Yieldable prop

1. A yieldable prop comprising:

a first hollow conduit having a first end and an opposite second end;

a second conduit having a first end and an opposite second end;

a clamp assembly positioned on outer surface of the second conduit, the clamp assembly comprising a first side and an opposite second side, with the first side of the clamp assembly facing and spaced from the first end of the second conduit, and the second side of the clamp assembly facing and spaced from the second end of the second conduit, wherein the portion of the second conduit between the first end of the second conduit and the first side of the clamp assembly is slidably mounted in the first conduit through the second end of the first conduit;

a bearing plate mounted on the second end of the second conduit; and

a jack assembly comprising a base mounted on the bearing plate of the second conduit and a moveable clamp plate mounted on the base of the jack assembly and in engagement with the second side of the clamp assembly to move the first side of the clamp assembly against the second end of the first conduit to at least move a predetermined length of the portion of the second conduit between the first side of the clamp assembly and the first end of the second conduit out of the first conduit.

2. The prop as claimed in claim 1 , further comprising a visual tension indicator.

3. The prop as claimed in claim 2 , wherein the visual tension indicator is a chain having one end connected to the bearing plate and the other end connected to the first hollow conduit or the clamp assembly.

4. The prop as claimed in claim 1 , wherein the clamp assembly is a first clamp assembly and the jack assembly further comprises:

a jack body having a first jack end, a second jack end and defining a fluid inlet opening;

a piston having a plunger and a piston arm, the plunger connected to one end of the piston arm and the plunger housed in the jack body and acting on the first clamp assembly;

the base defining a first partial orifice positioned at the other end of the piston arm, opposite the plunger; and

a guide defining a second partial orifice positioned adjacent to the first jack end of the jack body.

5. A yieldable prop having a first end and an opposite second end, the yieldable prop comprising;

a first hollow conduit having a first end and an opposite second end, with the first end of the first conduit providing the first end of the prop;

a second conduit having a first end and an opposite second end, with the second end of the second conduit providing the second end of the prop, the first end of the second conduit slidably mounted in the first conduit through the second end of the first conduit; and

a restraint arrangement comprising:

a clamp assembly detachably secured to outer surface of the second conduit to prevent movement of the clamp assembly and the second conduit relative to one another and extending above the outer surface of the second conduit to limit movement of the second conduit into the first conduit, wherein the clamp assembly comprises a side facing and spaced from the first end of the second conduit and the restraint arrangement prevents movement of a portion of the second conduit between the side of the clamp assembly and the first end of the second conduit into and out of the first conduit,

wherein the clamp assembly comprises:

a first split conduit defining an inner major surface and an opposite outer major surface;

a second split conduit defining an inner major surface and an opposite outer major surface, with the inner surface of the first and second split conduits engaging the outer surface of the second conduit;

at least one bolt having a U-shaped portion and two threaded legs with a U-shaped portion of the at least one bolt engaging portion of the outer surface of at least one of the split conduits;

a brace defining a first orifice to receive one of the threaded legs of the at least one bolt and a second orifice to receive the other one of the threaded legs of the at least one threaded leg;

a threaded nut on each of the threaded legs of the at least one bolt to bias the brace and the at least one bolt against the outer surface of the first and second split conduits to bias the inner surface of the first and second split conduits against the outer surface of the second conduit; and

friction members along the inner major surface of the first and second split conduits.

6. The prop as claimed in claim 5 , further comprising a bearing plate positioned at least on one of the ends of the yieldable prop.

7. The prop as claimed in claim 6 , wherein the bearing plate is selected from a shape comprising planar, volcano, C-shaped, and I-shaped.

8. The prop as claimed in claim 5 , further comprising a visual tension indicator.