Document Type : Original Research Paper

Authors

1 Soil Conservation and Watershed Management Research Institute, Teran, Iran

2 Tarbiat Moallem University, Tehran, Iran.

Abstract

Stabilization of potentially sliding terraces and natural slopes are of great importance from view point of resident security, environment protection, river engineering and water and soil conversation. Soil reinforcement using tree toots is one of methods being studied by many researchers. Most of them have worked on the effect of root density and few of them on the root diameter leading to contradicting results. In this paper the combined effect of root diameter and density on the shear resistance of soil is investigated by series of in-situ direct shear tests. Eighteen tests were carried out on soil having Willow roots and the results were compared with those of non rooted soil as reference. To explain the observations, a new parameter referred to as root diameter-density index (RDDI) was defined. The results reveal that an increase in RDDI causes a significant increase in the apparent cohesion of rooted soil, but a little decrease in the internal friction angle. In both cases the rate of variation decreases with increasing RDDI and tends to a little value; however the extreme values of 212% and -15% were observed respectively. As general conclusion for rooted soils, the dominance of variation of apparent cohesion with respect to that of internal friction angle results the shear resistance ameliorates within a range of RDDI, and for further values it tends to a stabilized value. Also, for practical purposes, a relation was developed to be used by designer engineers.
 

Keywords

کتابنگاری

استیری، غ .ر.، فتاحی، م. ع .، 1380- "استفاده از روش بیو مهندسی در تثبیت شیبها".دومین سمینار زمین لغزش و کاهش خسارات آن، تهران، ص 401-408
 داودی، م. ه.،  فاطمی‌عقدا،  م.،   نوذری، ح .، شاه‌علیپور، غ، ر.، 1383- بررسی اثر قطر ریشه درخت بر مقاومت برشی خاک"، مجله تحقیقات مهندسی کشاورزی.
 داودی، م، ه .،  نیک کامی، د.،  امام جمعه، س،  ر.ف 1383-  " تأثیر ریشه درخت بر مقاومت برشی خاک با استفاده از آزمایشات بزرگ مقیاس".پژوهشکده حفاظت خاک و آبخیزداری، گزارش نهایی طرح تحقیقاتی. 155 ص.
شفاعی بجستان، م. و سلیمی گل شیخی، م.،  1381- "تعیین اثر ریشه درختان پده و گز بر مقاومت برشی خاک ساحل کارون در محل"، مجله علوم و فنون کشاورزی و منابع طبیعی، جلد ششم، شماره چهارم، ص. 27-40
 عامل سخی، م.،   قضاوی، م.،  1380- "تأثیر تراشه لاستیک‌های فرسوده بر پارامترهای مقاومت برشی خاک"، دومین کنفرانس زمین‌شناسی مهندسی و محیط زیست ایران، تهران، ص 483-491
 
References
Burroughs, E.R., Thomas, B.R.,1977- Declining root strength in Douglas-fir after felling as a factor in slope stability, USDA For Serv. Res. Pap. INT-190.
Nilaweera, N.S., 1994- Influence of Hardwood Roots On Soil Shear Strength And Slope Stability In Southern Thailand, Ph.D. Dissertation, Asian Institute of Technology, Bankok.
O’Loghlin, C.L.,1984- Effective of Introduced Forest Vegetation For Protecting Against Landslides And Erosion In New Zealand Steep Lands, Paper presented to Symposium on effects of forest landuse on erosion and slope stability, Honolulu, Hawaii.
Tengbeh, G.T., 1989- The Effect of grass cover on Bank Erosion, Ph.D. Thesis, Silsoe College, Cranfield Institute of Technology.
Waldron, L.J., 1977- Shear Resistance of Root-Permeated Homogeneous And Stratified Soils, Soil science Society of America Jour., 41: 343-349.
Yarbrough, L.D., 2000- Channel Bank Stability Analysis And Design Considering the Effects of Riparian Vegetation And Root Reinforcement, University of Mississippi, Thesis for Master Degree.
Ziemer, R., 1981- Roots And Shallow Stability of Forested Slopes, International Association of Hydrological Sciences, Publications No .132.pp.343-361.