海相软土场地水泥土劣化机理室内试验研究

将水泥土和周围土体作为研究对象,利用室内化学分析试验得到了离子浓度的时空分布规律,并从腐蚀离子干预水化反应进程和分解水化产物两个过程揭示了海相软土场地水泥土劣化机理。Ca^2+由水泥土向土体中扩散,Mg^2+、SO42^-及Cl^-从土体向水泥土扩散;随着水化反应的进行,Ca^2+不断生成,水泥土中足够多的Ca^2+是保证水化反应进行并维持水化产物稳定的必要条件,Ca^2+不断向土体扩散是水泥土劣化的原因之一;水泥土内部的SO42^-及Cl^-在浓度较低(分别低于9和15 g/L)时有利于水泥土强度的提高,浓度较高时则导致水泥土发生胀裂;水泥土中Mg^2+的存在会阻碍水化产物的生成并分解水化产物,但浓度较低(低于3 g/L)时,影响不明显;土体中Mg^2+、SO42^-及Cl^-浓度高于水泥土中的浓度,在水泥土表层与水化产物反应生成胶结性差及膨胀性高的物质,促使水泥土劣化。     

扩底抗拔桩动态变形全过程承载特性模型试验研究

利用砂土中扩底抗拔桩的模型试验,研究从开始加载到破坏时扩底抗拔桩地基动态变形全过程的承载特性。试验结果表明:半模试验得到的极限荷载和破坏面均略小于全模试验结果,采用半模试验测量地基变形过程与破坏模式有明显优势,用半模试验代替全模试验是可行的;随着桩顶荷载的增加,扩大头上方的土体由压缩变形逐渐发展为局部的压缩—剪切破坏;扩大头对其上部的桩侧摩阻力有增强作用,对其下部的桩侧摩阻力有削弱作用;扩大头在工作荷载、极限荷载和破坏荷载作用时分担的荷载比例为15%~20%。     

土层抗浮锚杆承载力关键影响因素现场试验研究

工程实践及理论研究均表明,锚土界面特性和锚杆的几何形状是影响抗浮锚杆承载力的2个关键因素。采用不同的施工工艺进行现场试验施工,得到了具有不同锚土界面特性和锚杆几何形状的抗浮锚杆。通过现场锚杆抗拔试验得到锚杆的应力应变关系及极限抗拔承载力。研究结果表明,改善锚土界面特性和采用变截面的锚固体可显著提高锚杆的抗拔承载力。同时,提出了1种经济高效的抗浮锚杆施工工法。     

广西隆安都结剖面下石炭统都安组上部鲕粒类型及其地质意义*

鲕粒是一类特殊的沉积颗粒,为古气候和古海洋环境的重要指示器。为了深入认识此类特殊颗粒的成因机制、形成环境及地质意义,对广西隆安地区都结剖面下石炭统都安组上部含鲕粒地层开展了古生物学、沉积学和岩相学研究。研究区共识别出5种主要的鲕粒类型: 放射状纹层鲕粒(O1)、规则同心放射状纹层鲕粒(O2)、不规则同心放射状纹层鲕粒(O3)、泥晶鲕粒(O4-A和O4-B)和复合鲕粒(O5)。各类鲕粒的显微组构和沉积环境指示其具有不同的形成过程,其中水动力条件影响和控制着鲕粒的发育和分布情况。研究区含鲕粒地层形成于维宪期末—谢尔普霍夫期,恰好对应早石炭世晚期冰川作用的开始。受冰川作用影响,全球海平面频繁波动,研究区地处低纬度地区并以浅滩和潮坪沉积环境为主,为鲕粒的形成提供了适宜的水体条件,即温暖、动荡的浅水环境。此外,含鲕粒岩层内广泛发育钙质微生物和微生物席,说明微生物活动在研究区较为常见,可能与鲕粒的形成过程具有一定的关联。     

