Subsurface Drainage

Subsurface Drainage

Source: “Making Edge Drains Work,” Better Roads, January 2007

(Untreated orAsphalt Treated)

(Aggregate Filter,Geotextile or ATPB)

Flow from Groundwater

Flow from Groundwater

Flow net slide

Flow from Groundwater

Radius of influence slide

Flow from Groundwater

Radius of influence slide

03.8L H H

Flow from Groundwater

20

1 2

i

k H Hq

L

permeability drawdown

radius ofinfluence

Note that the equation in the book is missing the square!

Flow from Groundwater

Flow from Groundwater

Symmetrical drawdown slide

Flow from Groundwater

Flow from Groundwater

22g

qqW

Two Edge Drains

1 22g

q qqW

One Edge Drain

Example 1

Silty Sand (SM)k = 0.07 ft/day

Flow from Groundwater

Flow from Infiltration

Source: WSDOT Pavement Guide Interactive CD-ROM

Subgrade (Existing Soil)Base / Subbase (Optional)

Crack

Typical Soil Permeability

Flow from Infiltration

c c

i c ps

I Wq N kW C

length of transversecracks/joints

spacing oftransversecracks/joints

number of longitudinalcracks/joints

distance betweenthe outermostlongitudinalcracks/joints

crack/jointinfiltration

rate uncrackedpermeability

Flow from Infiltration

subjected to infiltradesign infiltration rate (volume per day per foot of crack)width of drainage blanket number of contributing longitudinal cracks or jointslength of contributing tran

tion

c

c

c

IWNW sverse cracks or joints

spacing of transverse cracks or jointssC

FHWA Highway Subdrainage Design ManualPublication FHWA‐TS‐80‐224 dated July 1990

Flow from Infiltration

ci L T p

Iq L L kW

avg. length of transverse

cracks/jointsper foot of travel

avg. length oflongitudinalcracks/jointsper foot of travel

distance betweenthe outermostlongitudinalcracks/joints

infiltrationper foot ofcrack/joint uncracked

permeability

Flow from Infiltration

Source: WSDOT Pavement Guide Interactive CD-ROM

Subgrade (Existing Soil)Base / Subbase (Optional)

Crack

1 ft

Flow from Infiltration

It is recommended that the “normal” values of Cs be taken as

the transverse joint spacing for new JPCP and JRCP and as the

anticipated average transverse crack spacing for new CRCP

and asphalt concrete pavements. A value of 40 feet has been

suggested for new asphalt pavements; however “normal”

transverse cracking as a result of thermal and moisture

changes can be extremely variable.

FHWA Highway Subdrainage Design ManualPublication FHWA‐TS‐80‐224 dated July 1990

Example 1 (Continued)

Silty Sand (SM)k = 0.07 ft/day

Example 2

Artesian Flow

0

a

k HqH

Excesshydraulichead

Example 3

Flow due to Spring Thaw

Flow due to Spring Thaw

Flow due to Spring Thaw

Flow due to Spring Thaw

Example 1 (Continued)

Silty Sand (SM)k = 0.07 ft/day

Flow due to Spring Thaw

Flow due to Spring Thaw

Drainage Blanket Design Flow

max , , n i g a mq q q q q

Edge Drain Design Flow

1 d nq q q WOne Edge Drain

1 2 d n

Wq q qTwo Edge Drains