# Field Pull-Out Tests of Percussion Driven Earth Anchors (PDEAs)
## 5 Results and Analysis
### Prediction of Ultimate Pull-Out Load  
Typical failure modes for shallow and deep anchors in sandy soil have been developed in previous studies. However, to the author's knowledge, soil failure patterns from PDEA anchors embedded in clayey soil have not been well studied. In this study, there was not a defined failure pattern for anchors installed 3 m into the channel bank slope. Existing methods available to estimate the ultimate pull-out of anchors in clayey soils have been examined throughout the literature review. An equation was identified for assessing the pull-out capacity of rectangular plates using the soil's shape factors, weight factors, and undrained shear strength parameters. The following Equation (1) was suggested by [PERSON] 1980 [38] for deep anchors in clayey soils. The equation was developed based on an \(\alpha-\beta\) parameter curve derived from experimental pull-out test results and using the breakout factor (F\({}_{\text{c}}\)) with respect to embedment ratio, developed by [PERSON], 1978 [39]. Per [PERSON], the \(\alpha\) value is the ratio of embedment ratio to critical embedment ratio, (H/B)/(H/B)\({}_{\text{cr}}\), and the \(\beta\) value is the corresponding breakout factor ratio, \(F_{\text{c}}/F_{\text{c}}^{*}\). The equation is shown below as Equation (1). Equation (1) was used to calculate the maximum pull-out resistance, Q\({}_{0}\). \[\text{Q}_{\text{o}}=\text{BL}\left\{\left[7.56+1.44(\frac{\text{L}}{\text{B}} )\right]\text{C}_{\text{u}}+\gamma\text{H}\right\}\text{;Q}_{\text{u}}=\text {Q}_{\text{o}}+\text{W}_{f}. \tag{1}\]  
In Equation (1), B (cm) is the width of the anchor, L (cm) is the length of the anchor, C\({}_{\text{u}}\) (kN/m\({}^{2}\)) is the representative undrained cohesion value of the soil, \(\gamma\) (kN/m\({}^{3}\)) is the unit weight of the soil, H (m) is the depth of the anchor, Q\({}_{\text{u}}\)(kN/m\({}^{3}\)) is the ultimate pull-out resistance, and W\({}_{f}\) (kN) is the self-weight of the anchor itself. W\({}_{f}\) (kN) can reasonably be ignored for small anchors as the self-weight effect is negligible. For this study, the anchor was approximated as a rectangular plate anchor to utilize the existing pull-out capacity estimation techniques from previous studies. The following values are used in the pull-out capacity estimation calculation: L = 30.5 cm, B = 6.4 cm, C\({}_{\text{u}}\) = 29.3 kN/m\({}^{2}\), H = 3 m, and \(\gamma\) = 19.6 kN/m\({}^{3}\). The half of the unconfined compressive strength from Table 1 was used as the undrained shear strength C\({}_{\text{u}}\). The ultimate pull-out  
Figure 16: Anchor 1 post-load-lock pull-out test on the southwest slope. capacity calculated based on this equation was 9.23 kN. This study's three field pull-out tests found the maximum experimental field pull-out resistance to be in the 13.2 kN to 17 kN range. The average TCP-N number was utilized to obtain \(\mathrm{C_{u}}\) values based on the correlation suggested by TxDOT, as shown in Equation (2). Another set of calculations was performed based on \(\mathrm{C_{u}}\) values 46.2 kN/m\({}^{2}\) from TCP data in the boring logs. The estimated \(\mathrm{P_{u}}\) values were 13.8 kN. Figure 7 indicates strong spatial variabilities of soils, for example, moisture content, within the slope embankment. This nonuniformity results in different TCP-N values at different locations, generating different correlated \(\mathrm{C_{u}}\) values. In addition, the laboratory \(\mathrm{C_{u}}\) values were obtained using UCS test based on soil optimum moisture content. This also results in errors when utilizing Equation (1) to estimate ultimate pullout resistance, since the equation was developed for saturated clay. Table 3 tabulates the pull-out load obtained from field and laboratory and TCP data through Equation (1). The field pull-out test showed higher pull-out resistance by an average of 37% than the predicted value from empirical Equation (1) using \(\mathrm{C_{u}}\) values generated by the laboratory test.