Cost effective sustainable slope protection solution of rural roads at flooding regions.

Transcription

1 Cost effective sustainable slope protection solution of rural roads at flooding regions. Md. Abul Kalam Azad Additional Chief Engineer, Local Government Engineering Department (LGED)

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3 A funnel shaped country that carries 100 % catchment water having only 8% area of the total catchment. Frequently flooded country

4 Highways/Regional Roads/Rural Roads are often subjected to erosion due to flood flow and wind generated flood waves. Rural Roads are worst victim as they are more in numbers and length. They also get low budget and priority.

5 Slope Protection work depends on steepness of slope, severity of erosion, scouring, cost effectiveness, soil type etc.

6 Steep slopes in rural roads is common in Bangladesh. As some roads are close to rivers/ canals/ ponds/property line ; LGED often requires slope protection with steep slopes in rural roads. Retaining wall and palisading are the options for slope protection with steep slopes.

7 Common Slope Protection measures in Bangladesh

8 LGED under a Technical Assistance Project has developed another cost effective sustainable solution for slope protection with SOIL BAGS Dr. Kenichi Matsushima of JICA team was the In-Charge of the Action Research.

9 The eroded road after the flood 2009 Boundary Situations during construction : The height is 2.9m, the slope is 1.0V : 0.6H. The soil type was silt sand. West East Road after Flood, 2009

10 Structure Soil bag Refilled soil Brick chips + sand (Filter materials) Wood pile Geo-synthetic bag (a) Cross section Sub slab concrete Soling Bricks Jute bag (b) Front view

11 Work flow Measurement Foundation cutting Excavated soil stocking Technical feature 1 Enforce the foundation Wood pile driving Brick soling Sub slab concrete placing (Cement, sand, brick chips)

12 Based on the situation, it may be with or without pile (A) With wood pile : = 80mm, L = 1,200mm Slab concrete was placed up to the head of the wood pile 1,040mm out of 1,200mm was driven in the earth (B) Without wood pile : based on the observation of the foundation

13 Peak shear stress B (Kpa) Peak shear stress, ( vh ) peak (kpa) Work flow - continued Mixing the materials Technical feature 2 Bag works as framework Filling the bag δ = 18 =18 τ tan( φ δ ) σ vh sb gravel φ sb gravel v δ B vh 330 mm A v 950 mm Placing the bag 1st bag : 10 inclined 2nd bag and above : 18 inclined δ = 0 =0 vh sb- gravel σ v τ tan φ φ sb gravel Vertical stress v (kpa) Vertical stress A (Kpa) Technical feature 3 18 inclination twice as resistant as flat prevent the suction of backfilled materials by water

14 Work flow - continued Space Technical feature 4 Bags are stacked so as the space works as drain hole Stacking the bags Technical feature 5 Easy to manage for workers Well compacted Compacting the bags Compacting backside refilled soil (One layer is same as a bag thickness) Completion

15 Construction process : 1Cut-off eroded loosen embankment manually. 2Set up a bamboo scaffold and strike wood piles into the basement by falling a weight of 100kg. The head of the wood pile is stopped at 160mm above the basement to unify the wood pile and the base concrete. 3Bricks are placed between wood piles, then base concrete is placed. 4Place the first base soil bag. 5Soil bags are stacked with the inclination of 18 backwards and tamp well with a compaction tool. At the back of soil bags, filter material and refilled soil are placed and tamp well with a compaction tool. 6After slope protection work is constructed, refill the slope with soil.

16 Quality Management : 1) Compaction management of back-filled materials. Compaction guideline was fixed as 5 times fall of local compaction tool from the height of 30 cm based on the field compaction test. 2) Cement and material mixing management. 3) Mixing field soil management. Field soil block was subdivided into small pieces smaller than 1 2 cm so as to improve the mixture with the cement. 4) Cement curing management. After the cement mixed mortar was made, all the works of filling the bag, conveying it, placing it, compacting it were completed within 40 minutes and its wet condition was kept by timely watering to get the required strength.

17 Different Mixing Ingredients and Ratios for Soil Bag Cement : Sand = 1 : 6 Cement : Soil = 1: 4 Cement : Sand = 1: 8 ( Cost-effective)

18 Different types of Soil bags and mixing ratios Geosynthetic bag No deterioration Nov, 2011 (after 1.5 years) (A) Soil cement Bags are worn out Even soil cement lasts 5 years (B) Dec, 2014 (after 4.5 years) 1:8 is better than1:6 Sand cement (1:6) Sand cement is better than soil cement Sand cement (1:8)

19 Soil bag method L=25m L=10m L=15m Geosynthetic bag Jute bag

20 Concrete block wall L=15m L=15m

21 3. Transit West East Road after Flood, 2009 Before construction, 2010 Soil bag Completion, Apr Concrete block

22 Situation during floods/ monsoons Trial works

23 Advantages of the method 1High technology and special construction machines are not necessary. 2Locally available materials can be used. 3Work process is simple and easy to follow by semi-skilled labors. (if guided by experts) 4Back-fill materials are well compacted. 5Land for construction can be saved since the slope is steep. Limitation : It requires careful monitoring by skilled professional during the whole construction procedure. However, it can be managed by providing training regarding the method.

24 Economic consideration The cost of the slope protection works is nearly forty percent of construction of retaining wall along the slopes. It is also less costlier than cement concrete block. Considering the soil bags; cost of construction with geo-synthetic bag is 1.5 times higher than the ordinary soil bag (jute bag) available in Bangladesh. Cost of a single geo-synthetic bag is 10 times higher than local bags. Geo-synthetic bag is more durable than local soil bags. Conclusion This method of slope protection can be replicated as a best practice in flooded regions as well as in hilly region where stability of slope is a great concern.

25 Thank you very much