Soil and water conservation in Tigray (Northern Ethiopia): the traditional dagat technique and its integration with introduced techniques

Between the cultivated fields in the highlands of Tigray, one finds, besides the recently introduced stone bunds, many lynchets, with a height ranging from 0·3–3 m. Grasses occupy the riser and a more or less large strip on the shoulder. Traditionally, farmers established an untilled strip of about 2 m wide at the lower plot limit. This grass strip reduced runoff velocity, allowed for water to infiltrate and trapped sediment. Year after year, these lynchets, locally called dagat, continued to grow. In this study, the dagat technique is characterized and its evolution and reasons for partial destruction are outlined. Stereoscopic aerial photo analysis shows for the study area near Hagere Selam (13 °39′N, 39 °10′E, 2650 m a.s.l.) that 20·7 per cent of the major dagats (more than 1 metre high) have disappeared between 1974 and 1994. These lynchets, however, remain an important linear element in the landscape (22·7 m ha⁻¹, i.e. their density on cultivated fields is much higher). Of the smaller lynchets, a great proportion has been levelled in order to increase plot surfaces and spread fertile soil over the field. Famines and impoverishment caused the farmers to increase short‐term agricultural production in this way. Since the 1980s, the farmers built stone bunds on most of the cultivated land. Their average length equals 56·1 m ha⁻¹ in the study area. The establishment of stone bunds results in the development of small terraces. Especially during recent years, there is a tendency to integrate the traditional knowledge of dagat with the building of stone bunds. A quantitative assessment of the effectiveness of both techniques must be made. Copyright © 2000 John Wiley & Sons, Ltd.     

浅谈特殊地区桥梁桩基础的设计

桩基础在桥梁设计中使用非常广泛,许多桩基础在特殊地质条件下的设计和施工过程中,都存在一些特殊的尚未解决好的技术问题,导致不安全因素或事故的发生.本文对特殊地区(软弱土层、黄土地区、多年冻土区)的桥梁桩基础设计中的部分值得注意的问题进行了简单阐述.     

银杏种核采后处理对氰化物含量的影响

以银杏核用主栽品种佛指和洞庭皇为试材,对采收的种核进行CaCl_2溶液浸泡、~(60)Co辐照处理后,贮藏于室内,期间每隔20 d测定种核氰化物的含量和种胚的长度变化.结果表明:银杏种核内氰化物含量随着贮藏时间的延长而上升,在148 d左右后逐渐下降,其最低值比贮藏前高出35%~55%;CaCl_2溶液浸泡和~(60)Co辐照均能明显降低种核氰化物的含量,且品种间存在一定差异;银杏种核氰化物含量与种胚的长度呈极显著相关.     

群桩基础沉降计算的近似混合法

基于混合法的基本思想,提出了用于群桩沉降非线性计算的近似混合法。近似混合法通过构造单桩沉降荷载曲线的插值函数以及采用相互作用系数考虑群桩之间的弹性影响,避免了因各桩离散成许多单元而导致土体柔度矩阵[δs]集成的费时,从而可进行多桩数群桩的非线性计算而不受微机内存和运算速度的限制。算例证明,本法与混合法的计算结果非常吻合。     

景观设计中石材的使用要点浅析

石材作为景观设计中最常见、用量最大的材料,能否娴熟科学地使用石材对景观设计效果的把握和工程造价的控制起到关键性的作用。     

麦饭石对家禽酵母饲料消化率的影响

采用Ｓｉｂｂａｌｄ的ＴＭＥ法进行盲肠未取盲肠公鸡的消化试验,以酵母饲料为基础对照日粮,以酵母饲料＋麦饭石（１００：１）为试验日粮。结果表明,麦饭石对去盲肠和未取盲肠公鸡的日粮摄入量和粪便排泄量无显著影响,面对排泄量与摄入量的比率产生显著影响;日粮消化率在基础日粮和试验日粮分别为：干物质７８．０３、７５．９２和８０．７５、７８．４２;能量８０．０７、８０．２５和８０．３４、８１．１６;氮２８．７４、     

石材在园林驳岸中的应用形式探讨

石材是园林驳岸中使用历史最悠久也是最广泛的材料。研究分析石材在驳岸中的应用形式,阐述每种驳岸形式的具体做法和注意事项,并相互比较,总结各自不同形式的优缺点和适用场所,为风景园林设计师提供一个很好的借鉴。     

松针粉-麦饭石复合添加剂对肉鸡法氏囊生长发育的影响

试验取144只1日龄健康AA肉仔鸡,随机分为2组,每组72只,组内设2个重复,每个重复36只。对照组饲喂基础日粮,试验组饲喂添加1%松针粉、1%麦饭石的基础日粮,饲养期42d。分别于7、14、21、28、35、42日龄随机取鸡12只,每组6只,各重复3只。颈静脉放血致死,解剖取法氏囊称重,取材制作石蜡切片,光镜观察,显微摄影。结果表明:试验组与对照组鸡法氏囊指数在7、35日龄差异极显著(P<0.01),14、42日龄差异显著(P<0.05);法氏囊小结皮质均显著厚于对照组。本试验从组织学角度证明,在基础日粮中添加松针粉和麦饭石可显著促进肉鸡法氏囊的早期发育,延缓退化的时间。     

探地雷达在碎石桩检测中的应用

将探地雷达检测技术应用于碎石桩的质量检测,判定碎石桩的桩身完整性,具有快捷、准确和实时处理及显示的优点。结果表明:该技术可为复合地基的质量检测提供大量相关信息。     

林区桥梁桩基质量检测问题浅析

桩基础是林区桥梁常用的 1种基础式。本文从如何检测桩基础施工质量等方面阐述了几种检测方法 ,可供林区桥梁施工技术人员参考。