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Rigid Pavements with a Triplanar Subsurface Drainage Layer - Design Calculator

Problem Statement

This calculator designs rigid pavements with and without a geocomposite drainage layer. The basic design method is AASHTO "Guide for Design of Pavement Structures" (1993). The structural contribution of a geocomposite drainage layer is quantified by an improved drainage coefficient.

Rigid Cross Section

The AASHTO rigid pavement design method consists of two main steps. 1.) Develop Effective Modulus of Subgrade Reaction, k. For purpose of this technical note, k is assumed to be known, or determined from the CBR. 2.) Determine Required Slab Thickness, D. The equation shown below determines the slab thickness utilizing the given inputs. The basic design equation for rigid pavements in the AASHTO 93 design guide is as follows:

Equation 1

where

Symbol	Description	Unit
W₁₈	predicted number of 18-kip equivalent single axle load (ESAL)
Z_R	standard normal deviate
S₀	overall standard deviation
D	concrete slab thickness
DPSI	difference between the initial design serviceability index p₀ and the design terminal serviceability index p_t
p_t	terminal serviceability index
S'_c	concrete modulus of rupture	psi
E_c	concrete elastic modulus	psi
J	load transfer coefficient
C_d	drainage coefficient

Input Values

**Please note - The user can opt to input data for these values (if known), or leave 0. If left 0, the values k and W₁₈ will be calculated from [=CBR*1500/19.4) and [=1,700,000 *F_R], respectively.

Click on Calculate Time to Drain [first] to calculate the time to drain for the designed pavement cross section with and without the use of a triplanar subsurface drainage layer. Based on the time to drain, you can select a corresponding drainage coefficient (m_i).

Calculate Time to Drain

Thickness of Base Course Design

Subgrade California Bearing Ratio	CBR
Effective Modulus of Subgrade Reaction	**k	pci
Design Traffic Load	W₁₈	ESAL
Reliability	R		<Help!
Standard Deviation	S₀
Terminal Serviceability	p_t
Total Serviceability Loss	DPSI	inch
Concrete Modulus of Rupture	S'_c	psi
Concrete Elastic Modulus	E_c	psi
Load Transfer Coefficient	J		<Help!
Drainage Coefficient	C_d1		<Help!
	C_d2		<Help!

calculation time could take up to 30 sec

References

American Association of State Highway and Transportation Officials, "AASHTO Guide for Design of Pavement Structures", Washington, D.C., 1993.

Cedergren, H.R., 1987. "Drainage of Highway and Airfield Pavements", Robert E. Krieger Publishing Co. Inc.,Malabar, FL.

Christopher, R. B and McGuffey, V.C., 1997. "Synthesis of Highway Practice 239: Pavement Subsurface Drainage Systems", National Cooperative Highway Research Program, Transportation Research Board, National Academy Press, Washington, D.C.

Christopher, R. B. and Zhao, A., 2001, "Design Manual for Roadway Geocomposite Underdrain Systems".

FHWA, 1990. "FHWA Technical Guide Paper 90-01: Subsurface Pavement Drainage", Federal Highway Administration, Office of Engineering, Pavement Division, Washington, D.C., October.

FHWA, 1992. "Demonstration Project 87: Drainable Pavement Systems, Participant Notebook", Federal Highway Administration, Publication No. FHWA-SA-92-008, Washington, D.C.

US Army Corps of Engineers,1992. "Engineering and Design Drainage Layers for Pavements", Engineer Technical Letter 1110-3-435, Department of the Army, US army Corps of Engineers, Washington, DC.