Under the patronage of the Dean of the College of Engineering, Professor Dr. Jumaa Salman Jiyad.it was conducted at nine o’clock in the morning on Thursday, 12/21/2023, in the Council Hall of the Civil Engineering Department / College of Engineering / Al-Nahrain University, the discussion of the doctoral student in the Civil Engineering Department (Hassan Muhammad Mahdi) in her thesis tagged:

  “Simulating the Subgrade properties on the Structural Response of Rigid Pavement”

The discussion committee was headed by Professor Dr. Muhammad Abbas Hassan / College of Engineering / University of Kufa, and the membership of Professor Dr. Qasioun Saad Al-Din Muhammad Shafiq / College of Engineering / Al-Nahrain University, Professor Dr. Alaa Hussein Abdel Hafez / College of Engineering / Al-Nahrain University, and Professor Dr. Ahmed Sultan Ali / College of Engineering / Al-Nahrain University and Assistant Professor Dr. Hassan Musa Jawad / College of Engineering / Al-Nahrain University. The thesis was completed under the supervision of Assistant Professor Dr. Asmaa Thamer Ibrahim / College of Engineering / Al-Nahrain University.

The thesis was evaluated scientifically by the first scientific evaluator (Prof. Dr. Bassem Hassan Shanawa) / College of Engineering / Al-Qadisiyah University and the second scientific evaluator (Prof. Dr. Ali Abdul-Mir Alloush / College of Engineering / University of Babylon) and linguistically by (Dr. Ahmed Farhan Moiz / College of Engineering / Al-Nahrain University), where the thesis was accepted because it fulfilled the requirements for obtaining a doctorate degree.

Abstract

The soil properties of rigid pavement are very important for ensuring the longevity and performance of the pavement. It must provide a stable foundation for the concrete slabs to prevent cracking, settling, or other forms of damage.

This thesis's methodology depends on different soil types, such as gypsum natural soil, emulsified asphalt-stabilized soil by ploycoat REB, and soil with subbase layers. It also deals with different concrete compressive strengths (C25, C30, and C35) that use Sika 905 as an admixture. Also, Ever FE software is used to figure out the stresses, deflections, and shear loads on dowel bars in three cases of rigid pavement: single panel, double panel, and quadruple panel, according to finite element theory.

According to the methodology presented above, the subgrade reaction modulus can be adjusted to reduce pavement slab thickness by 15mm or 25mm with constant concrete compressive strength and other design factors, depending on the change from 40 to 100 or 141 MN/m³, respectively. Also, the compressive strength of concrete goes from 25 MPa to 30 MPa or 35 MPa, and the slab thickness can go down by 15 mm or 30 mm as long as the design conditions and subgrade reaction modulus stay constant.

In single-panel rigid pavement analysis, an increase in axle load from single to tridem causes an increase in deflection, which is mitigated by 54% when the subgrade response modulus rises from 40 to 100 MN/m³ and by 69% when it increases to 141 MN/m³. Additionally, increasing slab thickness and the K value reduces stress on the panel. Changing the slab base reaction from 40 to 141 MN/m³ at C35 compressive strength resulted in stress reductions of 6.53%, 15.48%, and 12.56% for single, tandem, and tridem axles, respectively.

The analysis of the double-panel rigid pavement (10x4) meters revealed that deflection increased as axle loads went from single to tridem, peaking at the tridem axle. Also, it reduces by 57% and 68.5% when the subgrade reaction modulus changes from 40 to 100 MN/m³ and 40 to 141 MN/m³, respectively. Stress increased as slab thickness decreased, with increments of 19.3%, 7.2%, and 8.63% for single, tandem, and tridem axles, respectively, when the slab base reaction changed from 40 to 141 MN/m³ at C35 compressive strength. A single axle applied directly to the joint in double-panel rigid pavement yielded maximum dowel loads with a 35 MPa concrete strength and significant subgrade reaction moduli (40, 100, and 141 MN/m³). When changing the subgrade reaction modulus from 40 to 100 MN/m³, dowel loads decreased by 34%, 57%, and 46% for single, tandem, and tridem axles, and by 43%, 70%, and 52% when changing the modulus from 40 to 141 MN/m³.

In the four-panel (10x8)-meter rigid pavement analysis, deflection went up as the axle load went from single to tridem, reaching its highest point at the tridem axle. Also, it went down by 54% and 65.5% when the subgrade reaction modulus changed from 40 to 100 MN/m³ and 40 to 141 MN/m³, respectively. When the slab base reaction changed from 40 to 141 MN/m³ at C35 compressive strength, the stress increased by 9.2% for single axles and 7.24% for tridem axles. Furthermore, the stress decreased as the slab thickness increased for different axle loads and K values. A single axle on a four-panel rigid pavement joint experienced the highest dowel load at 35 MPa due to concrete and significant subgrade reaction moduli. When the subgrade reaction modulus was raised from 40 to 100 MN/m³, the dowel load decreased by 58%, 71%, and 72% for single, tandem, and tridem axles, respectively. Conversely, changing the modulus from 40 to 141 MN/m³ reduced the load by 72%, 85%, and 84%.