Chapter 4 Principals of Biotechnical and Soil Bioengineering Stabilization生物技術和土壤生物工程穩定的原則

Biotechnical and soil bioengineering slope stabilizationA practical guide for erosion control

by D. H. Gray and R. B. Sotir

Prepared by Walter Chen, Dept. of Civil Engineering, NTUTFor classroom teaching purpose

Prepared by Walter Chen ( 陳偉堯 )

Introduction Erosion can be minimized: 侵蝕可以最小化

Preserving native vegetation whenever possible 盡可能保留原始植生

Clearing the land in workable increments 依工作量分區整地 Installing facilities to handle increased runoff 安裝設施處理

逕流 Installing erosion control measures as early as possible 儘早

安裝控制侵蝕設施 Adaption of landform grading practices that mimic natural

slopes 使用自然地形式整地法

Prepared by Walter Chen ( 陳偉堯 )

Observing basic erosion control principals 遵守基本侵蝕控制原則 Proper handling and disposal of surface and

subsurface water – most critical 最關鍵的是地表水和地下水的處理

Preserving and utilizing natural slope vegetation whenever possible 儘可能保留自然邊坡植生

Take advantage of soil bioengineering methods (embedment of live cuttings in the ground in various arrays and combinations) 利用土壤生物工程方法 ( 在土中嵌入活的切枝 )

Prepared by Walter Chen ( 陳偉堯 )

Classification of slope protection 邊坡保護的分類 Live construction 活的植生營建

The traditional use of grass and other live plants, primarily for erosion control (less certain against mass wasting) 傳統用草和植物控制侵蝕的方法 ( 對土體滑動較無用 )

Mixed construction 混合式營建 The use of soil bioengineering and biotechnical methods 使

用土壤生物工程和生物技術方法

Inert construction 無生命的營建方式 The use of inert structural or mechanical systems 使用無生

命的結構和力學系統

Prepared by Walter Chen ( 陳偉堯 )

Prepared by Walter Chen ( 陳偉堯 )

Inert construction

Prepared by Walter Chen ( 陳偉堯 )

Advantage of inert systems 無生命系統的優點 Availability 可用性 Ease of installation 易施工性 Familiarity 熟悉度高 Advertising and promotion 廣告與宣傳多 Existence of standards 存在業界標準 Acceptance by specifiers 接受度高

Prepared by Walter Chen ( 陳偉堯 )

Live construction

Prepared by Walter Chen ( 陳偉堯 )

Mixed construction systems混合式營建系統 Biotechnical stabilization 生物技術穩定

The use of natural inclusions, living or inert, to reinforce soil and stabilize slopes 使用天然的內含物 ( 活的或無生命 ) 以加勁土壤穩定邊坡

Biotechnical slope protection describes the integrated or combined use of living vegetation and inert structural or mechanical components 生物技術邊坡保護指的是整合使用植生和無生命的結構物

Soil bioengineering 土壤生物工程 More specific term that refers primarily to the use of live plants and plant

parts alone 特定名稱指光是使用植生或植生部分

Reinforced grass 加勁草 A grassed surface that is augmented with either hard armor (articulated

blocks) or soft armors 輔助以硬式或軟式保護系統的草

Prepared by Walter Chen ( 陳偉堯 )

Live cuttings and stems 活的切枝

Are purposely imbedded and arranged in the ground or in earthen structures, where they serve as 故意嵌入地表或土質構造物 Soil reinforcement 土壤加勁 Hydraulic drains 排水 Barriers to earth movement 土壤移動屏障 Hydraulic pumps or wicks 吸水繩

Techniques Live staking 活樹樁（第七章） Live fascines 活捆樹枝、束枝捆（第七章） Brush-layering 樹枝層（第七章）

Prepared by Walter Chen ( 陳偉堯 )

Vegetation + inert structures 植生+ 無生命結構物 Plants

benches of stepped or tiered retaining wall systems 平台或臺階式擋土牆系統

Openings or interstices of porous retaining structures 多孔擋土構造物

Examples: Open-front crib walls and gabion walls 格框牆和石籠（第五章） Geogrid retaining structures 地工格網（第五章）

Prepared by Walter Chen ( 陳偉堯 )

