When we were building our house in 2021, I didn't do my due diligence with the concrete contractor. Now, I'm saddled with a failing driveway that is too thin, and is heaving due the crappy clay soil beneath it (measured plasticity index + 49). To make matters worse, there are a few small sections of our house foundation (near the garage corners) that are being lifted because the neighboring driveway was poured with rebar dowels into the foundation… and the soil beneath it is now expanding, which is lifting the driveway, which is in turn putting enough stress on the foundation to crack the garage walls. …this was the finding of engineers who came out and performed site measurements, not something that yours truly dreamt up.

It's a large (expensive) project, so I'm trying to get most bang for my buck.

My draft request for quote is provided below. Constructive comments are appreciated. I should also note that the engineer's recommended plan of action was to remove 2 feet of soil beneath the existing driveway and replace with select fill. When vetting that recommendation with others, some said that they were simply standard recommendations for pouring a house foundation, probably overkill for a driveway and/or not the best approach, money-wise.

If anyone has any leads on an engineering firm in the greater DFW area that might be willing to assist me in this endeavor, I would be very appreciative.


REQUEST FOR QUOTE:


1. SCOPE OF WORK OVERVIEW
The project consists of the complete demolition and disposal of approximately 5,300 sq. ft. of an existing 3"4" concrete driveway, structural isolation from the home/garage foundation, subgrade preparation, installation of a geotextile separation layer, 6" compacted crushed limestone base, and the pouring of a reinforced 4,000 PSI concrete slab featuring a 12" monolithic thickened edge beam.
2. DETAILED SPECIFICATIONS

• Demolition & Haul-Off:
  
  • Total removal of ~5,300 sq. ft. of existing 3"4" concrete slab.
  • Foundation Isolation: Prior to or during demolition, the contractor must saw-cut and completely sever any existing rebar, dowel, or structural connections between the old driveway slab and the home/garage foundation walls.
  • Complete off-site disposal of all concrete debris (estimated ~120 tons).
  • Subgrade clay must be kept dry and covered if weather threatens between demolition and base installation.
• Subgrade & Base Preparation:
  
  • Excavation to a uniform depth of 11.5 to 12 inches below final finished grade across the main body.
  • Subgrade Prep: Minimize disturbance to the existing consolidated clay. The subgrade should be smoothly graded and lightly rolled only to eliminate ruts or gouges from the demolition equipment. Do not scarify or heavily compact the native clay.
  • Perimeter Beam Trenching: Excavate an additional structural trench around the entire exterior perimeter of the driveway footprint to achieve a total concrete depth of 12 inches at the edges.
  • Installation of a high-strength woven geotextile stabilization/separator fabric directly over the clay bed (excluding the bottom of the perimeter beam trenches).
  • Fabric Overlap Rule: All adjacent fabric seams must be tightly unrolled and overlapped by a minimum of 12 to 18 inches to prevent clay migration into the stone base.
  • Supply, placement, and mechanical compaction of 6 inches of TxDOT-approved crushed limestone road base (flex base), installed and compacted in two (2) 3-inch lifts.
• Reinforcement Steel:
  
  • #4 (1/2") deformed rebar laid out in a strict 12-inch x 12-inch center-to-center grid.
  • All rebar intersections must be securely wire-tied.
  • The main rebar mat must be bent or tied down into the perimeter trench to ensure structural continuity.
  • Beam Reinforcement: Install a minimum of two (2) continuous horizontal strands of #4 rebar along the bottom of the 12-inch perimeter trench.
  • The entire rebar assembly must be elevated and supported on plastic or concrete chairs to ensure proper placement within the concrete.
• Concrete Mix Design & Isolation:
  
  • Isolation Joint: Install a 1/2-inch thick, full-depth compressible expansion/isolation joint board against all adjoining house, garage, or structural foundations before pouring to ensure completely independent slab movement.
  • Compressive Strength: 4,000 PSI @ 28 Days.
  • Thickness: Target pour thickness of 5.5 to 6 inches throughout the main slab, with an absolute structural minimum of 5 inches, turning down to 12 inches at the monolithic perimeter edge beams.
  • Coarse Aggregate: 1-inch maximum size (or 3/4-inch) to ensure proper flow through the 12" rebar grid.
  • Slump Target: 4 to 5 inches.
  • Fly Ash/Slag: Restricted to a maximum 20% cementitious replacement.
• Finishing & Joints:
  
