage to Taiyuan-Zhongwei-Yinchuan Railway Subgrade in Seasonal Permafrost Region

The paper took Taiyuan-Zhongwei-Yinchuan Railway as a background and the study focused on the frost damage there. First of all, the influence on the line operation was mentioned, discussing the status quo and the characteristics of the damage; next, by means of on-site investigation and testing, the phenomenon in the typical frost damage zone along the Railway was analyzed with the damages being classified; simultaneously, taking the track bed and the subgrade bed as the objectives, the damages were studied from the aspect of soil, water and temperature; last, the genesis and mechanism of the frost damage to the Lanzhou-Xinjiang Railway subgrade was generalized, offering the basis of the treatment.

Researching on the Mechanic Properties of Early-Strength Polyurethane Concrete and its Affecting Factors

The early-strength polyurethane concrete technology is the new outcomes of materials used in the structure engineering these years, which mixed polyurethane resin of fast concretion properties with certain combination materials to form stable organization, and it can be applied in the fast filling and surface repairing of the roads and concrete structure. According to the high standards of the aggregate used in the concrete, this paper presents a new formulation of aqueous polyurethane concrete. By comparing the effects of main parameters such as moisture content, temperature, addition etc. working on the solidification though formulations experiments and strength experiments, it was found that the solidification need different moisture content at different temperatures. It is testified that the compressive strength of this new polyurethane concrete is 22.70MPa in practical application and theres no melt and decompose phenomena after marinating for a long time in marinating experiments, which satisfied the engineering need.

Study on Engineering Behavior of Non-Embedded Pile-Board Structure Crossing Over-Shallow-Embedded Metro

It’s the first application of NEPBS crossing over-shallow-embedded metro in deep soft ground on new Shanghai-Hangzhou passenger dedicated railway (SHPDR) in China. It’s necessary to study the engineering behavior of NEPBS in complex geology field. Long-term observation systems were installed at the typical test sections of SHPDR; Combined with theoretical analysis model, the mechanical properties and deformation laws were analyzed and tested. Measurement results show that the test reinforcement stresses of loading plates and supporting beams are small; the test bending moments agree well with the theoretical bending moments, which are far less than the resistance bending moments; the piles improved the mechanical properties of deep soft ground, so the plate-soil contact stresses are small, the maximum value is 132 kPa; 45 days after the train operation, the post-construction settlement is 1.86 mm; the settlements of individual test points are not yet stable, but they tend toward stability, which can meet the requirements of settlement control of SHPDR.

Numerical Analysis and Calculation of Internal Forces of Steel Box Continuous Girder Bridge Construction Process

In order to determine the most unfavorable condition of the steel box girder, ensure its stress and deformation in the safe state, the steel box girder bridge should apply the finite element analysis software to modeling analysis. At the same time, data calculation can provide the theoretical evidence for the factory manufacturing lines. The tender DB01 of the continuous bridge of the Hong Kong-Zhuhai-Macao Bridge provides the backdrop for this essay, using MIDAS/Civil 2012 to do numeral simulation analysis on the hoisting, and then analyzing the stress and deformation of the main beam at the different construction stages. The analysis reveals that the temporary maximum of a hinged steel box girder should be 47.5MPa in the process of construction which is allowed by the stress of the steel Q 345.And after the No.1 beam has been put in the right place and connected, the maximum displacement of the No.6 joint is 19.4mm downward. With the construction stage CS7 completed, the maximum downward displacement is 14.2mm. Making the stress free alignment is superposing the minus figure of the cumulative displacement on the basis of designed line. Each beam segment has been made according to the stress free alignment .Also, after field construction, the ideology of designed lines of the bridge will be brought into reality.

Field Test and Analysis of Piled-Raft Structure of High-Speed Railway Foundation

Piled-raft structure is used in high-speed railway to deal with the deep quaternary strata compressibility foundation, which can effectively control total settlement and differential settlement, aiming at the efficient, economical and fast treatment subgrade deformation. In this paper, based on the field test of Beijing-Shanghai high-speed railway project, the dynamic response of high-speed railway piled-raft structure is investigated. The results agree fairly well with those obtained by theoretical approach and show that settlement of the subgrade is controlled effectively by the piled-raft structure.