Seeing who asked this question, I hope the mods will excuse a bit more technical/ sub-discipline specific language than I would normally include in an AskHistorian's post.

Fortifications - Absolutely.

Their fortification program is probably the single largest imprint the Chimú made on the archaeological record outside the city of Chan Chan. In order to understand why certain fortifications were built where they are, it's important to understand some of what we know about Chimú territorial expansion. There are a few different timelines, but most agree that Chan Chan was the seat of power in the Moche Valley by around 900-1000 CE. This coincides with the decline of the late Moche site of Galindo (Lockard 2009, Kolata 1982). From here on out, I'll use T. Topic's (1990) periodization and discussion of fortification building, because I think it's useful in that she discusses Chimú expansion inland as well as north-south along the coast.

The first big phase of Chimú expansion was to consolidate their power in the Moche Valley up to the western edge of the *chaupiyunga (*read: coca producing) zone between 900 and 1050 CE. At this juncture, the Chimú built two fortified sites and a wall over 1km long (Mullins 2016, fig 4 for a great map). While this might have been an effective barrier, I think it much more likely functioned to "stake a claim". (Side note: when I was writing grant proposals to study Chimú fortifications the last few years, I often mentioned how "walls are often more important to understand in terms of beliefs and identity than physical barriers" Ring any bells?) It seems that they controlled a similar part of the Chicama and Viru valleys by 1200 CE.

Sometime between ~1130 and 1200 CE the Chimú push past the western chaupiyunga border in the Moche Valley, up into the Sinsicap and La Cuesta tributary valleys. In order to hold this new found territory, they began an intensive program of fortification construction that seems to have formed a visual network (Mullins 2016, Ballance 2019). Some of these fortified sites were located in naturally defensible locations, surrounded by cliffs and approachable only from one side (Ballance 2019). On the other hand, some of them were heavily fortified, as evidenced by monumental walls and slingstone piles (Mullins 2012). (I don't want to get into the hilltop temples vs. pukara/ fortifications debate here, suffice it to say I'm very much on the fortifications side). We know they're Chimú because the sites are littered with tons of blackware and some Chimú diagnostic sherds (the C rim, piel de ganzo, etc) (Keatinge 1973). Expansion inland outside of the imperial heartland happened later Topic (1990) says around 1400, Moore and Mackey (2008) say 1320. Interestingly, evidence of "revenge killings" from the Jequetepeque valley dating to the LIP are dated earlier than this, but then again that it the first valley north of the Chicama/Moche/Viru core (Verano 1986). It may also be that Chimú forces were involved in military conflict for several generations before they established territorial control.

Roadways - a little more complicated

I think a big thing here is simply the nature of the environment and of the archaeological record. Roads in the mountains are going to have much longer lasting infrastructure, and the limits of slope and terrain mean paths are constantly repeated and engrained. A road through the coastal desert isn't nearly as topographically limited, and could be little more than a more densely consolidated area of sediment (at least west of the River Valleys). We know that the Chimú built tambo-ish structures along many of the main coastal-highland routes (their Inka rivals were doing largely the same further east) (Boswell 2016). We also know that road construction (if you define it as clearing, tamping, walling, elevating) started in the Moche Valley as early as the Early Horizon (Trombold 1991). I think it's likely that the Chimú controlled, connected and consolidated these early road networks in much the same way that the Inka did with Wari and earlier infrastructure. What labor force did the maintenance is unclear (at least, I haven't seen many people talk about Chimú labor outside the context of Chan Chan). I'm sure it was some sort of classic Andean reciprocal system, but I don't think we can assume a mita like system without some major leaps.