  • Standard medium-to-heavy broom finish for slip resistance.
  • Control joints to be saw-cut or tooled to a depth of 1.4 to 1.5 inches (1/4 of total slab thickness) on a maximum grid spacing of 10' to 12'.
  • Saw-cutting must be performed within 12 hours of the pour completion.

3. SUBMISSION REQUIREMENTS
Please provide a comprehensive bid breaking down costs for the following items:
[ol]

Demolition, foundation saw-cutting, labor, and dumpster/disposal fees for the existing concrete.

Excavation, perimeter trenching, grading, fabric, and base material supply & compaction labor.

Rebar material and placement labor (12" grid + perimeter beam steel).

Concrete material (Ready-Mix delivery), isolation joint installation, and placement/finishing labor.

Estimated project duration and timeline from start to finish.

Proof of General Liability Insurance and commercial references for similar scale residential/commercial pours in North Texas.

[/ol]

I think I would add 2 more horizontals to the beams and have them supported/spaced with "L" pieces that tie the mat and the beam horizontals together. Spaced every 24" minimum. The two sets of horizontals in the beam should be spaced apart horizontally 4-6". One set of the horizontals near the bottom and one 6" up between mat and bottom horizontals.

I tend to over engineer things, but given you already know your soil moves drastically, i would beef up the beam as this is where your strength is coming from.

My $.02.

ETA: I would also use a 15 mil vapor barrier. It will slow the cure of the concrete where it would contact the soil and thereby be stronger.

This part is a little odd to me. Could be correct but unless you know it's right or had someone that knows it's right I'd revise it:

Quote:

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Subgrade Prep: Minimize disturbance to the existing consolidated clay. The subgrade should be smoothly graded and lightly rolled only to eliminate ruts or gouges from the demolition equipment. Do not scarify or heavily compact the native clay.

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I don't get the point of saying don't compact the existing dirt there at the end.

I'd look in the 2024 TxDOT standard specifications book online and read the actual item number that talks about flex base if you care about it being TxDOT approved (linked at bottom of post). Idea being avoiding a contractor simply saying "yeah it's approved".

Your total thickness is inconsistent. You say 11.5" : 12" at the beginning but then give 6" of flexbase and minimum of 5" of concrete, so 11" minimum. Giving 0.0" tolerance on flexbase but a whole inch of concrete on a 6" pour could also be normal but just seems odd to me.

I have no experience with putting out a request for quotes on driveways or actually building residential driveways, so grains of salt here.

Flex base is item 247 page 164. I didn't read through it but it might direct you to DMS info elsewhere: https://www.txdot.gov/content/dam/docs/specifications/2024/spec-book-0924.pdf

I don't think there's any way to keep the subgrade from getting wet after demolition If it happens to rain. that area is gonna be lower than everything else anyway.

Thanks to all that have replied thus far. I will definitely make changes to incorporate these great suggestions. I agree that the wording regarding disturbing the soil following excavation is not good. I think the intention was to avoid intentionally overly (intentionally) compacting the remaining soil any further since it has already been compressed by the old concrete.... But I see that may not be really necessary to state such anyway. I will have to figure out the concern about rain.... maybe just change it to something to minimize the possibility of beginning the project when heavy rain is forecasted...but that is probably equally problematic.

Got a detail w/specs to cover you in a PM
Aggieland has high PI in places as well
Am from Dallas so lived over shallow pier/beam & slab-on-grade as well

That said, would
use the engineer's details/specs, a small extra charge, if any
use his past inspected "A" crews
pay for inspections prior to coverup

https://www.facebook.com/TgiVaughnArchitect/
should out last your lifetime, one last nail hammered down

Did you get the sub grade prep from a geotech report or did you just get it from AI?