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Pavement Subsurface Drainage Design
Transcript of Pavement Subsurface Drainage Design
What is it?
Three tests were preformed to determine the adequacy of the soils. These tests are according to the British Standard
Testing the adequacy of used base materials in Bahrain
Determining suitable available soil for use as a permeable base layer
Designing a subsurface drainage system
Pavement Subsurface Drainage Design
For Minor Roads
Due to drainage problems
Supervised by Dr. Raad Kadhum
Figure 1: Variation of material quality with depth in a pavement system with ideal drainage characteristics.
1. Cracking Due to Weak Base and Sub-base
Done by: Fatima Buasally 20103033, Noor Saeed 20100175, Hessa Al Jaber 20105586
Seepage or capillary rise from the water table.
Seepage from storm water.
Seepage from an aquifer or other groundwater flow.
Figure 3: Sources of moisture in pavement systems
Figure 2: Water source
Why do we use it?
A Geotextile filter is a layer that provides stability by preventing the fines in the sub-grade from being pumped into the permeable layer and directing the water infiltrating to the edge drains.
A permeable fabric that has the ability to filter, protect and drain. Typically made of polyster
Figure 4: Geotextile usage
1) Sieve analysis
2) Proctor test
3) Permeability test
Two types of soil were tested, Type A and B, based on the type of soil used in Bahrain
Maximum Dry Density = 2.118 Mg/m3
Optimum Moisture content = 7.8%
Type A: Permeability Test
Sources of water in pavement
may be caused due to:
Type A: Sieve Analysis
D60=15.5mm D10<0.063mm D60/D10>30
The Results show that the soil is not adequate to be used as a permeable base layer.
Maximum Dry Density 1.976 Mg/m3
Optimum Moisture content 11%
Type B: Permeability Test
Type B: Sieve Analysis
D60=48mm D10<0.063mm D60/D10>30
Like Type A the result shows that soil type B is not adequate to be used as a permeable base layer.
The results of Type A and B show that the coefficient of uniformity is greater than 30, this means that the finer particles in the soil will get washed away when water flows through it which consequently causes pavement failure.
Type B has more finer particles (clay) therefore Type A was chosen to be modified. The adequacy of Modified Type A was tested for use as a permeable base.
Modified Type A
The soil was modified according to the following specification
finer particles were removed
Modified Type A Tests
Maximum Dry Density 2.118 Mg/m3
Optimum Moisture content 8.25%
Modified Type A: Permeability Test
Modified Type A: Sieve Analysis
D60=18.2m D10=1.18mm D60/D10=15.42<30
Since the coefficient of uniformity is less than 30 the soil can be used as a permeable layer.
Base Layer Thickness Design
Using Moulton's Method
Moulton's method is based on the thickness of the base which should be equal or greater than the depth of the flow.
LR: length of drainage
qi: rate of uniform flow
Hi: depth of water at the upper end of flow path
The equations can be solved using the chart below, which is based on the assumption that H1 is equal to the maximum depth of flow.
Other data needed for finding the thickness
Rainfall intensity: 2.78X10-5 cm/s
Road length: 3.75 m
Road slope: 5%
Pavement surface runoff: 0.9
Seepage Coefficient: 0.1
(Obtained for Bahrain's Ministry of Works)
H=0.28 m (using Moulton's Nomograph)
So a thickness of 0.3m will be used as a base layer
Geotextile Filter Design
Design shows less than 50% is passing 0.075mm sieve.
where B is a function of the coefficient of uniformity (Cu)
Since Cu >8
From the Modified type A sieve analysis; D85=27mm
The equation above will give O95<= 27mm
A pavement is a system of layers, each having
their own function and design requirements. The layers function as a whole, and so when one layer weakens it effects the whole pavement.
This project aims to solve one layer (base layer) in
against the presence of moisture in it, hoping to improve Bahrain's pavements durability.
This sub-surface drainage system is specifically designed to be used in Bahrain, where the data used was obtained from Bahrain's Ministry of Works, and the soil used is available and can easily be acquired.
Hazen’s empirical is an equation that predicts the permeability of saturated soils using the relationship between the hydraulic conductivity and the grain size
Figure 5: Nomograph for solving Moulton method
AOS or O95 (geotextile) ≤ B D85 (soil)
1. BAPCO (2014). STANDARD SPECIFICATION OF BUILDING AND MINOR CIVIL ENGINEERING WORKS. BAHRAIN: BAPCO
2. BS5930: 1990 BRITISH STANDARD, CODE OF PRACTICE FOR SITE INVESTIGATIONS
3. Ten C. N. Geotextile filter design, application, and product selection guide. Retrieved May 27 2014 , from Ten Cate website: http://www.tencate.com/amer/images/tn_geofilter_tcm29-9120.pdf
4. ROAD DRAINAGE (2014). ROAD DESIGN MANUAL. KINGDOM OF BAHRAIN: MINISTRY OF WORKS
5. INTERNATIONAL LABORATORY SERVICES (2014). GEOTECHNICAL ENGINEERING SERVICES- MATERIAL SERVICES. BAHRAIN: INTERNATIONAL LABORATORY SERVICES
6. W. DAVID CARRIER III, F.ASCE (2003). GOODBYE, HAZEN; HELLO, KOZENY-CARMAN. RETRIEVED ON MARCH 30 2014