The specific study roads are Ogbia-Nembe in Bayalsa State, A section of East West Road from Eleme Junction to Akwa Ibom, and Section of Port Harcourt-Aba expressways from Eleme Junction to Osisioma Junction Aba, Abia State; all of which are located in within the Niger delta region of Nigeria. The Niger delta lies along the delta of the Niger River and considered sitting directly on the Gulf of Guinea on the Atlantic Ocean transversing Nigeria. It is rich in oil mineral deposit and therefore plays a vital role in the economy of Nigeria. States within this study region includes Abia, Akwa Ibom, Bayelsa, Cross River, Delta, Edo, Imo Ondo, and Rivers and are otherwise identified as the Nine (9) Niger Delta state (See Figure 1). According to available records, the Niger Delta extends over about 112,000 kms and constitutes 7.5% of the Nigerian landmass considering the size of the nine states that forms part of the region. The region lies within the geographical coordinates of Latitude 5˚19'20.40"N and Longitude 6˚28'8.99"E and made up of various ethnic tribes notable among which includes Itsekiri, Urhobo, Isoko, Ijaw, Ogbia, Kalabari, Ahua, Ibani, Andoni, Ogoni, Ikwerre, Ndoki, Omuma, Ogba Egbema, Etche, Esan, Bonny Ukwani, Auchi, Esako Igara, Ilaje, Igbo, Ibibio among others. Figure 2 shows three study alignments on any enlarged map of the region.

Disturbed soil samples were collected at equal depths (0.3 m - 1.3 m) at twenty points along the failed sections of each of the study alignments viz: Ogbia-Nembe road, the study section of East-West Road and study section of Port

Harcourt-Aba Road at different chainages below the pavement surface using hand Alger.

Laboratory test investigations was carried out on the collected soil samples which included; Standard Compaction Test, and California Bearing Ratio (CBR) Test. Results obtained from these experimental tests formed part of the data used in this research. 3 kg of dry soil sample was used to carry out compaction test. From the compaction test carried out, the optimum moisture content of the soil was determined and the CBR value of the soil corresponding to this optimum moisture content was determined. The soil was stabilized by adding 6%, 8%, 10%, 12% and 14% of cement by weight to the collected soil samples. After stabilization, the laboratory tests were carried out to determine the new index properties of the soil samples.

From the result of the Standard Compaction test and the CBR of the untreated soil samples obtained from the respective study alignments on Tables 1-3; the untreated soil samples from Ogbia-Nembe Road in sections A, B, C, D, and E had CBR values of 26.6%, 17.7%, 27.0%, 30.4%, and 15.1% respectively. Section of the East-West Road at sections A, B, C, D, and E had CBR values of 4.5%, 6.3%, 5.1%, 2.5%, and 10.4% respectively, while the Section of Port Harcourt-Aba Express Road in sections A, B, C, D, and E had CBR values of 9.2%, 5.0%, 3.5%, 8.9%, and 4.5% respectively. These values signify low CBR values on each of the five sub-sections of the separate three selected roads [9] making the soil unfit for road engineering work purpose. In order to make the soil good for engineering work purpose, the option of stabilization or replacement of the soil may be considered [10]. This resulted to the stabilization of the soil to improve the CBR of the soils using cement content of different percentages in each section. The results of the stabilization various percentage cement contents are tabulated in Table 4 for the various sub-sections of the three study road alignment.

The outcome of the soil to improve process on the CBR of the soil was done using cement content of different percentages in each section and are as follows:

Stabilization results of the soil sample collected from the Ogbia-Nemeb Road with 6%, 8%, and 10% cement content is presented in Figure 3. From Figure 3, it can be seen that CBR Value of the untreated soil samples in sections A, B, C, D, and E improved as follows: Stabilization with 6% cement content increases the CBR value in each of the Sub-Sections of the road represented as A, B, C, D and E increased respectively to 27.3%, 21.8%, 29.7%, 31.3% and 17.3% as against the CBR value of the untreated soil, representing the following percentage increment 2.63%, 23.16%, 10%, 2.96% and 14.57% respectively. From Figure 4, it can be seen that the average percentage increase in the soil CBR for all five (5) sections was 10.66%. The result gives an indication that stabilization of the soils which have similar soil index properties as those found in Ogbia-Nembe with 6% cement content will increase the CBR value by about 11%. Similarly with 8% cement content stabilization as shown in Figure 5, each of the Sub-Sections of the road represented as A, B, C, D and E increased respectively to 33.4%, 29.8%, 33.7%, 35.2%, and 29.7% as against the CBR value of the untreated soil, representing the following percentage increment 25.56%, 68.36%, 24.81%, 15.79% and 96.69% respectively.

From Figure 5, it can be seen that the average percentage increase in the soil CBR for all the five (5) sub-sections was 46.24%. The result gives an indication

that stabilization of the soils which have similar soil index properties as those found in Ogbia-Nembe with 8% cement content will increase the CBR value by about 46%. Again with 10% cement content stabilization as shown in Figure 6,

each of the Sub-Sections of the road represented as A, B, C, D and E increased respectively to 43.0%, 42.6%, 43.3%, 45.2% and 39.4% as against the CBR value of the untreated soil, representing the following percentage increment 61.65%, 140.68%, 60.37%, 48.68% and 160.93% respectively. From Figure 6, it can be seen that the average percentage increase in the soil CBR for all the five (5) sub-sections was 94.46%. The result gives an indication that stabilization of the soils which have similar soil index properties as those found in Ogbia-Nembe with 10% cement content will increase the CBR value by about 94%. The effect of the stabilization process also shows an increased in the soil density which has a direct proportional relationship to the soil strength. Also, the results on the optimum moisture content indicates a decreased with increasing cement content showing that the subgrade material is improved by the stabilization process and is optimized at a 10% sand-cement ratio with optimum moisture content ranging from 6.2% - 14%, maximum dry density ranging from 1700 kg/m³ - 1780 kg/m³, delivering an average CBR of 42.7% for soaked samples.

