Hydraulic Conductivity Characteristics of a Clayey Soil Incorporating Recycled Rubber and Glass Granules

Round 1

Reviewer 1 Report

 

The paper is focused on the compressibility and hydraulic conductivity of a reactive soil after addition of recycled materials. It introduces interesting data from a wide experimental program. However, the manuscript contains some lacks and poor discussion. An extensive revision is recommended on the basis of the following comments and suggestions.

MAJOR REVIEW

 

1.       According to the USCS the research is conducted on a clayey soil of low plasticity (lean clay, CL). It is not a clay of moderate plasticity. It is not very reactive, on the basis of its limit liquid (28%), plasticity index (15%) and mineralogical composition (kaolinite and illite). The grain size distribution, or at least the fine percentage, should be reported as well as the value of Activity and the organic content if any. The Authors should explain the reason why they selected a low plastic clay.

2.       The grain size distribution or at least the range of the particle size of the glass granules should be reported.

3.       Why did the Authors use distilled water to prepare samples and for testing? This type of water strongly influences the hydraulic behaviour of a clayey soil and it is not used in practice.

4.       Which compaction method was used? It should be specified. The compaction curves of the differently treated soils and that of the untreated soil should be reported and discussed.

5.       The trimming procedure is not clear and should be described in detail. Is the diameter of the specimens the same of the compacted samples?

6.       How did the authors calculate the void ratio of the treated samples? This should be specified in the manuscript (§3.1).

7.       The compressibility of the soil additivated with RC should be discussed considering that the rubber is a flexible material.

8.       Table 3: one value of the compression index Cc is listed for each type of specimen but it is evident from figure 6 that Cc increases with the effective stress. The values should be reported, analysed and discussed with reference to different ranges of the effective stresses.

9.       The hydraulic conductivity of the treated and untreated samples was not measured. It was derived from the Terzaghi’s one-dimensional consolidation theory which is based on several hypotheses: small strains, saturated soil and linear elastic soil among them. It is known that a significant difference can be observed between the direct (real) and indirect values of k, in particular for expansive soils. The reliability of indirect k strongly depends on the accuracy of cv and mv. The authors should perform at least some direct measurements of k to demonstrate, for the specific treated and untreated soil investigated, the reliability of indirect evaluation of k.

10.   The Authors do not consider and discuss at all the reliability of estimation of k by the Terzaghi’s theory and indeed they do not give info concerning strain levels as well as degree of saturation of the tested samples. The hypotheses of the 1-D consolidation theory with reference to the investigated materials should be discussed. In particular, with reference to the degree of saturation, the samples they tested can be supposed to have a degree of saturation of 70-80% since they were compacted at the optimum water content. The test conditions (oedometer tests) do not assure the samples saturation, therefore the different k values of the different samples (differently treated and untreated) can be influenced by their different degree of saturation.

11.   The k values of the treated and untreated soil are very similar, effective stress being equal. As an example, at 100 kPa, the soil-rubber samples have k values of 1.63, 1.34, 1.47 and 1.31 x 10-6 cm/s with 0, 5%, 10% and 20% respectively. Considering the indirect evaluation of k, such values do not allow to individuate a trend and, even less, the best proportion of the incorporated material. The same considerations can be done with reference to the values of k in Table 4.

12.   Is it not clear why, “when being adding CG, large inter-aggregate pores were disrupted and re-formed into small pores, leading to higher k value”. A reduction in the size of pores cannot lead to higher k.

13.   Conclusions should be changed accordingly.

MINOR REVIEW

Title.

The title should be “Compressibility and hydraulic conductivity of a clayey soil incorporating recycled rubber and glass granules” (just one soil was investigated).

§ 2.1

The description of XRD graph of figure 2 (i.e., the horizontal axis represents…) can be omitted.

According to the USCS the soil is a lean clay (CL). It is not a clay of moderate plasticity.

Table 1. Values of liquid limit and plasticity index should be reported without decimals. The value of the Plastic limit is superfluous and should be eliminated.

§ 2.3  

The accuracy of measurement of the sample thickness should be reported.

§2.4

Kv is the hydraulic conductivity in the vertical direction.

§ 3.1

The sentence “As the effective stress increases the soil becomes denser and the void ratio declines” is obvious and should be deleted.

§3.2 and §3.3

The values of k should be reported in m/s.

 

 

Author Response

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Reviewer 2 Report

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