筑垱机筑垱形状与拦蓄雨水能力研究

通过分析筑垱机筑垱过程和调查实际筑垱形状,比较实际土垱与理想形状土垱拦蓄雨水能力差异及现有筑垱机存在的问题。提出在筑垱机翻转铲上设置压土板以改善筑垱形状和增加密实度的方法,并探讨压土板形状尺寸对筑垱形状的影响,得出最佳压土板形状为外圆弧形,其半径为7.5 cm。为研究开发垄沟筑垱技术及其设备提供技术依据。

Horizontal trap-door investigation on face failure zone of shield tunneling in sands

A novel horizontal trap-door test system was devised in this study to analyze the face stability of shield tunnels in sands.The test system can be used to investigate both the longitudinal and cross sections of the face failure simultaneously at one single apparatus and was employed to perform face stability tests on small-scaled tunnel models at single gravity.The lateral support pressures and failure zones were studied with varying sand materials and earth covers.The results demonstrate that the tunnel face moves back,the lateral active earth pressure on the tunnel face decreases rapidly to a residual value,and the lateral pressure distribution can be categorized into three stages during the failure process:1)initial state;2)pressure dissipation stage;and 3)pressure zone diminution stage.Furthermore,face failure firstly develops from a stable condition to the local failure state,and then continues to develop to the global failure state that can be divided into two sub-zones with different failure mechanisms:rotational failure zone(lower zone)and gravitational failure zone(upper zone).Further discussion shows that under the effects of soil arching,the shape of the gravitational failure zone can adopt arch shaped(most frequent)and column shaped(in shallow tunnels).Limit support pressure for face stability usually appears atδ/D=0.2%−0.5%(ratio of face displacement to tunnel diameter).

A Refined Formula for the Allowable Soil Pressure Using Shear Wave Velocities

Based on a variety of case histories of site investigations, including extensive bore hole data, laboratory testing and geophysical prospecting at more than 550 construction sites, an empirical formulation is proposed for the rapid determination of allowable bearing pressure of shallow foundations in soils and rocks. The proposed expression corroborates consistently with the results of the classical theory and is proven to be rapid, and reliable. Plate load tests have been also carried out at three different sites, in order to further confirm the validity of the proposed method. It consists of only two soil parameters, namely, the in situ measured shear wave velocity and the unit weight. The unit weight may be also determined with sufficient accuracy, by means of other empirical expressions proposed, using P or S -- wave velocities. It is indicated that once the shear and P-wave velocities are measured in situ by an appropriate geophysical survey, the allowable bearing pressure as well as the coefficient of subgrade reaction and many other elasticity parameters may be determined rapidly and reliably.

Impact of Mechanical Aeration on the Soil Resistance to Penetration and Density of Grassy Sward

The aim of this study was to analyze the effects of mechanical perforation of a golf course grassy sward, subject to maintenance machinery traffic and golf players trampling on its compaction and density. The evolution of soil compaction state after aeration was also conducted in four stages of measurement. This operation aims to improve the structure and soil texture, which is also called ＂perforation＂ or ＂coring＂. The taken cores leaving on the soil holes of adjustable depth and density （350 holes/mE） are made with an aerator machine called Vertidrain. Soil resistance to penetration and density were determined at the initial state before aeration as well as 10, 20, and 30 days after aeration. Compared to the initial state, the results show that mechanical aeration greatly affects the grassy sward ground by reducing its resistance to penetration as 35% and 43% decrease in penetration resistance were noticed at 5 cm depth l0 and 20 days after aeration, respectively. Also, resistance to penetration decreased by 41% and 48% at 15 cm depth during the same two periods of time with a relatively constant moisture content. However, soil resistance to penetration at 5 and 15 cm depths only decreased by 21% and 26%, respectively. Regarding the soil density measured after aeration, a significant improvement at the 1% level with the method of variance analysis was observed compared to that at the initial state （e.g. 1.33 g·cm^-3） Indeed, the density was 1.29, 1.26 and 1.30 gcm^-3 10, 20 and 30 days after aeration, respectively.

Operation Phase Problems of Prefabricated Residential Buildings with Integrated Autoclaved Aerated Concrete Panel Walls

Growing technical problems with the maintenance of precast concrete housing stock result in the search for efficient repair methods. The paper analyses the effects of flaws in the design concept and assembly accuracy of integrated AAC （autoclaved aerated concrete） panel walls, type GWO （Gazobetonowa Wielka P｜yta Ostonowa which means large cover panel from aerated concrete in English）, used as curtain walls in a system of precast concrete housing blocks erected in Lublin. The results of in-situ observations and laboratory tests of the panel walls have been described, and the opinion on the further use of these elements has been presented. As for the analysed case, there is no possibility of replacing damaged elements, thus, additional reinforcement with steel tendons has been proposed as a repair measure.

Discussion on construction and type selection of China high dams

At the beginning of 21st century, with the rapid and steady development of China economy, a lot of large scale hydropower projects with large dams from 200 m to 300 m high are being or to be built. China dam constructions are reaching the level of 300 m high arch dam, 250 high CFRD (concrete face rockfill dam) and 200 m high RCC (roller compacted concrete) gravity dam. Due to the safety and the economy, the type selection for high dams has become the key issue during the argumentation for the hydropower projects, and further efforts are still needed in this aspect for high dams. After reviewing the high dam constructions in China and abroad, authors proposed some advices for the selection of dam types, and hope that it can provide some helpful information for the researches and the design of high dams.