Stepped-back retaining wall

Open-front concrete crib wall

Prepared by Walter Chen ( 陳偉堯 )

Vegetative treatment of a geogrid-reinforced earth buttress ( 拱壁、扶壁 )

Prepared by Walter Chen ( 陳偉堯 )

Prepared by Walter Chen ( 陳偉堯 )

Reinforced grass 加勁草

A typical soft-armor system consists of very porous, synthetic, three-dimensional mats (turf reinforcement mats) that are placed on the ground, filled with soil, and seeded 典型的軟式系統包括多孔合成三維墊放在地上填以土壤和種子

Mats tying plant roots together and bridging over weak spots 墊子可以連結植物根系並跨越軟弱地方

Resist the tractive force of high-velocity water flow better than a grassed surface by itself 比只有草更能抵抗高速水流的拉力

Prepared by Walter Chen ( 陳偉堯 )

Attributes of soil bioengineering (1/7) 土壤生物工程的屬性 Labor/skill requirements

Labor/skill intensive instead of energy/capital intensive 勞力密集

Requires the use of hand labor 手工 Prebid orientation, on-site training, and careful supervision

and inspection 現場訓練、仔細監督 Often costs less than conventional treatments because it is

normally performed in the dormant season (labor more available) 通常在淡季所以便宜

Prepared by Walter Chen ( 陳偉堯 )

Attributes of soil bioengineering (2/7)土壤生物工程的屬性 Utilization of natural and/or indigenous materials

native materials such as plants and plant stems or branches, rocks, wood, and earth 天然材料

Live fascines – live-cut brush and stems harvested in the wild, tied into bundles, and then placed in the ground in shallow trenches 活束枝捆

Appropriate vegetation can often be obtained from local stands of species such as willow, alder, dogwood, and others 柳樹、赤楊、山茱萸

Prepared by Walter Chen ( 陳偉堯 )

Live fascines

Prepared by Walter Chen ( 陳偉堯 )

Attributes of soil bioengineering (3/7)土壤生物工程的屬性 Cost effectiveness 價格競爭力

Field studies have shown instances where combined slope protection systems have proven more cost effective than either vegetative treatments or structural solutions alone

Use of indigenous material accounts for some of the cost savings

Where labor costs are reasonable, the combined systems are especially cost effective

Even where labor is scarce, labor costs can be offset in structural materials, grading, heavy equipment, and other costs

Prepared by Walter Chen ( 陳偉堯 )

Attributes of soil bioengineering (4/7)土壤生物工程的屬性 Environmental compatibility 環境調諧

Require minimal access for equipment and workers and cause relatively minor site disturbance during installation

Systems are visually non-intrusive and blend into the natural surroundings

Favorable attributes in environmentally sensitive areas such as parks, woodlands, riparian areas, and scenic corridors (where aesthetic quality, wildlife habitat, ecological restoration, and similar values are important)

Prepared by Walter Chen ( 陳偉堯 )

Prepared by Walter Chen ( 陳偉堯 )

visually non-intrusive and blend into the natural surroundings

Prepared by Walter Chen ( 陳偉堯 )

Attributes of soil bioengineering (5/7)土壤生物工程的屬性 Self-repairing characteristics 自我修復

Soil bioengineering systems become stronger with time as the vegetation roots become well established

Vegetation has the ability to regenerate when subject to stress that does not kill the plants

Replanting and infill planting can also be used to repair damaged areas

Prepared by Walter Chen ( 陳偉堯 )

Attributes of soil bioengineering (6/7)土壤生物工程的屬性 Planting times 種植時間

Most effective when the soil bioengineering systems are installed during the dormant season, usually the late fall, winter, and early spring

Coincides with a slowdown in other construction work The availability of the required quantities of suitable plant

material during the allowable planting time may limit the usefulness of soil bioengineering methods

Time constraint can be partly circumvented by placing cuttings or live plant materials in cold storage until ready for use

Prepared by Walter Chen ( 陳偉堯 )

Attributes of soil bioengineering (7/7)土壤生物工程的屬性 Difficult sites 困難地點

Useful alternative for highly sensitive or steep sites where the use of machinery is not feasible and hand labor is a necessity

But limited by a poor medium for plant growth, such as rocky or gravely slopes

Also limited on slope that are exposed to periodic, high-velocity flow or constant inundation (consider using structural reinforcement or augmentation with biotechnical ground covers)