Stabilization results of the soil sample collected from the section of East-West Road from Eleme Junction to Etteh Junction with 10%, 12%, and 14% cement content is presented in Figure 7. From Figure 7, it can be seen that CBR Value of the untreated soil samples in sections A, B, C, D, and E improved as follows: Stabilization with 10% cement content increases the CBR value in each of the Sub-Sections of the road represented as A, B, C, D and E increased respectively to 26.4%, 28.1%, 36.80%, 31.3% and 32.4% as against the CBR value of

the untreated soil, representing the following percentage increment 486.67%, 346.03%, 621.57%, 1.152% and 211.54% respectively. From Figure 8, it can be seen that the average percentage increase in the soil CBR for all sections was 563.562%. The result gives an indication that stabilization of the soils which have similar soil index properties as those found in section of East-West Road from Eleme Junction to Etteh Junction with 10% cement content will increase the CBR value by about 563% and yield an average CBR value of 31%. Similarly with 12% cement content stabilization as shown in Figure 9, each of the Sub-Sections of the road represented as A, B, C, D and E increased respectively to 38.6%, 38.1%, 43.2%, 39.9% and 44.4% as against the CBR value of the untreated soil, representing the following percentage increment 747.06%, 757.48%, 504.76%, 1,496.0% and 326.92% respectively. From Figure 9, it can be seen that the average percentage increase in the soil CBR for the five (5) sub-sections was 766.44%. The result gives an indication that stabilization of the soils which have similar soil index properties as those found in section of East-West Road from Eleme Junction to Etteh Junction with 12% cement content will increase the CBR value by about 766% yield an average CBR value of 40.88%. Again with 14% cement content stabilization as shown in Figure 10, each of the Sub-Sections of the road represented as A, B, C, D and E increased respectively to 42.1%, 43.6%, 44.8%, 40.9% and 48.2% as against the CBR value of the untreated soil, representing the following percentage increment 835.36%, 592.06%, 778.43%, 1,536% and 363.46% respectively. From Figure 10, it can be seen that the average

percentage increase in the soil CBR for the five (5) sub-sections was sections was 821.06% yield an average CBR value of 43.9%. The result gives an indication that stabilization of the soils which have similar soil index properties as those found in section of East-West Road from Eleme Junction to Etteh Junction with 14% cement content will increase the CBR value by about 821%. The effect of the stabilization process also shows an increased in the soil density which has a direct proportional relationship to the soil strength. Also, the results on the optimum moisture content indicates a decreased with increasing cement content showing that the subgrade material is improved by the stabilization process and is optimized at a 14% sand-cement ratio, with optimum moisture content ranging from 6.2% - 14.2%, maximum dry density ranges from 1660 kg/m³ - 1800 kg/m³, yielding an average CBR of 43.9% for soaked samples.

The result of stabilization of the soil sample collected from the Section of Port Harcourt-Aba Express Road from Eleme Junction to Osisioma Junction with 10%, 12%, and 14% cement content is presented in Figure 11. From Figure 11, it can be seen that CBR Value of the untreated soil samples in sections A, B, C, D, and E improved as follows: Implementing Stabilization with 10% cement content increases the CBR value in each of the Sub-Sections of the road represented as A, B, C, D and E increased respectively to 31.0%, 33.1%, 32.00%, 36% and 36.4% as against the CBR value of the untreated soil, representing the following percentage increment 236.96%, 562%, 814.29%, 304.49% and 708.89% respectively. From Figure 12, it can be seen that the average percentage increase

in the soil CBR for all sections was 525.33% yield an average CBR value of 33.7%. The result gives an indication that stabilization of the soils which have similar soil index properties as those found in Section of Port Harcourt-Aba Express Road from Eleme Junction to Osisioma Junction with 10% cement content will increase the CBR value by about 525.33%. Similarly for 12% cement stabilization, the CBR value in sections A, B, C, D, and E had CBR increased to 38.7%, 39.2%, 37.60%, 41.90% and 42.80% respectively. This gives an average CBR value of about 40.04%. The result gives an indication that stabilization of the soils which have similar soil index properties as those found in this section with 12% cement content will increase the CBR value to an average of 40%. In a similar vein, for 14% cement stabilization, the CBR value in sections A, B, C, D, and E had CBR increased to 42.3%, 41.7%, 39%, 35.1% and 45.20% respectively. This gives an average CBR value of about 40.6%. The result gives an indication that stabilization of the soils which have similar soil index properties as those found in this section with 14% cement content will increase the CBR value to 40.5%. Comparatively, on an economical scale at 12% cement content, the CBR on this road is said to be optimized as there is no much significant improvement in the CBR value when 14% cement content is used. The effect of the stabilization process also shows an increased in the soil density which has a direct proportional relationship to the soil strength. Also, the results on the optimum moisture content indicates a decreased with increasing cement content showing that the subgrade material is improved by the stabilization process and is optimized at a 12% sand-cement ratio, with optimum moisture content ranging from 5.4% - 17.3%, maximum dry density ranges from 1610 kg/m³ - 1740 kg/m³, yielding an average CBR of 40.0% for soaked samples.