一种新型的组合波航空电磁脉冲发射系统

由于在低压输入,多匝、低阻发射线圈条件下很难实现理想的方波电流脉冲,GEOTEM等国外经典的时间域航空电磁系统大都采用半正弦波发射电路来实现大磁矩发射。笔者设计了一种新型的准谐振组合波脉冲发射电路,能够在提高通断速度的同时实现近似方波的组合波脉冲发射,有利于提高航空电磁勘查系统的分辨能力。在此基础上,成功研发了一套固定翼航空电磁脉冲发射系统,可激发基频可选、脉宽可调的双极性组合波电流脉冲,电流脉冲的幅值达到650 A,峰值磁矩达到50万Am2。     

Molecular outflows and gas rotation associated with G20.08-0.14N

We present the results of a high-resolution study with the Submillimeter Array （SMA） toward the massive star-forming complex G20.08-0.14N. With the SMA data, we have detected and analyzed the transitions in the 12CO （3-2） and 12CO （2-1） molecular lines as well as CHaCN. The millimeter observations reveal highly collimated bipolar molecular outflows, traced by high-velocity 12CO （2-1） and 12CO （3-2） emissions. Using a rotation temperature diagram, we derive that the rota- tional temperature and the column density of CHaCN are 244 K and 1.2 ~ 1015 cm-2, respectively. We also suggest that the minor outflow is probably driven by the hy- percompact （HC） HII region A that is inside. We find the molecular gas （traced by ClrO, SO, CH3OH and SO2） surrounding G20.08-0.14N appears to be undergoing bulk rotation. The HCHII region A that is inside is most probably the main source of accretion and heating for G20.08-0.14N.     

Submillimeter/millimeter observations of the molecular clouds associated with Tycho's supernova remnant

We have carried out CO J = 2-1 and CO J = 3-2 observations toward Tycho's supernova remnant(SNR) using the KOSMA 3m-telescope.From these observations,we identified three molecular clouds(MCs) around the SNR.The small cloud in the southwest was discovered for the first time.In the north and east,two MCs(Cloud A and Cloud B) adjacent in space display a bow-shaped morphology,and have broad emission lines,which provide some direct evidences of the SNR-MCs interaction.The MCs are revealed at-69--59 km s-1,coinci...     

First Mapping Observations of Two Possible Cloud Collision Candidates IRAS 02459＋6029 and 05363＋3127

The first mapping observations of the cold infrared sources IRAS 02459 6029 and 05363 3127 in the molecular lines 12CO(1-0), 13CO(1-0) and C18o(1-0) were made using the 13.7 m millimeter wave telescope in Qinghai. Both the integrated intensity maps and position-velocity diagrams show that each has two components adjacent in both space and velocity which means possible cloud-cloud collisions in the two regions. The near-infrared color-color diagram from the 2MASS database reveals that the density of YSOs in the colliding site is much higher than in the surrounding regions. The results appear to indicate that star forming activities have taken place in the two regions due to the cloud-cloud collision. We conclude that both sources are cloud collision candidates.     

Seismic Passive Earth Pressure with Seepage for Cohesionless Soil

The authors deal with the computing seismic passive earth pressure acting on a vertical rigid wall. The wall is provided with a drainage system along soil-structure interface and retains the cohesionless backfill subjected to water seepage. A general solution for the seismic passive earth pressure is presented. The solution is based on Coulomb's theory wherein seismic forces are assumed to be pseudostatic. The solution considers the pore water pressures induced by water seepage and earthquake shaking. Some important parameters are included in the solution. The parameters are the soil effective internal friction angle, wall friction, soil unit weight, and horizontal and vertical seismic acceleration coefficients. The comparison of the total seismic passive earth pressure in horizontal direction from the present method with published works indicates that the present method may be reasonable. The variations of the passive earth pressure coefficient with the soil effective internal friction angle are investigated for different wall friction angles and seismic forces. The effect of the water seepage on the seismic passive earth pressure is also investigated.