Prepared by Walter Chen ( 陳偉堯 )

Limitations of soil bioengineering

Not a panacea for all slope failure and surface erosion problems 不是萬靈丹

Vegetation not appropriate where highly toxic conditions exist or in sites subjected to high water velocities or extreme wave action

Prepared by Walter Chen ( 陳偉堯 )

Compatibility between plants and structures (1/2) Free drainage 自由排水

Essential to the stability of earth-retaining structures Also important to vegetation, which generally does not

tolerate waterlogged soil conditions Backfill or cribfill material 回填材料

Engineering → coarse-grained, free-draining material Vegetation → fines in the soil to provide moisture and

nutrient retention Techniques available (section 8.2)

Prepared by Walter Chen ( 陳偉堯 )

Compatibility between plants and structures (2/2) Danger of physical damage by stems and roots of

woody vegetation 破壞建物？ Pry, dislodge, or heave the structure? The evidence is scant and mostly anecdotal Roots exhibit a property called edaphoecotropism (stress

avoidance) Roots will avoid zones of stress such as areas of moisture

deficiency, light, high temperature, mechanical obstacles (rocks), and low porosity (high density)

Roots will avoid the face of a porous, open retaining structure

Prepared by Walter Chen ( 陳偉堯 )

Will roots pry, dislodge, or heave the structure?

Prepared by Walter Chen ( 陳偉堯 )

Prepared by Walter Chen ( 陳偉堯 )

Prepared by Walter Chen ( 陳偉堯 )

Danger from planting trees Main danger from planting trees in and around

structures appears to come from soil moisture extraction that results in ground settlement in the vicinity of the tree

A large, mature pine tree can remove as much as 200 gallons (757 liters) of water from the ground a day by evapotranspiration 比較：人的心臟每小時輸送 343公升的血液，約每天 8000公升，一年三百萬公升，相當於四個奧林匹克標準游泳池

The area affected extends approximately 1 to 1.5 times the height of the tree

Prepared by Walter Chen ( 陳偉堯 )

Prepared by Walter Chen ( 陳偉堯 )

Impact of slope grading Transportation corridors and residential developments

in steep terrain require that some excavation and regrading be carried out

The manner grading is planned and executed affect not only the visual or aesthetic impact of the development but also the stability of the slopes and effectiveness of re-

vegetation efforts

Prepared by Walter Chen ( 陳偉堯 )

Prepared by Walter Chen ( 陳偉堯 )

Conventional grading Results in drastically altered slopes and the

replacement of natural hillside forms with artificial, sterile, and uniform shapes and patterns

Characterized by essentially linear, planar slope surface with constant gradients and angular intersections

Slope drainage devices are constructed in a rectilinear and exposed fashion

Landscaping and plants are applied in random or geometric patterns

Prepared by Walter Chen ( 陳偉堯 )

Prepared by Walter Chen ( 陳偉堯 )

Landform grading (1/3) Attempts to mimic nature’s hill Natural slopes consist of complex landforms covered

by vegetation that grows in patterns adjusted to hillside hydrology

Shrubs and other woody vegetation growing on natural slopes tend to cluster in valleys and swales where moisture is more abundant

Landform graded slopes are characterized by a variety of shapes including convex and concave forms

Prepared by Walter Chen ( 陳偉堯 )

Landform grading (2/3) Downslope drain devices either follow natural drop

lines in the slope or are tucked away and hidden from view in special concave凹的 swale and convex凸的berm combinations

Vegetation is placed where it has a better chance of surviving and where it does a better job holding soil

Cluster trees and shrubs in the swales and valleys of a slope

Prepared by Walter Chen ( 陳偉堯 )

Landform grading (3/3) By controlling the drainage pattern on a slope, runoff

can be concentrated in concave areas where it is needed or handled by woody slope vegetation

Runoff and seepage will be diverted away from convex-shaped areas

These areas should be planted with grasses or more drought-tolerant herbaceous vegetation

Irrigation needs reduced

Prepared by Walter Chen ( 陳偉堯 )

Prepared by Walter Chen ( 陳偉堯 )

Prepared by Walter Chen ( 陳偉堯 )