Determining the Quality of Backfill Compaction

This post is regarding "Determination of Quality of Backfill Compaction" underneath existing pavements/slabs on grade. The needed properties/parameters are as follows:

1. Subsurface Soil Exploration (SPT Nvalues of underlying soils)

2. Navfac 7.1 for correlation charts

3. Soils in Construction by W.L. Schroeder for correlation charts

4. Effective stress at level in question

To determine the quality of backfill compaction, the effective stress at level in question should be computed using the formula Po = γh (for unsaturated soil). Note that effective or submerged unit weight (γ-9.81kN/cu.m.) must be used if the water table is within the height or depth in question. γ is the unit weight of soil and h is the depth in question.

After obtaining the effective stress, refer to the example on the left for SPT=3 BPF and Effective stress = 36 kPa (0.751ksf) at -2.0M. The chart below is taken from Navfac 7.1 to determine Relative Density.

Relative Density are commonly used for cohesionless soils. It is defined as:

Relative density is a dimensionless ratio of the densities of two materials. The term specific gravity is similar, except that the reference material is water. A relative density can help quantify the buoyancy between two materials, or determine the density of one "unknown" material using the "known" density of another material. Mathematically, relative density is expressed as:

where G is the relative density, and ρ is the densities of the two materials in the same units (e.g., kg/m³, g/cm³). (http://www.wikopedia.org/)

It is shown in the figure above that the Relative Density is equal to 15 %. This value will be used in determining the Relative Compaction, RC using a correlation from "Soils in Construction" by W.L. Schroeder as shown on the right.

Projecting the value of relative density down to the line of relative compaction will give the value of relative compaction. In this expample, it is 84%. Thus, the very low RC represents little or no compactive effort.

Design of Reinforced Concrete Silo

Oh well, a new project assigned to me.. actually it was already assigned to me months earlier and right now we received the NTP. I am supposed to do it while I'm doing the Uniliver Bars Area Analysis.

Design of Reinforced Concrete Silo:

References:
ACI Manual of Concrete Practice Part 4
Structural Engineering Handbook

Resources:
Staad Pro 2003
Mathcad 2001 or Mathcad 13

I am currently on the "research" part of the project. I have just finished reading the section in ACI Manual regarding the design of concrete silos.

Few definition of terms (from ACI Manual of Concrete Practice:

1. SILO - Any upright container for storing bulk granular material
2. Hopper - Sloping-walled portion at the bottom of the silo; independent shallow silo (bunker) with sloping walls
3. Stave silos - Silos assembled from small precast concrete units called "staves", usually tounged & grooved, and held together by exterior, adjustable steel hoops

.. construction procedures ( I have never heard these terms before.. maybe because I am not a site engineer.. but of I am supposed to know these stuffs)..

4. SLIPFORMING - construction method in which the forms move continuously during the palcement of concrete; continuity in operation to minimize formation of construction joints; used in casting walls of great height
5. JUMPFORMING - construction method in which fixed forms are used to cast a short increment of height and are then loosened and raised to a higher position after the concrete has hardened; concrete placement not continuous

Others:
6. Homogenizing silos - Silos in which air pressure is used to mix dust-like materials

There are lot of formulas involved and I will not be posting it. It is all in the ACI concrete manual anyway.

So far, all I have are basic understanding on this Silo design. I do expect to know more..

Uniliver Bars Area

Unilver Bars Area Project - This project was handed over to me as the original engineer assigned to do the project left the company.

I am currently reviewing the drawing fiels provided by the client and the area is relatively "huge". I can say that this is the biggest (with reference to area) I have handled so far.

I do expect a lot of difficulties while doing this project. Oh, well, I am very optimistic that I will be able to push this through.

The area by the way is inside Unilever plant. Bars area - well it is where they manufacture the "Surf" bars that are being sold here in the Philippines. It is an existing building that was affected by a recent earthquake (Intensity 4.0) that happened here in Manila. I am not very particular yet with the other details but will posts as soon as I discussed it with my boss.